On the movements and habits of climbing plants

ON THE

MOVEMENTS AND HABITS

OF

CLIMBING PLANTS.

BY

CHARLES DARWIN, Ese., F.R.S., F.LS. evc.
gE OLOGICAL Slips

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| From the JourNAL oF THE LinNEAN Society. |

LONDON:
SOLD AT THE SOCIETY’S APARTMENTS, BURLINGTON HOUSE;
AND BY
LONGMAN, GREEN, LONGMAN, ROBERTS & GREEN,
: AND

WILLIAMS AND NORGATE.
1865.

ON THE

MOVEMENTS AND HABITS

OF

OL IMSI ye faa NTS.

TABLE OF CONTENTS.

PAGE PAGE

Introductiony «wea wee es Part IIT.—TENDRIL-BEARERS.
Part I.—SPrRaLLy TWINING PLANTS. | Bignoniacer . . . . . + - 49
Axial twisting . . Stee 5 | Polemoniacéew ss. «44 Ree oO
Nature of the revolving movement 7 ORION? ee 6B
Purpose of the revolving move- ONION ee Sw b. SBT
ment, and manner of the spiral ie Oe ke ee OO
ascent . 7 o ebumermeee se fk TO
Table of the rates of revolution . 14 | Oucurbitacee. ..... . 78
Anomalous revolvers . . 21 | Vitacese . aes « Wa
Variations in the power of twining 24 | Sapindaces’*) 4° “ot te OT
Passifloracer . - 89

4 -CLID .
Cl ae 8 26 Spiral contraction of tendrils . - 92
si Pgh Bag een Summary of the nature and ac-

Troprmoluin..- 5 + eens “So OA . -
Antimrhines® ss 6 wa we ee co sinless sl inattatiti

1 Ee

Soli esse aa ee is ash
ae oS ee CLIMBERS ; CONCLUDING REMARKS.
Gloriosa ° 40-1 thook-climbers =. 0°.’ <°'s 4 105
Flagellaria . soe «© « .° 46.| Root-climbers. olen: LOG
Nepenthes . . : - 46 | Concluding remarks on Climbing-

Summary on Leaf-climbers . . Sf | “i PS a gee

I was led to this subject by an interesting, but too short, paper
by Professor Asa Gray on the movements of the tendrils of some
Cucurbitaceous plants*. My observations were more than half
completed before I became aware 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 yon Mohlf, and had subsequently been the subject of two

* Proc. Amer. Acad. of Arts and Sciences, vol. iy. Aug. 12, 1858, p. 98.
t Ludwig H. Palm, Ueber das Winden der Pflanzen ; Hugo von Mohl, Ueber
den Bau and das Winden der Ranken und Sellinepflanzen, 1827. Palm’s

B

2 MR. DARWIN ON CLIMBING PLANTS.

memoirs by Dutrochet*. Nevertheless I believe that my obser-
vations, founded on the close examination of above a hundred
widely distinct living plants, contain sufficient novelty to justify
me in laying them before the Society.

Climbing plants may be conveniently divided into those which
spirally twine round a support, those which ascend by the move-
ment of the foot-stalks or tips of their leaves, and those which
ascend by true tendrils,—these tendrils being either modified
leaves or flower-peduncles, or perhaps branches. But these sub-
divisions, as we shall see, nearly all graduate into each other.
There are two other distinct classes of climbing-plants, namely
those furnished with hooks and those with rootlets; but, as such
plants exhibit no special movements, we are but little concerned
with them ; and generally, when I speak of climbing plants, I refer
exclusively to the first great class.

Part 1—SprraLiy TWINING PLants.

This is the largest subdivision, and is apparently the primor-
dial 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 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 obser-
vatlons 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 was 2h. 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
grows old, ceases to move.

To ascertain more precisely what amount of movement each in-
ternode underwent, I kept a potted plant in a well-warmed room
to which I was confined during the night and day. A long in-
clined shoot projected beyond the upper end of the supporting

Treatise was published only a few weeks before Mohl’s. See also ‘The Vege-
table Cell’ (translated by Henfrey), by H. von Mohl, p. 147 to end.

* Des Mouyements révolutifs spontanés,” &e., ‘ Comptes Rendus,’ tom. xvii.
(1843) p. 989; ‘Recherches sur la Volubilité des Tiges,” &c., tom. xix. (1844)
p. 295,

SPIRAL TWINERS. 3

stick, and was steadily revolving. I then took a longer stick and
tied up the shoot, so that only a very young internode, 1? 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 be-
came concave, which, as we shall hereafter sce, is a sure sign of
the revolving movement. I will assume that it made at least one
revolution during the first twenty-four hours. arly the next
morning its position was marked, and it made the second revolu-
tion in 9h.; during the latter part of this revolution it moved much
quicker, and the third circle was performed in the evening in a
little over 3h. As on the succeeding morning I found that the
shoot revolved in 2h. 45 m., it must have made during the night
four revolutions, each at the average rate of a little over 3h. I
should add that the temperature of the room varied only a little.
The shoot had now grown 84 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 in2h. 80m. 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
quite completed ; for the internode abruptly became upright, and,
after moving to the centre, remained motionless. I tied a weight
to its upper end, so as to slightly bow it, and thus to detect any
movement; but there was none. Some time before the last revo-
lution the lower part of the internode had ceased to move.

A few more remarks will complete all that need be said on this
one internode. It moved during five days; but the more rapid
movement after the third revolution lasted during three days and
twenty hours. The regular revolutions, from the ninth to thirty-
sixth inclusive, were performed at the average rate of 2h. 31m.: the
weather was cold; and this affected the temperature of the room,
especially during the night, and consequently retarded a little
the rate of movement. There was only one irregular movement,
when a segment of a circle was rapidly performed (not counted in
the above enumeration) ; and this occurred after an unusually slow
revolution of 2h. 49m. After the seventeenth reyolution the inter-
node had grown from 14 to 6 inches in length, and carried an inter-
node 14 inch long, which was just perceptibly moving; and this
carried a very minute ultimate internode. After the twenty-first
revolution, the penultimate internode was 23 inches long, and
probably revolved in a period of about three hours. At the:

B2

4, MR. DARWIN ON CLIMBING PLANTS.

twenty-seventh revolution our lower internode was 83, the penul-
timate 34, and ultimate 23 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 inter-
node was 9 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 continued to grow unsupported,
it became nearly horizontal, the uppermost and growing inter-
nodes still revolving at the extremity, but of course no longer
round the old central point of the supporting stick. J'rom the
change in the position of the centre of gravity of the revolving
extremity, a slight and slow swaying movement was given to the
long and horizontally projecting shoot, which I mistook at first
for a spontaneous movement. As the shoot grew, it depended
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 revolved; so
that by the time one had ceased, that above it was in full action,
with a terminal internode just commencing to revolve. With
Hoya carnosa, on the other hand, a depending shoot, 32 inches in
length, without any developed leaves, and consisting of seven in-
ternodes (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 inter-
nodes, 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 5h. 15m. and 6h. 45 m. for each revolution. Hence, as
the extreme tip made a circle of above 5 feet (or 62 inches) in dia-
meter and 16 feet in circumference, the tip travelled at the rate
(assuming the circuit to have been completed in six hours) 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

4
SPIRAL TWINERS. vo

spectacle to watch the long shoot sweeping, night and day, this
grand circle in search of some object round which to twine.
If we take hold of a growing sapling, we can of course bend it
so as to make its tip describe a circle, like that performed by the
tip 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
revolying 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 Convolvyulus, which revolves in an op-
posite course to the Hop, becomes twisted in an opposite direction.
Hence it is not surprising that Hugo von Mohl (S. 105, 108,
&c.) thought that the twisting of the axis caused the revolving
movement. I cannot fully understand how the one movement is
supposed to cause the other; but it is scarcely possible that the
twisting of the axis of the Hop three times could have caused
thirty-seven revolutions. Moreover, the revolving movement
commenced in the young internode before any twisting of the
axis could be detected ; and the internode of a young Siphomeris
or Lecontea revolved during several days, and became twisted
only once on its own axis. But the best evidence that the
twisting does not cause the revolving movement is afforded by
many leaf-climbing and tendril-bearing plants (as Piswm 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 regularly twisted,
but which regularly perform, as we shall hereafter sce, revolvin g
movements like those of true twining-plants. Moreover, accord-
ing to Palm (S. 30,95) and Mohl (S. 149), and Léon*, internodes
may occasionally, and even not yery rarely, be found which are
* Bull. Bot, Soc. de France, tom. y. 1858, p. 356.

6 MR, DARWIN ON CLIMBING PLANTS,

twisted in an opposite direction to the other internodes on the
same plant, and to the course of revolution; and this, according
to Léon (p. 356), is the case with all the internodes of a variety
of the Phaseolus multiflorus. Internodes which have become
twisted round their own axes, if they have not ceased revolving,
are still capable of twining, as I have several times observed.

Mohl has remarked (S. 111) that when a stem twines round a
smooth cylindrical stick, it does not become twisted. 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 the 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 were fixed in split
sticks below, and were secured above to cross sticks, and the stems
in passing these places became very 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 ap-
parently occurred more quickly during windy weather. Several
other facts could be given, showing that the axial twisting stands
in 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*; 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 most probable view, as it seems to me, is that the stem twists
itself to gain rigidity (on the same principle that a much twisted
rope is stiffer than a slackly twisted one), so as to be enabled
either to pass over inequalities in its spiral ascent, or to carry its
own weight when allowed to revolve freely t.

* Professor Asa Gray has remarked to me, in a letter, that in Thuja oeciden-
talis the twisting of the bark is very conspicuous. The twist is generally to
the right of the observer; but, in noticing about a hundred trunks, four or five
were observed to be twisted in an opposite direction.

+ It is well known that stems of many plants occasionally become spirally
twisted in a monstrous manner; and since the reading of this paper, Dr.
Maxwell Masters has remarked to me in a letter that “some of these cases, if
not all, are dependent upon some obstacle or resistance to their upward growth.”
This conclusion agrees with, and perhaps explains, the normal axial twisting of
twining-plants ; but does not preclude the twisting being of service to the plant
and giving greater rigidity to the stem,

SPIRAL TWINERS. Pf

I havo just alluded to the twisting which necessarily follows
from the spiral ascent of the stem, namely, one twist for each
spire completed. This was well shown by painting straight lines
on 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.

I have already compared the revolving movement of a twining
plant to that of the tip of a sapling, moved round and round by
the hand held some way down the stem; but there is a most im-
portant difference. The upper part of the sapling moves as a
rigid body, and remains straight; but with twining plants every
inch 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 quietly tied to a stick, the
upper free part steadily continues revolving: even if the whole
shoot, except the terminal tip of an inch or two in length, be tied
up, this tip, as I have seen in the case of the Hop, Ceropegia,
Conyolvulus, &¢., 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 revolying 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 line of surface, this coloured streak will after a time (de-
pending on the rate of revolution) be found to lie along one side
of the bow, then along the concave side, then on the opposite side,
and, lastly, again on the original convex surface. This clearly
proves that the internodes, during the revolving movement, be-
come bowed in every direction. ‘The movement is, in fact, a con-
tinuous self-bowing of the whole shoot, successively directed to
all points of the compass.

As this movement is rather difficult to understand, it will be
well to give an illustration. Let us take the tip of a sapling and
bend it to the south, and paint a black line on the convex surface ;
then let the sapling spring up and bend it to the east, the black
line will then be seen on the lateral face (fronting the north) of
the shoot; bend it to the north, the black line will be on the
concave surface; bend it to the west, the line will be on the
southern lateral face; and when again bent to the south, the line
will again be on the original convex surface. Now, instead of
bending the sapling, let us suppose that the cells on its whole
southern surface were to contract from the base to the tip, the

.whole shoot would be bowed to the south; and let the longi-

8 MR. DARWIN ON CLIMBING PLANTS,

tudinal contracting surface slowly creep round the shoot, desert-
ing by slow degrees the southern side and encroaching on the
eastern side, and so round by the north, by the west, again to the
south; in this case the shoot would remain always bowed with
the painted line appearing on the convex, on the lateral, and con-
cave surfaces, and with the point of the shoot successively di-
rected to all points of the compass. In fact, we should then have
the exact kind of movement seen in the revolving shoots of twi-
ning plants. I have spoken in the illustration, for brevity’s sake,
of the cells along each face successively contracting ; of course
turgescence of the cells on the opposite face, or both forces com-
bined, would do equally well.

It must not be supposed that the revolving movement of twi-
ning plants is as regular as that given in this 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
the southern and then the northern face of the sapling to con-
tract, the summit would describe a simple arc; if the contraction
first travelled a very little to the eastern face, and during the
return avery little to the western face, a narrow ellipse would be
described; and the sapling would become straight as it passed to
and fro by the central point. A complete straightening of the
shoot may often be observed in revolving plants; but the weight
of the shoot apparently interferes with the regularity of the
movement, and with the place of straitening. The movement is
often (in appearance at least) as if the southern, eastern, and
northern faces had contracted, but not the western face; so that
a semicircle is described, and the shoot becomes straight and up-
right in one part of its course.

