The Movements and Habits of Climbing Plants
Charles Darwin

Part 1 out of 3

This etext was prepared by David Price, email
from the 1906 John Murray edition.



This Essay first appeared in the ninth volume of the 'Journal of the
Linnean Society,' published in 1865. It is here reproduced in a
corrected and, I hope, clearer form, with some additional facts. The
illustrations were drawn by my son, George Darwin. Fritz Muller,
after the publication of my paper, sent to the Linnean Society
(Journal, vol. ix., p. 344) some interesting observations on the
climbing plants of South Brazil, to which I shall frequently refer.
Recently two important memoirs, chiefly on the difference in growth
between the upper and lower sides of tendrils, and on the mechanism
of the movements of twining-plants, by Dr. Hugo de Vries, have
appeared in the 'Arbeiten des Botanischen Instituts in Wurzburg,'
Heft. iii., 1873. These memoirs ought to be carefully studied by
every one interested in the subject, as I can here give only
references to the more important points. This excellent observer, as
well as Professor Sachs, {1} attributes all the movements of tendrils
to rapid growth along one side; but, from reasons assigned towards
the close of my fourth chapter, I cannot persuade myself that this
holds good with respect to those due to a touch. In order that the
reader may know what points have interested me most, I may call his
attention to certain tendril-bearing plants; for instance, Bignonia
capreolata, Cobaea, Echinocystis, and Hanburya, which display as
beautiful adaptations as can be found in any part of the kingdom of
nature. It is, also, an interesting fact that intermediate states
between organs fitted for widely different functions, may be observed
on the same individual plant of Corydalis claviculata and the common
vine; and these cases illustrate in a striking manner the principle
of the gradual evolution of species.


Since the publication of this Edition two papers by eminent botanists
have appeared; Schwendener, 'Das Winden der Pflanzen' (Monatsberichte
der Berliner Akademie, Dec. 1881), and J. Sachs, 'Notiz uber
Schlingpflanzen' (Arbeiten des botanischen Instituts in Wurzburg, Bd.
ii. p. 719, 1882). The view "that the capacity of revolving, on
which most climbers depend, is inherent, though undeveloped, in
almost every plant in the vegetable kingdom" ('Climbing Plants,' p.
205), has been confirmed by the observations on circumnutation since
given in 'The Power of Movement in Plants.'


On pp. 28, 32, 40, 53, statements are made with reference to the
supposed acceleration of the revolving movement towards the light.
It appears from the observations given in 'The Power of Movement in
Plants,' p. 451, that these conclusions were drawn from insufficient
observations, and are erroneous.



Introductory remarks--Description of the twining of the Hop--Torsion
of the stems--Nature of the revolving movement, and manner of ascent-
-Stems not irritable--Rate of revolution in various plants--Thickness
of the support round which plants can twine--Species which revolve in
an anomalous manner.

I was led to this subject by an interesting, but short paper by
Professor Asa Gray on the movements of the tendrils of some
Cucurbitaceous plants. {2} My observations were more than half
completed before I learnt that the surprising phenomenon of the
spontaneous revolutions of the stems and tendrils of climbing plants
had been long ago observed by Palm and by Hugo von Mohl, {3} and had
subsequently been the subject of two memoirs by Dutrochet. {4}
Nevertheless, I believe that my observations, founded on the
examination of above a hundred widely distinct living species,
contain sufficient novelty to justify me in publishing them.

Climbing plants may be divided into four classes. First, those which
twine spirally round a support, and are not aided by any other
movement. Secondly, those endowed with irritable organs, which when
they touch any object clasp it; such organs consisting of modified
leaves, branches, or flower-peduncles. But these two classes
sometimes graduate to a certain extent into one another. Plants of
the third class ascend merely by the aid of hooks; and those of the
fourth by rootlets; but as in neither class do the plants exhibit any
special movements, they present little interest, and generally when I
speak of climbing plants I refer to the two first great classes.


This is the largest subdivision, and is apparently the primordial and
simplest condition of the class. My observations will be best given
by taking a few special cases. When the shoot of a Hop (Humulus
lupulus) rises from the ground, the two or three first-formed joints
or internodes are straight and remain stationary; but the next-
formed, whilst very young, may be seen to bend to one side and to
travel slowly round towards all points of the compass, moving, like
the hands of a watch, with the sun. The movement very soon acquires
its full ordinary velocity. From seven observations made during
August on shoots proceeding from a plant which had been cut down, and
on another plant during April, the average rate during hot weather
and during the day is 2 hrs. 8 m. for each revolution; and none of
the revolutions varied much from this rate. The revolving movement
continues as long as the plant continues to grow; but each separate
internode, as it becomes old, ceases to move.

To ascertain more precisely what amount of movement each internode
underwent, I kept a potted plant, during the night and day, in a
well-warmed room to which I was confined by illness. A long shoot
projected beyond the upper end of the supporting stick, and was
steadily revolving. I then took a longer stick and tied up the
shoot, so that only a very young internode, 1.75 of an inch in
length, was left free. This was so nearly upright that its
revolution could not be easily observed; but it certainly moved, and
the side of the internode which was at one time convex became
concave, which, as we shall hereafter see, is a sure sign of the
revolving movement. I will assume that it made at least one
revolution during the first twenty-four hours. Early the next
morning its position was marked, and it made a second revolution in 9
hrs.; during the latter part of this revolution it moved much
quicker, and the third circle was performed in the evening in a
little over 3 hrs. As on the succeeding morning I found that the
shoot revolved in 2 hrs. 45 m., it must have made during the night
four revolutions, each at the average rate of a little over 3 hrs. I
should add that the temperature of the room varied only a little.
The shoot had now grown 3.5 inches in length, and carried at its
extremity a young internode 1 inch in length, which showed slight
changes in its curvature. The next or ninth revolution was effected
in 2 hrs. 30 m. From this time forward, the revolutions were easily
observed. The thirty-sixth revolution was performed at the usual
rate; so was the last or thirty-seventh, but it was not completed;
for the internode suddenly became upright, and after moving to the
centre, remained motionless. I tied a weight to its upper end, so as
to bow it slightly and thus detect any movement; but there was none.
Some time before the last revolution was half performed, the lower
part of the internode ceased to move.

A few more remarks will complete all that need be said about this
internode. It moved during five days; but the more rapid movements,
after the performance of the third revolution, lasted during three
days and twenty hours. The regular revolutions, from the ninth to
thirty-sixth inclusive, were effected at the average rate of 2 hrs.
31 m.; but the weather was cold, and this affected the temperature of
the room, especially during the night, and consequently retarded the
rate of movement a little. There was only one irregular movement,
which consisted in the stem rapidly making, after an unusually slow
revolution, only the segment of a circle. After the seventeenth
revolution the internode had grown from 1.75 to 6 inches in length,
and carried an internode 1.875 inch long, which was just perceptibly
moving; and this carried a very minute ultimate internode. After the
twenty-first revolution, the penultimate internode was 2.5 inches
long, and probably revolved in a period of about three hours. At the
twenty-seventh revolution the lower and still moving internode was
8.375, the penultimate 3.5, and the ultimate 2.5 inches in length;
and the inclination of the whole shoot was such, that a circle 19
inches in diameter was swept by it. When the movement ceased, the
lower internode was 9 inches, and the penultimate 6 inches in length;
so that, from the twenty-seventh to thirty-seventh revolutions
inclusive, three internodes were at the same time revolving.

The lower internode, when it ceased revolving, became upright and
rigid; but as the whole shoot was left to grow unsupported, it became
after a time bent into a nearly horizontal position, the uppermost
and growing internodes still revolving at the extremity, but of
course no longer round the old central point of the supporting stick.
From the changed position of the centre of gravity of the extremity,
as it revolved, a slight and slow swaying movement was given to the
long horizontally projecting shoot; and this movement I at first
thought was a spontaneous one. As the shoot grew, it hung down more
and more, whilst the growing and revolving extremity turned itself up
more and more.

With the Hop we have seen that three internodes were at the same time
revolving; and this was the case with most of the plants observed by
me. With all, if in full health, two internodes revolved; so that by
the time the lower one ceased to revolve, the one above was in full
action, with a terminal internode just commencing to move. With Hoya
carnosa, on the other hand, a depending shoot, without any developed
leaves, 32 inches in length, and consisting of seven internodes (a
minute terminal one, an inch in length, being counted), continually,
but slowly, swayed from side to side in a semicircular course, with
the extreme internodes making complete revolutions. This swaying
movement was certainly due to the movement of the lower internodes,
which, however, had not force sufficient to swing the whole shoot
round the central supporting stick. The case of another
Asclepiadaceous plant, viz., Ceropegia Gardnerii, is worth briefly
giving. I allowed the top to grow out almost horizontally to the
length of 31 inches; this now consisted of three long internodes,
terminated by two short ones. The whole revolved in a course opposed
to the sun (the reverse of that of the Hop), at rates between 5 hrs.
15 m. and 6 hrs. 45 m. for each revolution. The extreme tip thus
made a circle of above 5 feet (or 62 inches) in diameter and 16 feet
in circumference, travelling at the rate of 32 or 33 inches per hour.
The weather being hot, the plant was allowed to stand on my study-
table; and it was an interesting spectacle to watch the long shoot
sweeping this grand circle, night and day, in search of some object
round which to twine.

If we take hold of a growing sapling, we can of course bend it to all
sides in succession, so as to make the tip describe a circle, like
that performed by the summit of a spontaneously revolving plant. By
this movement the sapling is not in the least twisted round its own
axis. I mention this because if a black point be painted on the
bark, on the side which is uppermost when the sapling is bent towards
the holder's body, as the circle is described, the black point
gradually turns round and sinks to the lower side, and comes up again
when the circle is completed; and this gives the false appearance of
twisting, which, in the case of spontaneously revolving plants,
deceived me for a time. The appearance is the more deceitful because
the axes of nearly all twining-plants are really twisted; and they
are twisted in the same direction with the spontaneous revolving
movement. To give an instance, the internode of the Hop of which the
history has been recorded, was at first, as could be seen by the
ridges on its surface, not in the least twisted; but when, after the
37th revolution, it had grown 9 inches long, and its revolving
movement had ceased, it had become twisted three times round its own
axis, in the line of the course of the sun; on the other hand, the
common Convolvulus, which revolves in an opposite course to the Hop,
becomes twisted in an opposite direction.

Hence it is not surprising that Hugo von Mohl (p. 105, 108, &c.)
thought that the twisting of the axis caused the revolving movement;
but it is not possible that the twisting of the axis of the Hop three
times should have caused thirty-seven revolutions. Moreover, the
revolving movement commenced in the young internode before any
twisting of its axis could be detected. The internodes of a young
Siphomeris and Lecontea revolved during several days, but became
twisted only once round their own axes. The best evidence, however,
that the twisting does not cause the revolving movement is afforded
by many leaf-climbing and tendril-bearing plants (as Pisum sativum,
Echinocystis lobata, Bignonia capreolata, Eccremocarpus scaber, and
with the leaf-climbers, Solanum jasminoides and various species of
Clematis), of which the internodes are not twisted, but which, as we
shall hereafter see, regularly perform revolving movements like those
of true twining-plants. Moreover, according to Palm (pp. 30, 95) and
Mohl (p. 149), and Leon, {5} internodes may occasionally, and even
not very rarely, be found which are twisted in an opposite direction
to the other internodes on the same plant, and to the course of their
revolutions; and this, according to Leon (p. 356), is the case with
all the internodes of a certain variety of Phaseolus multiflorus.
Internodes which have become twisted round their own axes, if they
have not ceased to revolve, are still capable of twining round a
support, as I have several times observed.

