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B. M. Bower (B.M. Sinclair) - "Rowdy of the Cross L"

Alexandre Dumas, fils - "Camille (La Dame aux Camilias)"

H. Rider Haggard - "King Solomon's Mines"

William J. Long - "Secret of the Woods"

The Movements and Habits of Climbing Plants

C >> Charles Darwin >> The Movements and Habits of Climbing Plants




Cissus discolor.--The young shoots show no more movement than can be
accounted for by daily variations in the action of the light. The
tendrils, however, revolve with much regularity, following the sun;
and, in the plants observed by me, swept circles of about 5 inches in
diameter. Five circles were completed in the following times:- 4
hrs. 45 m., 4 hrs. 50 m., 4 hrs. 45 m., 4 hrs. 30 m., and 5 hrs. The
same tendril continues to revolve during three or four days. The
tendrils are from 3.5 to 5 inches in length. They are formed of a
long foot-stalk, bearing two short branches, which in old plants
again bifurcate. The two branches are not of quite equal length; and
as with the vine, the longer one has a scale at its base. The
tendril stands vertically upwards; the extremity of the shoot being
bent abruptly downwards, and this position is probably of service to
the plant by allowing the tendril to revolve freely and vertically.

Both branches of the tendril, whilst young, are highly sensitive. A
touch with a pencil, so gentle as only just to move a tendril borne
at the end of a long flexible shoot, sufficed to cause it to become
perceptibly curved in four or five minutes. It became straight again
in rather above one hour. A loop of soft thread weighing one-seventh
of a grain (9.25 mg.) was thrice tried, and each time caused the
tendril to become curved in 30 or 40 m. Half this weight produced no
effect. The long foot-stalk is much less sensitive, for a slight
rubbing produced no effect, although prolonged contact with a stick
caused it to bend. The two branches are sensitive on all sides, so
that they converge if touched on their inner sides, and diverge if
touched on their outer sides. If a branch be touched at the same
time with equal force on opposite sides, both sides are equally
stimulated and there is no movement. Before examining this plant, I
had observed only tendrils which are sensitive on one side alone, and
these when lightly pressed between the finger and thumb become
curved; but on thus pinching many times the tendrils of the Cissus no
curvature ensued, and I falsely inferred at first that they were not
at all sensitive.

Cissus antarcticus.--The tendrils on a young plant were thick and
straight, with the tips a little curved. When their concave surfaces
were rubbed, and it was necessary to do this with some force, they
very slowly became curved, and subsequently straight again. They are
therefore much less sensitive than those of the last species; but
they made two revolutions, following the sun, rather more rapidly,
viz., in 3 hrs. 30 m. and 4 hrs. The internodes do not revolve.

Ampelopsis hederacea (Virginian Creeper).--The internodes apparently
do not move more than can be accounted for by the varying action of
the light. The tendrils are from 4 to 5 inches in length, with the
main stem sending off several lateral branches, which have their tips
curved, as may be seen in the upper figure (fig. 11). They exhibit
no true spontaneous revolving movement, but turn, as was long ago
observed by Andrew Knight, {31} from the light to the dark. I have
seen several tendrils move in less than 24 hours, through an angle of
180 degrees to the dark side of a case in which a plant was placed,
but the movement is sometimes much slower. The several lateral
branches often move independently of one another, and sometimes
irregularly, without any apparent cause. These tendrils are less
sensitive to a touch than any others observed by me. By gentle but
repeated rubbing with a twig, the lateral branches, but not the main
stem, became in the course of three or four hours slightly curved;
but they seemed to have hardly any power of again straightening
themselves. The tendrils of a plant which had crawled over a large
box-tree clasped several of the branches; but I have repeatedly seen
that they will withdraw themselves after seizing a stick. When they
meet with a flat surface of wood or a wall (and this is evidently
what they are adapted for), they turn all their branches towards it,
and, spreading them widely apart, bring their hooked tips laterally
into contact with it. In effecting this, the several branches, after
touching the surface, often rise up, place themselves in a new
position, and again come down into contact with it.