When a revolving shoot consists of several internodes, the
several lower ones bend together at the same rate, but the one
or two terminal internodes bend at a slower rate; hence, though
at times all the internodes may be bowed in the same line, at
other times the shoot is rendered slightly serpentine, as I have
often observed. The rate of revolution of the whole shoot, if
judged by the movement of the extreme tip, is thus at times
accelerated and 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 Asclepiadaces. The hooked tip, in all the cases which
I observed, viz. in Ceropegia, Spherostema, Clerodendron, Wis-
taria, Stephania, Akebia, and Siphomeris, has exactly the same kind
of moyement as the other revolving internodes ; for a line painted

SPIRAL TWINERS. 9

on the convex surface becomes lateral and then concave; but,
owing to the youth of these terminal internodes, the reversal of
the hook is a slower process than the revolving movement. ‘This
strongly marked tendency in the young terminal and flexible in-
ternodes to bend 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 much more closely its support than it otherwise could
have done, and thus aids in preventing the stem from being
blown away from it during windy weather, as I have many times
observed. In Lonicera brachypoda the hook only straightened
itself periodically, and never became reversed. I will not assert
that the tips of all twining plants, when hooked, move as above
described; for this position may in some cases be due to the
manner of growth, as with the bent tips of the shoots of the com-
mon vine, and more plainly with those of Cissus discolor; these
plants, however, are not spiral twiners.

The purpose of the spontaneous revolving movement, or, more
strictly speaking, of the continuous bending movement succes-
sively directed to all points of the compass, is, as Mohl has re-
marked, obviously in part to favour the shoot finding a support.
This is admirably effected by the revolutions carried on night and
day, with a wider and wider circle swept as the shoot increases in
length. But as we now understand the nature of the movement,
we can see that, when at last the shoot meets with a support, the
motion at the point of contact is necessarily arrested, but the free
projecting part goes on revolving. Almost immediately another
and upper point of the shoot is brought into contact with the sup-
port and is arrested ; and so onwards to the extremity of the shoot ;
and thus it winds round its support. When the shoot follows the
sun in its revolving course, it winds itself 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 loses its power of spirally twining round a
support. Ifa 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 rope ; so it is with twining plants, the continued contrac-
tion or turgescence of the cells along the free part of the shoot
replacing the momentum of each atom of the free end of the rope.

All the authors, except Von Mohl, who haye discussed the

10 MR. DARWIN ON CLIMBING PLANTS.

spiral twining of plants maintain that such plants have a natural
tendency to grow spirally. Mohl believes (S, 112) that twining
stems have a dull kind of irritability, so that they bend towards
any object which they touch. Even before reading Mohl’s in-
teresting treatise, this view seemed to me so probable that I
tested it in every way that I could, but always with negative
results. I rubbed many shoots much harder than is necessary to
excite movement in any tendril or in any foot-stalk of a lJeaf-
climber, but without result. I then tied avery light forked twig
to a shoot of a Hop, a Ceropegia, Spherostema, and Adhatoda,
so that the fork pressed on one side alone of the shoot and re-
volved with it; I purposely selected some very slow revolvers, as
it seemed most likely that these would profit from possessing irri-
tability; but im no case was any effect produced. Moreover,
when a shoot winds round a support, the movement is always
slower, as we shall immediately see, than whilst its 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
be 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, Lophospermwm scandens is, as we shall here-
after see, certainly irritable; but this case gives me confidence
that ordinary twiners do not possess this quality, for directly after
putting a stick to the Lophospermum, I saw that it behaved
differently from any true twiner or any other leaf-climber.

The belief that twiners have a natural tendency to grow spirally
probably arose from their assuming this form when wound round
a support, and from the extremity, even whilst remaining free,
sometimes assuming this same form. The free internodes of
vigorously growing plants, when they cease to revolve, become
straight, and show no tendency to be spiral; but when any 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 degree with the ends of the shoots of the Stauntonia
and of the allied Akebia, which became closely wound up spirally,
just like a tendril, especially after the small, ill-formed leaves had
perished. The explanation of this fact is, I believe, that the
lower parts of such 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.

SPIRAL TWINERS. i

When a revolving shoot strikes a stick, it winds round it rather
more slowly than it revolves. or instance, a shoot of the Cero-
pegia took 9h, 80m. to make one complete spire round a stick,
whilst it revolved in 6h.; Aristolochia gigas revolved in about 5h.,
but took 9h. 15 m. to complete its spire. This, I presume, is due to
the continued disturbance of the moving force by its arrestment
at each successive point; we shall hereafter see that even shaking
a plant retards the revolying movement. The terminal internodes
of a long, much-inelined, 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
evidently 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 in a very close spire, which
remained unchanged; but subsequently, as the shoot grew, 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, well
served to keep the shoots in contact with their support; but as
the penultimate internodes grew in length, they pushed them-
selves 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.

It follows from this latter fact that the position occupied by
each leaf with respect to the support, in fact, 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
(S. 34), who states that the opposite leaves of the Hop always
stand exactly over each other, in a row, on the same side of the
supporting stick, though this may differ in thickness. My sons
visited a hop-field for me, and reported that though they gene-
rally found the points of insertion of the leaves over each other
for a space of two or three feet in height, yet this never occurred
up the whole length of a pole, the point 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. rom casual inspection, it appeared to me that the op-
posite leaves of Thunbergia alata were arranged in a line up the
sticks round which they had twined; accordingly I raised a
dozen plants, and gaye them sticks of various thicknesses and
string to twine round; and in this case one alone out of the

12 MR. DARWIN ON CLIMBING PLANTS.

dozen had its leaves arranged in a perpendicular line: so I con-
clude that there is nothing remarkable in Palm’s statement.

The leaves of twining-plants rise from the stem (before it has
twined) either alternately, or oppositely, or in a spire; in this
latter case the line of insertion of the leaves and the course of
revolution or of twining coincide. This fact has been well shown
by Dutrochet *, who found different individuals of Solanum Dul-
camara twining in opposite directions, and these had their leaves
spirally arranged in opposite directions. A dense whorl of many
leaves would apparently be incommodious: for a twining plant,
and some authors have supposed that none have their leaves
thus arranged; but a twining Siphomeris has whorls of three.

If a stick which has arrested a revolving shoot, but has not as
yet been wound round, be suddenly taken away, the shoot gene-
rally springs forward, showing that it has continued to press
against the stick. If the stick, shortly after having been wound
round, be withdrawn, the shoot retains for a time its spiral form,
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 inter-
nodes, which continued to revolve, had become so stiff that they
were incapable, on repeated trials, of twining round a thin stick,
showing that the power of movement was retained after flexi-
bility had been lost. I then moved the stick to a greater dis-
tance, so that it was struck by a point 23 inches from the extre-
mity of the penultimate internode ; and it was then neatly wound
round by this part 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 part 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 the lower
part of this internode had likewise recovered its revolving power.
These several facts show that, in the arrested portion of a re-
volving shoot, the power of movement is not immediately lost,
and that when temporarily lost it can be recovered. When a
shoot has remained for a considerable time wound round its
support, it permanently retains its spiral form even when the
support is removed.

* Comptes Rendus, 1844, tom. xix. p. 295, and Annales des Soc. Nat.
3rd series, Bot., tom. ii. p. 163.

SPIRAT, TWINERS. n B33

When a stick was placed so as to arrest the lower and rigid
internodes of the Oeropegia at the distance at first of 15 and
then of 21 inches from the centre of revolution, the shoot slowly
and gradually slid up the stick, so as to become more and more
highly inclined; and then, after an interval sufficient to have al-
lowed of a semirevolution, it suddenly bounded from the stick
and fell over to the opposite side, to its ordinary slight inclina-
tion. It now recommenced revolving in its usual course, so that
after a semirevolution it again came into contact with the stick,
again slid up it, and again bounded from it. This movement
of the shoot had a very odd appearance, as if it were disgusted
with its failure but resolved to try again. We shall, I think,
understand this movement by considering the former illustration
of the sapling, in which the contracting surface was supposed to
creep from the southern, by the eastern, to the northern, and
thence back again by the western side to the southern face, suc-
cessively bowing the sapling in all directions. Now with the
Ceropegia, the stick being placed a very little to the east of due
south of the plant, the eastern contraction could produce no
effect beyond pressing the rigid internode against the stick; but
as soon as the contraction on the northern face began, it would
slowly drag the shoot up the stick; and then, as soon as the
western contraction had well begun, the shoot would be drawn
from the stick, and its weight, coinciding with the north-western
contraction, would cause it suddenly to fall to the opposite side
with its proper slightly inclined positions; and the ordinary
revolving moyement would go on. I haye described this case
because it first made me understand the order in which the con-
tracting or turgescent cells of revolving shoots must act.

The view just given further explains, as I believe, a fact ob-
served by Von Mohl (S. 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 they could not, though aided by me in many ways, wind
round it, This apparently is owing to the flexure of the shoot,
when winding round an object so gently curved as this post, not
being sufficient to hold the shoot to its place when the con-
tracting force creeps round to the opposite surface of the shoot ;
so that it is at each revolution withdrawn from its support.

When a shoot has grown far beyond its support, it sinks down-
wards from its weight, as already explained in the case of the

14 MR. DARWIN ON CLIMBING PLANTS.

Hop, with the revolving end always turning upwards. If the
support be not lofty, it falls to the ground, and, resting there, the
extremity rises again. Sometimes several shoots, when flexible,
twine together into a cable, and thus support each other. Single
thin depending shoots, such as those of the Sollya Drummondii,
will turn abruptly back and wind upwards 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 Oryptostegia grandiflora,
several internodes which at first were flexible and revolved, if
they did not succeed in twining round a support, became quite
rigid, and, supporting themselves upright, carried on their summit
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 to show that all kinds behave
in a nearly uniform manner*.

Twining plants not aided by tendrils or by irritable leaf-stalks.

(AcoryLEepons.)
Lygodium scandens (Polypodiacer) moves against the sun.
h, m. h. m.
June 18, Ist circle6 0 [ing). | June 19, 4th circle 5 0 (very hot day).
3» 18,2nd ,, 615 (late in even-| ,, 20,5th ,, 6 0
3 19,8rd ,, 5 32 (very hot day).

Lygodium articulatum moves against the sun.

h. m. h. m,
July 19, 1st circle 16 30 (shoot very July 21, 3rd cirele ...... 8 “0
» 20,2nd ,, 15 0 [young). ilk ABR ow ans 3 10 30
(MonocoryiEpons.)
Ruscus androgynus (Liliacew), placed in the hot-house, moves against the sun.
h. m. h. m.
May 24, Ist circle 6 14 (shoot very May 26, 5th cirele...... 2 50
» 26,2nd ,, 221 [young). ef gk hs Se ae 8 52
ye 25;. 8rd 53-8. 87 BT TA of tsi ss 4 11
» 25,4th ,, 8 22

aati ee

* Tam much indebted to Dr. Hooker for having sent me many plants from
Kew; and to Mr. Veitch, of the Royal Exotic Nursery, for having generously
given me a large collection of fine specimens of climbing plants. Professor Asa
Gray, Prof, Oliver, and Dr. Hooker have afforded me, as on many previous
occasions, much information and many valuable references,

SPIRAL TWINERS. 15

(Monocoryriupons, continued.)
Asparagus (unnamed species from Kew) (Liliacew) moves against the sun,

placed in hothouse. i iii.
Decor 26; Ist circle aici ti divccaivei 5 0
POA OOM se agers aegy uae apeanke 5 40

Tamus communis (Dioscoreacere). A young shoot from a potted tuber placed
in the greenhouse; follows the sun.

h. m. h. m.
July 7, Ist circle ...... 810 July 8, 4th circle ...... 2 56
5° 4, one Spa 2 38 pee TOs ER ee es tea nas 2 30
sy. S&S) SEA: ay ee 35 an 2 30
Lapagerea rosea (Philesiacese), in greenhouse, follows the sun.
h. m.
March 9, Ist circle ...... 26 15 (shoot young).
», LO, semicircle ...... 8 15
3 LA; 2nd crcle ai LO
5 BE Br 55 RS 15 30
ER Mite © yo Ts ose 14.15
go Sa DEL coreg ene 8 40 when placed in the hothouse; but the

next day the shoot remained stationary.

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

(DicoryLepons.)

Humulus Inpulus (Urticacese) follows the sun.

h. m. Ms: ts

April 9, 2 circles © .. cv. 416 August 14, 6th circle...... eee

Aug. 18, 3rd circle ...... QrcQ | aye NR a Sa 2 0

eg a AGE SSS ete 2 20 4 HAE BD oy ar 2 4
i A the ae 2 16 |

A plant placed in a room ; a semicircle was performed in travelling from the
light in 1h. 33 m., in travelling to the light in 1h. 13 m.: difference of rate 20m.

