More Letters of Charles Darwin Volume II
Part 8 out of 14
not at all surprised that you cannot digest pangenesis: it is enough to
give any one an indigestion; but to my mind the idea has been an immense
relief, as I could not endure to keep so many large classes of facts all
floating loose in my mind without some thread of connection to tie them
together in a tangible method.
With respect to the men who have recently written on the crossing of
plants, I can at present remember only Hildebrand, Fritz Muller, Delpino,
and G. Henslow; but I think there are others. I feel sure that Hildebrand
is a very good observer, for I have read all his papers, and during the
last twenty years I have made unpublished observations on many of the
plants which he describes. [Most of the criticisms which I sometimes meet
with in French works against the frequency of crossing I am certain are the
result of mere ignorance. I have never hitherto found the rule to fail
that when an author describes the structure of a flower as specially
adapted for self-fertilisation, it is really adapted for crossing. The
Fumariaceae offer a good instance of this, and Treviranus threw this order
in my teeth; but in Corydalis Hildebrand shows how utterly false the idea
of self-fertilisation is. This author's paper on Salvia (694/1.
Hildebrand, "Pringsheim's Jahrbucher," IV.) is really worth reading, and I
have observed some species, and know that he is accurate]. (694/2. The
passage within  was published in the "Life and Letters," III., page 279.)
Judging from a long review in the "Bot. Zeitung", and from what I know of
some the plants, I believe Delpino's article especially on the Apocynaea,
is excellent; but I cannot read Italian. (694/3. Hildebrand's paper in
the "Bot. Zeitung," 1867, refers to Delpino's work on the Asclepiads,
Apocyneae and other Orders.) Perhaps you would like just to glance at such
pamphlets as I can lay my hands on, and therefore I will send them, as if
you do not care to see them you can return them at once; and this will
cause you less trouble than writing to say you do not care to see them.
With respect to Primula, and one point about which I feel positive is that
the Bardfield and common oxlips are fundamentally distinct plants, and that
the common oxlip is a sterile hybrid. (694/4. For a general account of
the Bardfield oxlip (Primula elatior) see Miller Christy, "Linn. Soc.
Journ." Volume XXXIII., page 172, 1897.) I have never heard of the common
oxlip being found in great abundance anywhere, and some amount of
difference in number might depend on so small a circumstance as the
presence of some moth which habitually sucked the primrose and cowslip. To
return to the subject of crossing: I am experimenting on a very large
scale on the difference in power and growth between plants raised from
self-fertilised and crossed seeds, and it is no exaggeration to say that
the difference in growth and vigour is sometimes truly wonderful. Lyell,
Huxley, and Hooker have seen some of my plants, and been astonished; and I
should much like to show them to you. I always supposed until lately that
no evil effects would be visible until after several generations of
self-fertilisation, but now I see that one generation sometimes suffices,
and the existence of dimorphic plants and all the wonderful contrivances of
orchids are quite intelligible to me.
LETTER 695. TO T.H. FARRER (Lord Farrer).
Down, June 5th, 1868.
I must write a line to cry peccavi. I have seen the action in Ophrys
exactly as you describe, and am thoroughly ashamed of my inaccuracy.
(695/1. See "Fertilisation of Orchids," Edition II., page 46, where Lord
Farrer's observations on the movement of the pollinia in Ophrys muscifera
are given.) I find that the pollinia do not move if kept in a very damp
atmosphere under a glass; so that it is just possible, though very
improbable, that I may have observed them during a very damp day.
I am not much surprised that I overlooked the movement in Habenaria, as it
takes so long. (695/2. This refers to Peristylus viridis, sometimes known
as Habenaria viridis. Lord Farrer's observations are given in
"Fertilisation of Orchids," Edition II., page 63.)
I am glad you have seen Listera; it requires to be seen to believe in the
co-ordination in the position of the parts, the irritability, and the
chemical nature of the viscid fluid. This reminds me that I carefully
described to Huxley the shooting out of the pollinia in Catasetum, and
received for an answer, "Do you really think that I can believe all that!"
(695/3. See Letter 665.)
LETTER 696. TO J.D. HOOKER.
Down, December 2nd, 1868.
It is a splendid scheme, and if you make only a beginning on a "Flora,"
which shall serve as an index to all papers on curious points in the
life-history of plants, you will do an inestimable good service. Quite
recently I was asked by a man how he could find out what was known on
various biological points in our plants, and I answered that I knew of no
such book, and that he might ask half a dozen botanists before one would
chance to remember what had been published on this or that point. Not long
ago another man, who had been experimenting on the quasi-bulbs on the
leaves of Cardamine, wrote to me to complain that he could not find out
what was known on the subject. It is almost certain that some early or
even advanced students, if they found in their "Flora" a line or two on
various curious points, with references for further investigation, would be
led to make further observations. For instance, a reference to the viscid
threads emitted by the seeds of Compositae, to the apparatus (if it has
been described) by which Oxalis spurts out its seeds, to the sensitiveness
of the young leaves of Oxalis acetosella with reference to O. sensitiva.
Under Lathyrus nissolia it would [be] better to refer to my hypothetical
explanation of the grass-like leaves than to nothing. (696/1. No doubt the
view given in "Climbing Plants," page 201, that L. nissolia has been
evolved from a form like L. aphaca.) Under a twining plant you might say
that the upper part of the shoot steadily revolves with or against the sun,
and so, when it strikes against any object it turns to the right or left,
as the case may be. If, again, references were given to the parasitism of
Euphrasia, etc., how likely it would be that some young man would go on
with the investigation; and so with endless other facts. I am quite
enthusiastic about your idea; it is a grand idea to make a "Flora" a guide
for knowledge already acquired and to be acquired. I have amused myself by
speculating what an enormous number of subjects ought to be introduced into
a Eutopian (696/2. A mis-spelling of Utopian.) Flora, on the quickness of
the germination of the seeds, on their means of dispersal; on the
fertilisation of the flower, and on a score of other points, about almost
all of which we are profoundly ignorant. I am glad to read what you say
about Bentham, for my inner consciousness tells me that he has run too many
forms together. Should you care to see an elaborate German pamphlet by
Hermann Muller on the gradation and distinction of the forms of Epipactis
and of Platanthera? (696/3. "Verhand. d. Nat. Ver. f. Pr. Rh. u. Wesfal."
Jahrg. XXV.: see "Fertilisation of Orchids," Edition II., pages 74, 102.)
It may be absurd in me to suggest, but I think you would find curious
facts and references in Lecoq's enormous book (696/4. "Geographie
Botanique," 9 volumes, 1854-58.), in Vaucher's four volumes (696/5.
"Plantes d'Europe," 4 volumes, 1841.), in Hildebrand's "Geschlechter
Vertheilung" (696/6 "Geschlechter Vertheilung bei den Pflanzen," 1 volume,
Leipzig, 1867.), and perhaps in Fournier's "De la Fecondation." (696/7.
"De la Fecondation dans les Phanerogames," par Eugene Fournier: thesis
published in Paris in 1863. The facts noted in Darwin's copy are the
explosive stamens of Parietaria, the submerged flowers of Alisma containing
air, the manner of fertilisation of Lopezia, etc.) I wish you all success
in your gigantic undertaking; but what a pity you did not think of it ten
years ago, so as to have accumulated references on all sorts of subjects.
Depend upon it, you will have started a new era in the floras of various
countries. I can well believe that Mrs. Hooker will be of the greatest
possible use to you in lightening your labours and arranging your
LETTER 697. TO J.D. HOOKER.
Down, December 5th, 1868.
...Now I want to beg for assistance for the new edition of "Origin."
Nageli himself urges that plants offer many morphological differences,
which from being of no service cannot have been selected, and which he
accounts for by an innate principle of progressive development. (697/1.
Nageli's "Enstehung und Begriff der Naturhistorischen Art." An address
delivered at the public session of the Royal Academy of Sciences of Munich,
March 28th, 1865; published by the Academy. Darwin's copy is the 2nd
edition; it bears signs, in the pencilled notes on the margins, of having
been read with interest. Much of it was translated for him by a German
lady, whose version lies with the original among his pamphlets. At page 27
Nageli writes: "It is remarkable that the useful adaptations which Darwin
brings forward in the case of animals, and which may be discovered in
numbers among plants, are exclusively of a physiological kind, that they
always show the formation or transformation of an organ to a special
function. I do not know among plants a morphological modification which
can be explained on utilitarian principles." Opposite this passage Darwin
has written "a very good objection": but Nageli's sentence seems to us to
be of the nature of a truism, for it is clear that any structure whose
evolution can be believed to have come about by Natural Selection must have
a function, and the case falls into the physiological category. The
various meanings given to the term morphological makes another difficulty.
Nageli cannot use it in the sense of "structural"--in which sense it is
often applied, since that would mean that no plant structures have a
utilitarian origin. The essence of morphology (in the better and more
precise sense) is descent; thus we say that a pollen-grain is
morphologically a microspore. And this very example serves to show the
falseness of Nageli's view, since a pollen-grain is an adaptation to aerial
as opposed to aquatic fertilisation. In the 5th edition of the "Origin,"
1869, page 151, Darwin discusses Nageli's essay, confining himself to the
simpler statement that there are many structural characters in plants to
which we cannot assign uses. See Volume I., Letter 207.) I find old notes
about this difficulty; but I have hitherto slurred it over. Nageli gives
as instances the alternate and spiral arrangement of leaves, and the
arrangement of the cells in the tissues. Would you not consider as a
morphological difference the trimerous, tetramerous, etc., divisions of
flowers, the ovules being erect or suspended, their attachment being
parietal or placental, and even the shape of the seed when of no service to
Now, I have thought, and want to show, that such differences follow in some
unexplained manner from the growth or development of plants which have
passed through a long series of adaptive changes. Anyhow, I want to show
that these differences do not support the idea of progressive development.
Cassini states that the ovaria on the circumference and centre of Compos.
flowers differ in essential characters, and so do the seeds in sculpture.
The seeds of Umbelliferae in the same relative positions are coelospermous
and orthospermous. There is a case given by Augt. St. Hilaire of an erect
and suspended ovule in the same ovarium, but perhaps this hardly bears on
the point. The summit flower, in Adoxa and rue differ from the lower
flowers. What is the difference in flowers of the rue? how is the ovarium,
especially in the rue? As Augt. St. Hilaire insists on the locularity of
the ovarium varying on the same plant in some of the Rutaceae, such
differences do not speak, as it seems to me, in favour of progressive
development. Will you turn the subject in your mind, and tell me any more
facts. Difference in structure in flowers in different parts of the same
plant seems best to show that they are the result of growth or position or
amount of nutriment.
I have got your photograph (697/2. A photograph by Mrs. Cameron.) over my
chimneypiece, and like it much; but you look down so sharp on me that I
shall never be bold enough to wriggle myself out of any contradiction.