In the course of about two days after a tendril has arranged its
branches so as to press on any surface, the curved tips swell, become
bright red, and form on their under-sides the well-known little discs
or cushions with which they adhere firmly. In one case the tips were
slightly swollen in 38 hrs. after coming into contact with a brick;
in another case they were considerably swollen in 48 hrs., and in an
additional 24 hrs. were firmly attached to a smooth board; and
lastly, the tips of a younger tendril not only swelled but became
attached to a stuccoed wall in 42 hrs. These adhesive discs
resemble, except in colour and in being larger, those of Bignonia
capreolata. When they were developed in contact with a ball of tow,
the fibres were separately enveloped, but not in so effective a
manner as by B. capreolata. Discs are never developed, as far as I
have seen, without the stimulus of at least temporary contact with
some object. {32} They are generally first formed on one side of the
curved tip, the whole of which often becomes so much changed in
appearance, that a line of the original green tissue can be traced
only along the concave surface. When, however, a tendril has clasped
a cylindrical stick, an irregular rim or disc is sometimes formed
along the inner surface at some little distance from the curved tip;
this was also observed (p. 71) by Mohl. The discs consist of
enlarged cells, with smooth projecting hemispherical surfaces,
coloured red; they are at first gorged with fluid (see section given
by Mohl, p. 70), but ultimately become woody.

As the discs soon adhere firmly to such smooth surfaces as planed or
painted wood, or to the polished leaf of the ivy, this alone renders
it probable that some cement is secreted, as has been asserted to be
the case (quoted by Mohl, p. 71) by Malpighi. I removed a number of
discs formed during the previous year from a stuccoed wall, and left
them during many hours, in warm water, diluted acetic acid and
alcohol; but the attached grains of silex were not loosened.
Immersion in sulphuric ether for 24 hrs. loosened them much, but
warmed essential oils (I tried oil of thyme and peppermint)
completely released every particle of stone in the course of a few
hours. This seems to prove that some resinous cement is secreted.
The quantity, however, must be small; for when a plant ascended a
thinly whitewashed wall, the discs adhered firmly to the whitewash;
but as the cement never penetrated the thin layer, they were easily
withdrawn, together with little scales of the whitewash. It must not
be supposed that the attachment is effected exclusively by the
cement; for the cellular outgrowth completely envelopes every minute
and irregular projection, and insinuates itself into every crevice.

A tendril which has not become attached to any body, does not
contract spirally; and in course of a week or two shrinks into the
finest thread, withers and drops off. An attached tendril, on the
other hand, contracts spirally, and thus becomes highly elastic, so
that when the main foot-stalk is pulled the strain is distributed
equally between all the attached discs. For a few days after the
attachment of the discs, the tendril remains weak and brittle, but it
rapidly increases in thickness and acquires great strength. During
the following winter it ceases to live, but adheres firmly in a dead
state both to its own stem and to the surface of attachment. In the
accompanying diagram (fig. 11.) we see the difference between a
tendril (B) some weeks after its attachment to a wall, with one (A)
from the same plant fully grown but unattached. That the change in
the nature of the tissues, as well as the spiral contraction, are
consequent on the formation of the discs, is well shown by any
lateral branches which have not become attached; for these in a week
or two wither and drop off, in the same manner as does the whole
tendril if unattached. The gain in strength and durability in a
tendril after its attachment is something wonderful. There are
tendrils now adhering to my house which are still strong, and have
been exposed to the weather in a dead state for fourteen or fifteen
years. One single lateral branchlet of a tendril, estimated to be at
least ten years old, was still elastic and supported a weight of
exactly two pounds. The whole tendril had five disc-bearing branches
of equal thickness and apparently of equal strength; so that after
having been exposed during ten years to the weather, it would
probably have resisted a strain of ten pounds!

SAPINDACEAE.--Cardiospermum halicacabum.--In this family, as in the
last, the tendrils are modified flower-peduncles. In the present
plant the two lateral branches of the main flower-peduncle have been
converted into a pair of tendrils, corresponding with the single
"flower-tendril" of the common vine. The main peduncle is thin,
stiff, and from 3 to 4.5 inches in length. Near the summit, above
two little bracts, it divides into three branches. The middle one
divides and re-divides, and bears the flowers; ultimately it grows
half as long again as the two other modified branches. These latter
are the tendrils; they are at first thicker and longer than the
middle branch, but never become more than an inch in length. They
taper to a point and are flattened, with the lower clasping surface
destitute of hairs. At first they project straight up; but soon
diverging, spontaneously curl downwards so as to become symmetrically
and elegantly hooked, as represented in the diagram. They are now,
whilst the flower-buds are still small, ready for action.

