The Life and Letters of Charles Darwin, Volume II

Part 9 out of 11

elbow to look at them. It was the first animation he showed. He said
only: "You must thank Professor Gray awfully." In the evening after a
long silence, there came out the oracular sentence: "He is awfully kind."
And indeed you are, overworked as you are, to take so much trouble for our
poor dear little man.--And now I must begin the "awfullys" on my own
account: what a capital notice you have published on the orchids! It
could not have been better; but I fear that you overrate it. I am very
sure that I had not the least idea that you or any one would approve of it
so much. I return your last note for the chance of your publishing any
notice on the subject; but after all perhaps you may not think it worth
while; yet in my judgment SEVERAL of your facts, especially Platanthera
hyperborea, are MUCH too good to be merged in a review. But I have always
noticed that you are prodigal in originality in your reviews...

[Sir Joseph Hooker reviewed the book in the "Gardeners' Chronicle", writing
in a successful imitation of the style of Lindley, the Editor. My father
wrote to Sir Joseph (November 12, 1862):--

"So you did write the review in the "Gardeners' Chronicle". Once or twice
I doubted whether it was Lindley; but when I came to a little slap at R.
Brown, I doubted no longer. You arch-rogue! I do not wonder you have
deceived others also. Perhaps I am a conceited dog; but if so, you have
much to answer for; I never received so much praise, and coming from you I
value it much more than from any other."

With regard to botanical opinion generally, he wrote to Dr. Gray, "I am
fairly astonished at the success of my book with botanists." Among
naturalists who were not botanists, Lyell was pre-eminent in his
appreciation of the book. I have no means of knowing when he read it, but
in later life, as I learn from Professor Judd, he was enthusiastic in
praise of the 'Fertilisation of Orchids,' which he considered "next to the
'Origin,' as the most valuable of all Darwin's works." Among the general
public the author did not at first hear of many disciples, thus he wrote to
his cousin Fox in September 1862: "Hardly any one not a botanist, except
yourself, as far as I know, has cared for it."

A favourable notice appeared in the "Saturday Review", October 18th, 1862;
the reviewer points out that the book would escape the angry polemics
aroused by the 'Origin.' (Dr. Gray pointed out that if the Orchid-book
(with a few trifling omissions) had appeared before the 'Origin,' the
author would have been canonised rather than anathematised by the natural
theologians.) This is illustrated by a review in the "Literary Churchman",
in which only one fault found, namely, that Mr. Darwin's expression of
admiration at the contrivances in orchids is too indirect a way of saying,
"O Lord, how manifold are Thy works!"

A somewhat similar criticism occurs in the 'Edinburgh Review' (October
1862). The writer points out that Mr. Darwin constantly uses phrases, such
as "beautiful contrivance," "the labellum is...IN ORDER TO attract," "the
nectar is PURPOSELY lodged." The Reviewer concludes his discussion thus:
"We know, too that these purposes and ideas are not our own, but the ideas
and purposes of Another."

The 'Edinburgh' reviewer's treatment of this subject was criticised in the
"Saturday Review", November 15th, 1862: With reference to this article my
father wrote to Sir Joseph Hooker (December 29th, 1862):--

"Here is an odd chance; my nephew Henry Parker, an Oxford Classic, and
Fellow of Oriel, came here this evening; and I asked him whether he knew
who had written the little article in the "Saturday", smashing the
[Edinburgh reviewer], which we liked; and after a little hesitation he
owned he had. I never knew that he wrote in the "Saturday"; and was it not
an odd chance?"

The 'Edinburgh' article was written by the Duke of Argyll, and has since
been made use of in his 'Reign of Law,' 1867. Mr. Wallace replied
('Quarterly Journal of Science,' October 1867. Republished in 'Natural
Selection,' 1871.) to the Duke's criticisms, making some specially good
remarks on those which refer to orchids. He shows how, by a "beautiful
self-acting adjustment," the nectary of the orchid Angraecum (from 10 to 14
inches in length), and the proboscis of a moth sufficiently long to reach
the nectar, might be developed by natural selection. He goes on to point
out that on any other theory we must suppose that the flower was created
with an enormously long nectary, and that then by a special act, an insect
was created fitted to visit the flower, which would otherwise remain
sterile. With regard to this point my father wrote (October 12 or 13,
1867):--

"I forgot to remark how capitally you turn the tables on the Duke, when you
make him create the Angraecum and Moth by special creation."

If we examine the literature relating to the fertilisation of flowers, we
do not find that this new branch of study showed any great activity
immediately after the publication of the Orchid-book. There are a few
papers by Asa Gray, in 1862 and 1863, by Hildebrand in 1864, and by
Moggridge in 1865, but the great mass of work by Axell, Delpino,
Hildebrand, and the Mullers, did not begin to appear until about 1867. The
period during which the new views were being assimilated, and before they
became thoroughly fruitful, was, however, surprisingly short. The later
activity in this department may be roughly gauged by the fact that the
valuable 'Bibliography,' given by Prof. D'Arcy Thompson in his translation
of Muller's 'Befruchtung' (1883), contains references to 814 papers.

Besides the book on Orchids, my father wrote two or three papers on the
subject, which will be found mentioned in the Appendix. The earliest of
these, on the three sexual forms of Catasetum, was published in 1862; it is
an anticipation of part of the Orchid-book, and was merely published in the
Linnean Society's Journal, in acknowledgment of the use made of a specimen
in the Society's possession. The possibility of apparently distinct
species being merely sexual forms of a single species, suggested a
characteristic experiment, which is alluded to in the following letter to
one of his earliest disciples in the study of the fertilisation of
flowers:]

CHARLES DARWIN TO J. TRAHERNE MOGGRIDGE. (The late Mr. Moggridge, author
of 'Harvesting Ants and Trap-door Spiders,' 'Flora of Mentone,' etc.)
Down, October 13 [1865].

My dear Sir,

I am especially obliged to you for your beautiful plates and letter-press;
for no single point in natural history interests and perplexes me so much
as the self-fertilisation (He once remarked to Dr. Norman Moore that one of
the things that made him wish to live a few thousand years, was his desire
to see the extinction of the Bee-orchis,--an end to which he believed its
self-fertilising habit was leading.) of the Bee-orchis. You have already
thrown some light on the subject, and your present observations promise to
throw more.

I formed two conjectures: first, that some insect during certain seasons
might cross the plants, but I have almost given up this; nevertheless, pray
have a look at the flowers next season. Secondly, I conjectured that the
Spider and Bee-orchis might be a crossing and self-fertile form of the same
species. Accordingly I wrote some years ago to an acquaintance, asking him
to mark some Spider-orchids, and observe whether they retained the same
character; but he evidently thought the request as foolish as if I had
asked him to mark one of his cows with a ribbon, to see if it would turn
next spring into a horse. Now will you be so kind as to tie a string round
the stem of a half-a-dozen Spider-orchids, and when you leave Mentone dig
them up, and I would try and cultivate them and see if they kept constant;
but I should require to know in what sort of soil and situations they grow.
It would be indispensable to mark the plant so that there could be no
mistake about the individual. It is also just possible that the same plant
would throw up, at different seasons different flower-scapes, and the
marked plants would serve as evidence.

With many thanks, my dear sir,
Yours sincerely,
CH. DARWIN.

P.S.--I send by this post my paper on climbing plants, parts of which you
might like to read.

[Sir Thomas Farrer and Dr. W. Ogle were also guided and encouraged by my
father in their observations. The following refers to a paper by Sir
Thomas Farrer, in the 'Annals and Magazine of Natural History,' 1868, on
the fertilisation of the Scarlet Runner:]

CHARLES DARWIN TO T.H. FARRER.
Down, September 15, 1868.

My dear Mr. Farrer,

I grieve to say that the MAIN features of your case are known. I am the
sinner and described them some ten years ago. But I overlooked many
details, as the appendage to the single stamen, and several other points.
I send my notes, but I must beg for their return, as I have NO OTHER COPY.
I quite agree, the facts are most striking, especially as you put them.
Are you sure that the Hive-bee is the cutter? it is against my experience.
If sure, make the point more prominent, or if not sure, erase it. I do not
think the subject is quite new enough for the Linnean Society; but I dare
say the 'Annals and Magazine of Natural History,' or "Gardeners' Chronicle"
would gladly publish your observations, and it is a great pity they should
be lost. If you like I would send your paper to either quarter with a
note. In this case you must give a title, and your name, and perhaps it
would be well to premise your remarks with a line of reference to my paper
stating that you had observed independently and more fully.

I have read my own paper over after an interval of several years, and am
amused at the caution with which I put the case that the final end was for
crossing distinct individuals, of which I was then as fully convinced as
now, but I knew that the doctrine would shock all botanists. Now the
opinion is becoming familiar.

To see penetration of pollen-tubes is not difficult, but in most cases
requires some practice with dissecting under a one-tenth of an inch focal
distance single lens; and just at first this will seem to you extremely
difficult.

What a capital observer you are--a first-rate Naturalist has been
sacrificed, or partly sacrificed to Public life.

Believe me, yours very sincerely,
CH. DARWIN.

P.S.--If you come across any large Salvia, look at it--the contrivance is
admirable. It went to my heart to tell a man who came here a few weeks ago
with splendid drawings and MS. on Salvia, that the work had been all done
in Germany. (Dr. W. Ogle, the observer of the fertilisation of Salvia here
alluded to, published his results in the 'Pop. Science Review,' 1869. He
refers both gracefully and gratefully to his relationship with my father in
the introduction to his translation of Kerner's 'Flowers and their Unbidden
Guests.')

[The following extract is from a letter, November 26th, 1868, to Sir Thomas
Farrer, written as I learn from him, "in answer to a request for some
advice as to the best modes of observation."

"In my opinion the best plan is to go on working and making copious notes,
without much thought of publication, and then if the results turn out
striking publish them. It is my impression, but I do not feel sure that I
am right, that the best and most novel plan would be, instead of describing
the means of fertilisation in particular plants, to investigate the part
which certain structures play with all plants or throughout certain orders;
for instance, the brush of hairs on the style, or the diadelphous condition
of the stamens, in the Leguminosae, or the hairs within the corolla, etc.
etc. Looking to your note, I think that this is perhaps the plan which you
suggest.

"It is well to remember that Naturalists value observations far more than
reasoning; therefore your conclusions should be as often as possible
fortified by noticing how insects actually do the work."