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

h, m. h. m.
March 17, 1st circle 4 0 (shoot March 18, 3rd circle ...... 1 30
», 18,2nd ,, 1 40 [young). oF. ci Op AR we Byes aes 1 45

Stauntonia latifolia (Lardizabalacese), placed in hothouse, moves against

the sun. h. m.
March 28, Ist circle... .......0.... erste 8 30
PAS 1 Sage rc 8 45

Spherostema marmoratum (Schizandraces) follows the sun.
August 5th, 1st circle in about 24h.; 2nd circle in 18h. 80 m.

Stephania rotunda (Menispermaces) moves against the sun.

: hk. m. RB, i;
May 27, Ist circle ...... 5 5 June 2, 8rd circle ...... 5 15
Bi Oy AO. 5 ois 76 iy By. 4th -,, — ities B28

16 MR. DARWIN ON CLIMBING-PLANTS.

(DicoryLEepons, continued.)

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

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

Sollya Drummondii (Pittosporacese) moves against the sun; in greenhouse.

h. m. h. m,
April 4, Ist circle 4 25 [day.) April 6, 3rd circle...... 6 25
» 5,2nd ,, 8 O (very cold if. ROS owl 7%

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

Wistaria Chinensis (Leguminose), in greenhouse, moves against the sun.

h. m. h, m.
May 13, Ist circle...... 3 5 May 24, 4th cirele..,.., 8 21
BONG ge ire 3 20 se .2by bth eee 2 37
pe kG BUG: 95 wus 2 5 jp BD: Ctl a5 ereetin 2 35
Phaseolus vulgaris (Leguminose), in greenhouse, moves against the sun.
h. m,
May; 156 SHBG acarrvissece aver 2 0
9 BE gg Porcine wan 1 55
9 B20 ny endian imines 1 55
Dipladenia urophylla (Apocynacee) moyes against the sun.
h. m.
p18, Ist crrolodtowviervese ver sex.- Oy O
ee DORI NOE 8 ae Nivivivtessvise > 9 LD

es Sr oe iiiiiiiecn ns 9°40

Dipladenia crassinoda moves against the sun.

h. m.
May 16, Ist ‘circle ive catwe OO
July 20; 2nd? —5> > caehepeeeerte tee 8 0

» 21, 8rd gg: remind) 886

Ceropegia Gardnerii (Asclepiadacer) moves against the sun.
h.m.
Shoot very young, 2 inches in length. 1st circle in 7 55

RecOv seul reette peo PN Sind. ng
SRO DOUG se nw See, ce 4 8s. BL ice Cop.
SeBRERNOUU < yo oe kee ee 4 OAS
Bee BHOO ea eo ee OE » 645

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

SPIRAL TWINERS. 17

(DicoryLEpons, continued.)
Hoya carnosa (Asclepiadacere) made several circles in from 16h. to 22h.
or 24h.
Convoloulus major (Convolvyulacese) moves against the sun.
room with lateral light. : — lil gs Pet tit
: emicirele, from light in . 14m, g
Ist circle... 2h. 42m. RISA dite id mn.

Semicircle, from light in lh. 17m., to light
Lh. 30m.: difference 13 m.

Plant placed in

2nd circle... 2h. 47m.

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

Ipomea jucunda (Convolvulacese) moves against the sun, placed in my study,
with windows facing the north-east. Weather hot.
“Semicirele, from light in 4h. 30m., to light

ircle 5h. 3 pagers
Et ee ee lh. Om.: difference 3h. 30m.

PE a ee com: | Semi from light in 3h. 50m., to light

in afternoon: circle com- g
pleted at 6 m, 40 h. P.4.) Lh. 80m.: difference 2h. 20 m.

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

Rivea tiliefolia (Conyolyulacese) moves against the sun, and made four revo-
lutions in 9h.; so that each, on average, was performed in 2h. 15 m.

Plumbago rosea (Plumbaginacee) follows the sun. The shoot did not begin
to revolve until nearly a yard in height ; it then made a fine circle in 10h. 45 m.
During the next few days it continued to move, but irregularly. On August 15th
the shoot followed, during a period of 10h. 40m., a long and deeply zigzag course
and then made a broad ellipse. The figure thus traced altogether apparently
represented three ellipses, each of which averaged 3h. 33 m. for its completion.

Jasminum pauciflorum, Bentham (Jasminacee), moves against the sun. First
circle in 7h. 15 m., second circle rather more quickly.

Clerodendrum Thomsonii (Verbenacee) follows the sun.

April 12, 1st circle .,.... 3 45 (shoot very young).
a5. UA na ee 3 30
», 18, semicircle ...... 5 0O (directly after the plant was shaken in
» 19, 8rd circle ...... 3 0 [being moved).
op MB aera” 1s digs 4 20

Tecoma jasminoides (Bignoniacer) moves against sun.

h. m. h. m.
March 17, 1st circle 6 30 | March 22, 8rd circle 8 30 (very cold
Me, » 24,4th ,, 645 [day).

Thunbergia alata (Acanthacese) moves against sun.

h, m.
April 18, 3rd circle 2 55 [noon).
» 18,4th ,, 3 55 (late in alter-

j h, m.
April 14, 1st circle 3 20
3 Send ».,, 250

Adhadota cydonefolia (Acanthacee) follows the sun. A young shoot made
C

18 MR. DARWIN ON CLIMBING PLANTS.

(DicoryLEvons, continued.)

asemicircle in 24h.; subsequently made a circle in between 40 h, and 48 h.; sub-
sequently did not complete a circle in 50h. Another shoot, however, made a

circle in 26 h. 30 m.
Mikania scandens (Composite) moves against the sun.

h. m.

March 14, Ist circle 3 10
erie ae
ple, bed 80

ee kt, aa sO Oe

April 7, 5th ,, 250 ¥. ; ee es
‘his ci e after a copious in 10
a 7,6th , 2 404 This circle was ma a cop ntiona

watering with cold water at 47° Fahr.

Combretum argenteum (Combretaces) moves against the sun.

. h. M: F Harly inmorning,when the tempera-

Jan, 24, Ist circle...... ines 2 55 a ee non had fallen a little.
» 24, 2 circles, each at an) 2 20
average of ............ 2 20
5) D5 SUNPOMNOID, re astsoas ss 2 25

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

Loasa aurantiaca (Loasacee). First plant moved against the sun,

h. m. h. m,
June 20, 1st circle...... 2 37 June 21, 4th circle...... 2 35
Sy MAO WATS Bh 2 13 oe AOD Oth) aes 8 26
ee ota 6 en 2 4 0 ie OE OWNS a ececen 3 5
Second plant followed the sun. WA:
July 11, Ist circle............ 1 51
70 Tp Ant & ak Geiccne: 1 46 3
5 Dpard? get awnl as t ae ee
i Mphthi? jecstend a 1 48
OE. yo nat am ey 2 35 Cool morning.
Scyphanthus elegans (Loasaceg) follows the sun.
h., m. h, m.
June 18, Ist circle...... 1 45 June 14, 4th circle...... 1 59
3p LOy AO Se eee ipa, Be rd Ae ODN teat gigas 2 8
3 14, ord ee 1 36
Siphomeris or Lecontea (unnamed sp.) (Cinchonacee) follows the sun.
h. m,
May 25, semicircle ......... 10 27 (shoot extremely young).
Wi 20} 180. CINGIO-. <iever, 10 15 (shoot still young).
3 80; 2nd" i eae 8 55
vues SIO: ho ee, 8 11
pe reribipe Ver he ore 6 8
SOs OU ek Ten ce Sa 7 20 | Taken from the hothouse and placed
Wee POUR 55 2-255 -ba 55s 8 36J ina room in my house.
Manettia bicolor (Cinchonacese), young plant, follows the’ sun,
h. m.
Bdly Slaviavdle.ccisa dead 6 18
gels 7416 Uae SUA ene eee co 6 53

SPIRAL TWINERS, 19
(DicorynEpons, continued.)
Lonicera brachypoda (Caprifoliacee) follows the sun, in a warm room in

the house.

h. m.
April, 1st circle about 9 10
3,0 gs », 12 20 (another shoot very young).

5 Or yy i bak om
In this latter circle, the semicircle from the

95. At Bice ato of light took 5h, 23m., and to the light
2h. 87m.: difference 2h. 46 m.

Aristolochia gigas (Aristolochiacee) moves against the sun.

h. m.
July 22, 1st circle......... 8 0 (rather young shoot).
Se eS eaters 715 .
ay PAP ORO By eet cease 5 0 (about). —

In the foregoing table, which includes twining plants belonging
to as widely different orders as is possible, we see that the con-
traction or turgescence of the cells circulating round the axis, on
which the revolving movement depends, differs muchin rate. As
long as a plant remains under the same conditions, the rate is
often remarkably uniform, as we see with the Hop, Aikania,
Phaseolus, &c. The Scyphanthus made one revolution in 1h. 17m.,
and this is the quickest rate observed; but we shall afterwards
see a tendril-bearing Passiflora revolving even more rapidly. A
shoot of the Akebia quinata made a revolution in 1h. 30m., and
three revolutions at the average rate of Lh. 88m.; a Convolyulus
made two revolutions at the average of 1h. 42 m., and Phaseolus
vulgaris three at the average of 1h.57m. On the other hand, some
plants take 24h. for a single revolution, and the Adhadota some-
times required 48h.; 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 slower than the
thick and fleshy shoots of the Ruseus, which seems so little fitted
for movement of any kind; the shoots of the Wistaria, which be-
come woody, move faster than those of the Jpomea or Phunbergia.

We know that the internodes, whilst very young, do not ac-
quire their proper rate of movement ; hence 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 perennial root-stock, do not
move; these first-formed shoots can support themselves, and
nothing superfluous is granted them.

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

c2

20 MR. DARWIN ON CLIMBING PLANTS.

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 (S. 125) gives a case in the Leguminose, and we have in
the table another in the Acanthacer. At present no instance is
known of two species of the same genus twining in opposite di-
rections; and this is a singular fact, because different individuals
of Solanum dulcamara (Dutrochet, tom. xix. p. 299) revolve and
twine in both directions: this plant, however, is a most feeble
twiner. Loasa aurantiaca (Léon, p. 351) offers a much more
striking 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 re.
volved and twined first in one direction, and then reversed their
course*, the petioles of the opposite leaves affording a point
@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. These individuals of the Zoasa are interesting, as
showing how almost every change is effected most gradually,
For another plant in the same family, the Scyphanthus elegans,
habitually twines in this 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.
Tt could hardly occur with any plant which ascended above a few
feet in height, or which lived in an exposed situation; for the
stem could be easily pulled from its support with little unwinding ;
nor could it have adhered at all, had not the internodes soon be-
come 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 petioles.

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 Ipomea jucunda; but frequently with Hib-
bertia dentata. This plant at first much perplexed me, for I con-
tinually observed its long and flexible shoots, evidently well fitted
for twining, make a whole or half or quarter circle in one direction

* T raised nine plants of the hybrid Loasa Herbertii, and six of these re-
versed their spire in ascending their supports.

SPIRAL TWINERS. 21

and then in the opposite direction; consequently, when I placed
the shoots near thin or thick sticks, or stretched string, they
seemed perpetually to be trying to ascend these supports, but
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 sel-
dom turned upwards as is usual with twining plants. Finally,
I surrounded another plant with many thin upright sticks, and
placed this plant near the other plant with the twigs; and now
the Hibbertia had got what it liked, for it twined up the parallel
sticks, sometimes winding round one and sometimes round several ;
and the shoots travelled laterally from one to the other plant ;
but as the plants grew older, some of the shoots twined regularly
up a thin upright stick. Though the revolving movement was
sometimes in one direction and sometimes in the other, the twi-
ning was invariably from left to right; so that the more potent
or persistent movement of revolution must have been in oppo-
sition to the course of the sun. It would appear that this H7b-
bertia is adapted to ascend by twining, and to ramble laterally over
the thick Australian scrub.

I have described this case in some detail, because, as far as I
have seen, it is rare to find with twining plants any especial
adaptations, in which respect they differ much from the more
highly organized tendril-bearers. The Solanwm dulcamara, as we
shall presently see, can twine only round such stems as are both
thin and flexible. Most twining plants apparently are adapted
to ascend supports 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 44 inches in diameter.
Mohl (S. 184) found that the Phaseolus multiflorus and Ipomea
purpurea could not, when placed in a room with the light entering
on one side, twine round sticks between 3 and 4 inches in dia-
meter; 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 ascends a column 9 inches in dia-
meter ; 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

22 MR. DARWIN ON CLIMBING PLANTS.

thickness, yet at Kew a plant ascended a trunk above 6 inches in
diameter. The tropical twiners, on the other hand, can ascend
thick trees. I hear from Drs. Thomson and Hooker that this is
the case with the Butea parviflora, one of the Menispermacee,
and with some Dalbergias and other Leguminose. This power
would evidently be almost necessary for twining plants inhabiting
tropical forests, as otherwise they could hardly ever reach the
light. In our temperate countries twining plants which die down
every year to the root would suffer 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 some twining plants are adapted to ascend only
thin stems, whilst others can twine round thick trees, I do not
know. It appeared to me probable that twining plants with very
long revolving shoots might 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
length and power of movement apparently serving merely to find
some distant but thin stem round which to twine. The Sphero-
stemma marmoratum is a vigorous tropical twiner, and as it is a
very slow revolver, I thought that this latter circumstance might
aid it in ascending a thick support; but though it was able to
wind round the 6-inch post, it could do this only on the same level
or plane, and could not ascend in a spire. We can, however, see,
in accordance with the views previously explained, that a re-
volving shoot, which, after coming into contact with any support,
quickly lost its power of movement, would not again be drawn
away from its support by the returning or opposite movement,
and therefore remaining in contact with it, might thus ascend
a thick support. But whether this slight difference in retaining
for some time or in quickly losing the power of movement after
coming into contact with a support alone determines how thick
an object the stem can ascend I do not know.