Mohl has remarked (p. 111) that when a stem twines round a smooth
cylindrical stick, it does not become twisted. {6} Accordingly I
allowed kidney-beans to run up stretched string, and up smooth rods
of iron and glass, one-third of an inch in diameter, and they became
twisted only in that degree which follows as a mechanical necessity
from the spiral winding. The stems, on the other hand, which had
ascended ordinary rough sticks were all more or less and generally
much twisted. The influence of the roughness of the support in
causing axial twisting was well seen in the stems which had twined up
the glass rods; for these rods were fixed into split sticks below,
and were secured above to cross sticks, and the stems in passing
these places became much twisted. As soon as the stems which had
ascended the iron rods reached the summit and became free, they also
became twisted; and this apparently occurred more quickly during
windy than during calm weather. Several other facts could be given,
showing that the axial twisting stands in some relation to
inequalities in the support, and likewise to the shoot revolving
freely without any support. Many plants, which are not twiners,
become in some degree twisted round their own axes; {7} but this
occurs so much more generally and strongly with twining-plants than
with other plants, that there must be some connexion between the
capacity for twining and axial twisting. The stem probably gains
rigidity by being twisted (on the same principle that a much twisted
rope is stiffer than a slackly twisted one), and is thus indirectly
benefited so as to be enabled to pass over inequalities in its spiral
ascent, and to carry its own weight when allowed to revolve freely.

I have alluded to the twisting which necessarily follows on
mechanical principles from the spiral ascent of a stem, namely, one
twist for each spire completed. This was well shown by painting
straight lines on living stems, and then allowing them to twine; but,
as I shall have to recur to this subject under Tendrils, it may be
here passed over.

The revolving movement of a twining plant has been compared with that
of the tip of a sapling, moved round and round by the hand held some
way down the stem; but there is one important difference. The upper
part of the sapling when thus moved remains straight; but with
twining plants every part of the revolving shoot has its own separate
and independent movement. This is easily proved; for when the lower
half or two-thirds of a long revolving shoot is tied to a stick, the
upper free part continues steadily revolving. Even if the whole
shoot, except an inch or two of the extremity, be tied up, this part,
as I have seen in the case of the Hop, Ceropegia, Convolvulus, &c.,
goes on revolving, but much more slowly; for the internodes, until
they have grown to some little length, always move slowly. If we
look to the one, two, or several internodes of a revolving shoot,
they will be all seen to be more or less bowed, either during the
whole or during a large part of each revolution. Now if a coloured
streak be painted (this was done with a large number of twining
plants) along, we will say, the convex surface, the streak will after
a time (depending on the rate of revolution) be found to be running
laterally along one side of the bow, then along the concave side,
then laterally on the opposite side, and, lastly, again on the
originally convex surface. This clearly proves that during the
revolving movement the internodes become bowed in every direction.
The movement is, in fact, a continuous self-bowing of the whole
shoot, successively directed to all points of the compass; and has
been well designated by Sachs as a revolving nutation.

As this movement is rather difficult to understand, it will be well
to give an illustration. Take a sapling and bend it to the south,
and paint a black line on the convex surface; let the sapling spring
up and bend it to the east, and the black line will be seen to run
along the lateral face fronting the north; bend it to the north, the
black line will be on the concave surface; bend it to the west, the
line will again be on the lateral face; and when again bent to the
south, the line will be on the original convex surface. Now, instead
of bending the sapling, let us suppose that the cells along its
northern surface from the base to the tip were to grow much more
rapidly than on the three other sides, the whole shoot would then
necessarily be bowed to the south; and let the longitudinal growing
surface creep round the shoot, deserting by slow degrees the northern
side and encroaching on the western side, and so round by the south,
by the east, again to the north. In this case the shoot would remain
always bowed with the painted line appearing on the several above
specified surfaces, and with the point of the shoot successively
directed to each point of the compass. In fact, we should have the
exact kind of movement performed by the revolving shoots of twining
plants. {9}

It must not be supposed that the revolving movement is as regular as
that given in the above illustration; in very many cases the tip
describes an ellipse, even a very narrow ellipse. To recur once
again to our illustration, if we suppose only the northern and
southern surfaces of the sapling alternately to grow rapidly, the
summit would describe a simple arc; if the growth first travelled a
very little to the western face, and during the return a very little
to the eastern face, a narrow ellipse would be described; and the
sapling would be straight as it passed to and fro through the
intermediate space; and a complete straightening of the shoot may
often be observed in revolving plants. The movement is frequently
such that three of the sides of the shoot seem to be growing in due
order more rapidly than the remaining side; so that a semi-circle
instead of a circle is described, the shoot becoming straight and
upright during half of its course.

When a revolving shoot consists of several internodes, the lower ones
bend together at the same rate, but one or two of the terminal ones
bend at a slower rate; hence, though at times all the internodes are
in the same direction, at other times the shoot is rendered slightly
serpentine. The rate of revolution of the whole shoot, if judged by
the movement of the extreme tip, is thus at times accelerated or
retarded. One other point must be noticed. Authors have observed
that the end of the shoot in many twining plants is completely
hooked; this is very general, for instance, with the Asclepiadaceae.
The hooked tip, in all the cases observed by me, viz, in Ceropegia,
Sphaerostemma, Clerodendron, Wistaria, Stephania, Akebia, and
Siphomeris, has exactly the same kind of movement as the other
internodes; for a line painted on the convex surface first becomes
lateral and then concave; but, owing to the youth of these terminal
internodes, the reversal of the hook is a slower process than that of
the revolving movement. {10} This strongly marked tendency in the
young, terminal and flexible internodes, to bend in a greater degree
or more abruptly than the other internodes, is of service to the
plant; for not only does the hook thus formed sometimes serve to
catch a support, but (and this seems to be much more important) it
causes the extremity of the shoot to embrace the support much more
closely than it could otherwise have done, and thus aids in
preventing the stem from being blown away during windy weather, as I
have many times observed. In Lonicera brachypoda the hook only
straightens itself periodically, and never becomes reversed. I will
not assert that the tips of all twining plants when hooked, either
reverse themselves or become periodically straight, in the manner
just described; for the hooked form may in some cases be permanent,
and be due to the manner of growth of the species, as with the tips
of the shoots of the common vine, and more plainly with those of
Cissus discolor--plants which are not spiral twiners.

The first purpose of the spontaneous revolving movement, or, more
strictly speaking, of the continuous bowing movement directed
successively to all points of the compass, is, as Mohl has remarked,
to favour the shoot finding a support. This is admirably effected by
the revolutions carried on night and day, a wider and wider circle
being swept as the shoot increases in length. This movement likewise
explains how the plants twine; for when a revolving shoot meets with
a support, its motion is necessarily arrested at the point of
contact, but the free projecting part goes on revolving. As this
continues, higher and higher points are brought into contact with the
support and are arrested; and so onwards to the extremity; and thus
the shoot winds round its support. When the shoot follows the sun in
its revolving course, it winds round the support from right to left,
the support being supposed to stand in front of the beholder; when
the shoot revolves in an opposite direction, the line of winding is
reversed. As each internode loses from age its power of revolving,
it likewise loses its power of spirally twining. If a man swings a
rope round his head, and the end hits a stick, it will coil round the
stick according to the direction of the swinging movement; so it is
with a twining plant, a line of growth travelling round the free part
of the shoot causing it to bend towards the opposite side, and this
replaces the momentum of the free end of the rope.

All the authors, except Palm and Mohl, who have discussed the spiral
twining of plants, maintain that such plants have a natural tendency
to grow spirally. Mohl believes (p. 112) that twining stems have a
dull kind of irritability, so that they bend towards any object which
they touch; but this is denied by Palm. Even before reading Mohl's
interesting treatise, this view seemed to me so probable that I
tested it in every way that I could, but always with a negative
result. I rubbed many shoots much harder than is necessary to excite
movement in any tendril or in the foot-stalk of any leaf climber, but
without any effect. I then tied a light forked twig to a shoot of a
Hop, a Ceropegia, Sphaerostemma, and Adhatoda, so that the fork
pressed on one side alone of the shoot and revolved with it; I
purposely selected some very slow revolvers, as it seemed most likely
that these would profit most from possessing irritability; but in no
case was any effect produced. {11} Moreover, when a shoot winds
round a support, the winding movement is always slower, as we shall
immediately see, than whilst it revolves freely and touches nothing.
Hence I conclude that twining stems are not irritable; and indeed it
is not probable that they should be so, as nature always economizes
her means, and irritability would have been superfluous.
Nevertheless I do not wish to assert that they are never irritable;
for the growing axis of the leaf-climbing, but not spirally twining,
Lophospermum scandens is, certainly irritable; but this case gives me
confidence that ordinary twiners do not possess any such quality, for
directly after putting a stick to the Lophopermum, I saw that it
behaved differently from a true twiner or any other leaf-climber.

The belief that twiners have a natural tendency to grow spirally,
probably arose from their assuming a spiral form when wound round a
support, and from the extremity, even whilst remaining free,
sometimes assuming this form. The free internodes of vigorously
growing plants, when they cease to revolve, become straight, and show
no tendency to be spiral; but when a shoot has nearly ceased to grow,
or when the plant is unhealthy, the extremity does occasionally
become spiral. I have seen this in a remarkable manner with the ends
of the shoots of the Stauntonia and of the allied Akebia, which
became wound up into a close spire, just like a tendril; and this was
apt to occur after some small, ill-formed leaves had perished. The
explanation, I believe, is, that in such cases the lower parts of the
terminal internodes very gradually and successively lose their power
of movement, whilst the portions just above move onwards and in their
turn become motionless; and this ends in forming an irregular spire.

When a revolving shoot strikes a stick, it winds round it rather more
slowly than it revolves. For instance, a shoot of the Ceropegia,
revolved in 6 hrs., but took 9 hrs. 30 m. to make one complete spire
round a stick; Aristolochia gigas revolved in about 5 hrs., but took
9 hrs. 15 m. to complete its spire. This, I presume, is due to the
continued disturbance of the impelling force by the arrestment of the
movement at successive points; and we shall hereafter see that even
shaking a plant retards the revolving movement. The terminal
internodes of a long, much-inclined, revolving shoot of the
Ceropegia, after they had wound round a stick, always slipped up it,
so as to render the spire more open than it was at first; and this
was probably in part due to the force which caused the revolutions,
being now almost freed from the constraint of gravity and allowed to
act freely. With the Wistaria, on the other hand, a long horizontal
shoot wound itself at first into a very close spire, which remained
unchanged; but subsequently, as the shoot twined spirally up its
support, it made a much more open spire. With all the many plants
which were allowed freely to ascend a support, the terminal
internodes made at first a close spire; and this, during windy
weather, served to keep the shoots in close contact with their
support; but as the penultimate internodes grew in length, they
pushed themselves up for a considerable space (ascertained by
coloured marks on the shoot and on the support) round the stick, and
the spire became more open. {13}

It follows from this latter fact that the position occupied by each
leaf with respect to the support depends on the growth of the
internodes after they have become spirally wound round it. I mention
this on account of an observation by Palm (p. 34), who states that
the opposite leaves of the Hop always stand in a row, exactly over
one another, on the same side of the supporting stick, whatever its
thickness may be. My sons visited a hop-field for me, and reported
that though they generally found the points of insertion of the
leaves standing over each other for a space of two or three feet in
height, yet this never occurred up the whole length of the pole; the
points of insertion forming, as might have been expected, an
irregular spire. Any irregularity in the pole entirely destroyed the
regularity of position of the leaves. From casual inspection, it
appeared to me that the opposite leaves of Thunbergia alata were
arranged in lines up the sticks round which they had twined;
accordingly, I raised a dozen plants, and gave them sticks of various
thicknesses, as well as string, to twine round; and in this case one
alone out of the dozen had its leaves arranged in a perpendicular
line: I conclude, therefore, Palm's statement is not quite accurate.