In 1869, Sir Thomas Farrer corresponded with my father on the fertilisation
of Passiflora and of Tacsonia. He has given me his impressions of the
correspondence:--

"I had suggested that the elaborate series of chevaux-de-frise, by which
the nectary of the common Passiflora is guarded, were specially calculated
to protect the flower from the stiff-beaked humming birds which would not
fertilise it, and to facilitate the access of the little proboscis of the
humble bee, which would do so; whilst, on the other hand, the long pendent
tube and flexible valve-like corona which retains the nectar of Tacsonia
would shut out the bee, which would not, and admit the humming bird which
would, fertilise that flower. The suggestion is very possibly worthless,
and could only be verified or refuted by examination of flowers in the
countries where they grow naturally...What interested me was to see that on
this as on almost any other point of detailed observation, Mr. Darwin could
always say, 'Yes; but at one time I made some observations myself on this
particular point; and I think you will find, etc. etc.' That he should
after years of interval remember that he had noticed the peculiar structure
to which I was referring in the Passiflora princeps struck me at the time
as very remarkable."

With regard to the spread of a belief in the adaptation of flowers for
cross-fertilisation, my father wrote to Mr. Bentham April 22, 1868:

"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 is really worth reading, and I have observed some
species, and know that he is accurate."

The next letter refers to Professor Hildebrand's paper on Corydalis,
published in the 'Proc. Internat. Hort. Congress,' London, 1866, and in
Pringsheim's 'Jahrbucher,' volume v. The memoir on Salvia alluded to is
contained in the previous volume of the same Journal:]

CHARLES DARWIN TO F. HILDEBRAND. (Professor of Botany at Freiburg.)
Down, May 16 [1866].

My dear Sir,

The state of my health prevents my attending the Hort. Congress; but I
forwarded yesterday your paper to the secretary, and if they are not
overwhelmed with papers, yours will be gladly received. I have made many
observations on the Fumariaceae, and convinced myself that they were
adapted for insect agency; but I never observed anything nearly so curious
as your most interesting facts. I hope you will repeat your experiments on
the Corydalis on a larger scale, and especially on several distinct plants;
for your plant might have been individually peculiar, like certain
individual plants of Lobelia, etc., described by Gartner, and of Passiflora
and Orchids described by Mr. Scott...

Since writing to you before, I have read your admirable memoir on Salvia,
and it has interested me almost as much as when I first investigated the
structure of Orchids. Your paper illustrates several points in my 'Origin
of Species,' especially the transition of organs. Knowing only two or
three species in the genus, I had often marvelled how one cell of the
anther could have been transformed into the movable plate or spoon; and how
well you show the gradations; but I am surprised that you did not more
strongly insist on this point.

I shall be still more surprised if you do not ultimately come to the same
belief with me, as shown by so many beautiful contrivances, that all plants
require, from some unknown cause, to be occasionally fertilized by pollen
from a distinct individual. With sincere respect, believe me, my dear Sir,

Yours very faithfully,
CH. DARWIN.

[The following letter refers to the late Hermann Muller's 'Befruchtung der
Blumen,' by far the most valuable of the mass of literature originating in
the 'Fertilisation of Orchids.' An English translation, by Prof. D'Arcy
Thompson was published in 1883. My father's "Prefatory Notice" to this
work is dated February 6, 1882, and is therefore almost the last of his
writings:]

CHARLES DARWIN TO H. MULLER.
Down, May 5, 1873.

My dear Sir,

Owing to all sorts of interruptions and to my reading German so slowly, I
have read only to page 88 of your book; but I must have the pleasure of
telling you how very valuable a work it appears to me. Independently of
the many original observations, which of course form the most important
part, the work will be of the highest use as a means of reference to all
that has been done on the subject. I am fairly astonished at the number of
species of insects, the visits of which to different flowers you have
recorded. You must have worked in the most indefatigable manner. About
half a year ago the editor of 'Nature' suggested that it would be a grand
undertaking if a number of naturalists were to do what you have already
done on so large a scale with respect to the visits of insects. I have
been particularly glad to read your historical sketch, for I had never
before seen all the references put together. I have sometimes feared that
I was in error when I said that C.K. Sprengel did not fully perceive that
cross-fertilisation was the final end of the structure of flowers; but now
this fear is relieved, and it is a great satisfaction to me to believe that
I have aided in making his excellent book more generally known. Nothing
has surprised me more than to see in your historical sketch how much I
myself have done on the subject, as it never before occurred to me to think
of all my papers as a whole. But I do not doubt that your generous
appreciation of the labours of others has led you to over-estimate what I
have done. With very sincere thanks and respect, believe me,

Yours faithfully,
CHARLES DARWIN.

P.S.--I have mentioned your book to almost every one who, as far as I know,
cares for the subject in England; and I have ordered a copy to be send to
our Royal Society.

[The next letter, to Dr. Behrens, refers to the same subject as the last:]

CHARLES DARWIN TO W. BEHRENS.
Down, August 29 [1878].

Dear Sir,

I am very much obliged to you for having sent me your 'Geschichte der
Bestaubungs-Theorie' (Progr. der K. Gewerbschule zu Elberfeld, 1877,
1878.), and which has interested me much. It has put some things in a new
light, and has told me other things which I did not know. I heartily agree
with you in your high appreciation of poor old C. Sprengel's work; and one
regrets bitterly that he did not live to see his labours thus valued. It
rejoices me also to notice how highly you appreciate H. Muller, who has
always seemed to me an admirable observer and reasoner. I am at present
endeavouring to persuade an English publisher to bring out a translation of
his 'Befruchtung.'

Lastly, permit me to thank you for your very generous remarks on my works.
By placing what I have been able to do on this subject in systematic order,
you have made me think more highly of my own work than I ever did before!
Nevertheless, I fear that you have done me more than justice.

I remain, dear Sir, yours faithfully and obliged,
CHARLES DARWIN.

[The letter which follows was called forth by Dr. Gray's article in
'Nature,' to which reference has already been made, and which appeared June
4, 1874:]

CHARLES DARWIN TO ASA GRAY.
Down, June 3 [1874].

My dear Gray,

I was rejoiced to see your hand-writing again in your note of the 4th, of
which more anon. I was astonished to see announced about a week ago that
you were going to write in 'Nature' an article on me, and this morning I
received an advance copy. It is the grandest thing ever written about me,
especially as coming from a man like yourself. It has deeply pleased me,
particularly some of your side remarks. It is a wonderful thing to me to
live to see my name coupled in any fashion with that of Robert Brown. But
you are a bold man, for I am sure that you will be sneered at by not a few
botanists. I have never been so honoured before, and I hope it will do me
good and make me try to be as careful as possible; and good heavens, how
difficult accuracy is! I feel a very proud man, but I hope this won't
last...

[Fritz Muller has observed that the flowers of Hedychium are so arranged
that the pollen is removed by the wings of hovering butterflies. My
father's prediction of this observation is given in the following letter:]

CHARLES DARWIN TO H. MULLER.
Down, August 7, 1876.

...I was much interested by your brother's article on Hedychium; about two
years ago I was so convinced that the flowers were fertilized by the tips
of the wings of large moths, that I wrote to India to ask a man to observe
the flowers and catch the moths at work, and he sent me 20 to 30 Sphinx-
moths, but so badly packed that they all arrived in fragments; and I could
make out nothing...

Yours sincerely,
CH. DARWIN.

[The following extract from a letter (February 25, 1864), to Dr. Gray
refers to another prediction fulfilled:--

"I have of course seen no one, and except good dear Hooker, I hear from no
one. He, like a good and true friend, though so overworked, often writes
to me.

"I have had one letter which has interested me greatly, with a paper, which
will appear in the Linnean Journal, by Dr. Cruger of Trinidad, which shows
that I am all right about Catasetum, even to the spot where the pollinia
adhere to the bees, which visit the flower, as I said, to gnaw the
labellum. Cruger's account of Coryanthes and the use of the bucket-like
labellum full of water beats everything: I SUSPECT that the bees being
well wetted flattens their hairs, and allows the viscid disc to adhere."]

CHARLES DARWIN TO THE MARQUIS DE SAPORTA.
Down, December 24, 1877.

My dear Sir,

I thank you sincerely for your long and most interesting letter, which I
should have answered sooner had it not been delayed in London. I had not
heard before that I was to be proposed as a Corresponding Member of the
Institute. Living so retired a life as I do, such honours affect me very
little, and I can say with entire truth that your kind expression of
sympathy has given and will give me much more pleasure than the election
itself, should I be elected.

Your idea that dicotyledonous plants were not developed in force until
sucking insects had been evolved seems to me a splendid one. I am
surprised that the idea never occurred to me, but this is always the case
when one first hears a new and simple explanation of some mysterious
phenomenon...I formerly showed that we might fairly assume that the beauty
of flowers, their sweet odour and copious nectar, may be attributed to the
existence of flower-haunting insects, but your idea, which I hope you will
publish, goes much further and is much more important. With respect to the
great development of mammifers in the later Geological periods following
from the development of dicotyledons, I think it ought to be proved that
such animals as deer, cows, horses, etc. could not flourish if fed
exclusively on the gramineae and other anemophilous monocotyledons; and I
do not suppose that any evidence on this head exists.

Your suggestion of studying the manner of fertilisation of the surviving
members of the most ancient forms of the dicotyledons is a very good one,
and I hope that you will keep it in mind yourself, for I have turned my
attention to other subjects. Delpino I think says that Magnolia is
fertilised by insects which gnaw the petals, and I should not be surprised
if the same fact holds good with Nymphaea. Whenever I have looked at the
flowers of these latter plants I have felt inclined to admit the view that
petals are modified stamens, and not modified leaves; though Poinsettia
seems to show that true leaves might be converted into coloured petals. I
grieve to say that I have never been properly grounded in Botany and have
studied only special points--therefore I cannot pretend to express any
opinion on your remarks on the origin of the flowers of the Coniferae,
Gnetaceae, etc.; but I have been delighted with what you say on the
conversion of a monoecious species into a hermaphrodite one by the
condensations of the verticils on a branch bearing female flowers near the
summit, and male flowers below.

I expect Hooker to come here before long, and I will then show him your
drawing, and if he makes any important remarks I will communicate with you.
He is very busy at present in clearing off arrears after his American
Expedition, so that I do not like to trouble him, even with the briefest
note. I am at present working with my son at some Physiological subjects,
and we are arriving at very curious results, but they are not as yet
sufficiently certain to be worth communicating to you...

[In 1877 a second edition of the 'Fertilisation of Orchids' was published,
the first edition having been for some time out of print. The new edition
was remodelled and almost re-written, and a large amount of new matter
added, much of which the author owed to his friend Fritz Muller.

With regard to this edition he wrote to Dr. Gray:--

"I do not suppose I shall ever again touch the book. After much doubt I
have resolved to act in this way with all my books for the future; that is
to correct them once and never touch them again, so as to use the small
quantity of work left in me for new matter."