As ferns differ so much from phanerogamic plants, it may be
worth while here to show that twining ferns act in no respect
differently from other twining plants. In Lygodiwm articulatum
the two internodes first formed above the root-stock did not move ;
the third from the ground revolved, and at first very slowly. This
species is a slow revolver: but ZL. scandens made five revolutions
at an average rate of 5h. 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. The

SPIRAL TWINERS. 23

two young upper internodes alone moved. A line painted along
the surface of a revolving internode which was at the time convex,
became first lateral, then concave, and ultimately convex again.
Neither the internodes nor petioles are irritable when rubbed. The
movement is in the more usual direction, namely in opposition to
the course of the sun; and when the stem has twined 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 con-
tinued growth causes them to slip a little upwards and onwards.
If the stick be soon removed, the internodes straighten themselves,
and recommence revolving. The extremities of the depending
shoots turn upwards, and twine on themselves. In all these re-
spects we have complete identity with phanerogamic twining
plants; and the above enumeration may serve as a summary of
the leading characteristics of common twining plants.

The power of revolving depends on the general health and
vigour of the plant, as has laboriously been shown to be the case
by Palm. But the movement of each separate internode is so in-
dependent 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 20h. and
the other in 23 h., whereas they ought to have revolved in between
2h. and 2h. 30m. Cut shoots of the Kidney-bean were similarly
retarded, but in a less degree. I have repeatedly observed that
carrying a plant from the greenhouse to my house, or from one to
another part of the greenhouse, always stopped the movement for
a time; hence I conclude that naturally exposed plants would
not make their revolutions during 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
tendril-bearing Pea that I need say nothing more. When twi-
ning plants are placed near a window in a room, the light in some
cases has a remarkable power (as was likewise observed by Du-
trochet, p. 998, with the Pea) on the revolving movement, but
different in degree with different plants: thus Jpomea jucunda
(as may be seen in the table) revolved in 5 h. 20 m., the semicircle
from the light taking 4h. 80m., and that towards the light only
Lh.; Lonicera brachypoda revolved, in a reversed direction to the
Ipomea, in &h., the semicircle from the light taking 5h. 23 m., and
that to the light only 2h. 37m. From the rate of revolution in all

24 MR. DARWIN ON CLIMBING PLANTS,

the plants which I have observed 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 greatly modify the whole rate. This action is remarkable when
we reflect how little the leaves are developed on the young and
very thin revolving internodes. It is the more remarkable, ag
botanists have thought (Mohl, 8.119) that twining plants are but
little sensitive to the action of light.

I will conclude my account of twining plants by collecting a
few miscellaneons and curious cases. With most twining plants
all the branches, however many there may be, go on revolving
together ; but, according to Mohl (S. 4), the main stem of Zamus
elephantipes does not twine—only the branches. On the other
hand, with the Asparagus, given in the table, 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 CO. purpureum made nume-
rous short healthy shoots; but they showed no signs of revoly-
ing, and I could not conceive how these plants could be climbers ;
but at last C. argentewm 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 from its leaves
being little developed, and this shoot revolved vigorously and
twined. So that this plant produces shoots of two sorts. With
Periploca Greca (Palm, 8.43) the uppermost shoots alone twine.
Polygonum convoloulus twines only during the middle of the sum-
mer (Palm. 8S. 48, 94): plants growing vigorously in the autumn
show no inclination to twine. The majority of Asclepiadacew are
twiners ; but Asclepias nigra only “in fertiliori solo incipit scan-
dere sub volubili caule” (Willdenow, quoted and confirmed by
Palm, S. 41). <Asclepias vincetoxicum does not regularly twine,
but only occasionally (Palm, 8. 42; Mohl, 8. 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 Convolvulacee are excellent
twiners ; but Ipomea argyreoides in South Africa 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. Seedlings, on the other hand, raised near

LEAF-CLIMBERS. 25
Dublin twined up sticks above 8 feet in height. These facts
are highly remarkable; for there can hardly be a doubt that in
the dryer provinces of South Africa these plants must have propa-
gated themselves for thousands of generations in an erect eondi-
tion; and yet during this whole period they have retained 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 (Léon, 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 with
“Fulmer’s dwarf forcing-bean,’ on which occasionally a long
twining shoot appeared.

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 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 vertical stretched strings close to others, and
the strings alone were ascended by twining. We here, perhaps,
see the first stage in the habit of twining; and the stem twines
indifferently to the right or the left. Some other species of the
genus, and of another genus, viz. Habrothamnus, of the same family
of Solanacex, which are described in horticultural works as twining
plants, seemed to possess this faculty in a very feeble manner.
On the other hand, I suspect that with Zecoma radicans we have
the last vestige of a lost habit: this plant belongs to a group
abounding with twining and with tendril-bearing species, but it
ascends by rootlets like those of the Ivy ; yet I observed that the
young internodes seldom remained quite stationary, but performed
slight irregular movements which could hardly be accounted for
by changes in the action of the light. Anyhow it need not be
supposed that there would be any difficulty in the passage from a
spirally twining plant to a simple root-climber; for the young
internodes of Bignonia Tweedyana and of Hoya carnosa revolve
and twine, and likewise emit rootlets which adhere to any fitting
surface,

Part I1.—Lrar-crmmpers.

It has long been observed that several plants climb by the aid of
their leaves, either by the petiole or by the produced midrib ;
but beyond this simple fact nothing is known of them. Palm

26 MR. DARWIN ON CLIMBING PLANTS.

and Mohl class these plants with those which bear tendrils ; but
as a leaf is generally a defined object, the present classification
has, at least, some plain advantages. There are other advantages,
as leaf-climbers are intermediate in many respects between twiners
and certain tendril-bearing plants. I have observed eight species
of Clematis and seven of Tropeolum in order to discover what
amount of difference there may be within the same genus; and
the differences, as we shall see, are considerable.

Crematis.—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 3h.48m. 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 spire and wound two turns in an opposite course.
This was rendered possible by the straight piece between the
opposed spires having become rigid. The simple, broad, ovate
leaves of this tropical species, so unlike those of most of the other
species of the genus, with their short thick petioles, seem but ill-
fitted for any movement. 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 it
becomes straight again. The under side seemed to be the most
sensitive; but the sensitiveness or irritability is but slight com-
pared to that which we shall meet
with in some of the following spe-
cies ; for a loop of string, weighing
1:64 grain, 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
two twigs on each side of the stem.
A forked twig placed so as to
lightly press on the under side of a
young footstalk caused it,in 12h.,
to bend greatly, and ultimately to ) Cenaie dea with ie
such an extent that the leaf passed ?),, diye poxki hen ueceh ae.
to the opposite side of the stem ;
the forked stick having been removed, the leaf slowly recovered
its proper position.

LEAF-CLIMBERS. 27

The young leaves change their position in a rather odd manner:
when first developed the petioles are upturned, 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. If they come into contact with no object, they
retain this position for a considerable time, and then bending
upwards they reassume their original upturned position, which is
retained ever afterwards. The young leaves, being hooked, are
thus enabled to catch twigs when brought into contact with them
by the revolving movement of the internodes. The petioles
which have clasped any object soon become much thickened and
strengthened, as may be seen in the diagram.

Clematis montana.—The long and 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 caused them to bend; a loop
weighing only one-eighth of a grain sometimes acted and some-
times did not act. The sensitiveness extends to the angle between
the stem and leaf-stalk. I may here state that I ascertained the
weights of the string and thread used in all cases by carefully
weighing 50 inches in a chemical balance, and then cutting off mea-
sured lengths*. The main petiole carries three leaflets; but the
short petioles of these leaflets are not sensitive. A young inclined
shoot (the plant being in the greenhouse) made a large circle op-
posed to the course of the sun in 4h. 20 m., but the next day, being
very cold, the time was 5h. 10m. Astick placed near the revol-
ving stem was soon struck by the petioles which stand out at right
angles, and the revolving movement was arrested. The petiole
then began, being excited by the contact, to slowly wind round
the stick. When the stick was thin, the petiole sometimes wound
twice round it. The opposite leaf was in no way affected. The
attitude assumed by the stem after the petiole has clasped a stick,
is that of a man standing by a column, who throws his whole arm
horizontally round it. With respect to the stem’s power of twi-
ning, some remarks will be made under C. calycina.

Clematis Sieboldi.—A shoot made three revolutions against the
sun at an average rateof3h. 11m. The power of twining is like
that of the last species. Its leaves are nearly similar, except that

* Our English grain equals nearly 65 milligrammes.

/ = <\

28 MR. DARWIN ON CLIMBING PLANTS,

the 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 it took between two and three days to produce any
effect. The leaves have the remarkable habit and power of spon-
taneously revolving, generally in vertical ellipses, in the same
manner, but in a less degree, as will be described under C. miero-
phylla.

Clematis calycina—The young shoots are thin and flexible;
one revolved, describing a broad oval, in 5 h. 30m., and another in
6h. 12m.: they followed the course of the sun ; but in all the species
of the genus the course followed, if observed long enough, would
no doubt be found to differ. This isa rather better twiner than the
two last species: the stem, when a thin upright stick free from
twigs was placed near, sometimes made two spiral turns round it ;
then, being arrested by the clasping of the petioles, it would run
up for a space straight and then generally reversed its course and
took one or two spiral 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-fitted 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 becomes flat. I gently rubbed
with a thin twig the lower surfaces of two young petioles; and
in 2h. 80m. they were slightly curved downwards; in 5h., after
being rubbed, the end of one was bent completely back parallel
to the basal portion; and in 4h. subsequently it became nearly
straight again. To show how sensitive the young petioles are, I
may mention that I put, in order to mark them, short streaks of
water-colour on their under sides; an infinitely thin crust was
thus formed, but it sufficed in 24h. to cause both to bend down-
wards. Whilst the plant is young, each leaf consists of three
divided leaflets, which have barely distinct petioles, and these are
~ not then sensitive; but when the plant is well grown, the two
lateral and terminal leaflets have long petioles, and these now
become sensitive and are capable of clasping in any direction any
object. ,

When the petiole has clasped a twig, it undergoes some remark-
able changes, which occur with the several other species, but in a
less strongly marked manner, and will be here described once for

LEAF-CLIMBERS. 29

all. The clasped petiole in the course of two or three days swells
greatly, and ultimately becomes nearly twice as thick as the
opposite leaf-stalk which has clasped nothing. When thin trans-
verse slices of the two are placed under the microscope their
difference is conspicuous: the side of the footstalk which has been
in contact with the support is formed of a layer of colourless cells
with their longer axes directed from the centre of the petiole, and
very much larger than any cells found 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 externally visible:
the petiole of the unclasped leaf is flexible, and can be easily
snapped, whereas the clasped footstalk acquires an extraordi-
nary toughness and rigidity, so that considerable force is re-
quired 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
plain, namely, that the petioles may firmly and durably support
the stem.

Clematis microphylla, var. leptophylla.—The long and thin inter-
nodes of this Australian species revolve sometimes in one direc-
tion and sometimes in an opposite one, describing long, narrow,
irregular ellipses or large circles: four revolutions were com-
pleted within five minutes of the same average rate of 1 h.51m.; so
that this species moves more quickly than any other 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 general shape, and act
in the same manner like a hook, as will be described under C.
viticella; but the leaflets are more divided, as in C. calycina, and
each segment whilst young terminates in a hardish point, and is
much curved downwards and inwards; so that the whole leaf
readily catches and becomes entangled with any neighbouring
object. The petioles of the young terminal leaflets are acted on
by loops of thread weighing 1th and ,),th of a grain: the basal
portion of the main petiole is much less sensitive, but will clasp a
stick against which it presses.