The leaves of different twining-plants are arranged on the stem
(before it has twined) alternately, or oppositely, or in a spire. In
the latter case the line of insertion of the leaves and the course of
the revolutions coincide. This fact has been well shown by
Dutrochet, {14} who found different individuals of Solanum dulcamara
twining in opposite directions, and these had their leaves in each
case spirally arranged in the same direction. A dense whorl of many
leaves would apparently be incommodious for a twining plant, and some
authors assert that none have their leaves thus arranged; but a
twining Siphomeris has whorls of three leaves.

If a stick which has arrested a revolving shoot, but has not as yet
been encircled, be suddenly taken away, the shoot generally springs
forward, showing that it was pressing with some force against the
stick. After a shoot has wound round a stick, if this be withdrawn,
it retains for a time its spiral form; it then straightens itself,
and again commences to revolve. The long, much-inclined shoot of the
Ceropegia previously alluded to offered some curious peculiarities.
The lower and older internodes, which continued to revolve, were
incapable, on repeated trials, of twining round a thin stick; showing
that, although the power of movement was retained, this was not
sufficient to enable the plant to twine. I then moved the stick to a
greater distance, so that it was struck by a point 2.5 inches from
the extremity of the penultimate internode; and it was then neatly
encircled by this part of the penultimate and by the ultimate
internode. After leaving the spirally wound shoot for eleven hours,
I quietly withdrew the stick, and in the course of the day the curled
portion straightened itself and recommenced revolving; but the lower
and not curled portion of the penultimate internode did not move, a
sort of hinge separating the moving and the motionless part of the
same internode. After a few days, however, I found that this lower
part had likewise recovered its revolving power. These several facts
show that the power of movement is not immediately lost in the
arrested portion of a revolving shoot; and that after being
temporarily lost it can be recovered. When a shoot has remained for
a considerable time round a support, it permanently retains its
spiral form even when the support is removed.

When a tall stick was placed so as to arrest the lower and rigid
internodes of the Ceropegia, at the distance at first of 15 and then
of 21 inches from the centre of revolution, the straight shoot slowly
and gradually slid up the stick, so as to become more and more highly
inclined, but did not pass over the summit. Then, after an interval
sufficient to have allowed of a semi-revolution, the shoot suddenly
bounded from the stick and fell over to the opposite side or point of
the compass, and reassumed its previous slight inclination. It now
recommenced revolving in its usual course, so that after a semi-
revolution it again came into contact with the stick, again slid up
it, and again bounded from it and fell over to the opposite side.
This movement of the shoot had a very odd appearance, as if it were
disgusted with its failure but was resolved to try again. We shall,
I think, understand this movement by considering the former
illustration of the sapling, in which the growing surface was
supposed to creep round from the northern by the western to the
southern face; and thence back again by the eastern to the northern
face, successively bowing the sapling in all directions. Now with
the Ceropegia, the stick being placed to the south of the shoot and
in contact with it, as soon as the circulatory growth reached the
western surface, no effect would be produced, except that the shoot
would be pressed firmly against the stick. But as soon as growth on
the southern surface began, the shoot would be slowly dragged with a
sliding movement up the stick; and then, as soon as the eastern
growth commenced, the shoot would be drawn from the stick, and its
weight coinciding with the effects of the changed surface of growth,
would cause it suddenly to fall to the opposite side, reassuming its
previous slight inclination; and the ordinary revolving movement
would then go on as before. I have described this curious case with
some care, because it first led me to understand the order in which,
as I then thought, the surfaces contracted; but in which, as we now
know from Sachs and II. de Vries, they grow for a time rapidly, thus
causing the shoot to bow towards the opposite side.

The view just given further explains, as I believe, a fact observed
by Mohl (p. 135), namely, that a revolving shoot, though it will
twine round an object as thin as a thread, cannot do so round a thick
support. I placed some long revolving shoots of a Wistaria close to
a post between 5 and 6 inches in diameter, but, though aided by me in
many ways, they could not wind round it. This apparently was due to
the flexure of the shoot, whilst winding round an object so gently
curved as this post, not being sufficient to hold the shoot to its
place when the growing surface crept round to the opposite surface of
the shoot; so that it was withdrawn at each revolution from its

When a free shoot has grown far beyond its support, it sinks
downwards from its weight, as already explained in the case of the
Hop, with the revolving extremity turned upwards. If the support be
not lofty, the shoot falls to the ground, and resting there, the
extremity rises up. Sometimes several shoots, when flexible, twine
together into a cable, and thus support one another. Single thin
depending shoots, such as those of the Sollya Drummondii, will turn
abruptly backwards and wind up on themselves. The greater number of
the depending shoots, however, of one twining plant, the Hibbertia
dentata, showed but little tendency to turn upwards. In other cases,
as with the Cryptostegia grandiflora, several internodes which were
at first flexible and revolved, if they did not succeed in twining
round a support, become quite rigid, and supporting themselves
upright, carried on their summits the younger revolving internodes.

Here will be a convenient place to give a Table showing the direction
and rate of movement of several twining plants, with a few appended
remarks. These plants are arranged according to Lindley's 'Vegetable
Kingdom' of 1853; and they have been selected from all parts of the
series so as to show that all kinds behave in a nearly uniform
manner. {15}

The Rate of Revolution of various Twining Plants.


Lygodium scandens (Polypodiaceae) moves against the sun.

H. M.
June 18, 1st circle was made in 6 0
18, 2nd 6 15 (late in evening)
19, 3rd 5 32 (very hot day)
19, 4th 5 0 (very hot day)
20, 5th 6 0

Lygodium articulatum moves against the sun.

H. M.
July 19, 1st circle was made in 16 30 (shoot very young)
20, 2nd 15 0
21, 3rd 8 0
22, 4th 10 30


Ruscus androgynus (Liliaceae), placed in the hot-house, moves against
the sun.

H. M.
May 24, 1st circle was made in 6 14 (shoot very young)
25, 2nd 2 21
25, 3rd 3 37
25, 4th 3 22
26, 5th 2 50
27, 6th 3 52
27, 7th 4 11

Asparagus (unnamed species from Kew) (Liliaceae) moves against the
sun, placed in hothouse.

H. M.
Dec. 26, 1st circle was made in 5 0
27, 2nd 5 40

Tamus communis (Dioscoreaceae). A young shoot from a tuber in a pot
placed in the greenhouse: follows the sun.

H. M.
July, 7, 1st circle was made in 3 10
7, 2nd 2 38
8, 3rd 3 5
8, 4th 2 56
8, 5th 2 30
8, 6th 2 30

Lapagerea rosea (Philesiaceae), in greenhouse, follows the sun.

H. M.
March 9, 1st circle was made in 26 15 (shoot young)
10, semicircle 8 15
11, 2nd circle 11 0
12, 3rd 15 30
13, 4th 14 15
16, 5th 8 40 when placed in the
hothouse; but the next day the shoot remained stationary.

Roxburghia viridiflora (Roxburghiaceae) moves against the sun; it
completed a circle in about 24 hours.


Humulus Lupulus (Urticaceae) follows the sun. The plant was kept in
a room during warm weather.

H. M.
April 9, 2 circles were made in 4 16
Aug. 13, 3rd circle was 2 0
14, 4th 2 20
14, 5th 2 16
14, 6th 2 2
14, 7th 2 0
14, 8th 2 4

With the Hop a semicircle was performed, in travelling from the
light, in 1 hr. 33 m.; in travelling to the light, in 1 hr. 13 m.;
difference of rate, 20 m.

Akebia quinata (Lardizabalaceae), placed in hothouse, moves against
the sun.

H. M.
March 17, 1st circle was made in 4 0 (shoot young)
18, 2nd 1 40
18, 3rd 1 30
19, 4th 1 45

Stauntonia latifolia (Lardizabalaceae), placed in hothouse, moves
against the sun.

H. M.
March 28, 1st circle was made in 3 30
29, 2nd 3 45

Sphaerostemma marmoratum (Schizandraceae) follows the sun.

H. M.
August 5th, 1st circle was made in about 24 0
5th, 2nd circle was made in 18 30

Stephania rotunda (Menispermaceae) moves against the sun

H. M.
May 27, 1st circle was made in 5 5
30, 2nd 7 6
June 2, 3rd 5 15
3, 4th 6 28

Thryallis brachystachys (Malpighiaceae) moves against the sun: one
shoot made a circle in 12 hrs., and another in 10 hrs. 30 m.; but the
next day, which was much colder, the first shoot took 10 hrs. to
perform only a semicircle.

Hibbertia dentata (Dilleniaceae), placed in the hothouse, followed
the sun, and made (May 18th) a circle in 7 hrs. 20 m.; on the 19th,
reversed its course, and moved against the sun, and made a circle in
7 hrs.; on the 20th, moved against the sun one-third of a circle, and
then stood still; on the 26th, followed the sun for two-thirds of a
circle, and then returned to its starting-point, taking for this
double course 11 hrs. 46 m.

Sollya Drummondii (Pittosporaceae) moves against the sun kept in

H. M.
April 4, 1st circle was made in 4 25
5, 2nd 8 0 (very cold day)
6, 3rd 6 25
7, 4th 7 5

Polygonum dumetorum (Polygonaceae). This case is taken from
Dutrochet (p. 299), as I observed, no allied plant: follows the
sun. Three shoots, cut off a plant, and placed in water made circles
in 3 hrs. 10 m., 5 hrs. 20 m., and 7 hrs. 15 m.

Wistaria Chinensis (Leguminosae), in greenhouse, moves against the

H. M.
May 13, 1st circle was made in 3 5
13, 2nd 3 20
16, 3rd 2 5
24, 4th 3 21
25, 5th 2 37
25, 6th 2 35

Phaseolus vulgaris (Leguminosae), in greenhouse, moves against the

H. M.
May, 1st circle was made in 2 0
2nd 1 55
3rd 1 55

Dipladenia urophylla (Apocynaceae) moves against the sun.

H. M.
April 18, 1st circle was made in 8 0
19, 2nd 9 15
30, 3rd 9 40

Dipladenia crassinoda moves against the sun.

H. M.
May 16, 1st circle was made in 9 5
July 20, 2nd 8 0
21, 3rd 8 5

Ceropegia Gardnerii (Asclepiadaceae) moves against the sun.

H. M.
Shoot very young, 2 inches }
in length } 1st circle was performed in 7 55
Shoot still young 2nd 7 0
Long shoot 3rd 6 33
Long shoot 4th 5 15
Long shoot 5th 6 45

Stephanotis floribunda (Asclepiadaceae) moves against the sun and
made a circle in 6 hrs. 40 m., a second circle in about 9 hrs.

Hoya carnosa (Asclepiadaceae) made several circles in from 16 hrs. to
22 hrs. or 24 hrs.