He may have felt a diminution of his powers of reviewing large bodies of
facts, such as would be needed in the preparation of new editions, but his
powers of observation were certainly not diminished. He wrote to Mr. Dyer
on July 14, 1878:]

My dear Dyer,

Thalia dealbata was sent me from Kew: it has flowered and after looking
casually at the flowers, they have driven me almost mad, and I have worked
at them for a week: it is as grand a case as that of Catasetum.

Pistil vigorously motile (so that whole flower shakes when pistil suddenly
coils up); when excited by a touch the two filaments [are] produced
laterally and transversely across the flower (just over the nectar) from
one of the petals or modified stamens. It is splendid to watch the
phenomenon under a weak power when a bristle is inserted into a YOUNG
flower which no insect has visited. As far as I know Stylidium is the sole
case of sensitive pistil and here it is the pistil + stamens. In Thalia
(Hildebrand has described an explosive arrangement in some of the
Maranteae--the tribe to which Thalia belongs.) cross-fertilisation is
ensured by the wonderful movement, if bees visit several flowers.

I have now relieved my mind and will tell the purport of this note--viz. if
any other species of Thalia besides T. dealbata should flower with you, for
the love of heaven and all the saints, send me a few in TIN BOX WITH DAMP
MOSS.

Your insane friend,
CH. DARWIN.

[In 1878 Dr. Ogle's translation of Kerner's interesting book, 'Flowers and
their Unbidden Guests,' was published. My father, who felt much interest
in the translation (as appears in the following letter), contributed some
prefatory words of approval:]

CHARLES DARWIN TO W. OGLE.
Down, December 16 [1878].

...I have now read Kerner's book, which is better even than I anticipated.
The translation seems to me as clear as daylight, and written in forcible
and good familiar English. I am rather afraid that it is too good for the
English public, which seems to like very washy food, unless it be
administered by some one whose name is well-known, and then I suspect a
good deal of the unintelligible is very pleasing to them. I hope to heaven
that I may be wrong. Anyhow, you and Mrs. Ogle have done a right good
service for Botanical Science. Yours very sincerely,

CH. DARWIN.

P.S.--You have done me much honour in your prefatory remarks.

[One of the latest references to his Orchid-work occurs in a letter to Mr.
Bentham, February 16, 1880. It shows the amount of pleasure which this
subject gave to my father, and (what is characteristic of him) that his
reminiscence of the work was one of delight in the observations which
preceded its publication. Not to the applause which followed it:--

"They are wonderful creatures, these Orchids, and I sometimes think with a
glow of pleasure, when I remember making out some little point in their
method of fertilisation."]

CHAPTER 2.XI.

THE 'EFFECTS OF CROSS- AND SELF-FERTILISATION IN THE VEGETABLE KINGDOM.'

1876.

[This book, as pointed out in the 'Autobiography,' is a complement to the
'Fertilisation of Orchids,' because it shows how important are the results
of cross-fertilisation which are ensured by the mechanisms described in
that book.

By proving that the offspring of cross-fertilisation are more vigorous than
the offspring of self-fertilisation, he showed that one circumstance which
influences the fate of young plants in the struggle for life is the degree
to which their parents are fitted for cross-fertilisation. He thus
convinced himself that the intensity of the struggle (which he had
elsewhere shown to exist among young plants) is a measure of the strength
of a selective agency perpetually sifting out every modification in the
structure of flowers which can effect its capabilities for cross-
fertilisation.

The book is also valuable in another respect, because it throws light on
the difficult problems of the origin of sexuality. The increased vigour
resulting from cross-fertilisation is allied in the closest manner to the
advantage gained by change of conditions. So strongly is this the case,
that in some instances cross-fertilisation gives no advantage to the
offspring, unless the parents have lived under slightly different
conditions. So that the really important thing is not that two individuals
of different BLOOD shall unite, but two individuals which have been
subjected to different conditions. We are thus led to believe that
sexuality is a means for infusing vigour into the offspring by the
coalescence of differentiated elements, an advantage which could not follow
if reproductions were entirely asexual.

It is remarkable that this book, the result of eleven years of experimental
work, owed its origin to a chance observation. My father had raised two
beds of Linaria vulgaris--one set being the offspring of cross- and the
other of self-fertilisation. These plants were grown for the sake of some
observations on inheritance, and not with any view to cross-breeding, and
he was astonished to observe that the offspring of self-fertilisation were
clearly less vigorous than the others. It seemed incredible to him that
this result could be due to a single act of self-fertilisation, and it was
only in the following year when precisely the same result occurred in the
case of a similar experiment on inheritance in Carnations, that his
attention was "thoroughly aroused" and that he determined to make a series
of experiments specially directed to the question. The following letters
give some account of the work in question.]

CHARLES DARWIN TO ASA GRAY.
September 10, [1866?].

...I have just begun a large course of experiments on the germination of
the seed, and on the growth of the young plants when raised from a pistil
fertilised by pollen from the same flower, and from pollen from a distinct
plant of the same, or of some other variety. I have not made sufficient
experiments to judge certainly, but in some cases the difference in the
growth of the young plants is highly remarkable. I have taken every kind
of precaution in getting seed from the same plant, in germinating the seed
on my own chimney-piece, in planting the seedlings in the same flower-pot,
and under this similar treatment I have seen the young seedlings from the
crossed seed exactly twice as tall as the seedlings from the self-
fertilised seed; both seeds having germinated on the same day. If I can
establish this fact (but perhaps it will all go to the dogs), in some fifty
cases, with plants of different orders, I think it will be very important,
for then we shall positively know why the structure of every flower
permits, or favours, or necessitates an occasional cross with a distinct
individual. But all this is rather cooking my hare before I have caught
it. But somehow it is a great pleasure to me to tell you what I am about.
Believe me, my dear Gray,

Ever yours most truly, and with cordial thanks,
CH. DARWIN.

CHARLES DARWIN TO G. BENTHAM.
April 22, 1868.

...I am experimenting on a very large scale on the difference in power of
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.

With cordial thanks for your letter, which has pleased me greatly,

Yours very sincerely,
CHARLES DARWIN.

[An extract from a letter to Dr. Gray (March 11, 1873) mentions the
progress of the work:--

"I worked last summer hard at Drosera, but could not finish till I got
fresh plants, and consequently took up the effects of crossing and self-
fertilising plants, and am got so interested that Drosera must go to the
dogs till I finish with this, and get it published; but then I will resume
my beloved Drosera, and I heartily apologise for having sent the precious
little things even for a moment to the dogs."

The following letters give the author's impression of his own book.]

CHARLES DARWIN TO J. MURRAY.
Down, September 16, 1876.

My dear Sir,

I have just received proofs in sheet of five sheets, so you will have to
decide soon how many copies will have to be struck off. I do not know what
to advise. The greater part of the book is extremely dry, and the whole on
a special subject. Nevertheless, I am convinced that the book is of value,
and I am convinced that for MANY years copies will be occasionally sold.
Judging from the sale of my former books, and from supposing that some
persons will purchase it to complete the set of my works, I would suggest
1500. But you must be guided by your larger experience. I will only
repeat that I am convinced the book is of some permanent value...

CHARLES DARWIN TO VICTOR CARUS.
Down, September 27, 1876.

My dear Sir,

I sent by this morning's post the four first perfect sheets of my new book,
the title of which you will see on the first page, and which will be
published early in November.

I am sorry to say that it is only shorter by a few pages than my
'Insectivorous Plants.' The whole is now in type, though I have corrected
finally only half the volume. You will, therefore, rapidly receive the
remainder. The book is very dull. Chapters II. to VI., inclusive, are
simply a record of experiments. Nevertheless, I believe (though a man can
never judge his own books) that the book is valuable. You will have to
decide whether it is worth translating. I hope so. It has cost me very
great labour, and the results seem to me remarkable and well established.

If you translate it, you could easily get aid for Chapters II. to VI., as
there is here endless, but I have thought necessary repetition. I shall be
anxious to hear what you decide...

I most sincerely hope that your health has been fairly good this summer.

My dear Sir, yours very truly,
CH. DARWIN.

CHARLES DARWIN TO ASA GRAY.
Down, October 28, 1876.

My dear Gray,

I send by this post all the clean sheets as yet printed, and I hope to send
the remainder within a fortnight. Please observe that the first six
chapters are not readable, and the six last very dull. Still I believe
that the results are valuable. If you review the book, I shall be very
curious to see what you think of it, for I care more for your judgment than
for that of almost any one else. I know also that you will speak the
truth, whether you approve or disapprove. Very few will take the trouble
to read the book, and I do not expect you to read the whole, but I hope you
will read the latter chapters.

...I am so sick of correcting the press and licking my horrid bad style
into intelligible English.

[The 'Effects of Cross and Self-fertilisation' was published on November
10, 1876, and 1500 copies were sold before the end of the year. The
following letter refers to a review in 'Nature' (February 15, 1877.):]

CHARLES DARWIN TO W. THISELTON DYER.
Down, February 16, 1877.

Dear Dyer,

I must tell you how greatly I am pleased and honoured by your article in
'Nature,' which I have just read. You are an adept in saying what will
please an author, not that I suppose you wrote with this express intention.
I should be very well contented to deserve a fraction of your praise. I
have also been much interested, and this is better than mere pleasure, by
your argument about the separation of the sexes. I dare say that I am
wrong, and will hereafter consider what you say more carefully: but at
present I cannot drive out of my head that the sexes must have originated
from two individuals, slightly different, which conjugated. But I am aware
that some cases of conjugation are opposed to any such views.

With hearty thanks,
Yours sincerely,
CHARLES DARWIN.

CHAPTER 2.XII.

'DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES.'

1877.

[The volume bearing the above title was published in 1877, and was
dedicated by the author to Professor Asa Gray, "as a small tribute of
respect and affection." It consists of certain earlier papers re-edited,
with the addition of a quantity of new matter. The subjects treated in the
book are:--

1. Heterostyled Plants.

2. Polygamous, Dioecious, and Gynodioecious Plants.

3. Cleistogamic Flowers.

The nature of heterostyled plants may be illustrated in the primrose, one
of the best known examples of the class. If a number of primroses be
gathered, it will be found that some plants yield nothing but "pin-eyed"
flowers, in which the style (or organ for the transmission of the pollen to
the ovule) is long, while the others yield only "thrum-eyed" flowers with
short styles. Thus primroses are divided into two sets or castes differing
structurally from each other. My father showed that they also differ
sexually, and that in fact the bond between the two castes more nearly
resembles that between separate sexes than any other known relationship.
Thus for example a long-styled primrose, though it can be fertilised by its
own pollen, is not FULLY fertile unless it is impregnated by the pollen of
a short-styled flower. Heterostyled plants are comparable to hermaphrodite
animals, such as snails, which require the concourse of two individuals,
although each possesses both the sexual elements. The difference is that
in the case of the primrose it is PERFECT FERTILITY, and not simply
FERTILITY, that depends on the mutual action of the two sets of
individuals.