Owen pitches into me and Lyell in grand style in the last chapter of volume
3 of "Anat. of Vertebrates." He is a cool hand. He puts words from me in
inverted commas and alters them. (697/3. The passage referred to seems to
be in Owen's "Anatomy of Vertebrata," III., pages 798, 799, note. "I
deeply regretted, therefore, to see in a 'Historical Sketch' of the
Progress of Enquiry into the origin of species, prefixed to the fourth
edition of that work (1866), that Mr. Darwin, after affirming inaccurately
and without evidence, that I admitted Natural Selection to have done
something toward that end, to wit, the 'origin of species,' proceeds to
remark: 'It is surprising that this admission should not have been made
earlier, as Prof. Owen now believes that he promulgated the theory of
Natural Selection in a passage read before the Zoological Society in
February, 1850, ("Trans." Volume IV., page 15).'" The first of the two
passages quoted by Owen from the fourth edition of the "Origin" runs: "Yet
he [Prof. Owen] at the same time admits that Natural Selection MAY [our
italics] have done something towards this end." In the sixth edition of
the "Origin," page xviii., Darwin, after referring to a correspondence in
the "London Review" between the Editor of that Journal and Owen, goes on:
"It appeared manifest to the editor, as well as to myself, that Prof. Owen
claimed to have promulgated the theory of Natural Selection before I had
done so;...but as far as it is possible to understand certain recently
published passages (Ibid. ["Anat. of Vert."], Volume III., page 798), I
have either partly or wholly again fallen into error. It is consolatory to
me that others find Prof. Owen's controversial writings as difficult to
understand and to reconcile with each other, as I do. As far as the mere
enunciation of the principle of Natural Selection is concerned, it is quite
immaterial whether or no Prof. Owen preceded me, for both of us, as shown
in this historical sketch, were long ago preceded by Dr. Wells and Mr.
LETTER 698. TO J.D. HOOKER.
Down, December 29th, 1868.
Your letter is quite invaluable, for Nageli's essay (698/1. See preceding
Letter.) is so clever that it will, and indeed I know it has produced a
great effect; so that I shall devote three or four pages to an answer. I
have been particularly struck by your statements about erect and suspended
ovules. You have given me heart, and I will fight my battle better than I
should otherwise have done. I think I cannot resist throwing the
contrivances in orchids into his teeth. You say nothing about the flowers
of the rue. (698/2. For Ruta see "Origin," Edition V., page 154.) Ask
your colleagues whether they know anything about the structure of the
flower and ovarium in the uppermost flower. But don't answer on purpose.
I have gone through my long Index of "Gardeners' Chronicle," which was made
solely for my own use, and am greatly disappointed to find, as I fear,
hardly anything which will be of use to you. (698/3. For Hooker's
projected biological book, see Letter 696.) I send such as I have for the
chance of their being of use.
LETTER 699. TO J.D. HOOKER.
Down, January 16th .
Your two notes and remarks are of the utmost value, and I am greatly
obliged to you for your criticism on the term. "Morphological" seems quite
just, but I do not see how I can avoid using it. I found, after writing to
you, in Vaucher about the Rue (699/1. "Plantes d'Europe," Volume I., page
559, 1841.), but from what you say I will speak more cautiously. It is the
Spanish Chesnut that varies in divergence. Seeds named Viola nana were
sent me from Calcutta by Scott. I must refer to the plants as an "Indian
species," for though they have produced hundreds of closed flowers, they
have not borne one perfect flower. (699/2. The cleistogamic flowers of
Viola are used in the discussion on Nageli's views. See "Origin," Edition
V., page 153.) You ask whether I want illustrations "of ovules differing
in position in different flowers on the same plant." If you know of such
cases, I should certainly much like to hear them. Again you speak of the
angle of leaf-divergence varying and the variations being transmitted. Was
the latter point put in in a hurry to round the sentence, or do you really
know of cases?
Whilst looking for notes on the variability of the divisions of the
ovarium, position of the ovules, aestivation, etc., I found remarks written
fifteen or twenty years ago, showing that I then supposed that characters
which were nearly uniform throughout whole groups must be of high vital
importance to the plants themselves; consequently I was greatly puzzled
how, with organisms having very different habits of life, this uniformity
could have been acquired through Natural Selection. Now, I am much
inclined to believe, in accordance with the view given towards the close of
my MS., that the near approach to uniformity in such structures depends on
their not being of vital importance, and therefore not being acted on by
Natural Selection. (699/3. This view is given in the "Origin," Edition
VI., page 372.) If you have reflected on this point, what do you think of
it? I hope that you approved of the argument deduced from the
modifications in the small closed flowers.
It is only about two years since last edition of "Origin," and I am fairly
disgusted to find how much I have to modify, and how much I ought to add;
but I have determined not to add much. Fleeming Jenkin has given me much
trouble, but has been of more real use to me than any other essay or
review. (699/4. On Fleeming Jenkin's review, "N. British Review," June,
1867, see "Life and Letters," III., page 107.)
LETTER 700. TO J.D. HOOKER.
Down [January 22nd, 1869].
Your letter is quite splenditious. I am greatly tempted, but shall, I
hope, refrain from using some of your remarks in my chapter on
Classification. It is very true what you say about unimportant characters
being so important systematically; yet it is hardly paradoxical bearing in
mind that the natural system is genetic, and that we have to discover the
genealogies anyhow. Hence such parts as organs of generation are so useful
for classification though not concerned with the manner of life. Hence use
for same purpose of rudimentary organs, etc. You cannot think what a
relief it is that you do not object to this view, for it removes PARTLY a
heavy burden from my shoulders. If I lived twenty more years and was able
to work, how I should have to modify the "Origin," and how much the views
on all points will have to be modified! Well, it is a beginning, and that
LETTER 701. TO T.H. FARRER (Lord Farrer).
Down, August 10th, 1869.
Your view seems most ingenious and probable; but ascertain in a good many
cases that the nectar is actually within the staminal tube. (701/1. It
seems that Darwin did not know that the staminal tube in the diadelphous
Leguminosae serves as a nectar-holder, and this is surprising, as Sprengel
was aware of the fact.) One can see that if there is to be a split in the
tube, the law of symmetry would lead it to be double, and so free one
stamen. Your view, if confirmed, would be extremely well worth publication
before the Linnean Society. It is to me delightful to see what appears a
mere morphological character found to be of use. It pleases me the more as
Carl Nageli has lately been pitching into me on this head. Hooker, with
whom I discussed the subject, maintained that uses would be found for lots
more structures, and cheered me by throwing my own orchids into my teeth.
(701/2. See Letters 697-700.)
All that you say about changed position of the peduncle in bud, in flower,
and in seed, is quite new to me, and reminds me of analogous cases with
tendrils. (701/3. See Vochting, "Bewegung der Bluthen und Fruchte," 1882;
also Kerner, "Pflanzenleben," Volume I., page 494, Volume II., page 121.)
This is well worth working out, and I dare say the brush of the stigma.
With respect to the hairs or filaments (about which I once spoke) within
different parts of flowers, I have a splendid Tacsonia with perfectly
pendent flowers, and there is only a microscopical vestige of the corona of
coloured filaments; whilst in most common passion-flowers the flowers stand
upright, and there is the splendid corona which apparently would catch
pollen. (701/4. Sprengel ("Entdeckte Geheimniss," page 164) imagined that
the crown of the Passion-flower served as a nectar-guide and as a platform
for insects, while other rings of filaments served to keep rain from the
nectar. F. Muller, quoted in H. Muller ("Fertilisation," page 268), looks
at the crowns of hairs, ridges in some species, etc., as gratings serving
to imprison flies which attract the fertilising humming-birds. There is,
we believe, no evidence that the corona catches pollen. See Letter 704,
On the lower side of corolla of foxglove there are some fine hairs, but
these seem of not the least use (701/5. It has been suggested that the
hairs serve as a ladder for humble bees; also that they serve to keep out
"unbidden guests.")--a mere purposeless exaggeration of down on outside--as
I conclude after watching the bees at work, and afterwards covering up some
plants; for the protected flowers rarely set any seed, so that the hairy
lower part of corolla does not come into contact with stigma, as some
Frenchman says occurs with some other plants, as Viola odorata and I think
I heartily wish I could accept your kind invitation, for I am not by nature
a savage, but it is impossible. Forgive my dreadful handwriting, none of
my womenkind are about to act as amanuensis.
LETTER 702. TO WILLIAM C. TAIT.
(702/1. Mr. Tait, to whom the following letter is addressed, was resident
in Portugal. His kindness in sending plants of Drosophyllum lusitanicum is
acknowledged in "Insectivorous Plants.")
Down, March 12th, 1869.
I have received your two letters of March 2nd and 5th, and I really do not
know how to thank you enough for your extraordinary kindness and energy. I
am glad to hear that the inhabitants notice the power of the Drosophyllum
to catch flies, for this is the subject of my studies. (702/2. The
natives are said to hang up plants of Drosophyllum in their cottages to act
as fly-papers ("Insectivorous Plants," page 332).) I have observed during
several years the manner in which this is effected, and the results
produced in several species of Drosera, and in the wonderful American
Dionoea, the leaves of which catch insects just like a steel rat-trap.
Hence I was most anxious to learn how the Drosophyllum would act, so that
the Director of the Royal Gardens at Kew wrote some years ago to Portugal
to obtain specimens for me, but quite failed. So you see what a favour you
have conferred on me. With Drosera it is nothing less than marvellous how
minute a fraction of a grain of any nitrogenised matter the plant can
detect; and how differently it behaves when matter, not containing
nitrogen, of the same consistence, whether fluid or solid, is applied to
the glands. It is also exquisitely sensitive to a weight of even the
1/70000 of a grain. From what I can see of the glands on Drosophyllum I
suspect that I shall find only the commencement, or nascent state of the
wonderful capacities of the Drosera, and this will be eminently interesting
to me. My MS. on this subject has been nearly ready for publication during
some years, but when I shall have strength and time to publish I know not.
And now to turn to other points in your letter. I am quite ignorant of
ferns, and cannot name your specimen. The variability of ferns passes all
bounds. With respect to your Laugher Pigeons, if the same with the two
sub-breeds which I kept, I feel sure from the structure of the skeleton,
etc., that it is a descendant of C. livia. In regard to beauty, I do not
feel the difficulty which you and some others experience. In the last
edition of my "Origin" I have discussed the question, but necessarily very
briefly. (702/3. Fourth Edition, page 238.) A new and I hope amended
edition of the "Origin" is now passing through the press, and will be
published in a month or two, and it will give me great pleasure to send you
a copy. Is there any place in London where parcels are received for you,
or shall I send it by post? With reference to dogs' tails, no doubt you
are aware that a rudimentary stump is regularly inherited by certain breeds
of sheep-dogs, and by Manx cats. You speak of a change in the position of
the axis of the earth: this is a subject quite beyond me, but I believe
the astronomers reject the idea. Nevertheless, I have long suspected that
some periodical astronomical or cosmical cause must be the agent of the
incessant oscillations of level in the earth's crust. About a month ago I
suggested this to a man well capable of judging, but he could not conceive
any such agency; he promised, however, to keep it in mind. I wish I had
time and strength to write to you more fully. I had intended to send this
letter off at once, but on reflection will keep it till I receive the
LETTER 703. TO H. MULLER.
Down, March 14th, 1870.
I think you have set yourself a new, very interesting, and difficult line
of research. As far as I know, no one has carefully observed the structure
of insects in relation to flowers, although so many have now attended to
the converse relation. (703/1. See Letter 462, also H. Muller,
"Fertilisation of Flowers," English Translation, page 30, on "The insects
which visit flowers." In Muller's book references are given to several of
his papers on this subject.) As I imagine few or no insects are adapted to
suck the nectar or gather the pollen of any single family of plants, such
striking adaptations can hardly, I presume, be expected in insects as in
LETTER 704. TO T.H. FARRER (Lord Farrer).
Down, May 28th, 1870.
I suppose I must have known that the stamens recovered their former
position in Berberis (704/1. See Farrer, "Nature," II., 1870, page 164.
Lord Farrer was before H. Muller in making out the mechanism of the
barberry.), for I formerly tried experiments with anaesthetics, but I had
forgotten the facts, and I quite agree with you that it is a sound argument
that the movement is not for self-fertilisation. The N. American
barberries (Mahonia) offer a good proof to what an extent natural crossing
goes on in this genus; for it is now almost impossible in this country to
procure a true specimen of the two or three forms originally introduced.