Ipomaea purpurea (Convolvulaceae) moves against the sun. Plant
placed in room with lateral light.

{Semicircle, from the light in
1st circle was made in 2 hrs. 42 m. { 1 hr. 14 m., to the light
{ 1 hr. 28 m.: difference 14 m.

{Semicircle, from the light in
2nd circle was made in 2 hrs. 47 m. { 1 hr. 17 m., to the light 1 hr.
{ 30 m.: difference 13 m.

Ipomaea jucunda (Convolvulaceae) moves against the sun, placed in my
study, with windows facing the north-east. Weather hot.

{Semicircle, from the light in
1st circle was made in 5 hrs. 30 m. { 4 hrs. 30 m., to the light 1
{ 0 m.: difference 3 hrs. 30 m.

2nd circle was made in 5 hrs. {Semicircle, from the light in
20 m. (Late in afternoon: { 3 hrs. 50 m., to the light 1
circle completed at 6 hrs. 40 m. { 30 m.: difference 2 hrs. 20 m.

We have here a remarkable instance of the power of light in retarding
and hastening the revolving movement. (See ERRATA.)

Convolvulus sepium (large-flowered cultivated var.) moves against the
sun. Two circles, were made each in 1 hr. 42 m.: difference in
semicircle from and to the light 14 m.

Rivea tiliaefolia (Convolvulaceae) moves against the sun, made four
revolutions in 9 hrs.; so that, on an average, each was performed in
2 hrs. 15 m.

Plumbago rosea (Plumbaginaceae) follows the sun. The shoot did not
begin to revolve until nearly a yard in height; it then made a fine
circle in 10 hrs. 45 m. During the next few days it continued to
move, but irregularly. On August 15th the shoot followed, during a
period of 10 hrs. 40 m., a long and deeply zigzag course and then
made a broad ellipse. The figure apparently represented three
ellipses, each of which averaged 3 hrs. 38 m. for its completion.

Jasminum pauciflorum, Bentham (Jasminaceae), moves against the sun.
A circle was made in 7 hrs. 15 m., and a second rather more quickly.

Clerodendrum Thomsonii (Verbenaceae) follows the sun.

H. M.
April 12, 1st circle was made in 5 45 (shoot very young)
14, 2nd 3 30
{(directly after the
18, a semicircle 5 0 { plant was shaken
{ on being moved)
19, 3rd circle 3 0
20, 4th 4 20

Tecoma jasminoides (Bignoniaceae) moves against the sun.

H. M.
March 17, 1st circle was made in 6 30
19, 2nd 7 0
22, 3rd 8 30 (very cold day)
24, 4th 6 45

Thunbergia alata (Acanthaceae) moves against sun.

H. M.
April 14, 1st circle was made in 3 20
18, 2nd 2 50
18, 3rd 2 55
18, 4th 3 55 (late in afternoon)

Adhadota cydonaefolia (Acanthaceae) follows the sun. A young shoot
made a semicircle in 24 hrs.; subsequently it made a circle in
between 40 hrs. and 48 hrs. Another shoot, however, made a circle in
26 hrs. 30 m.

Mikania scandens (Compositae) moves against the sun.

H. M.
March 14, 1st circle was made in 3 10
15, 2nd 3 0
16, 3rd 3 0
17, 4th 3 33
April 7, 5th 2 50
7, 6th 2 40 {This circle was
{ after a copious
{ ing with cold
water at
{ 47 degrees Fahr.

Combretum argenteum (Combretaceae) moves against the sun. Kept in

H. M.
{Early in morning,
Jan. 24, 1st circle was made in 2 55 { the temperature of
{ house had fallen a
{ little.

24, 2 circles each at an }
average of } 2 20
25, 4th circle was made in 2 25

Combretum purpureum revolves not quite so quickly as C. argenteum.

Loasa aurantiaca (Loasaceae). Revolutions variable in their course:
a plant which moved against the sun.

H. M.
June 20, 1st circle was made in 2 37
20, 2nd 2 13
20, 3rd 4 0
21, 4th 2 35
22, 5th 3 26
23, 6th 3 5

Another plant which followed the sun in its revolutions.

H. M.
July 11, 1st circle was made in 1 51 }
11, 2nd 1 46 } Very hot day.
11, 3rd 1 41 }
11, 4th 1 48 }
12, 5th 2 35 }

Scyphanthus elegans (Loasaceae) follows the sun.

H. M.
June 13, 1st circle was made in 1 45
13, 2nd 1 17
14, 3rd 1 36
14, 4th 1 59
14, 5th 2 3

Siphomeris or Lecontea (unnamed sp.) (Cinchonaceae) follows the sun.

H. M.
{(shoot extremely
May 25, semicircle was made in 10 27 { young)
26, 1st circle 10 15 (shoot still young)
30, 2nd 8 55
June 2, 3rd 8 11
6, 4th 6 8
{ Taken from the
8, 5th 7 20 { hothouse, and
9, 6th 8 36 { placed in a room
{ in my house.

Manettia bicolor (Cinchonaceae), young plant, follows the sun.

H. M.
July 7, 1st circle was made in 6 18
8, 2nd 6 53
9, 3rd 6 30

Lonicera brachypoda (Caprifoliaceae) follows the sun, kept in a warm
room in the house.

H. M.
April, 1st circle was made in 9 10 (about)
{(a distinct shoot,
April, 2nd circle was made in 12 20 { young, on same
3rd 7 30
{In this latter
{ the semicircle from
{ the light took 5
4th 8 0 { 23 m., and to the
{ light 2 hrs. 37
{ difference 2 hrs

Aristolochia gigas (Aristolochiaceae) moves against the sun.

H. M.
July 22, 1st circle was made in 8 0 (rather young shoot)
23, 2nd 7 15
24, 3rd 5 0 (about)

In the foregoing Table, which includes twining plants belonging to
widely different orders, we see that the rate at which growth travels
or circulates round the axis (on which the revolving movement
depends), differs much. As long as a plant remains under the same
conditions, the rate is often remarkably uniform, as with the Hop,
Mikania, Phaseolus, &c. The Scyphanthus made one revolution in 1 hr.
17 m., and this is the quickest rate observed by me; but we shall
hereafter see a tendril-bearing Passiflora revolving more rapidly. A
shoot of the Akebia quinata made a revolution in 1 hr. 30 m., and
three revolutions at the average rate of 1 hr. 38 m.; a Convolvulus
made two revolutions at the average of 1 hr. 42 m., and Phaseolus
vulgaris three at the average of 1 hr. 57 m. On the other hand, some
plants take 24 hrs. for a single revolution, and the Adhadota
sometimes required 48 hrs.; yet this latter plant is an efficient
twiner. Species of the same genus move at different rates. The rate
does not seem governed by the thickness of the shoots: those of the
Sollya are as thin and flexible as string, but move more slowly than
the thick and fleshy shoots of the Ruscus, which seem little fitted
for movement of any kind. The shoots of the Wistaria, which become
woody, move faster than those of the herbaceous Ipomoea or

We know that the internodes, whilst still very young, do not acquire
their proper rate of movement; hence the several shoots on the same
plant may sometimes be seen revolving at different rates. The two or
three, or even more, internodes which are first formed above the
cotyledons, or above the root-stock of a perennial plant, do not
move; they can support themselves, and nothing superfluous is

A greater number of twiners revolve in a course opposed to that of
the sun, or to the hands of a watch, than in the reversed course,
and, consequently, the majority, as is well known, ascend their
supports from left to right. Occasionally, though rarely, plants of
the same order twine in opposite directions, of which Mohl (p. 125)
gives a case in the Leguminosae, and we have in the table another in
the Acanthaceae. I have seen no instance of two species of the same
genus twining in opposite directions, and such cases must be rare;
but Fritz Muller {16} states that although Mikania scandens twines,
as I have described, from left to right, another species in South
Brazil twines in an opposite direction. It would have been an
anomalous circumstance if no such cases had occurred, for different
individuals of the same species, namely, of Solanum dulcamara
(Dutrochet, tom. xix. p. 299), revolve and twine in two directions:
this plant, however; is a most feeble twiner. Loasa aurantiaca
(Leon, p. 351) offers a much more curious case: I raised seventeen
plants: of these eight revolved in opposition to the sun and
ascended from left to right; five followed the sun and ascended from
right to left; and four revolved and twined first in one direction,
and then reversed their course, {17} the petioles of the opposite
leaves affording a point d'appui for the reversal of the spire. One
of these four plants made seven spiral turns from right to left, and
five turns from left to right. Another plant in the same family, the
Scyphanthus elegans, habitually twines in this same manner. I raised
many plants of it, and the stems of all took one turn, or
occasionally two or even three turns in one direction, and then,
ascending for a short space straight, reversed their course and took
one or two turns in an opposite direction. The reversal of the
curvature occurred at any point in the stem, even in the middle of an
internode. Had I not seen this case, I should have thought its
occurrence most improbable. It would be hardly possible with any
plant which ascended above a few feet in height, or which lived in an
exposed situation; for the stem could be pulled away easily from its
support, with but little unwinding; nor could it have adhered at all,
had not the internodes soon become moderately rigid. With leaf-
climbers, as we shall soon see, analogous cases frequently occur; but
these present no difficulty, as the stem is secured by the clasping

In the many other revolving and twining plants observed by me, I
never but twice saw the movement reversed; once, and only for a short
space, in Ipomoea jucunda; but frequently with Hibbertia dentata.
This plant at first perplexed me much, for I continually observed its
long and flexible shoots, evidently well fitted for twining, make a
whole, or half, or quarter circle in one direction and then in an
opposite direction; consequently, when I placed the shoots near thin
or thick sticks, or perpendicularly stretched string, they seemed as
if constantly trying to ascend, but always failed. I then surrounded
the plant with a mass of branched twigs; the shoots ascended, and
passed through them, but several came out laterally, and their
depending extremities seldom turned upwards as is usual with twining
plants. Finally, I surrounded a second plant with many thin upright
sticks, and placed it near the first one with twigs; and now both had
got what they liked, for they twined up the parallel sticks,
sometimes winding round one and sometimes round several; and the
shoots travelled laterally from one to the other pot; but as the
plants grew older, some of the shoots twined regularly up thin
upright sticks. Though the revolving movement was sometimes in one
direction and sometimes in the other, the twining was invariably from
left to right; {18} so that the more potent or persistent movement of
revolution must have been in opposition to the course of the sun. It
would appear that this Hibbertia is adapted both to ascend by
twining, and to ramble laterally through the thick Australian scrub.

I have described the above case in some detail, because, as far as I
have seen, it is rare to find any special adaptations with twining
plants, in which respect they differ much from the more highly
organized tendril-bearers. The Solanum dulcamara, as we shall
presently see, can twine only round stems which are both thin and
flexible. Most twining plants are adapted to ascend supports of
moderate though of different thicknesses. Our English twiners, as
far as I have seen, never twine round trees, excepting the
honeysuckle (Lonicera periclymenum), which I have observed twining up
a young beech-tree nearly 4.5 inches in diameter. Mohl (p. 134)
found that the Phaseolus multiflorus and Ipomoea purpurea could not,
when placed in a room with the light entering on one side, twine
round sticks between 3 and 4 inches in diameter; for this interfered,
in a manner presently to be explained, with the revolving movement.
In the open air, however, the Phaseolus twined round a support of the
above thickness, but failed in twining round one 9 inches in
diameter. Nevertheless, some twiners of the warmer temperate regions
can manage this latter degree of thickness; for I hear from Dr.
Hooker that at Kew the Ruscus androgynus has ascended a column 9
inches in diameter; and although a Wistaria grown by me in a small
pot tried in vain for weeks to get round a post between 5 and 6
inches in thickness, yet at Kew a plant ascended a trunk above 6
inches in diameter. The tropical twiners, on the other hand, can
ascend thicker trees; I hear from Drs. Thomson and Hooker that this
is the case with the Butea parviflora, one of the Menispermaceae, and
with some Dalbergias and other Leguminosae. {19} This power would be
necessary for any species which had to ascend by twining the large
trees of a tropical forest; otherwise they would hardly ever be able
to reach the light. In our temperate countries it would be injurious
to the twining plants which die down every year if they were enabled
to twine round trunks of trees, for they could not grow tall enough
in a single season to reach the summit and gain the light.