The whole leaf,,whilst young, is in continual, spontaneous, slow
movement. The stem was secured close to the base of the leaves,
and, a bell-glass being placed over the shoot, the movements of
the leaves were traced on it during several days. A very irre-

30 MR. DARWIN ON CLIMBING PLANTS.

gular line was generally formed; but one day, in the course of
eight hours and three quarters, the figure traced, clearly repre-
sented three and a half irregular ellipses, the most perfect one of
which was completed in 2h. 85m. The two opposite leaves moved
quite independently of each other. This movement would aid
that of the internodes in bringing the petioles into contact with
surrounding objects. I discovered this spontaneous movement
too late to be enabled to observe the leaves in all the other spe-
cies; but from analogy I can hardly doubt that the leaves of at
least OC. viticella, O. flammula, and OC. vitalba move spontaneously ;
and, judging from ©. 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 moyement, though restricted, is not lost. In our pre-
sent species a young internode, placed in front of a window, made
three narrow ellipses, transversely to the light, at an average rate
of 2h. 40 m.; when placed so that the movement was to and from
the light, the rate was greatly accelerated and retarded, as in the
case of twining plants. The ellipses were small; the longer dia-
meter, described by the apex of a shoot bearing a pair of not ex-
panded leaves, being only 42 inches, and that by the apex of the
penultimate internode only 14 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 with the spontaneous movements in bringing the petioles
into contact with surrounding objects.

The leaves are of large size. There are three pairs of lateral
leaflets and a terminal one, all borne by rather long petioles. The
main petiole bends a little angularly downwards at each point
where a pair of leaflets arises, 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,
with the lateral petioles directed a little upwards, forms an ex-
cellent grappling apparatus by which the leaves readily become
entangled with surrounding objects. If they catch nothing, the

LEAF-CLIMBERS. 31

whole petiole ultimately grows straight. Both the medial and

lateral petioles are sensitive; and the three branches, into which

the basi-lateral petioles are generally subdivided, likewise are sen-

sitive. The basal portion of the main petiole between the stem

and the first pair of leaflets is less sensitive than the remainder,

but it will clasp a stick when in contact, On the other hand, the
Fig. 2.

A young leaf of Clematis viticella.

inferior surface of the rectangularly bent terminal portion (carry-
ing 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 distant supports. To show the difference
in sensibility, I gently placed loops of string of the same weight
(in one instance weighing ‘82 of a grain) on the several lateral and
on the terminal sub-petioles ; in a few hours the latter were bent,
but after 24h. no effect was produced on any of the lateral petioles.
Again, a terminal sub-petiole placed in contact with a thin stick
became sensibly curved in 45 m., and in 1h. 10m. had moved
through ninety degrees, whereas a lateral petiole did not become
sensibly curved until 3h. 80m. had elapsed. In this latter case,
and in all other such cases, if the sticks be taken away, the petioles
continue to move during many hours afterwards; so they do after
a slight rubbing; but ultimately, if the flexure has not been very
great or long-continued, they become, after about a day’s in-
terval, straight again.

The gradation in the extension of the sensitiveness in the
petioles of the several 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

32 MR. DARWIN ON CLIMBING PLANTS.

of OC. calycina; but in older plants it has spread to the three sub.
petioles. In C. viticella it has spread to the petioles of the seven
leaflets, and to the subdivisions of the basi-lateral sub-petioles,
In this latter species the sensitiveness has diminished in the basal
part of the main petiole, in which alone it resided in C. montana,
and has accumulated in the abruptly bent terminal portion.

Clematis flammula.—The shoots, which are rather thick, straight,
and stiff, whilst growing vigorously in the spring, made small oval
revolutions, following the sun in their course. Jour were made
at an ayerage rate of 3h. 45 m. The longer axis of the oval, de-
scribed by the extreme tip, was directed at right angles to the line
joining the opposite leaves; its length was in one case only 13,
and in another case 1$ inch; so that the young leaves are 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 Au-
gust 1st it had formed new and moderately vigorous shoots ; these,
when observed under a bell-glass, were on some days quite sta-
tionary, and on other days moved to and fro only about the
eighth of an inch. Consequently the revolving power is here
much enfeebled, and under unfavourable circumstances is com-
pletely lost. This species must depend on the probable, though
not ascertained, spontaneous movements of its leaves, on the
rapid growth of its shoots, and on movements from the wind, for
coming into contact with surrounding objects: hence, perhaps,
it is that the petioles have acquired, as we shall see, in compen-
sation a high degree of sensitiveness.

The petioles are bowed downwards, and have the same general
hook-like form as in C. viticella. The medial petiole and 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 each other, are not sensitive; when the
lamina of a leaflet has grown to 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 much more fully developed pro-
portionally than the laminew of the leaves. Full-grown petioles
are not in the least sensitive. A thin stick placed so as to press
lightly against a petiole, bearing a leaflet a quarter of an inch in
length, caused the petiole to bend in 3h. 15 m.; in another case a
petiole curled completely round a stick in 12h. These petioles

LEAF-CLIMBERS. 33

were left curled for 24h., and then the sticks were removed; but
they never straightened themselves. I took a twig, thinner than
the petiole itself, and lightly rubbed with it several petioles four -
times up and down; these in 1 h. 45 m. became slightly curled ; the
curvature increased during some hours and then began to de-
crease, but after 25 h. from the time of rubbing a vestige of the
curvature remained. Some other petioles similarly rubbed once
up and down became perceptibly curved in about 2h. 30m., a
terminal sub-petiole moving more than a lateral sub-petiole ; they
became quite straight again in between 12h. and 14h. Lastly,
a length of about one-eighth of an inch of a sub-petiole, lightly
rubbed with the same twig only once down, became slightly
curved in 3h., and remained so during 11 h., but the next morning
was quite straight.

The following observations are more precise. After finding
that heavier pieces of string and thread acted, I placed a loop of
string, weighing 1-04 gr., on a terminal petiole: in 6h. 40 m. a cur-
vature could be seen; in 24h. the petiole formed an open ring
round the string ; in 48 h. the ring had almost closed on the string,
and in 72h. it had firmly seized the fine twine so that it required
some force to withdraw it. A loop weighing ‘52 of a grain caused a
lateral sub-petiole just perceptibly to curve in 14h., but after 24h.
it had moved through ninety degrees. These observations were
made during the summer: the following were made in the spring,
when the petioles are apparently more sensitive:—A loop of
thread, weighing one-eighth of a grain, produced no effect on the
lateral sub-petioles, but placed on a terminal one caused, after 24h.,
« moderate curvature in it; the curvature, though the loop re-
mained suspended, was after 48h. diminished, but never dis-
appeared, showing that the petiole had become partially accus-
tomed to the insufficient stimulus. This experiment was twice
repeated with nearly similar results. Lastly, a loop of thread,
weighing only one-sixteenth of a grain (nearly equal to four milli-
grammes), 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 had moved through nearly ninety degrees: beyond
this it did not move; nor did the petiole, the loop remaining sus-
pended, 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-

D

34 MR. DARWIN ON CLIMBING PLANTS.

sixteenth of a grain is, these facts are remarkable. But I have
reason to believe that even a less weight causes a curvature when
acting over a broader surface than can be affected by thin thread,
Having noticed that the tail of a suspended string, which acci-
dentally touched a petiole, had 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 nature, after being
stretched, would permit; I then quietly placed their ends so as
just to rest on two petioles with their tips hanging about the
tenth of an inch beneath; both these petioles certainly became
curved in 36h. One of the ends of string, which just touched
the angle between a terminal and lateral sub-petiole, was in 48 h,
caught as by a forceps between them. 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.—My plants in pots were not healthy ; so that
I dare not trust my observations, which indicated much similarity
in habits with C. flammula. I mention this species only because
I saw many proofs that the petioles of plants growing naturally
are excited to movement by very slight pressure. or instance,
I found petioles which had clasped thin withered blades of grass,
the soft young leayes of a maple, and the lateral flower-peduncles
of the quaking-grass or Briza: the latter are only about as thick
as a hair from a man’s beard, but they were completely surrounded
and clasped. The petioles of a leaf, so young that none of the
leaflets had expanded, had partially seized on a twig. The petioles
of almost every old leaf, 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 sub-
sequently removed. With the several above-described species,
cultivated in pots and thus carefully observed, there never was
any bending of the petioles without the stimulus of contact. When
winter comes on, the blades of the leaves of C. vitalba drop off;
but the petioles (as was also observed by Mohl) remain, some-
times during two seasons, attached to the branches ; and, being
conyoluted, they curiously resemble true tendrils, such as those
occurring in the allied genus Naravelia. The petioles which
have clasped an object become much more woody, stiff, hard,
and polished than those which have failed in this their proper
purpose.

TropxoLuM.—I observed Z. tricolorum, T. azureum, T. penta-

LEAF-CLIMBERS, 35

phyllum, P. peregrinum, T. elegans, T. tuberosum, and a dwarf
variety of, as I believe, 7. minus.

Tropeolum tricolorum, var. grandiflorum.—The flexible shoot,
which first rises from the tuber, is as thin as thin twine. One
such shoot revolved in a course opposed to the sun, at an average
rate, judging from three revolutions, of 1h. 23m.; but no doubt
the direction of the revolving movement is variable. When the
plant had grown tall and much branched, all the many lateral
shoots continued to revolve. The stem, whilst young, twined regu-
larly round a thin vertical stick ; in one case I counted eight spiral
turns: 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 has grown to
a height of two or three feet, about a month after the first shoot
has appeared above ground, no true leaves, but in their place little
filaments, coloured like the stem, are produced. 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; and soon
other segments appear, until a perfect leaf is formed with seven
deep segments. So that on the same plant we may see every step
from tendril-like filaments to perfect leaves. Hence this plant,
whilst young, might be classed with tendril-bearers. After the
plant has grown to a considerable height, and is secured to its
support by the clasping 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, as well as the petioles of the perfect leaves,
whilst young, are highly sensitive on all sides to a touch. The
slightest rub causes them to curve towards the rubbed side in
about three minutes: one bent itself into a ring in six minutes;
they subsequently became straight again: if, however, they have
once completely clasped a stick, when this is removed, they do not
recover themselves. The most remarkable fact, and which I have
observed in no other species of the genus, is that the filaments
and petioles of the young leaves, if they catch no object, after
standing in their original position for some days spontaneously
and slowly move, oscillating a little from side to side, towards the
stem of the plant. Hence all the petioles and filaments, though
arising on different sides of the axis, ultimately bend towards and

D2

36 MR. DARWIN ON CLIMBING PLANTS.

clasp either their own stem or the supporting stick. The petioles
and filaments often become, after a time, in some degree spirally
contracted. In these spontaneous movements, and in the abortion
of their laminz, the sensitive filaments present a much nearer
approach to the condition of tendrils than do the petioles of any
other leaf-climber observed by me.

Tropeolum azureum.—An upper internode made four revolu-
tions, following the sun, at an average rate of Lh.47m. The stem
twined spirally in the same irregular manner as in the last species ;
it produced no filaments or rudimentary leaves. The petioles of
the young leaves are very sensitive: a single very light rub with a
twig caused one to move perceptibly in 5 m., and another in 6 m. ;
the former petiole became bent at mght angles in 15 m., and
became straight again in between 5h. and 6h. A loop of thread
weighing 1th of a grain caused a petiole to curve.

Tropeolum pentaphyllum.—tThe plant observed by me had not
the power of spirally twining, which seemed due, not to the want
of flexibility in the stem, but rather to continual interference from
the clasping petioles. An upper internode made three revolu-
tions, following the sun, at an average rate of lh. 46m. The main
purpose of the revolving movement in all the species is mani-
festly to bring the petioles into contact with some supporting ob-
ject. The petiole of a young leaf, after a slight rub, became curved
in 6m.; another, on a cold day, in 20m.; but others generally in
from 8m. to 10m.: the curvature usually increased greatly in from
15m. to 20m. The petioles became straight again in between 5h,
and 6h., and on one occasion in 3h. When a petiole had fairly
clasped a stick, it could not on the removal of the stick recover
itself; but the free upper part of a petiole, which had already
clasped a stick by its basal part, still had the power of movement.
A loop of thread weighing 4th of a grain certainly caused a petiole
to curve; but the stimulus was not sufficient, the loop remaining
suspended, to cause a permanent flexure. Ifa much heavier loop
be placed in the angle between the petiole and the stem, it pro-
duces no effect; whereas we have seen that the angle between the
stem and petiole of Clematis montana is sensitive.

Tropeolum peregrinum.—In a very young plant the inter-
nodes did not revolve, resembling in this respect a young twin-
ing plant. The four upper internodes in an older plant made
three irregular revolutions, in a course opposed to the sun,
at an average rate of 1h. 48m. It is remarkable how nearly the
same the average rate of revolution (taken, however, but from few

LEAEF-CLIMBERS, 37

observations) is in this and the two last species, namely, 1h. 47m.,
1h.46m, and 1h.48m. The present species cannot spirally twine,
which seems mainly due to the rigidity of its 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 leayes as much as an inch and a quarter in diameter, are sensi-
tive. A moderate rub caused one to curve in 10m., but others in
20m.; the petioles became straight again in from 5h. 45m. to 8h.
Petioles which have naturally come into contact with a stick, some-
times take two turns round it. When clasped round a support,
they become rigid and hard. The petioles are less sensitive to a
weight than in the previous species ; for loops of string weighing
‘82 of a grain did not cause any curvature, whilst a loop of
double this weight (1°64¢r.) did act.

Tropeolum elegans.—I did not make many observations on this
species. The short and stiff internodes revolve irregularly, and
describe extremely small oyal figures; one was completed in 3h.
A young petiole, when rubbed, became slightly curved in 17 m.;
then much more so; and was nearly straight again in 8 h.