The two or three upper internodes, whilst young, steadily revolve;
those on one plant made two circles, against the course of the sun,
in 3 hrs. 12 m.; in a second plant the same course was followed, and
the two circles were completed in 3 hrs. 41 m.; in a third plant, the
internodes followed the sun and made two circles in 3 hrs. 47 m. The
average rate of these six revolutions was 1 hr. 46 m. The stem shows
no tendency to twine spirally round a support; but the allied
tendril-bearing genus Paullinia is said (Mohl, p. 4) to be a twiner.
The flower-peduncles, which stand up above the end of the shoot, are
carried round and round by the revolving movement of the internodes;
and when the stem is securely tied, the long and thin flower-
peduncles themselves are seen to be in continued and sometimes rapid
movement from side to side. They sweep a wide space, but only
occasionally revolve in a regular elliptical course. By the combined
movements of the internodes and peduncles, one of the two short
hooked tendrils, sooner or later, catches hold of some twig or
branch, and then it curls round and securely grasps it. These
tendrils are, however, but slightly sensitive; for by rubbing their
under surface only a slight movement is slowly produced. I hooked a
tendril on to a twig; and in 1 hr. 45 m. it was curved considerably
inwards; in 2 hrs. 30 m. it formed a ring; and in from 5 to 6 hours
from being first hooked, it closely grasped the stick. A second
tendril acted at nearly the same rate; but I observed one that took
24 hours before it curled twice round a thin twig. Tendrils which
have caught nothing, spontaneously curl up to a close helix after the
interval of several days. Those which have curled round some object,
soon become a little thicker and tougher. The long and thin main
peduncle, though spontaneously moving, is not sensitive and never
clasps a support. Nor does it ever contract spirally, {33} although
a contraction of this kind apparently would have been of service to
the plant in climbing. Nevertheless it climbs pretty well without
this aid. The seed-capsules though light, are of enormous size
(hence its English name of balloon-vine), and as two or three are
carried on the same peduncle, the tendrils rising close to them may
be of service in preventing their being dashed to pieces by the wind.
In the hothouse the tendrils served simply for climbing.

The position of the tendrils alone suffices to show their homological
nature. In two instances one of two tendrils produced a flower at
its tip; this, however, did not prevent its acting properly and
curling round a twig. In a third case both lateral branches which
ought to have been modified into tendrils, produced flowers like the
central branch, and had quite lost their tendril-structure.

I have seen, but was not enabled carefully to observe, only one other
climbing Sapindaceous plant, namely, Paullinia. It was not in
flower, yet bore long forked tendrils. So that, Paullinia, with
respect to its tendrils, appears to bear the same relation to
Cardiospermum that Cissus does to Vitis.

PASSIFLORACEAE.--After reading the discussion and facts given by Mohl
(p. 47) on the nature of the tendrils in this family, no one can
doubt that they are modified flower-peduncles. The tendrils and the
flower-peduncles rise close side by side; and my son, William E.
Darwin, made sketches for me of their earliest state of development
in the hybrid P. floribunda. The two organs appear at first as a
single papilla which gradually divides; so that the tendril appears
to be a modified branch of the flower-peduncle. My son found one
very young tendril surmounted by traces of floral organs, exactly
like those on the summit of the true flower-peduncle at the same
early age.

Passiflora gracilis.--This well-named, elegant, annual species
differs from the other members of the group observed by me, in the
young internodes having the power of revolving. It exceeds all the
other climbing plants which I have examined, in the rapidity of its
movements, and all tendril-bearers in the sensitiveness of the
tendrils. The internode which carries the upper active tendril and
which likewise carries one or two younger immature internodes, made
three revolutions, following the sun, at an average rate of 1 hr. 4
m.; it then made, the day becoming very hot, three other revolutions
at an average rate of between 57 and 58 m.; so that the average of
all six revolutions was 1 hr. 1 m. The apex of the tendril describes
elongated ellipses, sometimes narrow and sometimes broad, with their
longer axes inclined in slightly different directions. The plant can
ascend a thin upright stick by the aid of its tendrils; but the stem
is too stiff for it to twine spirally round it, even when not
interfered with by the tendrils, these having been successively
pinched off at an early age.