By what means certain twining plants are adapted to ascend only thin
stems, whilst others can twine round thicker ones, I do not know. It
appeared to me probable that twining plants with very long revolving
shoots would be able to ascend thick supports; accordingly I placed
Ceropegia Gardnerii near a post 6 inches in diameter, but the shoots
entirely failed to wind round it; their great length and power of
movement merely aid them in finding a distant stem round which to
twine. The Sphaerostemma marmoratum is a vigorous tropical twiner;
and as it is a very slow revolver, I thought that this latter
circumstance might help it in ascending a thick support; but though
it was able to wind round a 6-inch post, it could do this only on the
same level or plane, and did not form a spire and thus ascend.

As ferns differ so much in structure from phanerogamic plants, it may
be worth while here to show that twining ferns do not differ in their
habits from other twining plants. In Lygodium articulatum the two
internodes of the stem (properly the rachis) which are first formed
above the root-stock do not move; the third from the ground revolves,
but at first very slowly. This species is a slow revolver: but L.
scandens made five revolutions, each at the average rate of 5 hrs. 45
m.; and this represents fairly well the usual rate, taking quick and
slow movers, amongst phanerogamic plants. The rate was accelerated
by increased temperature. At each stage of growth only the two upper
internodes revolved. A line painted along the convex surface of a
revolving internode becomes first lateral, then concave, then lateral
and ultimately again convex. Neither the internodes nor the petioles
are irritable when rubbed. The movement is in the usual direction,
namely, in opposition to the course of the sun; and when the stem
twines round a thin stick, it becomes twisted on its own axis in the
same direction. After the young internodes have twined round a
stick, their continued growth causes them to slip a little upwards.
If the stick be soon removed, they straighten themselves, and
recommence revolving. The extremities of the depending shoots turn
upwards, and twine on themselves. In all these respects we have
complete identity with twining phanerogamic plants; and the above
enumeration may serve as a summary of the leading characteristics of
all twining plants.

The power of revolving depends on the general health and vigour of
the plant, as has been laboriously shown by Palm. But the movement
of each separate internode is so independent of the others, that
cutting off an upper one does not affect the revolutions of a lower
one. When, however, Dutrochet cut off two whole shoots of the Hop,
and placed them in water, the movement was greatly retarded; for one
revolved in 20 hrs. and the other in 23 hrs., whereas they ought to
have revolved in between 2 hrs. and 2 hrs. 30 m. Shoots of the
Kidney-bean, cut off and placed in water, were similarly retarded,
but in a less degree. I have repeatedly observed that carrying a
plant from the greenhouse to my room, or from one part to another of
the greenhouse, always stopped the movement for a time; hence I
conclude that plants in a state of nature and growing in exposed
situations, would not make their revolutions during very stormy
weather. A decrease in temperature always caused a considerable
retardation in the rate of revolution; but Dutrochet (tom. xvii. pp.
994, 996) has given such precise observations on this head with
respect to the common pea that I need say nothing more. When twining
plants are placed near a window in a room, the light in some cases
has a remarkable power (as was likewise observed by Dutrochet, p.
998, with the pea) on the revolving movement, but this differs in
degree with different plants; thus Ipomoea jucunda made a complete
circle in 5 hrs. 30 m.; the semicircle from the light taking 4 hrs.
80 m., and that towards the light only 1 hr. Lonicera brachypoda
revolved, in a reversed direction to the Ipomoea, in 8 hrs.; the
semicircle from the light taking 5 hrs. 23 m., and that to the light
only 2 hrs. 37 m. From the rate of revolution in all the plants
observed by me, being nearly the same during the night and the day, I
infer that the action of the light is confined to retarding one
semicircle and accelerating the other, so as not to modify greatly
the rate of the whole revolution. This action of the light is
remarkable, when we reflect how little the leaves are developed on
the young and thin revolving internodes. It is all the more
remarkable, as botanists believe (Mohl, p. 119) that twining plants
are but little sensitive to the action of light.

I will conclude my account of twining plants by giving a few
miscellaneous and curious cases. With most twining plants all the
branches, however many there may be, go on revolving together; but,
according to Mohl (p. 4), only the lateral branches of Tamus
elephantipes twine, and not the main stem. On the other hand, with a
climbing species of Asparagus, the leading shoot alone, and not the
branches, revolved and twined; but it should be stated that the plant
was not growing vigorously. My plants of Combretum argenteum and C.
purpureum made numerous short healthy shoots; but they showed no
signs of revolving, and I could not conceive how these plants could
be climbers; but at last C. argenteum put forth from the lower part
of one of its main branches a thin shoot, 5 or 6 feet in length,
differing greatly in appearance from the previous shoots, owing to
its leaves being little developed, and this shoot revolved vigorously
and twined. So that this plant produces shoots of two kinds. With
Periploca Graeca (Palm, p. 43) the uppermost shoots alone twine.
Polygonum convolvulus twines only during the middle of the summer
(Palm, p. 43, 94); and plants growing vigorously in the autumn show
no inclination to climb. The majority of Asclepiadaceae are twiners;
but Asclepias nigra only "in fertiliori solo incipit scandere
subvolubili caule" (Willdenow, quoted and confirmed by Palm, p. 41).
Asclepias vincetoxicum does not regularly twine, but occasionally
does so (Palm, p. 42; Mohl, p. 112) when growing under certain
conditions. So it is with two species of Ceropegia, as I hear from
Prof. Harvey, for these plants in their native dry South African
home generally grow erect, from 6 inches to 2 feet in height,--a very
few taller specimens showing some inclination to curve; but when
cultivated near Dublin, they regularly twined up sticks 5 or 6 feet
in height. Most Convolvulaceae are excellent twiners; but in South
Africa Ipomoea argyraeoides almost always grows erect and compact,
from about 12 to 18 inches in height, one specimen alone in Prof.
Harvey's collection showing an evident disposition to twine. On the
other hand, seedlings raised near Dublin twined up sticks above 8
feet in height. These facts are remarkable; for there can hardly be
a doubt that in the dryer provinces of South Africa these plants have
propagated themselves for thousands of generations in an erect
condition; and yet they have retained during this whole period the
innate power of spontaneously revolving and twining, whenever their
shoots become elongated under proper conditions of life. Most of the
species of Phaseolus are twiners; but certain varieties of the P.
multiflorus produce (Leon, p. 681) two kinds of shoots, some upright
and thick, and others thin and twining. I have seen striking
instances of this curious case of variability in "Fulmer's dwarf
forcing-bean," which occasionally produced a single long twining

Solanum dulcamara is one of the feeblest and poorest of twiners: it
may often be seen growing as an upright bush, and when growing in the
midst of a thicket merely scrambles up between the branches without
twining; but when, according to Dutrochet (tom. xix. p. 299), it
grows near a thin and flexible support, such as the stem of a nettle,
it twines round it. I placed sticks round several plants, and
vertically stretched strings close to others, and the strings alone
were ascended by twining. The stem twines indifferently to the right
or left. Some others species of Solanum, and of another genus, viz.
Habrothamnus, belonging to the same family, are described in
horticultural works as twining plants, but they seem to possess this
faculty in a very feeble degree. We may suspect that the species of
these two genera have as yet only partially acquired the habit of
twining. On the other hand with Tecoma radicans, a member of a
family abounding with twiners and tendril-bearers, but which climbs,
like the ivy, by the aid of rootlets, we may suspect that a former
habit of twining has been lost, for the stem exhibited slight
irregular movements which could hardly be accounted for by changes in
the action of the light. There is no difficulty in understanding how
a spirally twining plant could graduate into a simple root-climber;
for the young internodes of Bignonia Tweedyana and of Hoya carnosa
revolve and twine, but likewise emit rootlets which adhere to any
fitting surface, so that the loss of twining would be no great
disadvantage and in some respects an advantage to these species, as
they would then ascend their supports in a more direct line. {20}


Plants which climb by the aid of spontaneously revolving and
sensitive petioles--Clematis--Tropaeolum--Maurandia, flower-peduncles
moving spontaneously and sensitive to a touch--Rhodochiton--
Lophospermum--internodes sensitive--Solanum, thickening of the
clasped petioles--Fumaria--Adlumia--Plants which climb by the aid of
their produced midribs--Gloriosa--Flagellaria--Nepenthes--Summary on

We now come to our second class of climbing plants, namely, those
which ascend by the aid of irritable or sensitive organs. For
convenience' sake the plants in this class have been grouped under
two sub-divisions, namely, leaf-climbers, or those which retain their
leaves in a functional condition, and tendril-bearers. But these
sub-divisions graduate into each other, as we shall see under
Corydalis and the Gloriosa lily.

It has long been observed that several plants climb by the aid of
their leaves, either by their petioles (foot-stalks) or by their
produced midribs; but beyond this simple fact they have not been
described. Palm and Mohl class these plants with those which bear
tendrils; but as a leaf is generally a defined object, the present
classification, though artificial, has at least some advantages.
Leaf-climbers are, moreover, intermediate in many respects between
twiners and tendril-bearers. Eight species of Clematis and seven of
Tropaeolum were observed, in order to see what amount of difference
in the manner of climbing existed within the same genus; and the
differences are considerable.

CLEMATIS.--C. glandulosa.--The thin upper internodes revolve, moving
against the course of the sun, precisely like those of a true twiner,
at an average rate, judging from three revolutions, of 3 hrs. 48 m.
The leading shoot immediately twined round a stick placed near it;
but, after making an open spire of only one turn and a half, it
ascended for a short space straight, and then reversed its course and
wound two turns in an opposite direction. This was rendered possible
by the straight piece between the opposed spires having become rigid.
The simple, broad, ovate leaves of this tropical species, with their
short thick petioles, seem but ill-fitted for any movement; and
whilst twining up a vertical stick, no use is made of them.
Nevertheless, if the footstalk of a young leaf be rubbed with a thin
twig a few times on any side, it will in the course of a few hours
bend to that side; afterwards becoming straight again. The under
side seemed to be the most sensitive; but the sensitiveness or
irritability is slight compared to that which we shall meet with in
some of the following species; thus, a loop of string, weighing 1.64
grain (106.2 mg.) and hanging for some days on a young footstalk,
produced a scarcely perceptible effect. A sketch is here given of
two young leaves which had naturally caught hold of two thin
branches. A forked twig placed so as to press lightly on the under
side of a young footstalk caused it, in 12 hrs., to bend greatly, and
ultimately to such an extent that the leaf passed to the opposite
side of the stem; the forked stick having been removed, the leaf
slowly recovered its former position.