The work on heterostyled plants has a special bearing, to which the author
attached much importance, on the problem of origin of species. (See
'Autobiography,' volume i.)

He found that a wonderfully close parallelism exists between hybridisation
and certain forms of fertilisation among heterostyled plants. So that it
is hardly an exaggeration to say that the "illegitimately" reared seedlings
are hybrids, although both their parents belong to identically the same
species. In a letter to Professor Huxley, my father writes as if his
researches on heterostyled plants tended to make him believe that sterility
is a selected or acquired quality. But in his later publications, e.g. in
the sixth edition of the 'Origin,' he adheres to the belief that sterility
is an incidental rather than a selected quality. The result of his work on
heterostyled plants is of importance as showing that sterility is no test
of specific distinctness, and that it depends on differentiation of the
sexual elements which is independent of any racial difference. I imagine
that it was his instinctive love of making out a difficulty which to a
great extent kept him at work so patiently on the heterostyled plants. But
it was the fact that general conclusions of the above character could be
drawn from his results which made him think his results worthy of
publication. (See 'Forms of Flowers,' page 243.)

The papers which on this subject preceded and contributed to 'Forms of
Flowers' were the following:--

"On the two Forms or Dimorphic Condition in the Species of Primula, and on
their remarkable Sexual Relations." Linn. Soc. Journal, 1862.)

"On the Existence of Two Forms, and on their Reciprocal Sexual Relations,
in several Species of the Genus Linum." Linn. Soc. Journal, 1863.

"On the Sexual Relations of the Three Forms of Lythrum salicaria," Ibid.
1864.

"On the Character and Hybrid-like Nature of the Offspring from the
Illegitimate Unions of Dimorphic and Trimorphic Plants." Ibid. 1869.

"On the Specific Differences between Primula veris, Brit. Fl. (var.
Officinalis, Linn.), P. vulgaris, Brit. Fl. (var. acaulis, Linn.) and P.
elatior, Jacq.; and on the Hybrid Nature of the Common Oxlip. With
Supplementary Remarks on Naturally Produced Hybrids in the Genus
Verbascum." Ibid. 1869.

The following letter shows that he began the work on heterostyled plants
with an erroneous view as to the meaning of the facts.]

CHARLES DARWIN TO J.D. HOOKER.
Down, May 7 [1860].

...I have this morning been looking at my experimental cowslips, and I find
some plants have all flowers with long stamens and short pistils, which I
will call "male plants," others with short stamens and long pistils, which
I will call "female plants." This I have somewhere seen noticed, I think
by Henslow; but I find (after looking at my two sets of plants) that the
stigmas of the male and female are of slightly different shape, and
certainly different degree of roughness, and what has astonished me, the
pollen of the so-called female plant, though very abundant, is more
transparent, and each granule is exactly only 2/3 of the size of the pollen
of the so-called male plant. Has this been observed? I cannot help
suspecting [that] the cowslip is in fact dioecious, but it may turn out all
a blunder, but anyhow I will mark with sticks the so-called male and female
plants and watch their seeding. It would be a fine case of gradation
between an hermaphrodite and unisexual condition. Likewise a sort of case
of balancement of long and short pistils and stamens. Likewise perhaps
throws light on oxlips...

I have now examined primroses and find exactly the same difference in the
size of the pollen, correlated with the same difference in the length of
the style and roughness of the stigmas.

CHARLES DARWIN TO ASA GRAY.
June 8 [1860].

...I have been making some little trifling observations which have
interested and perplexed me much. I find with primroses and cowslips, that
about an equal number of plants are thus characterised.

SO-CALLED (by me) MALE plant. Pistil much shorter than stamens; stigma
rather smooth,--POLLEN GRAINS LARGE, throat of corolla short.

SO-CALLED FEMALE plant. Pistil much longer than stamens, stigma rougher,
POLLEN-GRAINS SMALLER,--throat of corolla long.

I have marked a lot of plants, and expected to find the so-called male
plant barren; but judging from the feel of the capsules, this is not the
case, and I am very much surprised at the difference in the size of the
pollen...If it should prove that the so-called male plants produce less
seed than the so-called females, what a beautiful case of gradation from
hermaphrodite to unisexual condition it will be! If they produce about
equal number of seed, how perplexing it will be.

CHARLES DARWIN TO J.D. HOOKER.
Down, December 17 [1860?].

...I have just been ordering a photograph of myself for a friend; and have
ordered one for you, and for heaven's sake oblige me, and burn that now
hanging up in your room.--It makes me look atrociously wicked.

...In the spring I must get you to look for long pistils and short pistils
in the rarer species of Primula and in some allied Genera. It holds with
P. Sinensis. You remember all the fuss I made on this subject last spring;
well, the other day at last I had time to weigh the seeds, and by Jove the
plants of primroses and cowslip with short pistils and large grained pollen
(Thus the plants which he imagined to be tending towards a male condition
were more productive than the supposed females.) are rather more fertile
than those with long pistils, and small-grained pollen. I find that they
require the action of insects to set them, and I never will believe that
these differences are without some meaning.

Some of my experiments lead me to suspect that the large-grained pollen
suits the long pistils and the small-grained pollen suits the short
pistils; but I am determined to see if I cannot make out the mystery next
spring.

How does your book on plants brew in your mind? Have you begun it?...

Remember me most kindly to Oliver. He must be astonished at not having a
string of questions, I fear he will get out of practice!

[The Primula-work was finished in the autumn of 1861, and on November 8th
he wrote to Sir J.D. Hooker:--

"I have sent my paper on dimorphism in Primula to the Linn. Soc. I shall
go up and read it whenever it comes on; I hope you may be able to attend,
for I do not suppose many will care a penny for the subject."

With regard to the reading of the paper (on November 21st), he wrote to the
same friend:--

"I by no means thought that I produced a "tremendous effect" in the Linn.
Soc., but by Jove the Linn. Soc. produced a tremendous effect on me, for I
could not get out of bed till late next evening, so that I just crawled
home. I fear I must give up trying to read any paper or speak; it is a
horrid bore, I can do nothing like other people."

To Dr. Gray he wrote, (December 1861):--

"You may rely on it, I will send you a copy of my Primula paper as soon as
I can get one; but I believe it will not be printed till April 1st, and
therefore after my Orchid Book. I care more for your and Hooker's opinion
than for that of all the rest of the world, and for Lyell's on geological
points. Bentham and Hooker thought well of my paper when read; but no one
can judge of evidence by merely hearing a paper."

The work on Primula was the means of bringing my father in contact with the
late Mr. John Scott, then working as a gardener in the Botanic Gardens at
Edinburgh,--an employment which he seems to have chosen in order to gratify
his passion for natural history. He wrote one or two excellent botanical
papers, and ultimately obtained a post in India. (While in India he made
some admirable observations on expression for my father.) He died in 1880.

A few phrases may be quoted from letters to Sir J.D. Hooker, showing my
father's estimate of Scott:--

"If you know, do please tell me who is John Scott of the Botanical Gardens
of Edinburgh; I have been corresponding largely with him; he is no common
man."

"If he had leisure he would make a wonderful observer; to my judgment I
have come across no one like him."

"He has interested me strangely, and I have formed a very high opinion of
his intellect. I hope he will accept pecuniary assistance from me; but he
has hitherto refused." (He ultimately succeeded in being allowed to pay
for Mr. Scott's passage to India.)

"I know nothing of him excepting from his letters; these show remarkable
talent, astonishing perseverance, much modesty, and what I admire,
determined difference from me on many points."

So highly did he estimate Scott's abilities that he formed a plan (which
however never went beyond an early stage of discussion) of employing him to
work out certain problems connected with intercrossing.

The following letter refers to my father's investigations on Lythrum (He
was led to this, his first case of trimorphism by Lecoq's 'Geographie
Botanique,' and this must have consoled him for the trick this work played
him in turning out to be so much larger than he expected. He wrote to Sir
J.D. Hooker: "Here is a good joke: I saw an extract from Lecoq,
'Geograph. Bot.,' and ordered it and hoped that it was a good sized
pamphlet, and nine thick volumes have arrived!"), a plant which reveals
even a more wonderful condition of sexual complexity than that of Primula.
For in Lythrum there are not merely two, but three castes, differing
structurally and physiologically from each other:]

CHARLES DARWIN TO ASA GRAY.
Down, August 9 [1862].

My dear Gray,

It is late at night, and I am going to write briefly, and of course to beg
a favour.

The Mitchella very good, but pollen apparently equal-sized. I have just
examined Hottonia, grand difference in pollen. Echium vulgare, a humbug,
merely a case like Thymus. But I am almost stark staring mad over Lythrum
(On another occasion he wrote (to Dr. Gray) with regard to Lythrum: "I
must hold hard, otherwise I shall spend my life over dimorphism."); if I
can prove what I fully believe, it is a grand case of TRIMORPHISM, with
three different pollens and three stigmas; I have castrated and fertilised
above ninety flowers, trying all the eighteen distinct crosses which are
possible within the limits of this one species! I cannot explain, but I
feel sure you would think it a grand case. I have been writing to
Botanists to see if I can possibly get L. hyssopifolia, and it has just
flashed on me that you might have Lythrum in North America, and I have
looked to your Manual. For the love of heaven have a look at some of your
species, and if you can get me seed, do; I want much to try species with
few stamens, if they are dimorphic; Nesaea verticillata I should expect to
be trimorphic. Seed! Seed! Seed! I should rather like seed of
Mitchella. But oh, Lythrum!

Your utterly mad friend,
C. DARWIN.

P.S.--There is reason in my madness, for I can see that to those who
already believe in change of species, these facts will modify to a certain
extent the whole view of Hybridity. (A letter to Dr. Gray (July, 1862)
bears on this point: "A few days ago I made an observation which has
surprised me more than it ought to do--it will have to be repeated several
times, but I have scarcely a doubt of its accuracy. I stated in my Primula
paper that the long-styled form of Linum grandiflorum was utterly sterile
with its own pollen; I have lately been putting the pollen of the two forms
on the stigma of the SAME flower; and it strikes me as truly wonderful,
that the stigma distinguishes the pollen; and is penetrated by the tubes of
the one and not by those of the other; nor are the tubes exserted. Or
(which is the same thing) the stigma of the one form acts on and is acted
on by pollen, which produces not the least effect on the stigma of the
other form. Taking sexual power as the criterion of difference, the two
forms of this one species may be said to be generically distinct.")