When the stem is secured, the tendrils are seen to revolve in nearly
the same manner and at the same rate as the internodes. {34} The
tendrils are very thin, delicate, and straight, with the exception of
the tips, which are a little curved; they are from 7 to 9 inches in
length. A half-grown tendril is not sensitive; but when nearly full-
grown they are extremely sensitive. A single delicate touch on the
concave surface of the tip soon caused one to curve; and in 2 minutes
it formed an open helix. A loop of soft thread weighing one thirty-
second of a grain (2.02 mg.) placed most gently on the tip, thrice
caused distinct curvature. A bent bit of thin platina wire weighing
only fiftieth of a grain (1.23 mg.) twice produced the same effect;
but this latter weight, when left suspended, did not suffice to cause
a permanent curvature. These trials were made under a bell-glass, so
that the loops of thread and wire were not agitated by the wind. The
movement after a touch is very rapid: I took hold of the lower part
of several tendrils, and then touched their concave tips with a thin
twig and watched them carefully through a lens; the tips evidently
began to bend after the following intervals--31, 25, 32, 31, 28, 39,
31, and 30 seconds; so that the movement was generally perceptible in
half a minute after a touch; but on one occasion it was distinctly
visible in 25 seconds. One of the tendrils which thus became bent in
31 seconds, had been touched two hours previously and had coiled into
a helix; so that in this interval it had straightened itself and had
perfectly recovered its irritability.

To ascertain how often the same tendril would become curved when
touched, I kept a plant in my study, which from being cooler than the
hot-house was not very favourable for the experiment. The extremity
was gently rubbed four or five times with a thin stick, and this was
done as often as it was observed to have become nearly straight again
after having been in action; and in the course of 54 hrs. it answered
to the stimulus 21 times, becoming each time hooked or spiral. On
the last occasion, however, the movement was very slight, and soon
afterwards permanent spiral contraction commenced. No trials were
made during the night, so that the tendril would perhaps have
answered a greater number of times to the stimulus; though, on the
other hand, from having no rest it might have become exhausted from
so many quickly repeated efforts.

I repeated the experiment made on the Echinocystis, and placed
several plants of this Passiflora so close together, that their
tendrils were repeatedly dragged over each other; but no curvature
ensued. I likewise repeatedly flirted small drops of water from a
brush on many tendrils, and syringed others so violently that the
whole tendril was dashed about, but they never became curved. The
impact from the drops of water was felt far more distinctly on my
hand than that from the loops of thread (weighing one thirty-second
of a grain) when allowed to fall on it from a height, and these
loops, which caused the tendrils to become curved, had been placed
most gently on them. Hence it is clear, that the tendrils either
have become habituated to the touch of other tendrils and drops of
rain, or that they were from the first rendered sensitive only to
prolonged though excessively slight pressure of solid objects, with
the exclusion of that from other tendrils. To show the difference in
the kind of sensitiveness in different plants and likewise to show
the force of the syringe used, I may add that the lightest jet from
it instantly caused the leaves of a Mimosa to close; whereas the loop
of thread weighing one thirty-second of a grain, when rolled into a
ball and placed gently on the glands at the bases of the leaflets of
the Mimosa, caused no action.

Passiflora punctata.--The internodes do not move, but the tendrils
revolve regularly. A half-grown and very sensitive tendril made
three revolutions, opposed to the course of the sun, in 3 hrs. 5 m.,
2 hrs. 40 m. and 2 hrs. 50 m.; perhaps it might have travelled more
quickly when nearly full-grown. A plant was placed in front of a
window, and, as with twining stems, the light accelerated the
movement of the tendril in one direction and retarded it in the
other; the semicircle towards the light being performed in one
instance in 15 m. less time and in a second instance in 20 m. less
time than that required by the semicircle towards the dark end of the
room. Considering the extreme tenuity of these tendrils, the action
of the light on them is remarkable. The tendrils are long, and, as
just stated, very thin, with the tip slightly curved or hooked. The
concave side is extremely sensitive to a touch--even a single touch
causing it to curl inwards; it subsequently straightened itself, and
was again ready to act. A loop of soft thread weighing one
fourteenth of a grain (4.625 mg.) caused the extreme tip to bend;
another time I tried to hang the same little loop on an inclined
tendril, but three times it slid off; yet this extraordinarily slight
degree of friction sufficed to make the tip curl. The tendril,
though so sensitive, does not move very quickly after a touch, no
conspicuous movement being observable until 5 or 10 m. had elapsed.
The convex side of the tip is not sensitive to a touch or to a
suspended loop of thread. On one occasion I observed a tendril
revolving with the convex side of the tip forwards, and in
consequence it was not able to clasp a stick, against which it
scraped; whereas tendrils revolving with the concave side forward,
promptly seize any object in their path.