The young leaves spontaneously and gradually change their position:
when first developed the petioles are upturned and parallel to the
stem; they then slowly bend downwards, remaining for a short time at
right angles to the stem, and then become so much arched downwards
that the blade of the leaf points to the ground with its tip curled
inwards, so that the whole petiole and leaf together form a hook.
They are thus enabled to catch hold of any twig with which they may
be brought into contact by the revolving movement of the internodes.
If this does not happen, they retain their hooked shape for a
considerable time, and then bending upwards reassume their original
upturned position, which is preserved ever afterwards. The petioles
which have clasped any object soon become much thickened and
strengthened, as may be seen in the drawing.

Clematis montana.--The long, thin petioles of the leaves, whilst
young, are sensitive, and when lightly rubbed bend to the rubbed
side, subsequently becoming straight. They are far more sensitive
than the petioles of C. glandulosa; for a loop of thread weighing a
quarter of a grain (16.2 mg.) caused them to bend; a loop weighing
only one-eighth of a grain (8.1 mg.) sometimes acted and sometimes
did not act. The sensitiveness extends from the blade of the leaf to
the stem. I may here state that I ascertained in all cases the
weights of the string and thread used by carefully weighing 50 inches
in a chemical balance, and then cutting off measured lengths. The
main petiole carries three leaflets; but their short, sub-petioles
are not sensitive. A young, inclined shoot (the plant being in the
greenhouse) made a large circle opposed to the course of the sun in 4
hrs. 20 m., but the next day, being very cold, the time was 5 hrs. 10
m. A stick placed near a revolving stem was soon struck by the
petioles which stand out at right angles, and the revolving movement
was thus arrested. The petioles then began, being excited by the
contact, to slowly wind round the stick. When the stick was thin, a
petiole sometimes wound twice round it. The opposite leaf was in no
way affected. The attitude assumed by the stem after the petiole had
clasped the stick, was that of a man standing by a column, who throws
his arm horizontally round it. With respect to the stem's power of
twining, some remarks will be made under C. calycina.

Clematis Sieboldi.--A shoot made three revolutions against the sun at
an average rate of 3 hrs. 11 m. The power of twining is like that of
the last species. Its leaves are nearly similar in structure and in
function, excepting that the sub-petioles of the lateral and terminal
leaflets are sensitive. A loop of thread, weighing one-eighth of a
grain, acted on the main petiole, but not until two or three days had
elapsed. The leaves have the remarkable habit of spontaneously
revolving, generally in vertical ellipses, in the same manner, but in
a less degree, as will be described under C. microphylla.

Clematis calycina.--The young shoots are thin and flexible: one
revolved, describing a broad oval, in 5 hrs. 30 m., and another in 6
hrs. 12 m. They followed the course of the sun; but the course, if
observed long enough, would probably be found to vary in this
species, as well as in all the others of the genus. It is a rather
better twiner than the two last species: the stem sometimes made two
spiral turns round a thin stick, if free from twigs; it then ran
straight up for a space, and reversing its course took one or two
turns in an opposite direction. This reversal of the spire occurred
in all the foregoing species. The leaves are so small compared with
those of most of the other species, that the petioles at first seem
ill-adapted for clasping. Nevertheless, the main service of the
revolving movement is to bring them into contact with surrounding
objects, which are slowly but securely seized. The young petioles,
which alone are sensitive, have their ends bowed a little downwards,
so as to be in a slight degree hooked; ultimately the whole leaf, if
it catches nothing, becomes level. I gently rubbed with a thin twig
the lower surfaces of two young petioles; and in 2 hrs. 30 m. they
were slightly curved downwards; in 5 hrs., after being rubbed, the
end of one was bent completely back, parallel to the basal portion;
in 4 hrs. subsequently it became nearly straight again. To show how
sensitive the young petioles are, I may mention that I just touched
the under sides of two with a little water-colour, which when dry
formed an excessively thin and minute crust; but this sufficed in 24
hrs. to cause both to bend downwards. Whilst the plant is young,
each leaf consists of three divided leaflets, which barely have
distinct petioles, and these are not sensitive; but when the plant is
well grown, the petioles of the two lateral and terminal leaflets are
of considerable length, and become sensitive so as to be capable of
clasping an object in any direction.

When a petiole has clasped a twig, it undergoes some remarkable
changes, which may be observed with the other species, but in a less
strongly marked manner, and will here be described once for all. The
clasped petiole in the course of two or three days swells greatly,
and ultimately becomes nearly twice as thick as the opposite one
which has clasped nothing. When thin transverse slices of the two
are placed under the microscope their difference is conspicuous: the
side of the petiole which has been in contact with the support, is
formed of a layer of colourless cells with their longer axes directed
from the centre, and these are very much larger than the
corresponding cells in the opposite or unchanged petiole; the central
cells, also, are in some degree enlarged, and the whole is much
indurated. The exterior surface generally becomes bright red. But a
far greater change takes place in the nature of the tissues than that
which is visible: the petiole of the unclasped leaf is flexible and
can be snapped easily, whereas the clasped one acquires an
extraordinary degree of toughness and rigidity, so that considerable
force is required to pull it into pieces. With this change, great
durability is probably acquired; at least this is the case with the
clasped petioles of Clematis vitalba. The meaning of these changes
is obvious, namely, that the petioles may firmly and durably support
the stem.

Clematis microphylla, var. leptophylla.--The long and thin internodes
of this Australian species revolve sometimes in one direction and
sometimes in an opposite one, describing long, narrow, irregular
ellipses or large circles. Four revolutions were completed within
five minutes of the same average rate of 1 hr. 51 m.; so that this
species moves more quickly than the others of the genus. The shoots,
when placed near a vertical stick, either twine round it, or clasp it
with the basal portions of their petioles. The leaves whilst young
are nearly of the same shape as those of C. viticella, and act in the
same manner like a hook, as will be described under that species.
But the leaflets are more divided, and each segment whilst young
terminates in a hardish point, which is much curved downwards and
inwards; so that the whole leaf readily catches hold of any
neighbouring object. The petioles of the young terminal leaflets are
acted on by loops of thread weighing 0.125th and even 0.0625th of a
grain. The basal portion of the main petiole is much less sensitive,
but will clasp a stick against which it presses.

The leaves, whilst young, are continually and spontaneously moving
slowly. A bell-glass was placed over a shoot secured to a stick, and
the movements of the leaves were traced on it during several days. A
very irregular line was generally formed; but one day, in the course
of eight hours and three quarters, the figure clearly represented
three and a half irregular ellipses, the most perfect one of which
was completed in 2 hrs. 35 m. The two opposite leaves moved
independently of each other. This movement of the leaves would aid
that of the internodes in bringing the petioles into contact with
surrounding objects. I discovered this movement too late to be
enabled to observe it in the other species; but from analogy I can
hardly doubt that the leaves of at least C. viticella, C. flammula,
and C. vitalba move spontaneously; and, judging from C Sieboldi, this
probably is the case with C. montana and C. calycina. I ascertained
that the simple leaves of C. glandulosa exhibited no spontaneous
revolving movement.

Clematis viticella, var. venosa.--In this and the two following
species the power of spirally twining is completely lost, and this
seems due to the lessened flexibility of the internodes and to the
interference caused by the large size of the leaves. But the
revolving movement, though restricted, is not lost. In our present
species a young internode, placed in front of a window, made three
narrow ellipses, transversely to the direction of the light, at an
average rate of 2 hrs. 40 m. When placed so that the movements were
to and from the light, the rate was greatly accelerated in one half
of the course, and retarded in the other, as with twining plants.
The ellipses were small; the longer diameter, described by the apex
of a shoot bearing a pair of not expanded leaves, was only 4.625
inches, and that by the apex of the penultimate internode only 1.125
inch. At the most favourable period of growth each leaf would hardly
be carried to and fro by the movement of the internodes more than two
or three inches, but, as above stated, it is probable that the leaves
themselves move spontaneously. The movement of the whole shoot by
the wind and by its rapid growth, would probably be almost equally
efficient as these spontaneous movements, in bringing the petioles
into contact with surrounding objects.

The leaves are of large size. Each bears three pairs of lateral
leaflets and a terminal one, all supported on rather long sub-
petioles. The main petiole bends a little angularly downwards at
each point where a pair of leaflets arises (see fig. 2), and the
petiole of the terminal leaflet is bent downwards at right angles;
hence the whole petiole, with its rectangularly bent extremity, acts
as a hook. This hook, the lateral petioles being directed a little
upwards; forms an excellent grappling apparatus, by which the leaves
readily become entangled with surrounding objects. If they catch
nothing, the whole petiole ultimately grows straight. The main
petiole, the sub-petioles, and the three branches into which each
basi-lateral sub-petiole is generally subdivided, are all sensitive.
The basal portion of the main petiole, between the stem and the first
pair of leaflets, is less sensitive than the remainder; it will,
however, clasp a stick with which it is left in contact. The
inferior surface of the rectangularly bent terminal portion (carrying
the terminal leaflet), which forms the inner side of the end of the
hook, is the most sensitive part; and this portion is manifestly best
adapted to catch a distant support. To show the difference in
sensibility, I gently placed loops of string of the same weight (in
one instance weighing only 0.82 of a grain or 53.14 mg.) on the
several lateral sub-petioles and on the terminal one; in a few hours
the latter was bent, but after 24 hrs. no effect was produced on the
other sub-petioles. Again, a terminal sub-petiole placed in contact
with a thin stick became sensibly curved in 45 m., and in 1 hr. 10m.
moved through ninety degrees; whilst a lateral sub-petiole did not
become sensibly curved until 3 hrs. 30 m. had elapsed. In all cases,
if the sticks are taken away, the petioles continue to move during
many hours afterwards; so they do after a slight rubbing; but they
become straight again, after about a day's interval, that is if the
flexure has not been very great or long continued.

The graduated difference in the extension of the sensitiveness in the
petioles of the above-described species deserves notice. In C.
montana it is confined to the main petiole, and has not spread to the
sub-petioles of the three leaflets; so it is with young plants of C.
calycina, but in older plants it spreads to the three sub-petioles.
In C. viticella the sensitiveness has spread to the petioles of the
seven leaflets, and to the subdivisions of the basi-lateral sub-
petioles. But in this latter species it has diminished in the basal
part of the main petiole, in which alone it resided in C. montana;
whilst it has increased in the abruptly bent terminal portion.

Clematis flammula.--The rather thick, straight, and stiff shoots,
whilst growing vigorously in the spring, make small oval revolutions,
following the sun in their course. Four were made at an average rate
of 3 hrs. 45 m. The longer axis of the oval, described by the
extreme tip, was directed at right angles to the line joining the
opposite leaves; its length was in one case only 1.375, and in
another case 1.75 inch; so that the young leaves were moved a very
short distance. The shoots of the same plant observed in midsummer,
when growing not so quickly, did not revolve at all. I cut down
another plant in the early summer, so that by August 1st it had
formed new and moderately vigorous shoots; these, when observed under
a bell-glass, were on some days quite stationary, and on other days
moved to and fro only about the eighth of an inch. Consequently the
revolving power is much enfeebled in this species, and under
unfavourable circumstances is completely lost. The shoot must depend
for coming into contact with surrounding objects on the probable,
though not ascertained spontaneous movement of the leaves, on rapid
growth, and on movement from the wind. Hence, perhaps, it is that
the petioles have acquired a high degree of sensitiveness as a
compensation for the little power of movement in the shoots.