I hope the seeds of Passiflora will germinate, for the turning up of the
pendent flower must be full of meaning. (704/2. Darwin had (May 12th,
1870) sent to Farrer an extract from a letter from F. Muller, containing a
description of a Passiflora visited by humming-birds, in which the long
flower-stalk curls up so that "the flower itself is upright." Another
species visited by bees is described as having "dependent flowers." In a
letter, June 29th, 1870, Mr. Farrer had suggested that P. princeps, which
he described as having sub-erect flowers, is fitted for humming-birds'
visits. In another letter, October 13th, 1869, he says that Tacsonia,
which has pendent flowers and no corona, is not fertilised by insects in
English glass-houses, and may be adapted for humming-birds. See "Life and
Letters," III., page 279, for Farrer's remarks on Tacsonia and Passiflora;
also H. Muller's "Fertilisation of Flowers," page 268, for what little is
known on the subject; also Letter 701 in the present volume.) I am so glad
that you are able to occupy yourself a little with flowers: I am sure it
is most wise in you, for your own sake and children's sakes.
Some little time ago Delpino wrote to me praising the Swedish book on the
fertilisation of plants; as my son George can read a little Swedish, I
should like to have it back for a time, just to hear a little what it is
about, if you would be so kind as to return it by book-post. (704/3.
Severin Axell, "Om anordningarna for de Fanerogama Vaxternas Befruktning,"
I am going steadily on with my experiments on the comparative growth of
crossed and self-fertilised plants, and am now coming to some very curious
anomalies and some interesting results. I forget whether I showed you any
of them when you were here for a few hours. You ought to see them, as they
explain at a glance why Nature has taken such extraordinary pains to ensure
frequent crosses between distinct individuals.
If in the course of the summer you should feel any inclination to come here
for a day or two, I hope that you will propose to do so, for we should be
delighted to see you...
LETTER 705. TO ASA GRAY.
Down, December 7th, 1870.
I have been very glad to receive your letter this morning. I have for some
time been wishing to write to you, but have been half worked to death in
correcting my uncouth English for my new book. (705/1. "Descent of Man.")
I have been glad to hear of your cases appearing like incipient dimorphism.
I believe that they are due to mere variability, and have no significance.
I found a good instance in Nolana prostrata, and experimented on it, but
the forms did not differ in fertility. So it was with Amsinckia, of which
you told me. I have long thought that such variations afforded the basis
for the development of dimorphism. I was not aware of such cases in Phlox,
but have often admired the arrangement of the anthers, causing them to be
all raked by an inserted proboscis. I am glad also to hear of your curious
case of variability in ovules, etc.
I said that I had been wishing to write to you, and this was about your
Drosera, which after many fluctuations between life and death, at last made
a shoot which I could observe. The case is rather interesting; but I must
first remind you that the filament of Dionoea is not sensitive to very
light prolonged pressure, or to nitrogenous matter, but is exquisitely
sensitive to the slightest touch. (705/2. In another connection the
following reference to Dionoea is of some interest: "I am sure I never
heard of Curtis's observations on Dionoea, nor have I met with anything
more than general statements about this plant or about Nepenthes catching
insects." (From a letter to Sir J.D. Hooker, July 12th, 1860.)) In our
Drosera the filaments are not sensitive to a slight touch, but are
sensitive to prolonged pressure from the smallest object of any nature;
they are also sensitive to solid or fluid nitrogenous matter. Now in your
Drosera the filaments are not sensitive to a rough touch or to any pressure
from non-nitrogenous matter, but are sensitive to solid or fluid
nitrogenous matter. (705/3. Drosera filiformis: see "Insectivorous
Plants," page 281. The above account does not entirely agree with Darwin's
published statement. The filaments moved when bits of cork or cinder were
placed on them; they did not, however, respond to repeated touches with a
needle, thus behaving differently from D. rotundifolia. It should be
remembered that the last-named species is somewhat variable in reacting to
repeated touches.) Is it not curious that there should be such diversified
sensitiveness in allied plants?
I received a very obliging letter from Mr. Morgan, but did not see him, as
I think he said he was going to start at once for the Continent. I am
sorry to hear rather a poor account of Mrs. Gray, to whom my wife and I
both beg to be very kindly remembered.
LETTER 706. TO C.V. RILEY.
(706/1. In Riley's opinion his most important work was the series entitled
"Annual Report on the Noxious, Beneficial, and other Insects of the State
of Missouri" (Jefferson City), beginning in 1869. These reports were
greatly admired by Mr. Darwin, and his copies of them, especially of Nos. 3
and 4, show signs of careful reading.)
Down, June 1st .
I received some little time ago your report on noxious insects, and have
now read the whole with the greatest interest. (706/2. "Third Annual
Report on the Noxious, Beneficial, and other Insects of the State of
Missouri" (Jefferson City, Mo.). The mimetic case occurs at page 67; the
1875 pupae of Pterophorus periscelidactylus, the "Grapevine Plume," have
pupae either green or reddish brown, the former variety being found on the
leaves, the latter on the brown stems of the vine.) There are a vast
number of facts and generalisations of value to me, and I am struck with
admiration at your powers of observation.
The discussion on mimetic insects seems to me particularly good and
original. Pray accept my cordial thanks for the instruction and interest
which I have received.
What a loss to Natural Science our poor mutual friend Walsh has been; it is
a loss ever to be deplored...
Your country is far ahead of ours in some respects; our Parliament would
think any man mad who should propose to appoint a State Entomologist.
LETTER 707A. TO C.V. RILEY.
(706A/1. We have found it convenient to place the two letters to Riley
together, rather than separate them chronologically.)
Down, September 28th, 1881.
I must write half a dozen lines to say how much interested I have been by
your "Further Notes" on Pronuba which you were so kind as to send me.
(706A/2. "Proc. Amer. Assoc. Adv. Sci." 1880.) I had read the various
criticisms, and though I did not know what answer could be made, yet I felt
full confidence in your result, and now I see that I was right...If you
make any further observation on Pronuba it would, I think, be well worth
while for you to observe whether the moth can or does occasionally bring
pollen from one plant to the stigma of a distinct one (706A/3. Riley
discovered the remarkable fact that the Yucca moth (Pronuba yuccasella)
lays its eggs in the ovary of Yucca flowers, which it has previously
pollinated, thus making sure of a supply of ovules for the larvae.), for I
have shown that the cross-fertilisation of the flowers on the same plant
does very little good; and, if I am not mistaken, you believe that Pronuba
gathers pollen from the same flower which she fertilises.
What interesting and beautiful observations you have made on the
metamorphoses of the grasshopper-destroying insects.
LETTER 707. TO F. HILDEBRAND.
Down, February 9th .
Owing to other occupations I was able to read only yesterday your paper on
the dispersal of the seeds of Compositae. (707/1. "Ueber die
Verbreitungsmittel der Compositenfruchte." "Bot. Zeitung," 1872, page 1.)
Some of the facts which you mention are extremely interesting.
I write now to suggest as worthy of your examination the curious adhesive
filaments of mucus emitted by the achenia of many Compositae, of which no
doubt you are aware. My attention was first called to the subject by the
achenia of an Australian Pumilio (P. argyrolepis), which I briefly
described in the "Gardeners' Chronicle," 1861, page 5. As the threads of
mucus dry and contract they draw the seeds up into a vertical position on
the ground. It subsequently occurred to me that if these seeds were to
fall on the wet hairs of any quadruped they would adhere firmly, and might
be carried to any distance. I was informed that Decaisne has written a
paper on these adhesive threads. What is the meaning of the mucus so
copiously emitted from the moistened seeds of Iberis, and of at least some
species of Linum? Does the mucus serve as a protection against their being
devoured, or as a means of attachment. (707/2. Various theories have been
suggested, e.g., that the slime by anchoring the seed to the soil
facilitates the entrance of the radicle into the soil: the slime has also
been supposed to act as a temporary water-store. See Klebs in Pfeffer's
"Untersuchungen aus dem Bot. Inst. zu Tubingen," I., page 581.) I have
been prevented reading your paper sooner by attempting to read Dr.
Askenasy's pamphlet, but the German is too difficult for me to make it all
out. (707/3. E. Askenasy, "Beitrage zur Kritik der Darwin'schen Lehre."
Leipzig, 1872.) He seems to follow Nageli completely. I cannot but think
that both much underrate the utility of various parts of plants; and that
they greatly underrate the unknown laws of correlated growth, which leads
to all sorts of modifications, when some one structure or the whole plant
is modified for some particular object.
LETTER 708. TO T.H. FARRER. (Lord Farrer).
(708/1. The following letter refers to a series of excellent observations
on the fertilisation of Leguminosae, made by Lord Farrer in the autumn of
1869, in ignorance of Delpino's work on the subject. The result was
published in "Nature," October 10th and 17th, 1872, and is full of
interesting suggestions. The discovery of the mechanism in Coronilla
mentioned in a note was one of the cases in which Lord Farrer was
I declare I am almost as sorry as if I had been myself forestalled--indeed,
more so, for I am used to it. It is, however, a paramount, though
bothersome duty in every naturalist to try and make out all that has been
done by others on the subject. By all means publish next summer your
confirmation and a summary of Delpino's observations, with any new ones of
your own. Especially attend about the nectary exterior to the staminal
tube. (708/2. This refers to a species of Coronilla in which Lord Farrer
made the remarkable discovery that the nectar is secreted on the outside of
the calyx. See "Nature," July 2nd, 1874, page 169; also Letter 715.) This
will in every way be far better than writing to Delpino. It would not be
at all presumptuous in you to criticise Delpino. I am glad you think him
so clever; for so it struck me.
Look at hind legs yourself of some humble and hive-bees; in former take a
very big individual (if any can be found) for these are the females, the
males being smaller, and they have no pollen-collecting apparatus. I do
not remember where it is figured--probably in Kirby & Spence--but actual
Please do not return any of my books until all are finished, and do not
I feel certain you will make fine discoveries.
LETTER 709. TO T.H. FARRER. (Lord Farrer).
Sevenoaks, October 13th, 1872.
I must send you a line to say how extremely good your article appears to me
to be. It is even better than I thought, and I remember thinking it very
good. I am particularly glad of the excellent summary of evidence about
the common pea, as it will do for me hereafter to quote; nocturnal insects
will not do. I suspect that the aboriginal parent had bluish flowers. I
have seen several times bees visiting common and sweet peas, and yet
varieties, purposely grown close together, hardly ever intercross. This is
a point which for years has half driven me mad, and I have discussed it in
my "Var. of Animals and Plants under Dom." (709/1. In the second edition
(1875) of the "Variation of Animals and Plants," Volume I., page 348,
Darwin added, with respect to the rarity of spontaneous crosses in Pisum:
"I have reason to believe that this is due to their stignas being
prematurely fertilised in this country by pollen from the same flower."
This explanation is, we think, almost certainly applicable to Lathyrus
odoratus, though in Darwin's latest publication on the subject he gives
reasons to the contrary. See "Cross and Self-Fertilisation," page 156,
where the problem is left unsolved. Compare Letter 714 to Delpino. In
"Life and Letters," III., page 261, the absence of cross-fertilisation is
explained as due to want of perfect adaptation between the pea and our
native insects. This is Hermann Muller's view: see his "Fertilisation of
Flowers," page 214. See Letter 583, note.) I now suspect (and I wish I
had strength to experimentise next spring) that from changed climate both
species are prematurely fertilised, and therefore hardly ever cross. When
artificially crossed by removal of own pollen in bud, the offspring are
Farewell.--I wish I could compel you to go on working at fertilisation
instead of so insignificant a subject as the commerce of the country!
You pay me a very pretty compliment at the beginning of your paper.
LETTER 710. TO J.D. HOOKER.