[On the same subject he wrote to Sir Joseph Hooker in August 1862:--

"Is Oliver at Kew? When I am established at Bournemouth I am completely
mad to examine any fresh flowers of any Lythraceous plant, and I would
write and ask him if any are in bloom."

Again he wrote to the same friend in October:--

"If you ask Oliver, I think he will tell you I have got a real odd case in
Lythrum, it interests me extremely, and seems to me the strangest case of
propagation recorded amongst plants or animals, viz. a necessary triple
alliance between three hermaphrodites. I feel sure I can now prove the
truth of the case from a multitude of crosses made this summer."

In an article, 'Dimorphism in the Genitalia of Plants' ('Silliman's
Journal,' 1862, volume xxxiv. page 419), Dr. Gray pointed out that the
structural difference between the two forms of Primula had already been
defined in the 'Flora of North America,' as DIOECIO-DIMORPHISM. The use of
this term called forth the following remarks from my father. The letter
also alludes to a review of the 'Fertilisation of Orchids' in the same
volume of 'Silliman's Journal.']

CHARLES DARWIN TO ASA GRAY.
Down, November 26 [1862].

My dear Gray,

The very day after my last letter, yours of November 10th, and the review
in 'Silliman,' which I feared might have been lost, reached me. We were
all very much interested by the political part of your letter; and in some
odd way one never feels that information and opinions painted in a
newspaper come from a living source; they seem dead, whereas all that you
write is full of life. The reviews interested me profoundly; you rashly
ask for my opinion, and you must consequently endure a long letter. First
for Dimorphism; I do not AT PRESENT like the term "Dioecio-dimorphism;" for
I think it gives quite a false notion, that the phenomena are connected
with a separation of the sexes. Certainly in Primula there is unequal
fertility in the two forms, and I suspect this is the case with Linum; and,
therefore I felt bound in the Primula paper to state that it might be a
step towards a dioecious condition; though I believe there are no dioecious
forms in Primulaceae or Linaceae. But the three forms in Lythrum convince
me that the phenomenon is in no way necessarily connected with any tendency
to separation of sexes. The case seems to me in result or function to be
almost identical with what old C.K. Sprengel called "dichogamy," and which
is so frequent in truly hermaphrodite groups; namely, the pollen and stigma
of each flower being mature at different periods. If I am right, it is
very advisable not to use the term "dioecious," as this at once brings
notions of separation of sexes.

...I was much perplexed by Oliver's remarks in the 'Natural History Review'
on the Primula case, on the lower plants having sexes more often separated
than in the higher plants,--so exactly the reverse of what takes place in
animals. Hooker in his review of the 'Orchids' repeats this remark. There
seems to be much truth in what you say ("Forms which are low in the scale
as respects morphological completeness may be high in the scale of rank
founded on specialisation of structure and function."--Dr. Gray, in
'Silliman's Journal.'), and it did not occur to me, about no improbability
of specialisation in CERTAIN lines in lowly organised beings. I could
hardly doubt that the hermaphrodite state is the aboriginal one. But how
is it in the conjugation of Confervae--is not one of the two individuals
here in fact male, and the other female? I have been much puzzled by this
contrast in sexual arrangements between plants and animals. Can there be
anything in the following consideration: By ROUGHEST calculation about
one-third of the British GENERA of aquatic plants belong to the Linnean
classes of Mono and Dioecia; whilst of terrestrial plants (the aquatic
genera being subtracted) only one-thirteenth of the genera belong to these
two classes. Is there any truth in this fact generally? Can aquatic
plants, being confined to a small area or small community of individuals,
require more free crossing, and therefore have separate sexes? But to
return to our point, does not Alph. de Candolle say that aquatic plants
taken as a whole are lowly organised, compared with terrestrial; and may
not Oliver's remark on the separation of the sexes in lowly organised
plants stand in some relation to their being frequently aquatic? Or is
this all rubbish?

...What a magnificent compliment you end your review with! You and Hooker
seem determined to turn my head with conceit and vanity (if not already
turned) and make me an unbearable wretch.

With most cordial thanks, my good and kind friend,
Farewell,
C. DARWIN.

[The following passage from a letter (July 28, 1863), to Prof. Hildebrand,
contains a reference to the reception of the dimorphic work in France:--

"I am extremely much pleased to hear that you have been looking at the
manner of fertilisation of your native Orchids, and still more pleased to
hear that you have been experimenting on Linum. I much hope that you may
publish the result of these experiments; because I was told that the most
eminent French botanists of Paris said that my paper on Primula was the
work of imagination, and that the case was so improbable they did not
believe in my results."]

CHARLES DARWIN TO ASA GRAY.
April 19 [1864].

...I received a little time ago a paper with a good account of your
Herbarium and Library, and a long time previously your excellent review of
Scott's 'Primulaceae,' and I forwarded it to him in India, as it would much
please him. I was very glad to see in it a new case of Dimorphism (I
forget just now the name of the plant); I shall be grateful to hear of any
other cases, as I still feel an interest in the subject. I should be very
glad to get some seed of your dimorphic Plantagos; for I cannot banish the
suspicion that they must belong to a very different class like that of the
common Thyme. (In this prediction he was right. See 'Forms of Flowers,'
page 307.) How could the wind, which is the agent of fertilisation, with
Plantago, fertilise "reciprocally dimorphic" flowers like Primula? Theory
says this cannot be, and in such cases of one's own theories I follow
Agassiz and declare, "that nature never lies." I should even be very glad
to examine the two dried forms of Plantago. Indeed, any dried dimorphic
plants would be gratefully received...

Did my Lythrum paper interest you? I crawl on at the rate of two hours per
diem, with 'Variation under Domestication.'

CHARLES DARWIN TO J.D. HOOKER.
Down, November 26 [1864].

...You do not know how pleased I am that you have read my Lythrum paper; I
thought you would not have time, and I have for long years looked at you as
my Public, and care more for your opinion than that of all the rest of the
world. I have done nothing which has interested me so much as Lythrum,
since making out the complemental males of Cirripedes. I fear that I have
dragged in too much miscellaneous matter into the paper.

...I get letters occasionally, which show me that Natural Selection is
making GREAT progress in Germany, and some amongst the young in France. I
have just received a pamphlet from Germany, with the complimentary title of
"Darwinische Arten-Enstehung-Humbug"!

Farewell, my best of old friends,
C. DARWIN.

CHARLES DARWIN TO ASA GRAY.
September 10, [1867?].

...The only point which I have made out this summer, which could possibly
interest you, is that the common Oxlip found everywhere, more or less
commonly in England, is certainly a hybrid between the primrose and
cowslip; whilst the P. elatior (Jacq.), found only in the Eastern Counties,
is a perfectly distinct and good species; hardly distinguishable from the
common oxlip, except by the length of the seed-capsule relatively to the
calyx. This seems to me rather a horrid fact for all systematic
botanists...

CHARLES DARWIN TO F. HILDEBRAND.
Down, November 16, 1868.

My dear Sir,

I wrote my last note in such a hurry from London, that I quite forgot what
I chiefly wished to say, namely to thank you for your excellent notices in
the 'Bot. Zeitung' of my paper on the offspring of dimorphic plants. The
subject is so obscure that I did not expect that any one would have noticed
my paper, and I am accordingly very much pleased that you should have
brought the subject before the many excellent naturalists of Germany.

Of all the German authors (but they are not many) whose works I have read,
you write by far the clearest style, but whether this is a compliment to a
German writer I do not know.

[The two following letters refer to the small bud-like "Cleistogamic"
flowers found in the violet and many other plants. They do not open and
are necessarily self-fertilised:]

CHARLES DARWIN TO J.D. HOOKER.
Down, May 30 [1862].

...What will become of my book on Variation? I am involved in a
multiplicity of experiments. I have been amusing myself by looking at the
small flowers of Viola. If Oliver (Shortly afterwards he wrote: "Oliver,
the omniscient, has sent me a paper in the 'Bot. Zeitung,' with most
accurate description of all that I saw in Viola.") has had time to study
them, he will have seen the curious case (as it seems to me) which I have
just made clearly out, viz. that in these flowers, the FEW pollen grains
are never shed, or never leave the anther-cells, but emit long pollen
tubes, which penetrate the stigma. To-day I got the anther with the
included pollen grain (now empty) at one end, and a bundle of tubes
penetrating the stigmatic tissue at the other end; I got the whole under a
microscope without breaking the tubes; I wonder whether the stigma pours
some fluid into the anther so as to excite the included grains. It is a
rather odd case of correlation, that in the double sweet violet the small
flowers are double; i.e., have a multitude of minute scales representing
the petals. What queer little flowers they are.

Have you had time to read poor dear Henslow's life? it has interested me
for the man's sake, and, what I did not think possible, has even exalted
his character in my estimation...

[The following is an extract from the letter given in part above, and
refers to Dr. Gray's article on the sexual differences of plants:]

CHARLES DARWIN TO ASA GRAY.
NOVEMBER 26 [1862].

...You will think that I am in the most unpleasant, contradictory,
fractious humour, when I tell you that I do not like your term of
"precocious fertilisation" for your second class of dimorphism [i.e. for
cleistogamic fertilisation]. If I can trust my memory, the state of the
corolla, of the stigma, and the pollen-grains is different from the state
of the parts in the bud; that they are in a condition of special
modification. But upon my life I am ashamed of myself to differ so much
from my betters on this head. The TEMPORARY theory (This view is now
generally accepted.) which I have formed on this class of dimorphism, just
to guide experiment, is that the PERFECT flowers can only be perfectly
fertilised by insects, and are in this case abundantly crossed; but that
the flowers are not always, especially in early spring, visited enough by
insects, and therefore the little imperfect self-fertilising flowers are
developed to ensure a sufficiency of seed for present generations. Viola
canina is sterile, when not visited by insects, but when so visited forms
plenty of seed. I infer from the structure of three or four forms of
Balsamineae, that these require insects; at least there is almost as plain
adaptation to insects as in the Orchids. I have Oxalis acetosella ready in
pots for experiment next spring; and I fear this will upset my little
theory...Campanula carpathica, as I found this summer, is absolutely
sterile if insects are excluded. Specularia speculum is fairly fertile
when enclosed; and this seemed to me to be partially effected by the
frequent closing of the flower; the inward angular folds of the corolla
corresponding with the clefts of the open stigma, and in this action
pushing pollen from the outside of the stigma on to its surface. Now can
you tell me, does S. perfoliata close its flower like S. speculum, with
angular inward folds? if so, I am smashed without some fearful "wriggling."
Are the IMPERFECT flowers of your Specularia the early or the later ones?
very early or very late? It is rather pretty to see the importance of the
closing of flowers of S. speculum.