The petioles are bowed downwards, and have the same general hook-like
form as in C. viticella. The medial petiole and the lateral sub-
petioles are sensitive, especially the much bent terminal portion.
As the sensitiveness is here greater than in any other species of the
genus observed by me, and is in itself remarkable, I will give fuller
details. The petioles, when so young that they have not separated
from one another, are not sensitive; when the lamina of a leaflet has
grown to a quarter of an inch in length (that is, about one-sixth of
its full size), the sensitiveness is highest; but at this period the
petioles are relatively much more fully developed than are the blades
of the leaves. Full-grown petioles are not in the least sensitive.
A thin stick placed so as to press lightly against a petiole, having
a leaflet a quarter of an inch in length, caused the petiole to bend
in 3 hrs. 15 m. In another case a petiole curled completely round a
stick in 12 hrs. These petioles were left curled for 24 hrs., and the
sticks were then removed; but they never straightened themselves. I
took a twig, thinner than the petiole itself, and with it lightly
rubbed several petioles four times up and down; these in 1 hr. 45 m.
became slightly curled; the curvature increased during some hours and
then began to decrease, but after 25 hrs. from the time of rubbing a
vestige of the curvature remained. Some other petioles similarly
rubbed twice, that is, once up and once down, became perceptibly
curved in about 2 hrs. 30 m., the terminal sub-petiole moving more
than the lateral sub-petioles; they all became straight again in
between 12 hrs. and 14 hrs. Lastly, a length of about one-eighth of
an inch of a sub-petiole, was lightly rubbed with the same twig only
once; it became slightly curved in 3 hrs., remaining so during 11
hrs., but by the next morning was quite straight.

The following observations are more precise. After trying heavier
pieces of string and thread, I placed a loop of fine string, weighing
1.04 gr. (67.4 mg.) on a terminal sub-petiole: in 6 hrs. 40 m. a
curvature could be seen; in 24 hrs. the petiole formed an open ring
round the string; in 48 hrs. the ring had almost closed on the
string, and in 72 hrs. seized it so firmly, that some force was
necessary for its withdrawal. A loop weighing 0.52 of a grain (33.7
mg.) caused in 14 hrs. a lateral sub-petiole just perceptibly to
curve, and in 24 hrs. it moved through ninety degrees. These
observations were made during the summer: the following were made in
the spring, when the petioles apparently are more sensitive:- A loop
of thread, weighing one-eighth of a grain (8.1 mg.), produced no
effect on the lateral sub-petioles, but placed on a terminal one,
caused it, after 24 hrs., to curve moderately; the curvature, though
the loop remained suspended, was after 48 hrs. diminished, but never
disappeared; showing that the petiole had become partially accustomed
to the insufficient stimulus. This experiment was twice repeated
with nearly the same result. Lastly, a loop of thread, weighing only
one-sixteenth of a grain (4.05 mg.) was twice gently placed by a
forceps on a terminal sub-petiole (the plant being, of course, in a
still and closed room), and this weight certainly caused a flexure,
which very slowly increased until the petiole moved through nearly
ninety degrees: beyond this it did not move; nor did the petiole,
the loop remaining suspended, ever become perfectly straight again.

When we consider, on the one hand, the thickness and stiffness of the
petioles, and, on the other hand, the thinness and softness of fine
cotton thread, and what an extremely small weight one-sixteenth of a
grain (4.05 mg.) is, these facts are remarkable. But I have reason
to believe that even a less weight excites curvature when pressing
over a broader surface than that acted on by a thread. Having
noticed that the end of a suspended string which accidentally touched
a petiole, caused it to bend, I took two pieces of thin twine, 10
inches in length (weighing 1.64 gr.), and, tying them to a stick, let
them hang as nearly perpendicularly downwards as their thinness and
flexuous form, after being stretched, would permit; I then quietly
placed their ends so as just to rest on two petioles, and these
certainly became curved in 36 hrs. One of the ends touched the angle
between a terminal and lateral sub-petiole, and it was in 48 hours
caught between them as by a forceps. In these cases the pressure,
though spread over a wider surface than that touched by the cotton
thread, must have been excessively slight.

Clematis vitalba.--The plants were in pots and not healthy, so that I
dare not trust my observations, which indicate much similarity in
habits with C. flammula. I mention this species only because I have
seen many proofs that the petioles in a state of nature are excited
to movement by very slight pressure. For instance, I have found them
embracing thin withered blades of grass, the soft young leaves of a
maple, and the flower-peduncles of the quaking-grass or Briza. The
latter are about as thick as the hair of a man's beard, but they were
completely surrounded and clasped. The petioles of a leaf, so young
that none of the leaflets were expanded, had partially seized a twig.
Those of almost all the old leaves, even when unattached to any
object, are much convoluted; but this is owing to their having come,
whilst young, into contact during several hours with some object
subsequently removed. With none of the above-described species,
cultivated in pots and carefully observed, was there any permanent
bending of the petioles without the stimulus of contact. In winter,
the blades of the leaves of C. vitalba drop off; but the petioles (as
was observed by Mohl) remain attached to the branches, sometimes
during two seasons; and, being convoluted, they curiously resemble
true tendrils, such as those possessed by the allied genus Naravelia.
The petioles which have clasped some object become much more stiff,
hard, and polished than those which have failed in this their proper

TROPAEOLUM.--I observed T. tricolorum, T. azureum, T. pentaphyllum,
T. peregrinum, T. elegans, T. tuberosum, and a dwarf variety of, as I
believe, T. minus.

Tropaeolum tricolorum, var. grandiflorum.--The flexible shoots, which
first rise from the tubers, are as thin as fine twine. One such
shoot revolved in a course opposed to the sun, at an average rate,
judging from three revolutions, of 1 hr. 23 m.; but no doubt the
direction of the revolving movement is variable. When the plants
have grown tall and are branched, all the many lateral shoots
revolve. The stem, whilst young, twines regularly round a thin
vertical stick, and in one case I counted eight spiral turns in the
same direction; but when grown older, the stem often runs straight up
for a space, and, being arrested by the clasping petioles, makes one
or two spires in a reversed direction. Until the plant grows to a
height of two or three feet, requiring about a month from the time
when the first shoot appears above ground, no true leaves are
produced, but, in their place, filaments coloured like the stem. The
extremities of these filaments are pointed, a little flattened, and
furrowed on the upper surface. They never become developed into
leaves. As the plant grows in height new filaments are produced with
slightly enlarged tips; then others, bearing on each side of the
enlarged medial tip a rudimentary segment of a leaf; soon other
segments appear, and at last a perfect leaf is formed, with seven
deep segments. So that on the same plant we may see every step, from
tendril-like clasping filaments to perfect leaves with clasping
petioles. After the plant has grown to a considerable height, and is
secured to its support by the petioles of the true leaves, the
clasping filaments on the lower part of the stem wither and drop off;
so that they perform only a temporary service.

These filaments or rudimentary leaves, as well as the petioles of the
perfect leaves, whilst young, are highly sensitive on all sides to a
touch. The slightest rub caused them to curve towards the rubbed
side in about three minutes, and one bent itself into a ring in six
minutes; they subsequently became straight. When, however, they have
once completely clasped a stick, if this is removed, they do not
straighten themselves. The most remarkable fact, and one which I
have observed in no other species of the genus, is that the filaments
and the petioles of the young leaves, if they catch no object, after
standing for some days in their original position, spontaneously and
slowly oscillate a little from side to side, and then move towards
the stem and clasp it. They likewise often become, after a time, in
some degree spirally contracted. They therefore fully deserve to be
called tendrils, as they are used for climbing, are sensitive to a
touch, move spontaneously, and ultimately contract into a spire,
though an imperfect one. The present species would have been classed
amongst the tendril-bearers, had not these characters been confined
to early youth. During maturity it is a true leaf-climber.

Tropaeolum azureum.--An upper internode made four revolutions,
following the sun, at an average rate of 1 hr. 47 m. The stem twined
spirally round a support in the same irregular manner as that of the
last species. Rudimentary leaves or filaments do not exist. The
petioles of the young leaves are very sensitive: a single light rub
with a twig caused one to move perceptibly in 5 m., and another in 6
m. The former became bent at right angles in 15 min., and became
straight again in between 5 hrs. and 6 hrs. A loop of thread
weighing 0.125th of a grain caused another petiole to curve.

Tropaeolum pentaphyllum.--This species has not the power of spirally
twining, which seems due, not so much to a want of flexibility in the
stem, as to continual interference from the clasping petioles. An
upper internode made three revolutions, following the sun, at an
average rate of 1 hr. 46 m. The main purpose of the revolving
movement in all the species of Tropaeolum manifestly is to bring the
petioles into contact with some supporting object. The petiole of a
young leaf, after a slight rub, became curved in 6 m.; another, on a
cold day, in 20 m., and others in from 8 m. to 10 m. Their curvature
usually increased greatly in from 15 m. to 20 m., and they became
straight again in between 5 hrs. and 6 hrs., but on one occasion in 3
hrs. When a petiole has fairly clasped a stick, it is not able, on
the removal of the stick, to straighten itself. The free upper part
of one, the base of which had already clasped a stick, still retained
the power of movement. A loop of thread weighing 0.125th of a grain
caused a petiole to curve; but the stimulus was not sufficient, the
loop remaining suspended, to cause a permanent flexure. If a much
heavier loop be placed in the angle between the petiole and the stem,
it produces no effect; whereas we have seen with Clematis montana
that the angle between the stem and petiole is sensitive.

Tropaeolum peregrinum.--The first-formed internodes of a young plant
did not revolve, resembling in this respect those of a twining plant.
In an older plant the four upper internodes made three irregular
revolutions, in a course opposed to the sun, at an average rate of 1
hr. 48 min. It is remarkable that the average rate of revolution
(taken, however, but from few observations) is very nearly the same
in this and the two last species, namely, 1 hr. 47 m., 1 hr. 46 m.,
and 1 hr. 48 m. The present species cannot twine spirally, which
seems mainly due to the rigidity of the stem. In a very young plant,
which did not revolve, the petioles were not sensitive. In older
plants the petioles of quite young leaves, and of leaves as much as
an inch and a quarter in diameter, are sensitive. A moderate rub
caused one to curve in 10 m., and others in 20 m. They became
straight again in between 5 hrs. 45m. and 8 hrs. Petioles which have
naturally come into contact with a stick, sometimes take two turns
round it. After they have clasped a support, they become rigid and
hard. They are less sensitive to a weight than in the previous
species; for loops of string weighing 0.82 of a grain (53.14 mg.),
did not cause any curvature, but a loop of double this weight (1.64
gr.) acted.

Tropaeolum elegans.--I did not make many observations on this
species. The short and stiff internodes revolve irregularly,
describing small oval figures. One oval was completed in 3 hrs. A
young petiole, when rubbed, became slightly curved in 17 m.; and
afterwards much more so. It was nearly straight again in 8 hrs.

Tropaeolum tuberosum.--On a plant nine inches in height, the
internodes did not move at all; but on an older plant they moved
irregularly and made small imperfect ovals. These movements could be
detected only by being traced on a bell-glass placed over the plant.
Sometimes the shoots stood still for hours; during some days they
moved only in one direction in a crooked line; on other days they
made small irregular spires or circles, one being completed in about
4 hrs. The extreme points reached by the apex of the shoot were only
about one or one and a half inches asunder; yet this slight movement
brought the petioles into contact with some closely surrounding
twigs, which were then clasped. With the lessened power of
spontaneously revolving, compared with that of the previous species,
the sensitiveness of the petioles is also diminished. These, when
rubbed a few times, did not become curved until half an hour had
elapsed; the curvature increased during the next two hours, and then
very slowly decreased; so that they sometimes required 24 hrs. to
become straight again. Extremely young leaves have active petioles;
one with the lamina only 0.15 of an inch in diameter, that is, about
a twentieth of the full size, firmly clasped a thin twig. But leaves
grown to a quarter of their full size can likewise act.