(710/1. The following letters to Sir J.D. Hooker and the late Mr.
Moggridge refer to Moggridge's observation that seeds stored in the nest
of the ant Atta at Mentone do not germinate, though they are certainly
not dead. Moggridge's observations are given in his book, "Harvesting
Ants and Trap-Door Spiders," 1873, which is full of interesting details.
The book is moreover remarkable in having resuscitated our knowledge of
the existence of the seed-storing habit. Mr. Moggridge points out that
the ancients were familiar with the facts, and quotes the well-known
fable of the ant and the grasshopper, which La Fontaine borrowed from
Aesop. Mr. Moggridge (page 5) goes on: "So long as Europe was taught
Natural History by southern writers the belief prevailed; but no sooner
did the tide begin to turn, and the current of information to flood from
north to south, than the story became discredited."
In Moggridge's "supplement" on the same subject, published in 1874, the
author gives an account of his experiments made at Darwin's suggestion,
and concludes (page 174) that "the vapour of formic acid is incapable of
rendering the seeds dormant after the manner of the ants," and that
indeed "its influence is always injurious to the seeds, even when
present only in excessively minute quantities." Though unable to
explain the method employed, he was convinced "that the non-germination
of the seeds is due to some direct influence voluntarily exercised by
the ants, and not merely to the conditions found in the nest" (page
172). See Volume I., Letter 251.)
Down, February 21st .
You have given me exactly the information which I wanted.
Geniuses jump. I have just procured formic acid to try whether its
vapour or minute drops will delay germination of fresh seeds; trying
others at same time for comparison. But I shall not be able to try them
till middle of April, as my despotic wife insists on taking a house in
London for a month from the middle of March.
I am glad to hear of the Primer (710/2. "Botany" (Macmillan's Science
Primers).); it is not at all, I think, a folly. Do you know Asa Gray's
child book on the functions of plants, or some such title? It is very
good in giving an interest to the subject.
By the way, can you lend me the January number of the "London Journal of
Botany" for an article on insect-agency in fertilisation?
LETTER 711. TO J. TRAHERNE MOGGRIDGE.
Down, August 27th, 1873.
I thank you for your very interesting letter, and I honour you for your
laborious and careful experiments. No one knows till he tries how many
unexpected obstacles arise in subjecting plants to experiments.
I can think of no suggestions to make; but I may just mention that I had
intended to try the effects of touching the dampened seeds with the
minutest drop of formic acid at the end of a sharp glass rod, so as to
imitate the possible action of the sting of the ant. I heartily hope
that you may be rewarded by coming to some definite result; but I fail
five times out of six in my own experiments. I have lately been trying
some with poor success, and suppose that I have done too much, for I
have been completely knocked up for some days.
LETTER 712. TO J. TRAHERNE MOGGRIDGE.
Down, March 10th, 1874.
I am very sorry to hear that the vapour experiments have failed; but
nothing could be better, as it seems to me, than your plan of enclosing
a number of the ants with the seeds. The incidental results on the
power of different vapours in killing seeds and stopping germination
appear very curious, and as far as I know are quite new.
P.S.--I never before heard of seeds not germinating except during a
certain season; it will be a very strange fact if you can prove this.
(712/1. Certain seeds pass through a resting period before germination.
See Pfeffer's "Pflanzenphysiologie," Edition I., Volume II., page III.)
LETTER 713. TO H. MULLER.
Down, May 30th, 1873.
I am much obliged for your letter received this morning. I write now
chiefly to give myself the pleasure of telling you how cordially I
admire the last part of your book, which I have finished. (713/1. "Die
Befruchtung der Blumen durch Insekten": Leipzig, 1873. An English
translation was published in 1883 by Prof. D'Arcy Thompson. The
"Prefatory Notice" to this work (February 6th, 1882) is almost the last
of Mr. Darwin's writings. See "Life and Letters," page 281.) The whole
discussion seems to me quite excellent, and it has pleased me not a
little to find that in the rough MS. of my last chapter I have arrived
on many points at nearly the same conclusions that you have done, though
we have reached them by different routes. (713/2. "The Effects of
Cross and Self-Fertilisation in the Vegetable Kingdom": London, 1876.)
LETTER 714. TO F. DELPINO.
Down, June 25th .
I thank you sincerely for your letter. I am very glad to hear about
Lathyrus odoratus, for here in England the vars. never cross, and yet
are sometimes visited by bees. (714/1. In "Cross and
Self-Fertilisation," page 156, Darwin quotes the information received
from Delpino and referred to in the present letter--namely, that it is
the fixed opinion of the Italian gardeners that the varieties do
intercross. See Letter 709.) Pisum sativum I have also many times seen
visited by Bombus. I believe the cause of the many vars. not crossing
is that under our climate the flowers are self-fertilised at an early
period, before the corolla is fully expanded. I shall examine this
point with L. odoratus. I have read H. Muller's book, and it seems to
me very good. Your criticism had not occurred to me, but is, I think
just--viz. that it is much more important to know what insects
habitually visit any flower than the various kinds which occasionally
visit it. Have you seen A. Kerner's book "Schutzmittel des Pollens,"
1873, Innsbruck. (714/2. Afterwards translated by Dr. Ogle as "Flowers
and their Unbidden Guests," with a prefatory letter by Charles Darwin,
1878.) It is very interesting, but he does not seem to know anything
about the work of other authors.
I have Bentham's paper in my house, but have not yet had time to read a
word of it. He is a man with very sound judgment, and fully admits the
principle of evolution.
I have lately had occasion to look over again your discussion on
anemophilous plants, and I have again felt much admiration at your work.
(714/3. "Atti della Soc. Italiana di Scienze Nat." Volume XIII.)
(714/4. In the beginning of August, 1873, Darwin paid the first of
several visits to Lord Farrer's house at Abinger. When sending copies
of Darwin's letters for the "Life and Letters," Lord Farrer was good
enough to add explanatory notes and recollections, from which we quote
the following sketch.)
"Above my house are some low hills, standing up in the valley, below the
chalk range on the one hand and the more distant range of Leith Hill on
the other, with pretty views of the valley towards Dorking in one
direction and Guildford in the other. They are composed of the less
fertile Greensand strata, and are covered with fern, broom, gorse, and
heath. Here it was a particular pleasure of his to wander, and his tall
figure, with his broad-brimmed Panama hat and long stick like an
alpenstock, sauntering solitary and slow over our favourite walks, is
one of the pleasantest of the many pleasant associations I have with the
LETTER 715. TO T.H. FARRER (Lord Farrer).
(715/1. The following note by Lord Farrer explains the main point of
the letter, which, however, refers to the "bloom" problem as well as to
"I thought I had found out what puzzled us in Coronilla varia: in most
of the Papilionaceae, when the tenth stamen is free, there is nectar in
the staminal tube, and the opening caused by the free stamen enables the
bee to reach the nectar, and in so doing the bee fertilises the plant.
In Coronilla varia, and in several other species of Coronilla, there is
no nectar in the staminal tube or in the tube of the corolla. But there
are peculiar glands with nectar on the outside of the calyx, and
peculiar openings in the tube of the corolla through which the proboscis
of the bee, whilst entering the flower in the usual way and dusting
itself with pollen, can reach these glands, thus fertilising the plant
in getting the nectar. On writing this to Mr. Darwin, I received the
following characteristic note.
The first postscript relates to the rough ground behind my house, over
which he was fond of strolling. It had been ploughed up and then
allowed to go back, and the interest was to watch how the numerous
species of weeds of cultivation which followed the plough gradually gave
way in the struggle for existence to the well-known and much less varied
flora of an English common.")
Bassett, Southampton, August 14th, 1873.
You are the man to conquer a Coronilla. (715/2. In a former letter to
Lord Farrer, Darwin wrote: "Here is a maxim for you, 'It is disgraceful
to be beaten by a Coronilla.'") I have been looking at the half-dried
flowers, and am prepared to swear that you have solved the mystery. The
difference in the size of the cells on the calyx under the vexillum
right down to the common peduncle is conspicuous. The flour still
adhered to this side; I see little bracteae or stipules apparently with
glandular ends at the base of the calyces. Do these secrete? It seems
to me a beautiful case. When I saw the odd shape of the base of the
vexillum, I concluded that it must have some meaning, but little dreamt
what that was. Now there remains only the one serious point--viz.the
separation of the one stamen. I daresay that you are right in that
nectar was originally secreted within the staminal tube; but why has not
the one stamen long since cohered? The great difference in structure
for fertilisation within the same genus makes one believe that all such
points are vary variable. (715/3. Coronilla emerus is of the ordinary
papilionaceous type.) With respect to the non-coherence of the one
stamen, do examine some flower-buds at a very early age; for parts which
are largely developed are often developed to an unusual degree at a very
early age, and it seems to me quite possible that the base of the
vexillum (to which the single stamen adhered) might thus be developed,
and thus keep it separate for a time from the other stamens. The
cohering stamens to the right and left of the single one seem to me to
be pushed out a little laterally. When you have finished your
observations, you really ought to send an account with a diagram to
"Nature," recalling your generalisation about the diadelphous structure,
and now explaining the exception of Coronilla. (715/4. The
observations were published in "Nature," Volume X., 1874, page 169.)
Do add a remark how almost every detail of structure has a meaning where
a flower is well examined.
Your observations pleased me so much that I could not sit still for half
Please to thank Mr. Payne (715/5. Lord Farrer's gardener.) for his
remarks, which are of value to me, with reference to Mimosa. I am very
much in doubt whether opening the sashes can act by favouring the
evaporation of the drops; may not the movement of the leaves shake off
the drops, or change their places? If Mr. Payne remembers any plant
which is easily injured by drops, I wish he would put a drop or two on a
leaf on a bright day, and cover the plant with a clean bell-glass, and
do the same for another plant, but without a bell-glass over it, and
observe the effects.
Thank you much for wishing to see us again at Abinger, and it is very
doubtful whether it will be Coronilla, Mr. Payne, the new garden, the
children, E. [Lady Farrer], or yourself which will give me the most
pleasure to see again.
P.S. 1.--It will be curious to note in how many years the rough ground
becomes quite uniform in its flora.
P.S. 2.--One may feel sure that periodically nectar was secreted within
the flower and then secreted by the calyx, as in some species of Iris
and orchids. This latter being taken advantage of in Coronilla would
allow of the secretion within the flower ceasing, and as this change was
going on in the two secretions, all the parts of the flower would become
modified and correlated.
LETTER 716. TO J. BURDON SANDERSON.
Down, Tuesday, September 9th .
(716/1. Sir J. Burdon Sanderson showed that in Dionoea movement is
accompanied by electric disturbances closely analogous to those
occurring in muscle (see "Nature," 1874, pages 105, 127; "Proc. R. Soc."
XXI., and "Phil. Trans." Volume CLXXIII., 1883, where the results are
I will send up early to-morrow two plants [of Dionoea] with five goodish
leaves, which you will know by their being tied to sticks. Please
remember that the slightest touch, even by a hair, of the three
filaments on each lobe makes the leaf close, and it will not open for
twenty-four hours. You had better put 1/4 in. of water into the saucers
of the pots. The plants have been kept too cool in order to retard
them. You had better keep them rather warm (i.e. temperature of warm
greenhouse) for a day, and in a good light.
I am extremely glad you have undertaken this subject. If you get a
positive result, I should think you ought to publish it separately, and
I could quote it; or I should be most glad to introduce any note by you
into my account.
I have no idea whether it is troublesome to try with the thermo-electric
pile any change of temperature when the leaf closes. I could detect
none with a common thermometer. But if there is any change of
temperature I should expect it would occur some eight to twelve or
twenty-four hours after the leaf has been given a big smashed fly, and
when it is copiously secreting its acid digestive fluid.