['Forms of Flowers' was published in July; in June, 1877, he wrote to
Professor Carus with regard to the translation:--

"My new book is not a long one, viz. 350 pages, chiefly of the larger type,
with fifteen simple woodcuts. All the proofs are corrected except the
Index, so that it will soon be published.

"...I do not suppose that I shall publish any more books, though perhaps a
few more papers. I cannot endure being idle, but heaven knows whether I am
capable of any more good work."

The review alluded to in the next letter is at page 445 of the volume of
'Nature' for 1878:]

CHARLES DARWIN TO W. THISELTON DYER.
Down, April 5, 1878.

My dear Dyer,

I have just read in 'Nature' the review of 'Forms of Flowers,' and I am
sure that it is by you. I wish with all my heart that it deserved one
quarter of the praises which you give it. Some of your remarks have
interested me greatly...Hearty thanks for your generous and most kind
sympathy, which does a man real good, when he is as dog-tired as I am at
this minute with working all day, so good-bye.

C. DARWIN.

CHAPTER 2.XIII.

CLIMBING AND INSECTIVOROUS PLANTS.

[My father mentions in his 'Autobiography' (volume i.) that he was led to
take up the subject of climbing plants by reading Dr. Gray's paper, "Note
on the Coiling of the Tendrils of Plants." ('Proc. Amer. Acad. of Arts and
Sciences,' 1858.) This essay seems to have been read in 1862, but I am
only able to guess at the date of the letter in which he asks for a
reference to it, so that the precise date of his beginning this work cannot
be determined.

In June 1863 he was certainly at work, and wrote to Sir J.D. Hooker for
information as to previous publications on the subject, being then in
ignorance of Palm's and H. v. Mohl's works on climbing plants, both of
which were published in 1827.]

CHARLES DARWIN TO J.D. HOOKER.
Down [June] 25 [1863].

My dear Hooker,

I have been observing pretty carefully a little fact which has surprised
me; and I want to know from you and Oliver whether it seems new or odd to
you, so just tell me whenever you write; it is a very trifling fact, so do
not answer on purpose.

I have got a plant of Echinocystis lobata to observe the irritability of
the tendrils described by Asa Gray, and which of course, is plain enough.
Having the plant in my study, I have been surprised to find that the
uppermost part of each branch (i.e. the stem between the two uppermost
leaves excluding the growing tip) is CONSTANTLY and slowly twisting round
making a circle in from one-half to two hours; it will sometimes go round
two or three times, and then at the same rate untwists and twists in
opposite directions. It generally rests half an hour before it
retrogrades. The stem does not become permanently twisted. The stem
beneath the twisting portion does not move in the least, though not tied.
The movement goes on all day and all early night. It has no relation to
light for the plant stands in my window and twists from the light just as
quickly as towards it. This may be a common phenomenon for what I know,
but it confounded me quite, when I began to observe the irritability of the
tendrils. I do not say it is the final cause, but the result is pretty,
for the plant every one and a half or two hours sweeps a circle (according
to the length of the bending shoot and the length of the tendril) of from
one foot to twenty inches in diameter, and immediately that the tendril
touches any object its sensitiveness causes it immediately to seize it; a
clever gardener, my neighbour, who saw the plant on my table last night,
said: "I believe, Sir, the tendrils can see, for wherever I put a plant it
finds out any stick near enough." I believe the above is the explanation,
viz. that it sweeps slowly round and round. The tendrils have some sense,
for they do not grasp each other when young.

Yours affectionately,
C. DARWIN.

CHARLES DARWIN TO J.D. HOOKER.
Down, July 14 [1863].

My dear Hooker,

I am getting very much amused by my tendrils, it is just the sort of
niggling work which suits me, and takes up no time and rather rests me
whilst writing. So will you just think whether you know any plant, which
you could give or lend me, or I could buy, with tendrils, remarkable in any
way for development, for odd or peculiar structure, or even for an odd
place in natural arrangement. I have seen or can see Cucurbitaceae,
Passion-flower, Virginian-creeper, Cissus discolor, Common-pea and
Everlasting-pea. It is really curious the diversification of irritability
(I do not mean the spontaneous movement, about which I wrote before and
correctly, as further observation shows): for instance, I find a slight
pinch between the thumb and finger at the end of the tendril of the
Cucurbitaceae causes prompt movement, but a pinch excites no movement in
Cissus. The cause is that one side alone (the concave) is irritable in the
former; whereas both sides are irritable in Cissus, so if you excite at the
same time both OPPOSITE sides there is no movement, but by touching with a
pencil the two branches of the tendril, in any part whatever, you cause
movement towards that point; so that I can mould, by a mere touch, the two
branches into any shape I like...

CHARLES DARWIN TO ASA GRAY.
Down, August 4 [1863].

My present hobby-horse I owe to you, viz. the tendrils: their irritability
is beautiful, as beautiful in all its modifications as anything in Orchids.
About the SPONTANEOUS movement (independent of touch) of the tendrils and
upper internodes, I am rather taken aback by your saying, "is it not well-
known?" I can find nothing in any book which I have...The spontaneous
movement of the tendrils is independent of the movement of the upper
internodes, but both work harmoniously together in sweeping a circle for
the tendrils to grasp a stick. So with all climbing plants (without
tendrils) as yet examined, the upper internodes go on night and day
sweeping a circle in one fixed direction. It is surprising to watch the
Apocyneae with shoots 18 inches long (beyond the supporting stick),
steadily searching for something to climb up. When the shoot meets a
stick, the motion at that point is arrested, but in the upper part is
continued; so that the climbing of all plants yet examined is the simple
result of the spontaneous circulatory movement of the upper internodes.
Pray tell me whether anything has been published on this subject? I hate
publishing what is old; but I shall hardly regret my work if it is old, as
it has much amused me...

CHARLES DARWIN TO ASA GRAY.
May 28, 1864.

...An Irish nobleman on his death-bed declared that he could
conscientiously say that he had never throughout life denied himself any
pleasure; and I can conscientiously say that I have never scrupled to
trouble you; so here goes.--Have you travelled South, and can you tell me
whether the trees, which Bignonia capreolata climbs, are covered with moss
or filamentous lichen or Tillandsia? (He subsequently learned from Dr.
Gray that Polypodium incanum abounds on the trees in the districts where
this species of Bignonia grows. See 'Climbing Plants,' page 103.) I ask
because its tendrils abhor a simple stick, do not much relish rough bark,
but delight in wool or moss. They adhere in a curious manner by making
little disks, like the Ampelopsis...By the way, I will enclose some
specimens, and if you think it worth while, you can put them under the
simple microscope. It is remarkable how specially adapted some tendrils
are; those of Eccremocarpus scaber do not like a stick, will have nothing
to say to wool; but give them a bundle of culms of grass, or a bundle of
bristles and they seize them well.

CHARLES DARWIN TO J.D. HOOKER.
Down, June 10 [1864].

...I have now read two German books, and all I believe that has been
written on climbers, and it has stirred me up to find that I have a good
deal of new matter. It is strange, but I really think no one has explained
simple twining plants. These books have stirred me up, and made me wish
for plants specified in them. I shall be very glad of those you mention.
I have written to Veitch for young Nepenthes and Vanilla (which I believe
will turn out a grand case, though a root creeper), if I cannot buy young
Vanilla I will ask you. I have ordered a leaf-climbing fern, Lygodium.
All this work about climbers would hurt my conscience, did I think I could
do harder work. (He was much out of health at this time.)

[He continued his observations on climbing plants during the prolonged
illness from which he suffered in the autumn of 1863, and in the following
spring. He wrote to Sir J.D. Hooker, apparently in March 1864:--

"For several days I have been decidedly better, and what I lay much stress
on (whatever doctors say), my brain feels far stronger, and I have lost
many dreadful sensations. The hot-house is such an amusement to me, and my
amusement I owe to you, as my delight is to look at the many odd leaves and
plants from Kew...The only approach to work which I can do is to look at
tendrils and climbers, this does not distress my weakened brain. Ask
Oliver to look over the enclosed queries (and do you look) and amuse a
broken-down brother naturalist by answering any which he can. If you ever
lounge through your houses, remember me and climbing plants."

On October 29, 1864, he wrote to Dr. Gray:--

"I have not been able to resist doing a little more at your godchild, my
climbing paper, or rather in size little book, which by Jove I will have
copied out, else I shall never stop. This has been new sort of work for
me, and I have been pleased to find what a capital guide for observations a
full conviction of the change of species is."

On January 19, 1865, he wrote to Sir J.D. Hooker:--

"It is working hours, but I am trying to take a day's holiday, for I
finished and despatched yesterday my climbing paper. For the last ten days
I have done nothing but correct refractory sentences, and I loathe the
whole subject."

A letter to Dr. Gray, April 9, 1865, has a word or two on the subject:--

"I have begun correcting proofs of my paper on 'Climbing Plants.' I
suppose I shall be able to send you a copy in four or five weeks. I think
it contains a good deal new and some curious points, but it is so fearfully
long, that no one will ever read it. If, however, you do not SKIM through
it, you will be an unnatural parent, for it is your child."

Dr. Gray not only read it but approved of it, to my father's great
satisfaction, as the following extracts show:--

"I was much pleased to get your letter of July 24th. Now that I can do
nothing, I maunder over old subjects, and your approbation of my climbing
paper gives me VERY great satisfaction. I made my observations when I
could do nothing else and much enjoyed it, but always doubted whether they
were worth publishing. I demur to its not being necessary to explain in
detail about the spires in CAUGHT tendrils running in opposite directions;
for the fact for a long time confounded me, and I have found it difficult
enough to explain the cause to two or three persons." (August 15, 1865.)

"I received yesterday your article (In the September number of 'Silliman's
Journal,' concluded in the January number, 1866.) on climbers, and it has
pleased me in an extraordinary and even silly manner. You pay me a superb
compliment, and as I have just said to my wife, I think my friends must
perceive that I like praise, they give me such hearty doses. I always
admire your skill in reviews or abstracts, and you have done this article
excellently and given the whole essence of my paper...I have had a letter
from a good Zoologist in S. Brazil, F. Muller, who has been stirred up to
observe climbers and gives me some curious cases of BRANCH-climbers, in
which branches are converted into tendrils, and then continue to grow and
throw out leaves and new branches, and then lose their tendril character."
(October 1865.)

The paper on Climbing Plants was republished in 1875, as a separate book.
The author had been unable to give his customary amount of care to the
style of the original essay, owing to the fact that it was written during a
period of continued ill-health, and it was now found to require a great
deal of alteration. He wrote to Sir J.D. Hooker (March 3, 1875): "It is
lucky for authors in general that they do not require such dreadful work in
merely licking what they write into shape." And to Mr. Murray in September
he wrote: "The corrections are heavy in 'Climbing Plants,' and yet I
deliberately went over the MS. and old sheets three times." The book was
published in September 1875, an edition of 1500 copies was struck off; the
edition sold fairly well, and 500 additional copies were printed in June of
the following year.]