Passiflora quadrangularis.--This is a very distinct species. The
tendrils are thick, long, and stiff; they are sensitive to a touch
only on the concave surface towards the extremity. When a stick was
placed so that the middle of the tendril came into contact with it,
no curvature ensued. In the hothouse a tendril made two revolutions,
each in 2 hrs. 22 m.; in a cool room one was completed in 3 hrs., and
a second in 4 hrs. The internodes do not revolve; nor do those of
the hybrid P. floribunda.

Tacsonia manicata.--Here again the internodes do not revolve. The
tendrils are moderately thin and long; one made a narrow ellipse in 5
hrs. 20 m., and the next day a broad ellipse in 5 hrs. 7 m. The
extremity being lightly rubbed on the concave surface, became just
perceptibly curved in 7 m., distinctly in 10 m., and hooked in 20 m.

We have seen that the tendrils in the last three families, namely,
the Vitaceae, Sapindaceae and Passifloraceae, are modified flower-
peduncles. This is likewise the case, according to De Candolle (as
quoted by Mohl), with the tendrils of Brunnichia, one of the
Polygonaceae. In two or three species of Modecca, one of the
Papayaceae, the tendrils, as I hear from Prof. Oliver, occasionally
bear flowers and fruit; so that they are axial in their nature.


The Spiral Contraction of Tendrils.


This movement, which shortens the tendrils and renders them elastic,
commences in half a day, or in a day or two after their extremities
have caught some object. There is no such movement in any leaf-
climber, with the exception of an occasional trace of it in the
petioles of Tropaeolum tricolorum. On the other hand, the tendrils
of all tendril-bearing plants, contract spirally after they have
caught an object with the following exceptions. Firstly, Corydalis
claviculata, but then this plant might be called a leaf-climber.
Secondly and thirdly, Bignonia unguis with its close allies, and
Cardiospermum; but their tendrils are so short that their contraction
could hardly occur, and would be quite superfluous. Fourthly, Smilax
aspera offers a more marked exception, as its tendrils are moderately
long. The tendrils of Dicentra, whilst the plant is young, are short
and after attachment only become slightly flexuous; in older plants
they are longer and then they contract spirally. I have seen no
other exceptions to the rule that tendrils, after clasping with their
extremities a support, undergo spiral contraction. When, however,
the tendril of a plant of which the stem is immovably fixed, catches
some fixed object, it does not contract, simply because it cannot;
this, however, rarely occurs. In the common Pea the lateral branches
alone contract, and not the central stem; and with most plants, such
as the Vine, Passiflora, Bryony, the basal portion never forms a
spire.

I have said that in Corydalis claviculata the end of the leaf or
tendril (for this part may be indifferently so called) does not
contract into a spire. The branchlets, however, after they have
wound round thin twigs, become deeply sinuous or zigzag. Moreover
the whole end of the petiole or tendril, if it seizes nothing, bends
after a time abruptly downwards and inwards, showing that its outer
surface has gone on growing after the inner surface has ceased to
grow. That growth is the chief cause of the spiral contraction of
tendrils may be safely admitted, as shown by the recent researches of
H. de Vries. I will, however, add one little fact in support of this
conclusion.

If the short, nearly straight portion of an attached tendril of
Passiflora gracilis, (and, as I believe, of other tendrils,) between
the opposed spires, be examined, it will be found to be transversely
wrinkled in a conspicuous manner on the outside; and this would
naturally follow if the outer side had grown more than the inner
side, this part being at the same time forcibly prevented from
becoming curved. So again the whole outer surface of a spirally
wound tendril becomes wrinkled if it be pulled straight.
Nevertheless, as the contraction travels from the extremity of a
tendril, after it has been stimulated by contact with a support, down
to the base, I cannot avoid doubting, from reasons presently to be
given, whether the whole effect ought to be attributed to growth. An
unattached tendril rolls itself up into a flat helix, as in the case
of Cardiospermum, if the contraction commences at the extremity and
is quite regular; but if the continued growth of the outer surface is
a little lateral, or if the process begins near the base, the
terminal portion cannot be rolled up within the basal portion, and
the tendril then forms a more or less open spire. A similar result
follows if the extremity has caught some object, and is thus held
fast.

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