I forgot to say that, as far as I can make out, the inferior surface of
the leaf is always in a state of tension, and that the contraction is
confined to the upper surface; so that when this contraction ceases or
suddenly fails (as by immersion in boiling water) the leaf opens again,
or more widely than is natural to it.
Whenever you have quite finished, I will send for the plants in their
basket. My son Frank is staying at 6, Queen Anne Street, and comes home
on Saturday afternoon, but you will not have finished by that time.
P.S. I have repeated my experiment on digestion in Drosera with
complete success. By giving leaves a very little weak hydrochloric
acid, I can make them digest albumen--i.e. white of egg--quicker than
they can do naturally. I most heartily thank you for all your kindness.
I have been pretty bad lately, and must work very little.
LETTER 717. TO J. BURDON SANDERSON.
September 13th .
How very kind it was of you to telegraph to me. I am quite delighted
that you have got a decided result. Is it not a very remarkable fact?
It seems so to me, in my ignorance. I wish I could remember more
distinctly what I formerly read of Du Bois Raymond's results. My poor
memory never serves me for more than a vague guide. I really think you
ought to try Drosera. In a weak solution of phosphate of ammonia (viz.
1 gr. to 20 oz. of water) it will contract in about five minutes, and
even more quickly in pure warm water; but then water, I suppose, would
prevent your trial. I forget, but I think it contracts pretty quickly
(i.e. in an hour or two) with a large drop of a rather stronger solution
of the phosphate, or with an atom of raw meat on the disc of the leaf.
LETTER 718. TO J.D. HOOKER.
October 31st, 1873.
Now I want to tell you, for my own pleasure, about the movements of
1. When the plant goes to sleep, the terminal leaflets hang vertically
down, but the petioles move up towards the axis, so that the dependent
leaves are all crowded round it. The little leaflets never go to sleep,
and this seems to me very odd; they are at their games of play as late
as 11 o'clock at night and probably later. (718/1. Stahl ("Botanische
Zeitung," 1897, page 97) has suggested that the movements of the dwarf
leaflets in Desmodium serve to shake the large terminal leaflets, and
thus increase transpiration. According to Stahl's view their movement
would be more useful at night than by day, because stagnation of the
transpiration-current is more likely to occur at night.)
2. If the plant is shaken or syringed with tepid water, the terminal
leaflets move down through about an angle of 45 deg, and the petioles
likewise move about 11 deg downwards; so that they move in an opposite
direction to what they do when they go to sleep. Cold water or air
produces the same effect as does shaking. The little leaflets are not
in the least affected by the plant being shaken or syringed. I have no
doubt, from various facts, that the downward movement of the terminal
leaflets and petioles from shaking and syringing is to save them from
injury from warm rain.
3. The axis, the main petiole, and the terminal leaflets are all, when
the temperature is high, in constant movement, just like that of
climbing plants. This movement seems to be of no service, any more than
the incessant movement of amoeboid bodies. The movement of the terminal
leaflets, though insensible to the eye, is exactly the same as that of
the little lateral leaflets--viz. from side to side, up and down, and
half round their own axes. The only difference is that the little
leaflets move to a much greater extent, and perhaps more rapidly; and
they are excited into movement by warm water, which is not the case with
the terminal leaflet. Why the little leaflets, which are rudimentary in
size and have lost their sleep-movements and their movements from being
shaken, should not only have retained, but have their spontaneous
movements exaggerated, I cannot conceive. It is hardly credible that it
is a case of compensation. All this makes me very anxious to examine
some plant (if possible one of the Leguminosae) with either the terminal
or lateral leaflets greatly reduced in size, in comparison with the
other leaflets on the same leaf. Can you or any of your colleagues
think of any such plant? It is indirectly on this account that I so
much want the seeds of Lathyrus nissolia.
I hear from Frank that you think that the absence of both lateral
leaflets, or of one alone, is due to their having dropped off; I thought
so at first, and examined extremely young leaves from the tips of the
shoots, and some of them presented the same characters. Some
appearances make me think that they abort by becoming confluent with the
I hear also that you doubt about the little leaflets ever standing not
opposite to each other: pray look at the enclosed old leaf which has
been for a time in spirits, and can you call the little leaflets
opposite? I have seen many such cases on both my plants, though few so
LETTER 719. TO J.D. HOOKER.
Down, October 23rd .
How good you have been about the plants; but indeed I did not intend you
to write about Drosophyllum, though I shall be very glad to have a
specimen. Experiments on other plants lead to fresh experiments.
Neptunia is evidently a hopeless case. I shall be very glad of the
other plants whenever they are ready. I constantly fear that I shall
become to you a giant of bores.
I am delighted to hear that you are at work on Nepenthes, and I hope
that you will have good luck. It is good news that the fluid is acid;
you ought to collect a good lot and have the acid analysed. I hope that
the work will give you as much pleasure as analogous work has me.
(719/1. Hooker's work on Nepenthes is referred to in "Insectivorous
Plants," page 97: see also his address at the Belfast meeting of the
British Association, 1874.) I do not think any discovery gave me more
pleasure than proving a true act of digestion in Drosera.
LETTER 720. TO J.D. HOOKER.
Down, November 24th, 1873.
I have been greatly interested by Mimosa albida, on which I have been
working hard. Whilst your memory is pretty fresh, I want to ask a
question. When this plant was most sensitive, and you irritated it, did
the opposite leaflets shut up quite close, as occurs during sleep, when
even a lancet could not be inserted between the leaflets? I can never
cause the leaflets to come into contact, and some reasons make me doubt
whether they ever do so except during sleep; and this makes me wish much
to hear from you. I grieve to say that the plant looks more unhealthy,
even, than it was at Kew. I have nursed it like the tenderest infant;
but I was forced to cut off one leaf to try the bloom, and one was
broken by the manner of packing. I have never syringed (with tepid
water) more than one leaf per day; but if it dies, I shall feel like a
murderer. I am pretty well convinced that I shall make out my case of
movements as a protection against rain lodging on the leaves. As far as
I have as yet made out, M. albida is a splendid case.
I have had no time to examine more than one species of Eucalyptus. The
seedlings of Lathyrus nissolia are very interesting to me; and there is
something wonderful about them, unless seeds of two distinct leguminous
species have got somehow mingled together.
LETTER 721. TO W. THISELTON-DYER.
Down, December 4th, 1873.
As Hooker is so busy, I should be very much obliged if you could give me
the name of the enclosed poor specimen of Cassia. I want much to know
its name, as its power of movement, when it goes to sleep, is very
remarkable. Linnaeus, I find, was aware of this. It twists each
separate leaflet almost completely round (721/1. See "Power of Movement
in Plants," Figure 154, page 370.), so that the lower surface faces the
sky, at the same time depressing them all. The terminal leaflets are
pointed towards the base of the leaf. The whole leaf is also raised up
about 12 deg. When I saw that it possessed such complex powers of
movement, I thought it would utilise its power to protect the leaflets
from rain. Accordingly I syringed the plant for two minutes, and it was
really beautiful to see how each leaflet on the younger leaves twisted
its short sub-petiole, so that the blade was immediately directed at an
angle between 45 and 90 deg to the horizon. I could not resist the
pleasure of just telling you why I want to know the name of the Cassia.
I should add that it is a greenhouse plant. I suppose that there will
not be any better flowers till next summer or autumn.
LETTER 722. TO T. BELT.
(722/1. Belt's account, discussed in this letter, is probably that
published in his "Naturalist in Nicaragua" (1874), where he describes
"the relation between the presence of honey-secreting glands on plants,
and the protection to the latter secured by the attendance of ants
attracted by the honey." (Op. cit., pages 222 et seq.))
Your account of the ants and their relations seems to me to possess
extraordinary interest. I do not doubt that the excretion of sweet
fluid by the glands is in your cases of great advantage to the plants by
means of the ants, but I cannot avoid believing that primordially it is
a simple excretion, as occasionally occurs from the surface of the
leaves of lime trees. It is quite possible that the primordial
excretion may have been beneficially increased to serve the plant. In
the common laurel [Prunus laurocerasus] of our gardens the hive-bees
visit incessantly the glands of the young leaves, on their under sides;
and I should altogether doubt whether their visits or the occasional
visits of ants was of any service to the laurel. The stipules of the
common vetch secrete largely during sunshine, and hive-bees collect the
sweet fluid. So I think it is with the common bean.
I am writing this away from home, and I have come away to get some rest,
having been a good deal overworked. I shall read your book with great
interest when published, but will not trouble you to send the MS., as I
really have no spare strength or time. I believe that your book,
judging by the chapter sent, will be extremely valuable.
LETTER 723. TO J.D. HOOKER.
(723/1. The following letter refers to Darwin's prediction as to the
manner in which Hedychium (Zinziberaceae) is fertilised. Sir J.D.
Hooker seems to have made inquiries in India in consequence of which
Darwin received specimens of the moth which there visits the flower,
unfortunately so much broken as to be useless (see "Life and Letters,"
III., page 284).)
Down, March 25th .
I am glad to hear about the Hedychium, and how soon you have got an
answer! I hope that the wings of the Sphinx will hereafter prove to be
bedaubed with pollen, for the case will then prove a fine bit of
prophecy from the structure of a flower to special and new means of
By the way, I suppose you have noticed what a grand appearance the plant
makes when the green capsules open, and display the orange and crimson
seeds and interior, so as to attract birds, like the pale buff flowers
to attract dusk-flying lepidoptera. I presume you do not want seeds of
this plant, as I have plenty from artificial fertilisation.
(723/2. In "Nature," June 22nd, 1876, page 173, Hermann Muller
communicated F. Muller's observation on the fertilisation of a
bright-red-flowered species of Hedychium, which is visited by
Callidryas, chiefly the males of C. Philea. The pollen is carried by
the tips of the butterfly's wing, to which it is temporarily fixed by
the slimy layer produced by the degeneration of the anther-wall.
LETTER 724. TO W. THISELTON-DYER.
Down, June 4th .
I am greatly obliged to you about the Opuntia, and shall be glad if you
can remember Catalpa. I wish some facts on the action of water, because
I have been so surprised at a stream not acting on Dionoea and Drosera.
(724/1. See Pfeffer, "Untersuchungen Bot. Inst. zu Tubingen," Bd. I.,
1885, page 518. Pfeffer shows that in some cases--Drosera, for
instance--water produces movement only when it contains fine particles
in suspension. According to Pfeffer the stamens of Berberis, and the
stigma of Mimulus, are both stimulated by gelatine, the action of which
is, generally speaking, equivalent to that of water.) Water does not
act on the stamens of Berberis, but it does on the stigma of Mimulus.
It causes the flowers of the bedding-out Mesembryanthemum and Drosera to
close, but it has not this effect on Gazania and the daisy, so I can
make out no rule.
I hope you are going on with Nepenthes; and if so, you will perhaps like
to hear that I have just found out that Pinguicula can digest albumen,
gelatine, etc. If a bit of glass or wood is placed on a leaf, the
secretion is not increased; but if an insect or animal-matter is thus
placed, the secretion is greatly increased and becomes feebly acid,
which was not the case before. I have been astonished and much
disturbed by finding that cabbage seeds excite a copious secretion, and
am now endeavouring to discover what this means. (724/2. Clearly it
had not occurred to Darwin that seeds may supply nitrogenous food as
well as insects: see "Insectivorous Plants," page 390.) Probably in a
few days' time I shall have to beg a little information from you, so I
will write no more now.
P.S. I heard from Asa Gray a week ago, and he tells me a beautiful
fact: not only does the lid of Sarracenia secrete a sweet fluid, but
there is a line or trail of sweet exudation down to the ground so as to
tempt insects up. (724/3. A dried specimen of Sarracenia, stuffed with
cotton wool, was sometimes brought from his study by Mr. Darwin, and
made the subject of a little lecture to visitors of natural history
LETTER 725. TO W. THISELTON-DYER.