INSECTIVOROUS PLANTS.

[In the summer of 1860 he was staying at the house of his sister-in-law,
Miss Wedgwood, in Ashdown Forest, whence he wrote (July 29, 1860), to Sir
Joseph Hooker;--

"Latterly I have done nothing here; but at first I amused myself with a few
observations on the insect-catching power of Drosera; and I must consult
you some time whether my 'twaddle' is worth communicating to the Linnean
Society."

In August he wrote to the same friend:--

"I will gratefully send my notes on Drosera when copied by my copier: the
subject amused me when I had nothing to do."

He has described in the 'Autobiography' (volume i.), the general nature of
these early experiments. He noticed insects sticking to the leaves, and
finding that flies, etc., placed on the adhesive glands were held fast and
embraced, he suspected that the leaves were adapted to supply nitrogenous
food to the plant. He therefore tried the effect on the leaves of various
nitrogenous fluids--with results which, as far as they went, verified his
surmise. In September, 1860, he wrote to Dr. Gray:--

"I have been infinitely amused by working at Drosera: the movements are
really curious; and the manner in which the leaves detect certain
nitrogenous compounds is marvellous. You will laugh; but it is, at
present, my full belief (after endless experiments) that they detect (and
move in consequence of) the 1/2880 part of a single grain of nitrate of
ammonia; but the muriate and sulphate of ammonia bother their chemical
skill, and they cannot make anything of the nitrogen in these salts! I
began this work on Drosera in relation to GRADATION as throwing light on
Dionaea."

Later in the autumn he was again obliged to leave home for Eastbourne,
where he continued his work on Drosera. The work was so new to him that he
found himself in difficulties in the preparation of solutions, and became
puzzled over fluid and solid ounces, etc. etc. To a friend, the late Mr.
E. Cresy, who came to his help in the matter of weights and measures, he
wrote giving an account of the experiments. The extract (November 2, 1860)
which follows illustrates the almost superstitious precautions he often
applied to his researches:--

"Generally I have scrutinised every gland and hair on the leaf before
experimenting; but it occurred to me that I might in some way affect the
leaf; though this is almost impossible, as I scrutinised with equal care
those that I put into distilled water (the same water being used for
dissolving the carbonate of ammonia). I then cut off four leaves (not
touching them with my fingers), and put them in plain water, and four other
leaves into the weak solution, and after leaving them for an hour and a
half, I examined every hair on all eight leaves; no change on the four in
water; every gland and hair affected in those in ammonia.

"I had measured the quantity of weak solution, and I counted the glands
which had absorbed the ammonia, and were plainly affected; the result
convinced me that each gland could not have absorbed more than 1/64000 or
1/65000 of a grain. I have tried numbers of other experiments all pointing
to the same result. Some experiments lead me to believe that very
sensitive leaves are acted on by much smaller doses. Reflect how little
ammonia a plant can get growing on poor soil--yet it is nourished. The
really surprising part seems to me that the effect should be visible, and
not under very high power; for after trying a high power, I thought it
would be safer not to consider any effect which was not plainly visible
under a two-thirds object glass and middle eye-piece. The effect which the
carbonate of ammonia produces is the segregation of the homogeneous fluid
in the cells into a cloud of granules and colourless fluid; and
subsequently the granules coalesce into larger masses, and for hours have
the oddest movements--coalescing, dividing, coalescing ad infinitum. I do
not know whether you will care for these ill-written details; but, as you
asked, I am sure I am bound to comply, after all the very kind and great
trouble which you have taken."

On his return home he wrote to Sir J.D. Hooker (November 21, 1860):--

"I have been working like a madman at Drosera. Here is a fact for you
which is certain as you stand where you are, though you won't believe it,
that a bit of hair 1/78000 of one grain in weight placed on gland, will
cause ONE of the gland-bearing hairs of Drosera to curve inwards, and will
alter the condition of the contents of every cell in the foot-stalk of the
gland."

And a few days later to Lyell:--

"I will and must finish my Drosera MS., which will take me a week, for, at
the present moment, I care more about Drosera than the origin of all the
species in the world. But I will not publish on Drosera till next year,
for I am frightened and astounded at my results. I declare it is a certain
fact, that one organ is so sensitive to touch, that a weight seventy-eight
times less than that, viz., 1/1000 of a grain, which will move the best
chemical balance, suffices to cause a conspicuous movement. Is it not
curious that a plant should be far more sensitive to the touch than any
nerve in the human body? Yet I am perfectly sure that this is true. When
I am on my hobby-horse, I never can resist telling my friends how well my
hobby goes, so you must forgive the rider."

The work was continued, as a holiday task, at Bournemouth, where he stayed
during the autumn of 1862. The discussion in the following letter on
"nervous matter" in Drosera is of interest in relation to recent researches
on the continuity of protoplasm from cell to cell:]

CHARLES DARWIN TO J.D. HOOKER.
Cliff Cottage, Bournemouth.
September 26 [1862].

My dear Hooker,

Do not read this till you have leisure. If that blessed moment ever comes,
I should be very glad to have your opinion on the subject of this letter.
I am led to the opinion that Drosera must have diffused matter in organic
connection, closely analogous to the nervous matter of animals. When the
glands of one of the papillae or tentacles, in its natural position is
supplied with nitrogenised fluid and certain other stimulants, or when
loaded with an extremely slight weight, or when struck several times with a
needle, the pedicel bends near its base in under one minute. These varied
stimulants are conveyed down the pedicel by some means; it cannot be
vibration, for drops of fluid put on quite quietly cause the movement; it
cannot be absorption of the fluid from cell to cell, for I can see the rate
of absorption, which though quick, is far slower, and in Dionaea the
transmission is instantaneous; analogy from animals would point to
transmission through nervous matter. Reflecting on the rapid power of
absorption in the glands, the extreme sensibility of the whole organ, and
the conspicuous movement caused by varied stimulants, I have tried a number
of substances which are not caustic or corrosive,...but most of which are
known to have a remarkable action on the nervous matter of animals. You
will see the results in the enclosed paper. As the nervous matter of
different animals are differently acted on by the same poisons, one would
not expect the same action on plants and animals; only if plants have
diffused nervous matter, some degree of analogous action. And this is
partially the case. Considering these experiments, together with the
previously made remarks on the functions of the parts, I cannot avoid the
conclusion, that Drosera possesses matter at least in some degree analogous
in constitution and function to nervous matter. Now do tell me what you
think, as far as you can judge from my abstract; of course many more
experiments would have to be tried; but in former years I tried on the
whole leaf, instead of on separate glands, a number of innocuous (This line
of investigation made him wish for information on the action of poisons on
plants; as in many other cases he applied to Professor Oliver, and in
reference to the result wrote to Hooker: "Pray thank Oliver heartily for
his heap of references on poisons.") substances, such as sugar, gum,
starch, etc., and they produced no effect. Your opinion will aid me in
deciding some future year in going on with this subject. I should not have
thought it worth attempting, but I had nothing on earth to do.

My dear Hooker, Yours very sincerely,
CH. DARWIN.

P.S.--We return home on Monday 28th. Thank Heaven!

[A long break now ensued in his work on insectivorous plants, and it was
not till 1872 that the subject seriously occupied him again. A passage in
a letter to Dr. Asa Gray, written in 1863 or 1864, shows, however, that the
question was not altogether absent from his mind in the interim:--

"Depend on it you are unjust on the merits of my beloved Drosera; it is a
wonderful plant, or rather a most sagacious animal. I will stick up for
Drosera to the day of my death. Heaven knows whether I shall ever publish
my pile of experiments on it."

He notes in his diary that the last proof of the 'Expression of the
Emotions' was finished on August 22, 1872, and that he began to work on
Drosera on the following day.]

CHARLES DARWIN TO ASA GRAY.
[Sevenoaks], October 22 [1872].

...I have worked pretty hard for four or five weeks on Drosera, and then
broke down; so that we took a house near Sevenoaks for three weeks (where I
now am) to get complete rest. I have very little power of working now, and
must put off the rest of the work on Drosera till next spring, as my plants
are dying. It is an endless subject, and I must cut it short, and for this
reason shall not do much on Dionaea. The point which has interested me
most is tracing the NERVES! which follow the vascular bundles. By a prick
with a sharp lancet at a certain point, I can paralyse one-half the leaf,
so that a stimulus to the other half causes no movement. It is just like
dividing the spinal marrow of a frog:--no stimulus can be sent from the
brain or anterior part of the spine to the hind legs; but if these latter
are stimulated, they move by reflex action. I find my old results about
the astonishing sensitiveness of the nervous system (!?)of Drosera to
various stimulants fully confirmed and extended...

[His work on digestion in Drosera and other points in the physiology of the
plant soon led him into regions where his knowledge was defective, and here
the advice and assistance which he received from Dr. Burdon Sanderson was
of much value:]

CHARLES DARWIN TO J. BURDON SANDERSON.
Down, July 25, 1873.

My dear Dr. Sanderson,

I should like to tell you a little about my recent work with Drosera, to
show that I have profited by your suggestions, and to ask a question or
two.

1. It is really beautiful how quickly and well Drosera and Dionaea
dissolve little cubes of albumen and gelatine. I kept the same sized cubes
on wet moss for comparison. When you were here I forgot that I had tried
gelatine, but albumen is far better for watching its dissolution and
absorption. Frankland has told me how to test in a rough way for pepsin;
and in the autumn he will discover what acid the digestive juice contains.

2. A decoction of cabbage-leaves and green peas causes as much inflection
as an infusion of raw meat; a decoction of grass is less powerful. Though
I hear that the chemists try to precipitate all albumen from the extract of
belladonna, I think they must fail, as the extract causes inflection,
whereas a new lot of atropine, as well as the valerianate [of atropine],
produce no effect.

3. I have been trying a good many experiments with heated water...Should
you not call the following case one of heat rigor? Two leaves were heated
to 130 deg, and had every tentacle closely inflected; one was taken out and
placed in cold water, and it re-expanded; the other was heated to 145 deg,
and had not the least power of re-expansion. Is not this latter case heat
rigor? If you can inform me, I should very much like to hear at what
temperature cold-blooded and invertebrate animals are killed.

4. I must tell you my final result, of which I am sure, [as to] the
sensitiveness of Drosera. I made a solution of one part of phosphate of
ammonia by weight to 218,750 of water; of this solution I gave so much that
a leaf got 1/8000 of a grain of the phosphate. I then counted the glands,
and each could have got only 1/1552000 of a grain; this being absorbed by
the glands, sufficed to cause the tentacles bearing these glands to bend
through an angle of 180 deg. Such sensitiveness requires hot weather, and
carefully selected young yet mature leaves. It strikes me as a wonderful
fact. I must add that I took every precaution, by trying numerous leaves
at the same time in the solution and in the same water which was used for
making the solution.