Tropeolum tuberosum.—The internodes on a plant nine inches
high did not move at all; but on an older plant they moved irregu-
larly, and made very 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 4h. The movement of the apex of the shoot,
from extreme point to point of the oval, was only about one inch or
one anda half; yet this slight movement brought the petioles
into contact with closely surrounding twigs, which were then
clasped. With the lessened power of spontaneously revolving,
compared with the previous species, the sensitiveness of the
petioles is likewise 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 yery
slowly decreased ; so that the petioles sometimes required 24h. to
become straight again. The petioles of very young leaves can act
perfectly ; one with the lamina only -15 of an inch in diameter,
that is, about a twentieth of the full size, firmly clasped a thin
twig: but leaves grown to one quarter of their full size can like-
wise act.

Lropeolum minus (?).—The internodes of a variety named

38 MR. DARWIN ON CLIMBING PLANTS.

“ dwarf crimson Nasturtium” had no power of revolving ; but they
moved during the day to the light, and from it at night, in a
rather irregular course. The petioles, when well rubbed, showed
no power of curving; nor could I see that they ever clasped any
neighbouring support. We have seen in this genus a gradation
from species such as 7. tricolorum, which have exquisitely sensi-
tive petioles, and internodes which have rapid revolving powers
and can 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 alternative.

In this species and in 7. elegans, and probably in others, the
flower-peduncles, as soon as the seed-capsule begins to swell,
spontaneously bend abruptly downwards and become somewhat
convoluted: when a stick lies in the path, it is to a certain extent
clasped ; but, as far as I have been able to observe, the movement
of the peduncle is quite independent of the stimulus from contact.

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

Maurandia Barclayana.—A. thin, slightly bowed shoot made two
reyolutions, following the sun, each in 3h. 17m.; this same shoot,
the day before, revolved in an opposite direction. The shoots do
not spirally twine, but climb excellently by the aid of the young
sensitive petioles. These petioles, when lightly rubbed, move after
a considerable interval of time, and subsequently become straight
again; a loop of thread weighing 4th of a grain caused them to
bend.

Maurandia semperflorens.—This freely growing species climbs
exactly like the last, by its sensitive petioles. A young internode
made two circles, each in Lh. 46m.; so that it moves almost twice
as rapidly as the last species. But I should not have noticed the
present species, had it not been for the following unique case.
Mohl says (S. 45) that “the flower-peduncles, as well as the
petioles, are wound into tendrils; and he adds nothing more
about the genus. But it must be observed that Mohl classes as
tendrils even such objects as the spiral flower-stalks of the Vallis-
nerta. Nevertheless this remark, and the well-known fact that
the flower-peduneles of this M/awrandia are flexuous, led me eare-

LEAF-CLIMBERS. 39

They never act as tendrils: I repeatedly

fully to examine them.
and

placed thin sticks in contact with young and old peduncles,
I allowed nine vigorous plants to grow over an entangled mass of
branches ; but in no one instance did a peduncle bend round any
object. It is indeed in the highest degree improbable that this
should occur, for the flower-peduncles are generally developed on
branches which have already securely clasped a support by their
petioles; and when borne on free depending branches, they are
not produced by the terminal portion of the internode which
alone has the power of revolving; so that they can only acci-
dentally and rarely be brought into contact with any surrounding
object. Nevertheless (and this is the remarkable fact) these flower-
peduncles, whilst young, exhibit feeble revolving powers, and are
slightly sensitive to a touch. I selected some stems which had
firmly clasped a stick by their petioles, and, placing a bell-glass
over them, traced the movements of the young flower-peduncles.
Some days these moved over a short and extremely irregular line,
making little loops in their course. One day a young peduncle
1} inch in extreme length was carefully observed, and it made
four and a half narrow, vertical, irregular, and very short
ellipses—each at an average rate of about 2h. 25m. ; an adjoining
peduncle described during the same time similar, but fewer, ellipses.
As the plant had for some time occupied exactly the same position,
these movements could not be attributed to the varying action of
the light. Peduncles, old enough for the coloured petals to be
just visible, do not move. With respect to irritability, I rubbed
a few times very lightly with a thin twig two young peduncles (13
inch in length), one on the upper side and the other on the
lower side, and they became in between 4h. and 5h. plainly bowed
towards the rubbed sides ; in 24h. 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 bowed towards each other, that the ares of the bows stood
at nearly right angles to their previous positions ; 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 14 inch in length required to be
rubbed two or three times, and then became only just percep-
tibly curved. Loops of thread suspended on the peduncles pro-

40 MR. DARWIN ON CLIMBING PLANTS.

duced no eftect ; but loops of string weighing *82 and 1°64 grain
acted capriciously, sometimes causing a slight curvature ; but they
were never clasped, like the far lighter loops of thread by the
petioles.

In the nine vigorous plants which I observed, it is certain that
neither the slight spontaneous movements nor the slight sensitive-
ness of the flower-peduncles were of any service to the plants in
climbing. If any member of the Scrophulariacew had been known
to have flower-peduncles used for climbing, or had tendrils pro-
duced by their modification, I should have thought that this
Maurandia still retained a useless or rudimentary vestige of a
former habit; but this view cannot be maintained. We are
almost compelled to believe that by some correlation of growth
the power of movement has been transferred from the young
internodes to the young peduncles, and in the same manner sen-
sitiveness from the young petioles to the young peduncles; but
this latter supposition is the more improbable, as I could detect
no sensitiveness in the young internodes of the Maurandia,
though in a closely allied genus, Lophospermum, the young inter-
nodes, as we shall see, are sensitive. By whatever means the
peduncles of this Mawrandia have acquired their power of spon-
taneous movement and their sensitiveness, the case is interesting
for us; for we can see that if these now useless capacities were a
little perfected, the flower-peduncles could be made as useful for
climbing as are the flower-peduncles of Vitis and Cardiospermum,
as will hereafter be described.

Rhodochiton volubile.—A long flexible shoot swept a large circle,
following the sun, in 5h. 30m. ; and, as the day became warmer, a
second circle in 4h.10m. The shoots sometimes make a whole or
half spire round a vertical stick, then run up for a space straight,
and afterwards make spiral turns in an opposite direction. The
petioles of very young leaves, about one-tenth of their full size
are highly sensitive, and bend towards any side which has been
touched ; but they do not move quickly: one, after being lightly
rubbed, was perceptibly curved in 1h. 10 m., and became consider-
ably arched in 5h. 40m. after the rubbing; some other petioles,
after being rubbed, were scarcely curved in 5h. 380m., but in 6h.
30m. were distinctly curved. A curvature was perceptible in a
petiole in between 4h. 30m. and 5h., after the suspension of a little
loop of string. A loop of fine cotton thread, weighing one-sixteenth
of a grain, not only slowly caused a petiole to bend, but was ulti-
mately firmly clasped by it, so that it could be withdrawn only by

LEAF-CLIMBERS. 4)

some little force. The petioles, when coming into contact with a
stick, take either a complete or half turn round it ; ultimately they
increase much in thickness. Leaves arising on the side of the
stem opposite to the light move towards it; and, in doing so, the
petioles are sometimes brought into contact with the stem, and
consequently clasp it; but the petioles have no true spontaneous
movement.

Lophospermum scandens, var. purpureum.—Some long, mode-
rately thin internodes made four revolutions at an average rate of
3h.15m. The course pursued was very irregular—sometimes an
extremely narrow ellipse, sometimes a large circle, sometimes an
irregular spire or zigzag line, and sometimes the apex stood still.
The young petioles, when brought by the revolving movement into
contact with a stick, clasp it, and soon increase considerably in
thickness ; but they are not quite so sensitive to a light weight
as those of the Zhodochiton, for loops of thread weighing one-
eighth of a grain did not invariably cause them to bend.

This plant presents a case not observed in any other leaf-
climber or twiner or tendril-bearer, or in any other plant as far as
I know, namely, that the young internodes are sensitive to a
touch. When a petiole clasps a stick, it draws the base of the
internode against it ; and then the internode itself bends towards
the stick, which is thus caught between the stem and the petiole
as by a pair of pincers. The internode straightens itself again,
excepting the part in 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 lightly rubbing two or
three times with a thin twig several internodes ; and in about 2 h.,
but in one case in 3 h., all became bent: they became straight again
in about 4h., subsequently. An internode, which was rubbed as
much as six or seven times with a twig, became just perceptibly
curved in 1h. 15m., and subsequently in 3h. the curvature in-
creased much ; the internode became straight again in the course
of the night. I rubbed some internodes one day on one side, and
the next day on the opposite side or at right angles ; and the cur-
vature was always towards the rubbed side.

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

SoLanum.—S. jasminoides.—Some of the species of this large
genus are twiners ; but this is a true leaf-climber. A long, nearly
upright shoot made four revolut ions, moving against the sun, very

42 MR. DARWIN ON CLIMBING PLANTS.

regularly at an average rate of 3h. 26m. The shoots, however,
sometimes stand 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 7h. In the greenhouse a

Fig. 3.

Solanum jasminoides, with one of its leaves cJasping a stick.

petiole was not affected by a loop of string, suspended during
several days and weighing 23 grains; in the hothouse one
was made to curve by a loop weighing 1°64 (and, on the
removal of the string, became straight again), but was not at
all affected by another loop weighing ‘82 of a grain. We have seen
that the petioles of some other leaf-climbing plants were affected
by one-thirteenth of this latter weight. In this plant, and in no
other leaf-climber seen by me, a leaf grown to its full size was
capable of clasping a stick; but the movement was so extraordi-
narily slow that in the greenhouse the act required several weeks ;
but on each succeeding week it was clear thatthe petiole became
more and more curved, until finally it firmly clasped the stick.
When the flexible petiole of a half- or a quarter-grown leaf has
clasped any object, in three or four days it increases much in
thickness, and after several weeks becomes wonderfully hard and
rigid; so that I could hardly remove one from its support. On
comparing a thin transverse slice of this petiole with one from
the next or older leaf 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

LEAF-CLIMBERS. 43

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
Fig. 4.

Solanum jasminoides.

A. Section of a petiole. .
B. Section of a petiole some weeks after it had clasped a stick, as shown in

fig. 3.
semilunar band of cellular tissue slightly different from that out-
side it, and including three closely approximate groups of dark
vessels. Near the upper surface of the petiole, beneath two ridges,
there are two other small circular groups of vessels. In the sec-
tion of the petiole (B) which had during several weeks clasped
a stick, the two upper ridges haye become much less prominent,
and the two groups of woody vessels beneath them much in-
creased in diameter. The semilunar band is converted into a
complete ring of very hard, white, woody tissue, with lines radia-
ting from the centre. The three groups of vessels, which, though
closely approximate, were before distinct, are now completely
blended together. The upper part of the new ring of woody vessels,
formed by the prolongation of the horns of the original semilunar
band, is thinner than the lower part, and is slightly different in
appearance from being less compact. This clasped petiole had
actually become thicker than the stem close beneath ; and this was
chiefly due to the greater thickness of the ring of wood, which
presented, both in transverse and longitudinal sections, a closely
similar structure in the petiole and axis. The assumption by a
petiole of this structure is a singular morphological fact; but it
is a still more singular physiological fact that so great a change
should have been induced by the mere act of clasping a sup-
port *.

Fumariacrex.—Fumaria officmalis—It could not have been

* Dr. Maxwell Masters informs me that in most, or all, petioles which are
cylindrical, such as those bearing peltate leaves, the woody vessels form a closed
ring, and that the semilunar band of vessels is confined to petioles which are
channelled along their upper surfaces. In accordance with this statement, it

4A MR, DARWIN ON CLIMBING PLANTS.

anticipated that so lowly a plant would have been a climber. This
it effects by the aid of the main and lateral petioles of its com-
pound leaves; even the much-flattened terminal portion of the
petiole can seize a support. I have seen a substance as soft as a
withered blade of grass caught. Petioles which have clasped any
object ultimately became rather thicker and more cylindrical.
On lightly rubbing with a twig several petioles, they became per-
ceptibly curved in Lh. 15 m., and subsequently they straightened
themselves. <A stick gently placed in the angle between two sub-
petioles caused movement in 7h., and was almost clasped in 9h. A
loop of thread, weighing one-eighth of a grain, caused, after 12h,
and before 20h. had elapsed, a considerable curvature; but the
petiole never fairly clasped the thread. The young internodes
are in continual movement; the movement is considerable, but
very irregular in course; a zigzag line, or a spire crossing itself,
or a figure of 8 is formed; the course during 12h., being traced
on a bell-glass, apparently represented about four ellipses. The
leaves themselves also move spontaneously, the main petiole cury-
ing itself in accordance with the movement of the internodes ; so
that when the latter move to one side the petiole is curved to
that side, then, becoming straight, is curved to the opposite side.
Thus a wider space is swept for a support to be clasped. The
movement, however, is small, as could be seen when the shoot
was securely tied to a stick and the leaf alone allowed to move.
The leaf in this case followed an irregular course, like that made
by the young internodes.