Down, June 23rd, 1874.
I wrote to you about a week ago, thanking you for information on cabbage
seeds, asking you the name of Luzula or Carex, and on some other points;
and I hope before very long to receive an answer. You must now, if you
can, forgive me for being very troublesome, for I am in that state in
which I would sacrifice friend or foe. I have ascertained that bits of
certain leaves, for instance spinach, excite much secretion in
Pinguicula, and that the glands absorb matter from the leaves. Now this
morning I have received a lot of leaves from my future daughter-in-law
in North Wales, having a surprising number of captured insects on them,
a good many leaves, and two seed-capsules. She informs me that the
little leaves had excited secretion; and my son and I have ascertained
this morning that the protoplasm in the glands beneath the little leaves
has undoubtedly undergone aggregation. Therefore, absurd as it may
sound, I am prepared to affirm that Pinguicula is not only
insectivorous, but graminivorous, and granivorous! Now I want to beg
you to look under the simple microscope at the enclosed leaves and
seeds, and, if you possibly can, tell me their genera. The little
narrow leaves are remarkable (725/1. Those of Erica tetralix.); they
are fleshy, with the edges much curled from the axis of the plant, and
bear a few long glandular hairs; these grow in little tufts. These are
the commonest in Pinguicula, and seem to afford most nutritious matter.
A second leaf is like a miniature sycamore. With respect to the seeds,
I suppose that one is a Carex; the other looks like that of Rumex, but
is enclosed in a globular capsule. The Pinguicula grew on marshy, low,
I hope you will think this subject sufficiently interesting to make you
willing to aid me as far as you can. Anyhow, forgive me for being so
LETTER 726. TO J.D. HOOKER.
Down, August 30th .
I am particularly obliged for your address. (726/1. Presidential
address (Biological Section) at the Belfast meeting of the British
Association, 1874.) It strikes me as quite excellent, and has
interested me in the highest degree. Nor is this due to my having
worked at the subject, for I feel sure that I should have been just as
much struck, perhaps more so, if I had known nothing about it. You
could not, in my opinion, have put the case better. There are several
lights (besides the facts) in your essay new to me, and you have greatly
honoured me. I heartily congratulate you on so splendid a piece of
work. There is a misprint at page 7, Mitschke for Nitschke. There is a
partial error at page 8, where you say that Drosera is nearly
indifferent to organic substances. This is much too strong, though they
do act less efficiently than organic with soluble nitrogenous matter;
but the chief difference is in the widely different period of subsequent
re-expansion. Thirdly, I did not suggest to Sanderson his electrical
experiments, though, no doubt, my remarks led to his thinking of them.
Now for your letter: you are very generous about Dionoea, but some of
my experiments will require cutting off leaves, and therefore injuring
plants. I could not write to Lady Dorothy [Nevill]. Rollisson says
that they expect soon a lot from America. If Dionoea is not despatched,
have marked on address, "to be forwarded by foot-messenger."
Mrs. Barber's paper is very curious, and ought to be published (726/2.
Mrs. Barber's paper on the pupa of Papilio Nireus assuming different
tints corresponding to the objects to which it was attached, was
communicated by Mr. Darwin to the "Trans. Entomolog. Soc." 1874.); but
when you come here (and REMEMBER YOU OFFERED TO COME) we will consult
where to send it. Let me hear when you recommence on Cephalotus or
Sarracenia, as I think I am now on right track about Utricularia, after
wasting several weeks in fruitless trials and observations. The
negative work takes five times more time than the positive.
LETTER 727. TO J.D. HOOKER.
Down, September 18th .
I have had a splendid day's work, and must tell you about it.
Lady Dorothy sent me a young plant of U[tricularia] montana (727/1. See
"Life and Letters," III., page 327, and "Insectivorous Plants," page
431.), which I fancy is the species you told me of. The roots or
rhizomes (for I know not which they are; I can see no scales or
internodes or absorbent hairs) bear scores of bladders from 1/20 to
1/100 of an inch in diameter; and I traced these roots to the depth of 1
1/2 in. in the peat and sand. The bladders are like glass, and have the
same essential structure as those of our species, with the exception
that many exterior parts are aborted. Internally the structure is
perfect, as is the minute valvular opening into the bladder, which is
filled with water. I then felt sure that they captured subterranean
insects, and after a time I found two with decayed remnants, with clear
proof that something had been absorbed, which had generated protoplasm.
When you are here I shall be very curious to know whether they are roots
Besides the bladders there are great tuber-like swellings on the
rhizomes; one was an inch in length and half in breadth. I suppose
these must have been described. I strongly suspect that they serve as
reservoirs for water. (727/2. The existence of water-stores is quite in
accordance with the epiphytic habit of the plant.) But I shall
experimentise on this head. A thin slice is a beautiful object, and
looks like coarsely reticulated glass.
If you have an old plant which could be turned out of its pot (and can
spare the time), it would be a great gain to me if you would tear off a
bit of the roots near the bottom, and shake them well in water, and see
whether they bear these minute glass-like bladders. I should also much
like to know whether old plants bear the solid bladder-like bodies near
the upper surface of the pot. These bodies are evidently enlargements
of the roots or rhizomes. You must forgive this long letter, and make
allowance for my delight at finding this new sub-group of
insect-catchers. Sir E. Tennent speaks of an aquatic species of
Utricularia in Ceylon, which has bladders on its roots, and rises
annually to the surface, as he says, by this means. (727/3.
Utricularia stellaris. Emerson Tennent's "Ceylon," Volume I., page 124,
We shall be delighted to see you here on the 26th; if you will let us
know your train we will send to meet you. You will have to work like a
slave while you are here.
LETTER 728. TO J. JENNER WEIR.
(728/1. In 1870 Mr. Jenner Weir wrote to Darwin: "My brother has but
two kinds of laburnum, viz., Cytisus purpureus, very erect, and Cytisus
alpinus, very pendulous. He has several stocks of the latter grafted
with the purple one; and this year, the grafts being two years old, I
saw in one, fairly above the stock, about four inches, a raceme of
purely yellow flowers with the usual dark markings, and above them a
bunch of purely purple flowers; the branches of the graft in no way
showed an intermediate character, but had the usual rigid growth of
Early in July 1875, when Darwin was correcting a new edition of
"Variation under Domestication," he again corresponded with Mr. Weir on
Down, July 8th .
I thank you cordially. The case interests me in a higher degree than
anything which I have heard for a very long time. Is it your brother
Harrison W., whom I know? I should like to hear where the garden is.
There is one other very important point which I am most anxious to
hear--viz., the nature of the leaves at the base of the yellow racemes,
for leaves are always there produced with the yellow laburnums, and I
suppose so in the case of C. purpureus. As the tree has produced yellow
racemes several times, do you think you could ask your brother to cut
off and send me by post in a box a small branch of the purple stock with
the pods or leaves of the yellow sport? (728/2. "The purple stock"
here means the supposed C. purpureus, on which a yellow-flowered branch
was borne.) This would be an immense favour, for then I would cut the
point of junction longitudinally and examine slice under the microscope,
to be able to state no trace of bud of yellow kind having been inserted.
I do not suspect anything of the kind, but it is sure to be said that
your brother's gardener, either by accident or fraud, inserted a bud.
Under this point of view it would be very good to gather from your
brother how many times the yellow sport has appeared. The case appears
to me so very important as to be worth any trouble. Very many thanks
for all assistance so kindly given.
I will of course send a copy of new edition of "Variation under
Domestication" when published in the autumn.
LETTER 729. TO J. JENNER WEIR.
(729/1. On July 9th Mr. Weir wrote to say that a branch of the Cytisus
had been despatched to Down. The present letter was doubtless written
after Darwin had examined the specimen. In "Variation under
Domestication," Edition II., Volume I., page 417, note, he gives for a
case recorded in the "Gardeners' Chronicle" in 1857 the explanation here
offered (viz. that the graft was not C. purpureus but C. Adami), and
adds, "I have ascertained that this occurred in another instance." This
second instance is doubtless Mr. Weir's.)
Down, July 10th, 1875.
I do not know how to thank you enough; pray give also my thanks and kind
remembrances to your brother. I am sure you will forgive my expressing
my doubts freely, as I well know that you desire the truth more than
anything else. I cannot avoid the belief that some nurseryman has sold
C[ytisus] Adami to your brother in place of the true C. purpureus. The
latter is a little bush only 3 feet high (Loudon), and when I read your
account, it seemed to me a physical impossibility that a sporting branch
of C. alpinus could grow to any size and be supported on the extremely
delicate branches of C. purpureus. If I understand rightly your letter,
you consider the tuft of small shoots on one side of the sporting C.
alpinus from Weirleigh as C. purpureus; but these shoots are certainly
those of C. Adami. I earnestly beg you to look at the specimens
enclosed. The branch of the true C. purpureus is the largest which I
could find. If C. Adami was sold to your brother as C. purpureus,
everything is explained; for then the gardener has grafted C. Adami on
C. alpinus, and the former has sported in the usual manner; but has not
sported into C. purpureus, only into C. alpinus. C. Adami does not
sport less frequently into C. purpureus than into C. alpinus. Are the
purple flowers borne on moderately long racemes? If so, the plant is
certainly C. Adami, for the true C. purpureus bears flowers close to the
branches. I am very sorry to be so troublesome, but I am very anxious
to hear again from you.
C. purpureus bears "flowers axillary, solitary, stalked."
P.S.--I think you said that the purple [tree] at Weirleigh does not
seed, whereas the C. purpureus seeds freely, as you may see in enclosed.
C. Adami never produces seeds or pods.
LETTER 730. TO E. HACKEL.
(730/1. The following extract refers to Darwin's book on "Cross and
November 13th, 1875.
I am now busy in drawing up an account of ten years' experiments in the
growth and fertility of plants raised from crossed and self-fertilised
flowers. It is really wonderful what an effect pollen from a distinct
seedling plant, which has been exposed to different conditions of life,
has on the offspring in comparison with pollen from the same flower or
from a distinct individual, but which has been long subjected to the
same conditions. The subject bears on the very principle of life, which
seems almost to require changes in the conditions.
LETTER 731. TO G.J. ROMANES.
(731/1. The following extract from a letter to Romanes refers to
Francis Darwin's paper, "Experiments on the Nutrition of Drosera
rotundifolia." "Linn. Soc. Journ." , published 1880, page 17.)
August 9th .
The second point which delights me, seeing that half a score of
botanists throughout Europe have published that the digestion of meat by
plants is of no use to them (a mere pathological phenomenon, as one man
says!), is that Frank has been feeding under exactly similar conditions
a large number of plants of Drosera, and the effect is wonderful. On
the fed side the leaves are much larger, differently coloured, and more
numerous; flower-stalks taller and more numerous, and I believe far more
seed capsules,--but these not yet counted. It is particularly
interesting that the leaves fed on meat contain very many more starch
granules (no doubt owing to more protoplasm being first formed); so that
sections stained with iodine, of fed and unfed leaves, are to the naked
eye of very different colours.
There, I have boasted to my heart's content, and do you do the same, and
tell me what you have been doing.
LETTER 732. TO J.D. HOOKER.
Down, October 25th .
If you can put the following request into any one's hands pray do so;
but if not, ignore my request, as I know how busy you are.
I want any and all plants of Hoya examined to see if any imperfect
flowers like the one enclosed can be found, and if so to send them to
me, per post, damp. But I especially want them as young as possible.