5. If you can persuade your friend to try the effects of carbonate of
ammonia on the aggregation of the white blood corpuscles, I should very
much like to hear the result.

I hope this letter will not have wearied you.

Believe me, yours very sincerely,
CHARLES DARWIN.

CHARLES DARWIN TO W. THISELTON DYER.
Down, 24 [December 1873?].

My dear Mr. Dyer,

I fear that you will think me a great bore, but I cannot resist telling you
that I have just found out that the leaves of Pinguicula possess a
beautifully adapted power of movement. Last night I put on a row of little
flies near one edge of two YOUNGISH leaves; and after 14 hours these edges
are beautifully folded over so as to clasp the flies, thus bringing the
glands into contact with the upper surfaces of the flies, and they are now
secreting copiously above and below the flies and no doubt absorbing. The
acid secretion has run down the channelled edge and has collected in the
spoon-shaped extremity, where no doubt the glands are absorbing the
delicious soup. The leaf on one side looks just like the helix of a human
ear, if you were to stuff flies within the fold. Yours most sincerely,

CH. DARWIN.

CHARLES DARWIN TO ASA GRAY.
Down, June 3 [1874].

...I am now hard at work getting my book on Drosera & Co. ready for the
printers, but it will take some time, for I am always finding out new
points to observe. I think you will be interested by my observations on
the digestive process in Drosera; the secretion contains an acid of the
acetic series, and some ferment closely analogous to, but not identical
with, pepsin; for I have been making a long series of comparative trials.
No human being will believe what I shall publish about the smallness of the
doses of phosphate of ammonia which act.

...I began reading the Madagascar squib (A description of a carnivorous
plant supposed to subsist on human beings.) quite gravely, and when I found
it stated that Felis and Bos inhabited Madagascar, I thought it was a false
story, and did not perceive it was a hoax till I came to the woman...

CHARLES DARWIN TO F.C. DONDERS. (Professor Donders, the well-known
physiologist of Utrecht.)
Down, July 7, 1874.

My dear Professor Donders,

My son George writes to me that he has seen you, and that you have been
very kind to him, for which I return to you my cordial thanks. He tells me
on your authority, of a fact which interests me in the highest degree, and
which I much wish to be allowed to quote. It relates to the action of one
millionth of a grain of atropine on the eye. Now will you be so kind,
whenever you can find a little leisure, to tell me whether you yourself
have observed this fact, or believe it on good authority. I also wish to
know what proportion by weight the atropine bore to the water solution, and
how much of the solution was applied to the eye. The reason why I am so
anxious on this head is that it gives some support to certain facts
repeatedly observed by me with respect to the action of phosphate of
ammonia on Drosera. The 1/4000000 of a grain absorbed by a gland clearly
makes the tentacle which bears this gland become inflected; and I am fully
convinced that 1/20000000 of a grain of the crystallised salt (i.e.
containing about one-third of its weight of water of crystallisation) does
the same. Now I am quite unhappy at the thought of having to publish such
a statement. It will be of great value to me to be able to give any
analogous facts in support. The case of Drosera is all the more
interesting as the absorption of the salt or any other stimulant applied to
the gland causes it to transmit a motor influence to the base of the
tentacle which bears the gland.

Pray forgive me for troubling you, and do not trouble yourself to answer
this until your health is fully re-established.

Pray believe me,
Yours very sincerely,
CHARLES DARWIN.

[During the summer of 1874 he was at work on the genus Utricularia, and he
wrote (July 16th) to Sir J.D. Hooker giving some account of the progress of
his work:--

"I am rather glad you have not been able to send Utricularia, for the
common species has driven F. and me almost mad. The structure is MOST
complex. The bladders catch a multitude of Entomostraca, and larvae of
insects. The mechanism for capture is excellent. But there is much that
we cannot understand. From what I have seen to-day, I strongly suspect
that it is necrophagous, i.e. that it cannot digest, but absorbs decaying
matter."

He was indebted to Lady Dorothy Nevill for specimens of the curious
Utricularia montana, which is not aquatic like the European species, but
grows among the moss and debris on the branches of trees. To this species
the following letter refers:]

CHARLES DARWIN TO LADY DOROTHY NEVILL.
Down September 18 [1874].

Dear Lady Dorothy Nevill,

I am so much obliged to you. I was so convinced that the bladders were
with the leaves that I never thought of removing the moss, and this was
very stupid of me. The great solid bladder-like swellings almost on the
surface are wonderful objects, but are not the true bladders. These I
found on the roots near the surface, and down to a depth of two inches in
the sand. They are as transparent as glass, from 1/20 to 1/100 of an inch
in size, and hollow. They have all the important points of structure of
the bladders of the floating English species, and I felt confident I should
find captured prey. And so I have to my delight in two bladders, with
clear proof that they had absorbed food from the decaying mass. For
Utricularia is a carrion-feeder, and not strictly carnivorous like Drosera.

The great solid bladder-like bodies, I believe, are reservoirs of water
like a camel's stomach. As soon as I have made a few more observations, I
mean to be so cruel as to give your plant no water, and observe whether the
great bladders shrink and contain air instead of water; I shall then also
wash all earth from all roots, and see whether there are true bladders for
capturing subterranean insects down to the very bottom of the pot. Now
shall you think me very greedy, if I say that supposing the species is not
very precious, and you have several, will you give me one more plant, and
if so, please to send it to "Orpington Station, S.E.R., to be forwarded by
foot messenger."

I have hardly ever enjoyed a day more in my life than I have this day's
work; and this I owe to your Ladyship's great kindness.

The seeds are very curious monsters; I fancy of some plant allied to
Medicago, but I will show them to Dr. Hooker.

Your ladyship's very gratefully,
CH. DARWIN.

CHARLES DARWIN TO J.D. HOOKER.
Down, September 30, 1874.

My dear H.,

Your magnificent present of Aldrovanda has arrived quite safe. I have
enjoyed greatly a good look at the shut leaves, one of which I cut open.
It is an aquatic Dionaea, which has acquired some structures identical with
those of Utricularia!

If the leaves open and I can transfer them open under the microscope, I
will try some experiments, for mortal man cannot resist the temptation. If
I cannot transfer, I will do nothing, for otherwise it would require
hundreds of leaves.

You are a good man to give me such pleasure.

Yours affectionately,
C. DARWIN.

[The manuscript of 'Insectivorous Plants' was finished in March 1875. He
seems to have been more than usually oppressed by the writing of this book,
thus he wrote to Sir J.D. Hooker in February:--

"You ask about my book, and all that I can say is that I am ready to commit
suicide; I thought it was decently written, but find so much wants
rewriting, that it will not be ready to go to printers for two months, and
will then make a confoundedly big book. Murray will say that it is no use
publishing in the middle of summer, so I do not know what will be the
upshot; but I begin to think that every one who publishes a book is a
fool."

The book was published on July 2nd, 1875, and 2700 copies were sold out of
the edition of 3000.]

CHAPTER 2.XIV.

THE 'POWER OF MOVEMENT IN PLANTS.'

1880.

[The few sentences in the autobiographical chapter give with sufficient
clearness the connection between the 'Power of Movement,' and one of the
author's earlier books, that on 'Climbing Plants.' The central idea of the
book is that the movements of plants in relation to light, gravitation,
etc., are modifications of a spontaneous tendency to revolve or
circumnutate, which is widely inherent in the growing parts of plants.
This conception has not been generally adopted, and has not taken a place
among the canons of orthodox physiology. The book has been treated by
Professor Sachs with a few words of professorial contempt; and by Professor
Wiesner it has been honoured by careful and generously expressed criticism.

Mr. Thiselton Dyer ('Charles Darwin' ('Nature' Series), page 41.) has well
said: "Whether this masterly conception of the unity of what has hitherto
seemed a chaos of unrelated phenomena will be sustained, time alone will
show. But no one can doubt the importance of what Mr. Darwin has done, in
showing that for the future the phenomena of plant movement can and indeed
must be studied from a single point of view."

The work was begun in the summer of 1877, after the publication of
'Different Forms of Flowers,' and by the autumn his enthusiasm for the
subject was thoroughly established, and he wrote to Mr. Dyer: "I am all on
fire at the work." At this time he was studying the movements of
cotyledons, in which the sleep of plants is to be observed in its simplest
form; in the following spring he was trying to discover what useful purpose
these sleep-movements could serve, and wrote to Sir Joseph Hooker (March
25th, 1878):--

"I think we have PROVED that the sleep of plants is to lessen the injury to
the leaves from radiation. This has interested me much, and has cost us
great labour, as it has been a problem since the time of Linnaeus. But we
have killed or badly injured a multitude of plants: N.B.--Oxalis carnosa
was most valuable, but last night was killed."

His letters of this period do not give any connected account of the
progress of the work. The two following are given as being characteristic
of the author:]

CHARLES DARWIN TO W. THISELTON DYER.
Down, June 2, 1878.

My dear Dyer,

I remember saying that I should die a disgraced man if I did not observe a
seedling Cactus and Cycas, and you have saved me from this horrible fate,
as they move splendidly and normally. But I have two questions to ask:
the Cycas observed was a huge seed in a broad and very shallow pot with
cocoa-nut fibre as I suppose. It was named only Cycas. Was it Cycas
pectinata? I suppose that I cannot be wrong in believing that what first
appears above ground is a true leaf, for I can see no stem or axis.
Lastly, you may remember that I said that we could not raise Opuntia
nigricans; now I must confess to a piece of stupidity; one did come up, but
my gardener and self stared at it, and concluded that it could not be a
seedling Opuntia, but now that I have seen one of O. basilaris, I am sure
it was; I observed it only casually, and saw movements, which makes me wish
to observe carefully another. If you have any fruit, will Mr. Lynch (Mr.
R.I. Lynch, now Curator of the Botanic Garden at Cambridge was at this time
in the Royal Gardens, Kew.) be so kind as to send one more?

I am working away like a slave at radicles [roots] and at movements of true
leaves, for I have pretty well done with cotyledons...

That was an EXCELLENT letter about the Gardens (This refers to an attempt
to induce the Government to open the Royal Gardens at Kew in the morning.):
I had hoped that the agitation was over. Politicians are a poor truckling
lot, for [they] must see the wretched effects of keeping the gardens open
all day long.

Your ever troublesome friend,
CH. DARWIN.

CHARLES DARWIN TO W. THISELTON DYER.
4 Bryanston St., Portman Square,
November 21 [1878].

My dear Dyer,

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