Adlumia cirrhosa.—I raised some plants late in the summer;
they formed magnificent leaves, but threw up no central stem.
The first-formed leaves were not sensitive; but some of the later
leaves were sensitive, but only towards their extremities, and were
able to clasp sticks. This could be of no service to the plant, as
these leaves rose from the ground; but it showed what the future
character of the plant would be when it had grown tall enough to
climb. The tip of one of these ground leaves, whilst young, de-
scribed in 1 h. 86 m. a narrow ellipse, open at one end, and exactly
three inches in length; a second ellipse was broader, more irre-
gular, and shorter, viz. only 23 inches in length, and was com-
pleted in 2h.2m. From analogy with Fwmaria and Corydalis, I
have no doubt that the internodes have the power of revolving.
may be observed that the enlarged and clasped petiole of the Solanwm, with its

closed ring of woody vessels, has become much more cylindrical than it was in
its original unclasped condition,

LEAF-CLIMBERS. 45

Corydalis claviculata—This plant is interesting from being in
a condition so exactly intermediate between a leaf-climber and a
tendril-bearer that it might have been described under either
head ; but, for reasons hereafter assigned, it is classed amongst
tendril-bearers.

Besides the plants already described, Bignonia unguis and its
close allies, though aided by tendrils, as will hereafter be de-
scribed, have clasping petioles. According to Mohl (S. 40),
Cocculus Japonicus (one of the Menispermacez) and a fern, the
Ophioglosswm Japonicum (S. 39), climb by their leaf-stalks.

We now come to a small section of plants which climb by the
aid of the produced midribs or tips of their leaves.

Guortosa.— G. Plantii (Liliacee).—The stem of a half-
grown plant continually moved, generally describing an irregular
spire, but sometimes ovals, ite the longer axes running in differ-
ent directions. It either followed the sun, or moved in an oppo-
site course, and sometimes stood still before reversing its course.
One oval was completed in 3h. 40m.; of two horseshoe-shaped
figures, one was completed in 4h. 35 m. and the other in 3h. The
tip of the shoot, in its movements, reached points between four and
five inches asunder. The young leaves, when first developed,
stand up nearly vertically ; but by the growth of the axis, and by
the spontaneous bending down of the terminal half of the leaf,
they soon become much inclined, and ultimately horizontal. The
end of the leaf forms a narrow, ribbon-like, thickened projection,
which at first is nearly straight; but by the time the leaf has got
into an inclined position, the end has bent itself downwards into
a well-formed hook ; and this is now strong and rigid enough to
catch any object, cea when caught, to anchor the plant and stop
the revolving movement. This hook is sensitive on its inner sur-
face, but not in nearly so high a degree as with the many before-
described petioles ; for a loop of string, weighing 1-64 grain, pro-
duced no effect. When the hook has caught a thin twig or even
a rigid fibre, the point may be perceived in from 1h. to 3h. to have
curled a little inwards; and, under favourable circumstances, in
from 8 h. to 10 h. it fly curls round and seizes the object, which
it never again looses. The hook when first formed, before the leaf
has become inclined, is less sensitive. The hook, if it catches hold of
nothing, remains for a long period open and sensitive ; ultimately
the tip spontaneously and slowly curls inwards, nara makes a
button-like, flat, spiral coil at the end of the leaf. One leaf was

46 MR. DARWIN ON CLIMBING PLANTS.

watched, and the hook remained open for thirty-three days ; but
during the last week the tip had curled inwards so much that at
last only a very thin twig could have been inserted. As soon as
the curling-in of the tip has closed the hook and converted it into
a ring, its sensibility, both within and without, is lost; but as
long as the hook remains open its sensibility is retained.

When the plant had grown from the bulb to the height of only
about six inches, the leaves, four or five in number, were broader
than those subsequently produced, and their soft and but little-
attenuated tips did not form hooks, and were not sensitive; nor
did the stem revolve. At this early period of growth, the plant
can support itself; its climbing apparatus is not required, and
therefore is not acquired. On the other hand, a full-grown plant
which was flowering, and which would not have grown any taller,
had leaves on the summit, which were not sensitive, and could not
clasp a stick,

Flagellaria Indica (Commelynacee).—From dried specimens
it is manifest that this plant climbs exactly like Gloriosa. A
young plant, 12 inches in height, and bearing fifteen leaves, had
not one leaf as yet produced into a hook or tendril-like filament ;
nor did the stem revolve. Hence this plant acquires its climbing
power later in life than the Gloriosa lily. According to Mohl
(S. 41), Uvularia (Melanthacez) climbs like Gloriosa.

These three last-named genera are all Monocotyledons; but
there is one Dicotyledon, namely Nepenthes, which is rauked by
Mohl (S. 41) amongst tendril-bearers ; and I hear from Dr. Hooker
that most of the species climb well at Kew. This is effected by the
stalk or midrib between the leaf and the pitcher twisting round
any support. The twisted part becomes thicker; but 1 observed
at Mr. Veitch’s that the stalk often takes a turn when not in con-
tact with any object, and that this twisted part likewise becomes
thickened. ‘Two vigorous young plants of WV. levis and NV. distil-
latoria, in my hothouse, whilst less than a foot in height, showed
no sensitiveness in their leaves or power of movement or of climb-
ing. But when J. levis had grown to a height of 16 inches,
there were signs of these powers. Each young leaf when first
formed stands upright, but soon becomes inclined; at this period
of growth it terminates in a stalk or filament, with the pitcher at
the extremity so little developed that this part is not thicker than
any other part. The leaf in this state certainly exhibited slight
spontaneous movements; and when the stalk came into contact
with a stick, it very slowly bent round and firmly seized it. But

LEAF-CLIMBERS. 47

the leaf by its subsequent growth became quite slack, though the
terminal stalk remained coiled round the stick ; hence it would
appear that the chief use of the coiling, at least whilst the plant
is young, is to support the pitcher with its load of secreted fluid.

Summary on Leaf-climbers.—Plants belonging to eight families
are known to haye clasping petioles, and plants belonging to four
families climb by the tips of their leaves. With all the plants
observed by me, the young internodes revolved more or less
regularly, in some cases as regularly as does any twining plant,
and at various rates, but generally rather rapidly. Some few can
ascend by twining spirally round a support. Differently from
most twiners, there is a strong tendency in the same shoot to
revolve first in one and then in the opposite direction. The ob-
ject gained by the revolving movement, as could be plainly seen,
was to bring the petioles or the tips of the leaves into contact
with surrounding objects; without this aid there would be a poor
chance of success. With rare exceptions, the petioles are sensitive
only whilst young ; they are sensitive on all sides, but in differ-
ent degrees in different plants, and in some species of Clematis in
very different degrees in different parts of the same petiole. The
hooked tips of the leaves of the Gloriosa are sensitive only on their
inner or inferior surface. The petioles are sensitive toa touch and
to excessively slight continued pressure, even from a loop of soft
thread weighing only the one-sixteenth of a grain; and there is
reason to believe that the rather thick and stiff petioles of Clematis
flammula are sensitive to even a less weight when spread over a
wider surface. The petioles always bend towards the touched
or pressed side, at different rates in different plants, sometimes
within a few minutes, but generally after a much longer period.
After temporary contact with any object, the petiole continues to
bend for a considerable time ; afterwards it slowly becomes straight
again, and can then re-act. A petiole excited by an extremely
slight weight sometimes bends a little, and then becomes habi-
tuated to the stimulus, and either bends no more or becomes
straight again, the weight still remaining suspended. Petioles
which have clapsed any object for some little time cannot recover
their original position. After remaining clasped for two or three
days, they generally increase much in thickness, either through-
out or on one side alone; they subsequently become, sometimes
in a wonderful degree, stronger and more woody; and in some
cases they acquire an internal structure like that of the stem or
axis.

48 MR. DARWIN ON CLIMBING PLANTS.

The young internodes of the Lophospermum are sensitive as well
as the petioles, and by their combined movement seize any object,
The flower-peduncles of the Maurandia semperflorens revolve
spontaneously, and are sensitive to a touch, yet are certainly use-
less for climbing. The leaves of at least two and probably of most
of the species of Clematis, and of Fumaria and Adlumia, spon-
taneously curve from side to side, like the internodes, and are thus
better adapted to seize any distant object. The petioles of the per-
fect leaves, as well as the rudimentary or tendril-like leaves of
Tropeolum tricolorum move spontaneously and slowly towards
their own stem or the supporting stick, which they then clasp ;
these petioles also show some tendency to contract spirally. The
tips of the uncaught leaves of the Gloriosa, as they grow old, con-
tract into a flat spire. These several facts are interesting, as we
shall see, in relation to true tendrils.

It was observed in some cases that, as with twining plants, so
with leaf-climbers, the first internodes which rise from the ground
do not spontaneously revolve; nor are the petioles or tips of the
first-formed leaves sensitive. In.certain species of Clematis the
high development and spontaneous movements of the leaves, with
their highly sensitive petioles, apparently have rendered almost
superfluous the spontaneous movements of the internodes, which
have consequently become enfeebled. In certain species of Zro-
peolum it would appear as if both the spontaneous movements of
the internodes and the sensitiveness of the petioles have become
enfeebled ; and in one species they have been completely lost.

Part I1I.—Trnprit-Bpeartmna PLants.

By tendrils I mean filamentary organs, sensitive to contact and
used exclusively for climbing. By this definition, spines or hooks
and rootlets, all of which are used for climbing, are excluded.
True tendrils are formed by the modification of leaves with
their petioles, of flower-peduncles, perhaps also of branches and
stipules. Mohl, who includes with true tendrils various organs
having a similar external appearance, classes them according to
their homological nature, as being modified leaves, flower-pedun-
cles, &c. This would be an excellent scheme ; but I observe that
botanists, who are capable of judging, are by no means unanimous
on the nature of certain tendrils. Consequently I will describe
tendril-bearing plants by natural families, following Lindley,
and this will in most, or in all, cases keep those of the same homo-

TENDRIL-BEARERS. 49

logical nature together; but I shall treat of each family, one
after the other, according to convenience*. The species to be
described belong to ten families, and will be given in the following
order :—Bignoniacee, Polemoniacee, Leqguninose, Composite, Smi-
lacee, Fumariacee, Cucurbitacee, Vitacee, Sapindacee, Passiflo-
racee.

Breanontacex.—This family contains many tendril-bearers, some
twiners, and some root-climbers. The tendrils are always modified
leaves. Nine species of Bignonia, selected by hazard, are here
described, in order to show what diversity of structure and action
there may be in species of the same genus, and to show how re-
markable the action of the tendrils may be in some cases. The
species, taken together, afford connecting links between twiners,
leaf-climbers, tendril-bearers, and root-climbers.

Bignonia (an unnamed species from Kew, closely allied to B.
unguis, but with smaller and rather broader
leaves).—A_ young shoot from a cut-down
plant made three revolutions against the
sun, at an average rate of 2h.6m. The
stem is thin and flexible and twined, as-
cending, from left to right, round a slender
vertical stick as perfectly and as regularly
as any true twining-plant. When thus
ascending, it makes no use of its tendrils
or its petioles ; but when it twined round
a rather thick stick, and its petioles were pear
brought into contact with it, these curved ete Se api

species from Kew.
round the stick, showing that they have
some degree of irritability. The petioles also exhibit a slight

Fig. 5¢.

* As far as I can make out, the history of our knowledge on tendrils is as
follows :—We have seen that Palm and Von Mohl observed about the same
time the singular phenomenon of the spontaneous revolving movement of
twining-plants. Palm (S. 58), I presume, observed likewise the revolving move-
ment of tendrils ; but I do not feel sure of this, for he says very little on the
subject. Dutrochet fully described this movement of the tendril in the com-
mon Pea. Mohl first discovered that tendrils were sensitive to contact; but
from some cause, probably from observing too old tendrils, he was not aware
how sensitive they were, and thought that prolonged pressure was necessary to
excite movement. Professor Asa Gray, in a paper already quoted, first noticed
the extreme sensitiveness and rapidity of movements in the tendrils of certain
Cucurbitaceous plants.

t This and the following drawings, from which the woodcuts have been en-
graved, were carefully made for me from living plants by my son Mr, George
H. Darwin. wid

E

50 MR. DARWIN ON CLIMBING PLANTS.

degree of spontaneous movement; for in one case they certainly
described minute, irregular, vertical ellipses. The tendrils ap-
parently curve themselves spontaneously to the same side with
the petioles; but the movement was so slight that it may be
passed over. From various causes, it was difficult to observe
the movements of the petioles and tendrils in this and the two
following species. The tendrils are so closely similar in all
respects to those of the following species, that one description
will suffice.