They are very curious. I have examined some sent me from Abinger
(732/1. Lord Farrer's house.), but they were a month or two too old,
and every trace of pollen and anthers had disappeared or had never been
developed. Yet a very fine pod with apparently good seed had been
formed by one such flower. (732/2. The seeds did not germinate; see
the account of Hoya carnosa in "Forms of Flowers," page 331.)
LETTER 733. TO G.J. ROMANES.
(733/1. Published in the "Life of Romanes," page 62.)
Down, August 10th .
When I went yesterday I had not received to-day's "Nature," and I
thought that your lecture was finished. (733/2. Abstract of a lecture
on "Evolution of Nerves and Nervo-Systems," delivered at the Royal
Institution, May 25th, 1877. "Nature," July 19th, August 2nd, August
9th, 1877.) This final part is one of the grandest essays which I ever
It was very foolish of me to demur to your lines of conveyance like the
threads in muslin (733/3. "Nature," August 2nd, page 271.), knowing how
you have considered the subject: but still I must confess I cannot feel
quite easy. Everyone, I suppose, thinks on what he has himself seen,
and with Drosera, a bit of meat put on any one gland on its disc causes
all the surrounding tentacles to bend to this point, and here there can
hardly be differentiated lines of conveyance. It seems to me that the
tentacles probably bend to that point wherever a molecular wave strikes
them, which passes through the cellular tissue with equal ease in all
directions in this particular case. (733/4. Speaking generally, the
transmission takes place more readily in the longitudinal direction than
across the leaf: see "Insectivorous Plants," page 239.) But what a
fine case that of the Aurelia is! (733/5. Aurelia aurita, one of the
medusae. "Nature," pages 269-71.)
LETTER 734. TO W. THISELTON-DYER.
6, Queen Anne Street [December 1876].
Tell Hooker I feel greatly aggrieved by him: I went to the Royal
Society to see him for once in the chair of the Royal, to admire his
dignity and enjoy it, and lo and behold, he was not there. My outing
gave me much satisfaction, and I was particularly glad to see Mr.
Bentham, and to see him looking so wonderfully well and young. I saw
lots of people, and it has not done me a penny's worth of harm, though I
could not get to sleep till nearly four o'clock.
LETTER 735. TO D. OLIVER.
Down, October, 13th [1876?].
You must be a clair-voyant or something of that kind to have sent me
such useful plants. Twenty-five years ago I described in my father's
garden two forms of Linum flavum (thinking it a case of mere variation);
from that day to this I have several times looked, but never saw the
second form till it arrived from Kew. Virtue is never its own reward:
I took paper this summer to write to you to ask you to send me flowers,
[so] that I might beg plants of this Linum, if you had the other form,
and refrained, from not wishing to trouble you. But I am now sorry I
did, for I have hardly any doubt that L. flavum never seeds in any
garden that I have seen, because one form alone is cultivated by slips.
(735/1. Id est, because, the plant being grown from slips, one form
alone usually occurs in any one garden. It is also arguable that it is
grown by slips because only one form is common, and therefore seedlings
cannot be raised.)
(736/1. The following five letters refer to Darwin's work on "bloom"--a
subject on which he did not live to complete his researches:--
One of his earliest letters on this subject was addressed in August,
1873, to Sir Joseph Hooker (736/2. Published in "Life and Letters,"
III., page 339.):
"I want a little information from you, and if you do not yourself know,
please to enquire of some of the wise men of Kew.
"Why are the leaves and fruit of so many plants protected by a thin
layer of waxy matter (like the common cabbage), or with fine hair, so
that when such leaves or fruit are immersed in water they appear as if
encased in thin glass? It is really a pretty sight to put a pod of the
common pea, or a raspberry, into water. I find several leaves are thus
protected on the under surface and not on the upper.
"How can water injure the leaves, if indeed this is at all the case?"
On this latter point Darwin wrote to the late Lord Farrer:
"I am now become mad about drops of water injuring leaves. Please ask
Mr. Payne (736/3. Lord Farrer's gardener.) whether he believes, FROM
HIS OWN EXPERIENCE, that drops of water injure leaves or fruit in his
conservatories. It is said that the drops act as burning-glasses; if
this is true, they would not be at all injurious on cloudy days. As he
is so acute a man, I should very much like to hear his opinion. I
remember when I grew hothouse orchids I was cautioned not to wet their
leaves; but I never then thought on the subject."
The next letter, though of later date than some which follow it, is
printed here because it briefly sums his results and serves as guide to
the letters dealing with the subject.)
LETTER 736. TO W. THISELTON-DYER.
(736/4. Published in "Life and Letters," III., page 341.)
Down, September 5th .
One word to thank you. I declare, had it not been for your kindness, we
should have broken down. As it is we have made out clearly that with
some plants (chiefly succulent) the bloom checks evaporation--with some
certainly prevents attacks of insects; with SOME sea-shore plants
prevents injury from salt water, and, I believe, with a few prevents
injury from pure water resting on the leaves. This latter is as yet the
most doubtful and the most interesting point in relation to the
movements of plants.
(736/5. Modern research, especially that of Stahl on transpiration
("Bot. Zeitung," 1897, page 71) has shown that the question is more
complex than it appeared in 1877. Stahl's point of view is that
moisture remaining on a leaf checks the transpiration-current; and by
thus diminishing the flow of mineral nutriment interferes with the
process of assimilation. Stahl's idea is doubtless applicable to the
whole problem of bloom on leaves. For other references to bloom see
letters 685, 689 and 693.)
LETTER 737. TO J.D. HOOKER.
Down, August 19th, 1873.
The next time you walk round the garden ask Mr. Smith (737/1. Probably
John Smith (1798-1888), for some years Curator, Royal Gardens, Kew.), or
any of your best men, what they think about injury from watering during
sunshine. One of your men--viz., Mr. Payne, at Abinger, who seems very
acute--declares that you may water safely any plant out of doors in
sunshine, and that you may do the same for plants under glass if the
sashes are opened. This seems to me very odd, but he seems positive on
the point, and acts on it in raising splendid grapes. Another good
gardener maintains that it is only COLD water dripping often on the same
point of a leaf that ever injures it. I am utterly perplexed, but
interested on the point. Give me what you learn when you come to Down.
I should like to hear what plants are believed to be most injured by
being watered in sunshine, so that I might get such.
I expect that I shall be utterly beaten, as on so many other points; but
I intend to make a few experiments and observations. I have already
convinced myself that drops of water do NOT act as burning lenses.
LETTER 738. TO J.D. HOOKER.
December 20th .
I find that it is no use going on with my experiments on the evil
effects of water on bloom-divested leaves. Either I erred in the early
autumn or summer in some incomprehensible manner, or, as I suspect to be
the case, water is only injurious to leaves when there is a good supply
of actinic rays. I cannot believe that I am all in the wrong about the
movements of the leaves to shoot off water.
The upshot of all this is that I want to keep all the plants from Kew
until the spring or early summer, as it is mere waste of time going on
LETTER 739. TO W. THISELTON-DYER.
Down, July 22nd .
Many thanks for seeds of the Malva and information about Averrhoa, which
I perceived was sensitive, as A. carambola is said to be; and about
Mimosa sensitiva. The log-wood [Haematoxylon] has interested me much.
The wax is very easily removed, especially from the older leaves, and I
found after squirting on the leaves with water at 95 deg, all the older
leaves became coated, after forty-eight hours, in an astonishing manner
with a black Uredo, so that they looked as if sprinkled with soot and
water. But not one of the younger leaves was affected. This has set me
to work to see whether the "bloom" is not a protection against
parasites. As soon as I have ascertained a little more about the case
(and generally I am quite wrong at first) I will ask whether I could
have a very small plant, which should never be syringed with water above
60 deg, and then I suspect the leaves would not be spotted, as were the
older ones on the plant, when it arrived from Kew, but nothing like what
they were after my squirting.
In an old note of yours (which I have just found) you say that you have
a sensitive Schrankia: could this be lent me?
I have had lent me a young Coral-tree (Erythrina), which is very sickly,
yet shows odd sleep movements. I suppose I could buy one, but Hooker
told me first to ask you for anything.
Lastly, have you any seaside plants with bloom? I find that drops of
sea-water corrode sea-kale if bloom is removed; also the var. littorum
of Triticum repens. (By the way, my plants of the latter, grown in pots
here, are now throwing up long flexible green blades, and it is very odd
to see, ON THE SAME CULM, the rigid grey bloom-covered blades and the
green flexible ones.) Cabbages, ill-luck to them, do not seem to be
hurt by salt water. Hooker formerly told me that Salsola kali, a var.
of Salicornia, one species of Suaeda, Euphorbia peplis, Lathyrus
maritimus, Eryngium maritimum, were all glaucous and seaside plants. It
is very improbable that you have any of these or of foreigners with the
God forgive me: I hope that I have not bored you greatly.
By all the rules of right the leaves of the logwood ought to move (as if
partially going to sleep) when syringed with tepid water. The leaves of
my little plant do not move at all, and it occurs to me as possible,
though very improbable, that it would be different with a larger plant
with perhaps larger leaves. Would you some day get a gardener to
syringe violently, with water kept in a hothouse, a branch on one of
your largest logwood plants and observe [whether?] leaves move together
towards the apex of leaf?
By the way, what astonishing nonsense Mr. Andrew Murray has been writing
about leaves and carbonic acid! I like to see a man behaving
What a lot I have scribbled to you!
(FIGURE 13. Leaf of Trifolium resupinatum (from a drawing by Miss
LETTER 740. TO W. THISELTON-DYER.
There is no end to my requests. Can you spare me a good plant (or even
two) of Oxalis sensitiva? The one which I have (formerly from Kew) has
been so maltreated that I dare not trust my results any longer.
Please give the enclosed to Mr. Lynch. (740/1. Mr. Lynch, now Curator
of the Cambridge Botanic Garden, was at this time in the R. Bot. Garden,
Kew. Mr. Lynch described the movements of Averrhoa bilimbi in the
"Linn. Soc. Journ," Volume XVI., page 231. See also "The Power of
Movement in Plants," page 330.) The spontaneous movements of the
Averrhoa are very curious.
You sent me seeds of Trifolium resupinatum, and I have raised plants,
and some former observations which I did not dare to trust have proved
accurate. It is a very little fact, but curious. The half of the
lateral leaflets (marked by a cross) on the lower side have no bloom and
are wetted, whereas the other half has bloom and is not wetted, so that
the two sides look different to the naked eye. The cells of the
eipdermis appear of a different shape and size on the two sides of the
leaf [Figure 13].
When we have drawings and measurements of cells made, and are sure of
our facts, I shall ask you whether you know of any case of the same leaf
differing histologically on the two sides, for Hooker always says you
are a wonderful man for knowing what has been made out.
(740/2. The biological meaning of the curious structure of the leaves
of Trifolium resupinatum remains a riddle. The stomata and (speaking
from memory) the trichomes differ on the two halves of the lateral
LETTER 741. TO L. ERRERA.
(741/1. Professor L. Errera, of Brussels wrote, as a student, to
Darwin, asking permission to send the MS. of an essay by his friend S.
Gevaert and himself on cross and self-fertilisation, and which was
afterwards published in the "Bull. Soc. Bot. Belg." XVII., 1878. The
terms xenogamy, geitonogamy, and autogamy were first suggested by Kerner
in 1876; their definition will be found at page 9 of Ogle's translation
of Kerner's "Flowers and their Unbidden Guests," 1878. In xenogamy the
pollen comes from another PLANT; in geitonogamy from another FLOWER on
the same PLANT; in autogamy from the androecium of the fertilised
FLOWER. Allogamy embraces xenogamy and geitonogamy.)
Down, October 4th, 1877.