Tropaeolum minus (?).--The internodes of a variety named "dwarf
crimson Nasturtium" did not revolve, but moved in a rather irregular
course during the day to the light, and from the light at night. The
petioles, when well rubbed, showed no power of curving; nor could I
see that they ever clasped any neighbouring object. We have seen in
this genus a gradation from species such as T. tricolorum, which have
extremely sensitive petioles, and internodes which rapidly revolve
and spirally twine up a support, to other species such as T. elegans
and T. tuberosum, the petioles of which are much less sensitive, and
the internodes of which have very feeble revolving powers and cannot
spirally twine round a support, to this last species, which has
entirely lost or never acquired these faculties. From the general
character of the genus, the loss of power seems the more probable

In the present species, in T. elegans, and probably in others, the
flower-peduncle, as soon as the seed-capsule begins to swell,
spontaneously bends abruptly downwards and becomes somewhat
convoluted. If a stick stands in the way, it is to a certain extent
clasped; but, as far as I have been able to observe, this clasping
movement is independent of the stimulus from contact.

ANTIRRHINEAE.--In this tribe (Lindley) of the Scrophulariaceae, at
least four of the seven included genera have leaf-climbing species.

Maurandia Barclayana.--A thin, slightly bowed shoot made two
revolutions, following the sun, each in 3 hrs. 17 min.; on the
previous day this same shoot revolved in an opposite direction. The
shoots do not twine spirally, but climb excellently by the aid of
their young and sensitive petioles. These petioles, when lightly
rubbed, move after a considerable interval of time, and subsequently
become straight again. A loop of thread weighing 0.125th of a grain
caused them to bend.

Maurandia semperflorens.--This freely growing species climbs exactly
like the last, by the aid of its sensitive petioles. A young
internode made two circles, each in 1 hr. 46 mm.; so that it moved
almost twice as rapidly as the last species. The internodes are not
in the least sensitive to a touch or pressure. I mention this
because they are sensitive in a closely allied genus, namely,
Lophospermum. The present species is unique in one respect. Mohl
asserts (p. 45) that "the flower-peduncles, as well as the petioles,
wind like tendrils;" but he classes as tendrils such objects as the
spiral flower-stalks of the Vallisneria. This remark, and the fact
of the flower-peduncles being decidedly flexuous, led me carefully to
examine them. They never act as true tendrils; I repeatedly placed
thin sticks in contact with young and old peduncles, and I allowed
nine vigorous plants to grow through an entangled mass of branches;
but in no one instance did they bend round any object. It is indeed
in the highest degree improbable that this should occur, for they are
generally developed on branches which have already securely clasped a
support by the petioles of their leaves; and when borne on a free
depending branch, they are not produced by the terminal portion of
the internode which alone has the power of revolving; so that they
could be brought only by accident into contact with any neighbouring
object. Nevertheless (and this is the remarkable fact) the flower-
peduncles, whilst young, exhibit feeble revolving powers, and are
slightly sensitive to a touch. Having selected some stems which had
firmly clasped a stick by their petioles, and having placed a bell-
glass over them, I traced the movements of the young flower-
peduncles. The tracing generally formed a short and extremely
irregular line, with little loops in its course. A young peduncle
1.5 inch in length was carefully observed during a whole day, and it
made four and a half narrow, vertical, irregular, and short ellipses-
-each at an average rate of about 2 hrs. 25 m. An adjoining peduncle
described during the same time similar, though fewer, ellipses. As
the plant had occupied for some time exactly the same position, these
movements could not be attributed to any change in the action of the
light. Peduncles, old enough for the coloured petals to be just
visible, do not move. With respect to irritability, {21} I rubbed
two young peduncles (1.5 inch in length) a few times very lightly
with a thin twig; one was rubbed on the upper, and the other on the
lower side, and they became in between 4 hrs. and 5 hrs. distinctly
bowed towards these sides; in 24 hrs. subsequently, they straightened
themselves. Next day they were rubbed on the opposite sides, and
they became perceptibly curved towards these sides. Two other and
younger peduncles (three-fourths of an inch in length) were lightly
rubbed on their adjoining sides, and they became so much curved
towards one another, that the arcs of the bows stood at nearly right
angles to their previous direction; and this was the greatest
movement seen by me. Subsequently they straightened themselves.
Other peduncles, so young as to be only three-tenths of an inch in
length, became curved when rubbed. On the other hand, peduncles
above 1.5 inch in length required to be rubbed two or three times,
and then became only just perceptibly bowed. Loops of thread
suspended on the peduncles produced no effect; loops of string,
however, weighing 0.82 and 1.64 of a grain sometimes caused a slight
curvature; but they were never closely clasped, as were the far
lighter loops of thread by the petioles.

In the nine vigorous plants observed by me, it is certain that
neither the slight spontaneous movements nor the slight sensitiveness
of the flower-peduncles aided the plants in climbing. If any member
of the Scrophulariaceae had possessed tendrils produced by the
modification of flower-peduncles, I should have thought that this
species of Maurandia had perhaps retained a useless or rudimentary
vestige of a former habit; but this view cannot be maintained. We
may suspect that, owing to the principle of correlation, the power of
movement has been transferred to the flower-peduncles from the young
internodes, and sensitiveness from the young petioles. But to
whatever cause these capacities are due, the case is interesting;
for, by a little increase in power through natural selection, they
might easily have been rendered as useful to the plant in climbing,
as are the flower-peduncles (hereafter to be described) of Vitis or

Rhodochiton volubile.--A long flexible shoot swept a large circle,
following the sun, in 5 hrs. 30 m.; and, as the day became warmer, a
second circle was completed in 4 hrs. 10 m. The shoots sometimes
make a whole or a half spire round a vertical stick, they then run
straight up for a space, and afterwards turn spirally in an opposite
direction. The petioles of very young leaves about one-tenth of
their full size, are highly sensitive, and bend towards the side
which is touched; but they do not move quickly. One was perceptibly
curved in 1 hr. 10 m., after being lightly rubbed, and became
considerably curved in 5 hrs. 40 m.; some others were scarcely curved
in 5 hrs. 30 m., but distinctly so in 6 hrs. 30 m. A curvature was
perceptible in one petiole in between 4 hrs. 30 m. and 5 hrs., after
the suspension of a little loop of string. A loop of fine cotton
thread, weighing one sixteenth of a grain (4.05 mg.), not only caused
a petiole slowly to bend, but was ultimately so firmly clasped that
it could be withdrawn only by some little force. The petioles, when
coming into contact with a stick, take either a complete or half a
turn round it, and ultimately increase much in thickness. They do
not possess the power of spontaneously revolving.

Lophospermum scandens, var. purpureum.--Some long, moderately thin
internodes made four revolutions at an average rate of 3 hrs. 15 m.
The course pursued was very irregular, namely, an extremely narrow
ellipse, a large circle, an irregular spire or a zigzag line, and
sometimes the apex stood still. The young petioles, when brought by
the revolving movement into contact with sticks, clasped them, and
soon increased considerably in thickness. But they are not quite so
sensitive to a weight as those of the Rhodochiton, for loops of
thread weighing one-eighth of a grain did not always cause them to

This plant presents a case not observed by me in any other leaf-
climber or twiner, {22} namely, that the young internodes of the stem
are sensitive to a touch. When a petiole of this species clasps a
stick, it draws the base of the internode against it; and then the
internode itself bends towards the stick, which is caught between the
stem and the petiole as by a pair of pincers. The internode
afterwards straightens itself, excepting the part in actual contact
with the stick. Young internodes alone are sensitive, and these are
sensitive on all sides along their whole length. I made fifteen
trials by twice or thrice lightly rubbing with a thin twig several
internodes; and in about 2 hrs., but in one case in 3 hrs., all were
bent: they became straight again in about 4 hrs. afterwards. An
internode, which was rubbed as often as six or seven times, became
just perceptibly curved in 1 hr. 15 m., and in 3 hrs. the curvature
increased much; it became straight again in the course of the
succeeding night. I rubbed some internodes one day on one side, and
the next day either on the opposite side or at right angles to the
first side; and the curvature was always towards the rubbed side.

According to Palm (p. 63), the petioles of Linaria cirrhosa and, to a
limited degree, those of L. elatine have the power of clasping a

SOLANACEAE.--Solanum jasminoides.--Some of the species in this large
genus are twiners; but the present species is a true leaf-climber. A
long, nearly upright shoot made four revolutions, moving against the
sun, very regularly at an average rate of 3 hrs. 26 m. The shoots,
however, sometimes stood still. It is considered a greenhouse plant;
but when kept there, the petioles took several days to clasp a stick:
in the hothouse a stick was clasped in 7 hrs. In the greenhouse a
petiole was not affected by a loop of string, suspended during
several days and weighing 2.5 grains (163 mg.); but in the hothouse
one was made to curve by a loop weighing 1.64 gr. (106.27 mg.); and,
on the removal of the string, it became straight again. Another
petiole was not at all acted on by a loop weighing only 0.82 of a
grain (53.14 mg.) We have seen that the petioles of some other leaf-
climbing plants are affected by one-thirteenth of this latter weight.
In this species, and in no other leaf-climber seen by me, a full-
grown leaf is capable of clasping a stick; but in the greenhouse the
movement was so extraordinarily slow that the act required several
weeks; on each succeeding week it was clear that the petiole had
become more and more curved, until at last it firmly clasped the

The flexible petiole of a half or a quarter grown leaf which has
clasped an object for three or four days increases much in thickness,
and after several weeks becomes so wonderfully hard and rigid that it
can hardly be removed from its support. On comparing a thin
transverse slice of such a petiole with one from an older leaf
growing close beneath, which had not clasped anything, its diameter
was found to be fully doubled, and its structure greatly changed. In
two other petioles similarly compared, and here represented, the
increase in diameter was not quite so great. In the section of the
petiole in its ordinary state (A), we see a semilunar band of
cellular tissue (not well shown in the woodcut) differing slightly in
appearance from that outside it, and including three closely
approximate groups of dark vessels. Near the upper surface of the
petiole, beneath two exterior ridges, there are two other small
circular groups of vessels. In the section of the petiole (B) which
had clasped during several weeks a stick, the two exterior ridges
have become much less prominent, and the two groups of woody vessels
beneath them much increased in diameter. The semilunar band has been
converted into a complete ring of very hard, white, woody tissue,
with lines radiating from the centre. The three groups of vessels,
which, though near together, were before distinct, are now completely
blended. The upper part of this ring of woody vessels, formed by the
prolongation of the horns of the original semilunar band, is narrower
than the lower part, and slightly less compact. This petiole after
clasping the stick had actually become thicker than the stem from
which it arose; and this was chiefly due to the increased thickness
of the ring of wood. This ring presented, both in a transverse and
longitudinal section, a closely similar structure to that of the
stem. It is a singular morphological fact that the petiole should
thus acquire a structure almost identically the same with that of the
axis; and it is a still more singular physiological fact that so
great a change should have been induced by the mere act of clasping a
support. {23}


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