I have now read your MS. The whole has interested me greatly, and is
very clearly written. I wish that I had used some such terms as
autogamy, xenogamy, etc...I entirely agree with you on the a priori
probability of geitonogamy being more advantageous than autogamy; and I
cannot remember having ever expressed a belief that autogamy, as a
general rule, was better than geitonogamy; but the cases recorded by me
seem too strong not to make me suspect that there was some unknown
advantage in autogamy. In one place I insert the caution "if this be
really the case," which you quote. (741/2. See "Cross and
Self-Fertilisation," pages 352, 386. The phrase referred to occurs in
both passages; that on page 386 is as follows: "We have also seen
reason to suspect that self-fertilisation is in some peculiar manner
beneficial to certain plants; but if this be really the case, the
benefit thus derived is far more than counterbalanced by a cross with a
fresh stock or with a slightly different variety." Errera and Gevaert
conclude (pages 79-80) that the balance of the available evidence is in
favour of the belief that geitonogamy is intermediate, in effectiveness,
between autogamy and xenogamy.) I shall be very glad to be proved to be
altogether in error on this point.
Accept my thanks for pointing out the bad erratum at page 301. I hope
that you will experimentise on inconspicuous flowers (741/3. See Miss
Bateson, "Annals of Botany," 1888, page 255, "On the Cross-Fertilisation
of Inconspicuous Flowers:" Miss Bateson showed that Senecio vulgaris
clearly profits by cross-fertilisation; Stellaria media and Capsella
bursa-pastoris less certainly.); if I were not too old and too much
occupied I would do so myself.
Finally let me thank you for the kind manner in which you refer to my
work, and with cordial good wishes for your success...
LETTER 742. TO W. THISELTON-DYER.
Down, October 9th, 1877.
One line to thank you much about Mertensia. The former plant has begun
to make new leaves, to my great surprise, so that I shall be now well
supplied. We have worked so well with the Averrhoa that unless the
second species arrives in a very good state it would be superfluous to
send it. I am heartily glad that you and Mrs. Dyer are going to have a
holiday. I will look at you as a dead man for the next month, and
nothing shall tempt me to trouble you. But before you enter your grave
aid me if you can. I want seeds of three or four plants (not
Leguminosae or Cruciferae) which produce large cotyledons. I know not
in the least what plants have large cotyledons. Why I want to know is
as follows: The cotyledons of Cassia go to sleep, and are sensitive to
a touch; but what has surprised me much is that they are in constant
movement up and down. So it is with the cotyledons of the cabbage, and
therefore I am very curious to ascertain how far this is general.
LETTER 743. TO W. THISELTON-DYER.
Down, October 11th .
The fine lot of seeds arrived yesterday, and are all sown, and will be
most useful. If you remember, pray thank Mr. Lynch for his aid. I had
not thought of beech or sycamore, but they are now sown.
Perhaps you may like to see a rough copy of the tracing of movements of
one of the cotyledons of red cabbage, and you can throw it into the
fire. A line joining the two cotyledons stood facing a north-east
window, and the day was uniformly cloudy. A bristle was gummed to one
cotyledon, and beyond it a triangular bit of card was fixed, and in
front a vertical glass. A dot was made in the glass every quarter or
half hour at the point where the end of the bristle and the apex of card
coincided, and the dots were joined by straight lines. The observations
were from 10 a.m. to 8.45 p.m. During this time the enclosed figure was
described; but between 4 p.m. and 5.38 p.m. the cotyledon moved so that
the prolonged line was beyond the limits of the glass, and the course is
here shown by an imaginary dotted line. The cotyledon of Primula
sinensis moved in closely analogous manner, as do those of a Cassia.
Hence I expect to find such movements very general with cotyledons, and
I am inclined to look at them as the foundation for all the other
adaptive movements of leaves. They certainly are of the so-called sleep
I hope I have not bothered you. Do not answer. I am all on fire at the
I have had a short and very prosperous note from Asa Gray, who says
Hooker is very prosperous, and both are tremendously hard at work.
(743/1. "Hooker is coming over, and we are going in summer to the Rocky
Mountains together, according to an old promise of mine." Asa Gray to
G.F. Wright, May 24th, 1877 ("Letters of Asa Gray," II., page 666).)
LETTER 744. TO H. MULLER.
Down, January 1st [1878?].
I must write two or three lines to thank you cordially for your very
handsome and very interesting review of my last book in "Kosmos," which
I have this minute finished. (744/1. "Forms of Flowers," 1877. H.
Muller's article is in "Kosmos," II., page 286.) It is wonderful how
you have picked out everything important in it. I am especially glad
that you have called attention to the parallelism between illegitimate
offspring of heterostyled plants and hybrids. Your previous article in
"Kosmos" seemed to me very important, but for some unknown reason the
german was very difficult, and I was sadly overworked at the time, so
that I could not understand a good deal of it. (744/2. "Kosmos," II.,
pages 11, 128. See "Forms of Flowers," Edition II., page 308.) But I
have put it on one side, and when I have to prepare a new edition of my
book I must make it out. It seems that you attribute such cases as that
of the dioecious Rhamnus and your own of Valeriana to the existence of
two forms with larger and smaller flowers. I cannot follow the steps by
which such plants have been rendered dioecious, but when I read your
article with more care I hope I shall understand. (744/3. See "Forms
of Flowers," Edition II., pages 9 and 304. H. Muller's view is briefly
that conspicuous and less conspicuous varieties occurred, and that the
former were habitually visited first by insects; thus the less
conspicuous form would play the part of females and their pollen would
tend to become superfluous. See H. Muller in "Kosmos," II.) If you
have succeeded in explaining this class of cases I shall heartily
rejoice, for they utterly perplexed me, and I could not conjecture what
their meaning was. It is a grievous evil to have no faculty for new
With the most sincere respect and hearty good wishes to you and all your
family for the new year...
P.S.--What interesting papers your wonderful brother has lately been
LETTER 745. TO W. THISELTON-DYER.
(745/1. This letter refers to the purchase of instruments for the
Jodrell Laboratory in the Royal Gardens, Kew. "The Royal Commission on
Scientific Instruction and the Advancement of Science, commonly spoken
of as the Devonshire Commission, in its fourth Report (1874), page 10,
expressed the opinion that 'it is highly desirable that opportunities
for the pursuit of investigations in Physiological Botany should be
afforded at Kew to those persons who may be inclined to follow that
branch of science.' Effect was given to this recommendation by the
liberality of the late T.J. Phillips-Jodrell, M.A., who built and
equipped the small laboratory, which has since borne his name, at his
own expense. It was completed and immediately brought into use in
1876." The above is taken from the "Bulletin of Miscellaneous
Information," R. Botanic Gardens, Kew, 1901, page 102, which also gives
a list of work carried out in the laboratory between 1876 and 1900.)
Down, March 14th, 1878.
I have a very strong opinion that it would be the greatest possible pity
if the Phys[iological] Lab., now that it has been built, were not
supplied with as many good instruments as your funds can possibly
afford. It is quite possible that some of them may become antiquated
before they are much or even at all used. But this does not seem to me
any argument at all against getting them, for the Laboratory cannot be
used until well provided; and the mere fact of the instruments being
ready may suggest to some one to use them. You at Kew, as guardians and
promoters of botanical science, will then have done all in your power,
and if your Lab. is not used the disgrace will lie at the feet of the
public. But until bitter experience proves the contrary I will never
believe that we are so backward. I should think the German laboratories
would be very good guides as to what to get; but Timiriazeff of Moscow,
who travelled over Europe to see all Bot. Labs., and who seemed so good
a fellow, would, I should think, give the best list of the most
indispensable instruments. Lately I thought of getting Frank or Horace
to go to Cambridge for the use of the heliostat there; but our
observations turned out of less importance than I thought, yet if there
had been one at Kew we should probably have used it, and might have
found out something curious. It is impossible for me to predict whether
or not we should ever want this or that instrument, for we are guided in
our work by what turns up. Thus I am now observing something about
geotropism, and I had no idea a few weeks ago that this would have been
necessary. In a short time we might earnestly wish for a centrifugal
apparatus or a heliostat. In all such cases it would make a great
difference if a man knew that he could use a particular instrument
without great loss of time. I have now given my opinion, which is very
decided, whether right or wrong, and Frank quite agrees with me. You
can, of course, show this letter to Hooker.
LETTER 746. TO F. LUDWIG.
Down, May 29th, 1878.
I thank you sincerely for the trouble which you have taken in sending me
so long and interesting a letter, together with the specimens.
Gradations are always very valuable, and you have been remarkably
successful in discovering the stages by which the Plantago has become
gyno-dioecious. (746/1. See F. Ludwig, "Zeitsch. f. d. Geo.
Naturwiss." Bd. LII., 1879. Professor Ludwig's observations are quoted
in the preface to "Forms of Flowers," Edition II., page ix.) Your view
of its origin, from being proterogynous, seems to me very probable,
especially as the females are generally the later-flowering plants. If
you can prove the reverse case with Thymus your view will manifestly be
rendered still more probable. I have never felt satisfied with H.
Muller's view, though he is so careful and admirable an observer.
(746/2. See "Forms of Flowers," Edition II., page 308. Also letter
744.) It is more than seventeen years since I attended to Plantago, and
when nothing had been published on the subject, and in consequence I
omitted to attend to several points; and now, after so long an interval,
I cannot pretend to say to which of your forms the English one belongs;
I well remember that the anther of the females contained a good deal
[of] pollen, though not one sound grain.
P.S.--Delpino is Professor of Botany in Genoa, Italy (746/3. Now at
Naples.); I have always found him a most obliging correspondent.
LETTER 747. TO W. THISELTON-DYER.
Down, August 24th .
Many thanks for seeds of Trifolium resupinatum, which are invaluable to
us. I enclose seeds of a Cassia, from Fritz Muller, and they are well
worth your cultivation; for he says they come from a unique, large and
beautiful tree in the interior, and though looking out for years, he has
never seen another specimen. One of the most splendid, largest and
rarest butterflies in S. Brazil, he has never seen except near this one
tree, and he has just discovered that its caterpillars feed on its
I have just been looking at fine young pods beneath the ground of
Arachis. (747/1. Arachis hypogoea, cultivated for its "ground nuts.")
I suppose that the pods are not withdrawn when ripe from the ground; but
should this be the case kindly inform me; if I do not hear I shall
understand that [the] pods ripen and are left permanently beneath the
If you ever come across heliotropic or apheliotropic aerial roots on a
plant not valuable (but which should be returned), I should like to
observe them. Bignonia capreolata, with its strongly apheliotropic
tendrils (which I had from Kew), is now interesting me greatly. Veitch
tells me it is not on sale in any London nursery, as I applied to him
for some additional plants. So much for business.
I have received from the Geographical Soc. your lecture, and read it
with great interest. (747/2. "On Plant-Distribution as a field for
Geographical Research." "Geog. Soc. Proc." XXII., 1878, page 412.) But
it ought not merely to be read; it requires study. The sole criticism
which I have to make is that parts are too much condensed: but, good
Lord, how rare a fault is this! You do not quote Saporta, I think; and
some of his work on the Tertiary plants would have been useful to you.
In a former note you spoke contemptuously of your lecture: all I can
say is that I never heard any one speak more unjustly and shamefully of
another than you have done of yourself!
LETTER 748. TO H. MULLER.
Down, September 20th, 1878.
I am working away on some points in vegetable physiology, but though
they interest me and my son, yet they have none of the fascination which
the fertilisation of flowers possesses. Nothing in my life has ever
interested me more than the fertilisation of such plants as Primula and
Lythrum, or again Anacamptis (748/1. Orchis pyramidalis.) or Listera.
LETTER 749. TO H. MULLER.
Down, February 12th .
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