Bignonia unguis—The young shoots revolve, but less regularly
and less quickly than those of the last species. The stem twined
imperfectly round a vertical stick, sometimes reversing its direc-
tion, exactly in the same manner as has been described in so many
leaf-climbers ; and this plant is in itself a leaf-climber, though
possessing tendrils. Each leaf consists of a petiole bearing a pair
of leaflets, and terminating in a tendril, which is exactly like that
above figured, but a little larger. The whole tendril in a young
plant was only about half an inch in length, and is very unlike
most tendrils in shape. It curiously resembles the leg and foot
of a small bird with the hind toe cut off. The straight leg or
tarsus is longer than the three toes, which latter are of equal
length, and, diverging, lie in the same plane; the toes terminate
in sharp and hard claws, much curved downwards, exactly like
the claws on a bird’s foot. The whole tendril apparently repre-
sents three leaflets. The main petiole (but not the two sub-pe-
tioles of the lateral leaflets) is sensitive to contact with any object:
even a small loop of thread after two days caused one to bend up-
wards. The whole tendrils, namely the tarsus and three toes,
especially their under surfaces, are likewise sensitive to contact.
Hence, when a shoot grows through branched twigs, its revolving
movement soon brings the tendril into contact with some twig, and
then all three toes bend (or sometimes one alone), and, after several
hours, seize fast hold of the twig, exactly like a bird when perched.
The tarsus,also, when it comes into contact with a twig,slowly bends,
until the foot is carried quite round, and the toes pass on each side
of the tarsus, or seize hold of it. If the main petiole bearing the
leaflets comes into contact with a twig, it likewise bends round,
until the tendril touches its own petiole or that of the opposite
leaf, which is then seized. The petioles, and probably even
the tendrils in a slight degree, move spontaneously; hence
when a shoot attempted to twine round an upright stick, both
petioles after a time came into contact with it, and the contact

ad

TENDRIL-BEARERS. 51

caused still further bending; so that ultimately both petioles
clasped the stick in opposite directions, and the foot-lke tendrils,
seizing on each other or on their petioles, fastened the stem to the
support with surprising security. Hence this species, differently
from the last, uses its tendrils, by the intervention of the spon-
taneously moving and sensitive petioles, when the stem twines
round a thin vertical stick. Both species use their tendrils
in the same manner when passing through a thicket. This plant
seems to me the most efficient climber which I have examined ;
and it probably could ascend a polished stem incessantly tossed by
heavy storms. To show how important vigorous health is for the
action of all the parts, I may mention that when I first examined
a plant which was growing pretty well, though not vigorously,
I concluded that the tendrils acted only like the hooks on a
bramble, and that this was the most feeble and ineflicient of all
climbers !

Bignonia Tweedyana.—This species is closely allied to, and be-
haves in all respects like the last ; perhaps it twines round a ver-
tical stick rather better. On the same plant, one branch twined
in one direction and another in an opposite direction. The inter-
nodes in one ease made two circles, each in 2h. 33m. Iwas enabled
in this species to observe, better than in the two preceding, the
spontaneous movements of the petioles: one described three small
vertical ellipses in the course of eleven hours, another moved
laterally in an irregular spire. Some little time after the stem
has twined round an upright stick, and is securely fastened to
it by the clasping petioles and tendrils, it emits at the base of
its leaves aérial roots, which curve partly round and adhere to
the stick; so that this one species of Bignonia combines four
different methods of climbing, generally characteristic of distinct
plants, namely, twining, leaf-climbing, tendril-climbing, and root-
climbing.

In the foregoing three species, when the foot-like tendril has
caught any object, it continues to grow and to thicken, and ulti-
mately it becomes wonderfully strong, in the same manner as we
have seen with the petioles of leaf-climbers. If the tendril
catches nothing, it first slowly bends downwards, and then its
power of clasping is lost. Very soon afterwards it disarticulates
itself from the petiole, like a leaf in autumn from the stem, and
drops off. I have seen this process of disarticulation in no other
tendrils, but when uncaught they soon wither away.

Bignonia venusta,—The tendrils are here considerably modified

E2

52 MR. DARWIN ON CLIMBING PLANTS.

in comparison with those of the previous species. The lower .
part, or tarsus, is four times as long as the three toes; these
are of equal length ; they do notlie in the same plane, but diverge
equally on all sides; their tips are bluntly hooked, so that the
whole tendril makes an excellent grapnel. The tarsus is sensitive
on all sides; but the three toes are sensitive only on their outer
surfaces, which correspond with the under surfaces of the toes in the
tendrils of the previous species. The sensitiveness is not much
developed; for a slight rubbing with a twig did not cause the tar-
sus or toes to become slightly curved until an hour had elapsed ;
subsequently they straightened themselves. Both tarsus and toes
can seize well hold of sticks. ‘When the stem is secured, the ten-
drils are seen spontaneously to sweep large ellipses: the two
opposite tendrils move independently of each other. I have no
doubt, from the analogy of the two following allied species, that
the petioles move spontaneously ; but they are not irritable like
those of B. unguis and B. Tweedyana. The young internodes
also sweep fine large circles, one being completed in 2h. 15m.,
and a second in 2h. 55m. By these combined movements of the
internodes, petioles, and grapnel-like tendrils, the latter are soon
brought into contact with surrounding objects. When a shoot
stands near an upright stick, it twines regularly and spirally round
it ; as it ascends, it seizes the stick with only one of its tendrils,
and, if the stick be thin, the right- and left-hand tendrils
are alternately used. This. alternation follows from the stem
necessarily taking one twist round its own axis for each com-
pleted spire.

The tendrils a short time after catching any object contract
spirally. Those which have caught nothing slowly bend down-
wards, but do not contract spirally. With many plants the
tendrils after a time contract spirally, whether or not they have
caught any object. But this whole subject of the spiral contrac-
tion of tendrils will be discussed after the several tendril-bearing
plants have been described.

Bignonia littoralis —The young internodes revolve in fine large
ellipses. An internode bearing immature tendrils made two revo-
lutions, each in 8 h. 50 m.; but when grown older, with the tendrils
mature, two ellipses were performed, each at the rate of 2h. 44m.
But this species, unlike the preceding, is incapable of spirally
twining round any object: this did not appear due to any want
of flexibility in the internodes, or to the action of the tendrils,
and certainly not to any want of the revolving power ; nor can I

TENDRIL-BEARERS. 53
account for the circumstance. Nevertheless the plant readily
ascends a thin upright stick by its two opposite tendrils, both
seizing the stick some way above, and afterwards spirally con-
tracting. If the tendrils seize nothing, they do not contract
spirally. Bignonia venusta ascended a vertical stick by spirally
twining and by seizing it alternately with its two tendrils like a
sailor pulling himself up a rope hand over hand; our present
species pulls itself straight up, like a sailor seizing with both
hands together the rope above his head.

The tendrils are almost identical in structure with those of the
last species. They continue growing for some time, even after
clasping an object, and when fully grown, though borne by a young
plant, were 9 inches in length. The three divergent toes are
shorter relatively to the tarsus than in the former species; they
are blunt at their tips and but slightly hooked; they are not
quite equal in length, one being rather longer than the others.
The outer surfaces of the three toes are highly sensitive ; for when
lightly rubbed with a twig, they became perceptibly curved in 4m.
and greatly curved in 7 m.; in 7h. they became straight again and
ready to react. The tarsus, for a space of one inch close to the
toes, is sensitive, but in a rather less degree than the toes; for
after a slight rubbing this part required about twice as long a
time to bend. Even the middle part of the tarsus, if acted on
soon after the tendril has arrived at maturity, is sensitive to pro-
longed contact. After the tendrils have grown old, the sensitive-
ness is confined to the toes, when they will only curl very slowly
round a stick, The maturity of the tendril is shown by the
divergence of the three toes, at which period their outer sur-
faces first become irritable. The irritability of the tendril has
little power of spreading from one part to another: thus, when
a stick was caught by the part immediately beneath the three
toes, these often remained sticking out, and never clasped the
stick.

The tendrils revolve spontaneously, The movement begins
before the tendril is converted into a grapnel by the divergence
of the toes, and before any part has become sensitive ; so that the
revolving movement is at this early period quite useless. ‘The move-
ment is at this time slow, two ellipses being completed conjointly
in 24h. 18m. When the tendril was mature, an ellipse was per-
formed in 6h.; so that even at this period the movement is
much slower than that of the internodes. Large ellipses were
swept, both in vertical and horizontal planes, by the tendrils.

5A MR. DARWIN ON CLIMBING PLANTS.

Not only the tendrils, but the petioles bearing them, revolve ;
these petioles, however, are not in the least sensitive. Thus the
young internodes, the petioles, and the tendrils, all at the same
time, go on revolving together, but at different rates. Moreover,
the movements of the opposite petioles and tendrils are quite
independent of each other. Hence, when the whole shoot is
allowed freely to revolve, nothing can be more intricate than
the course and rate followed by the extremity of each tendril. A
wide hemisphere above the shoot is irregularly searched for some
object to be grasped.

One other curious point remains to be mentioned. Some few
days after the toes haye closely clasped a stick, their blunt extre-
mities become, though not invariably, developed into irregular
disk-like balls, which have the singular power of adhering firmly
to the wood. As similar cellular outgrowths will be fully de-
scribed under B. capreolata, I will here say nothing more about
them.

Bignonia equinoctialis, var. Chamberlaynii—The internodes,
the elongated non-sensitive petioles, and the tendrils all have the
power of revolving. The stem does not twine, but ascends a ver-
tical stick in the same manner as the last species. The tendrils
resemble those of the last species, but are shorter; the three
toes are more unequal in length, two of them being about one-
third shorter, and rather thinner than the third; but they vary
in these respects. They terminate in small hard points; and
what is important, they do not develope cellular adhesive disks.
The reduced size of two of the toes, and their lessened sensitive-
ness, seem to indicate a tendency to their abortion ; and the first-
formed tendrils on one of my plants were sometimes quite simple.
We are thus naturally led to the three following species with
simple undivided tendrils.

Bignonia speciosa.—The young shoots revolve irregularly,
making narrow ellipses, or spires or circles, at rates varying from
3h. 30m. to4h. 40 m.; but the plant shows no tendency to twine.
Whilst very young and not requiring any support it does not
produce tendrils. The tendrils of a rather young plant were five
inches in length; they revolve spontaneously, as do the short
and not sensitive petioles. The tendrils, when rubbed, slowly
bend to the rubbed side, and subsequently straighten themselves ;
but they are not highly sensitive. There is something strange in
their action: I repeatedly placed upright, thick and thin, rough
and smooth sticks and posts, and string suspended vertically, near

TENDRIL-BEARERS. 55

them ; but these objects were not well seized. The tendrils, after
clasping an upright stick, repeatedly loosed it again; often
they would not seize it at all, or their extremities did not coil
closely round it. I have observed hundreds of tendrils in Cucur-
pitaceous, Passifloraceous, and Leguminous plants, and never saw
one behave inthis manner. When, however, my plant had grown
to a height of eight or nine feet, the tendrils acted much better ;
and one or both regularly seized an adjoining, thin, upright stick,
not high up as with the three previous species, but in a nearly
horizontal plane; thus the non-twining stem was enabled to
ascend the stick.

The simple undivided tendril ends in an almost straight, sharp,
uncoloured point. The whole terminal part exhibits one odd
habit, which in an animal would be called an instinct; for it con-
tinually searches for any little dark hole into which to insert
itself, I had two young plants; and, after having observed this
habit, I placed near them posts, which either had been bored by
beetles, or which had become fissured in drying. The tendrils, by
their own movement and by that of the internodes, slowly travelled
over the surface of the wood, and when the apex came to a hole
or fissure it inserted itself; for this purpose the terminal part,
half or quarter of an inch in length, often bent itself at right
angles to the basal part. I have watched this process between
twenty and thirty times. The same tendril would frequently
withdraw from one hole and insert its point into a second one. I
have seen a tendril keep its point in one instance for 20 h. and
in another instance for 36 h. in a minute hole, and then with-
draw it.

Whilst the point of a tendril is thus temporarily inserted, the
opposite tendril goes on revolving. The whole length of a tendril
often fits itself closely to the surface of the wood with which
it is in contact; and I have seen a tendril bend at right angles
and place itself in a wide and deep fissure, with the apex again
abruptly bent and inserted into a minute lateral hole. After a
tendril has clasped a stick, it contracts spirally ; if it catches
nothing, it does not contract. When it has adapted itself to the
inequalities of a thick post, though it has clasped nothing, or
when it has inserted its apex into some little fissure, the stimulus
suffices to induce spiral contraction; and this contraction always
draws the tendril away from the post. So that in every case the
above-described nicely adapted movements were absolutely use-
less, excepting once when the tip became jammed in a narrow

56 MR. DARWIN ON CLIMBING PLANTS.

fissure. I fully expected, from the analogy of B. capreolata and
B. littoralis, that the tip would have developed itself into an
adhesive disk; but I could never detect even a trace of this
process. Improbable as the view may be, I am led to suspect that
this habit in the tendril of inserting its tip into dark holes and
crevices has been inherited by the plant after haying lost the power
of forming adhesive disks.

Bignonia picta—This species closely resembles the last in the
structure and movements of its tendrils. I casually examined a
fine growing plant of the allied B. Lindleyi, and this apparently
behaves in all respects in the same manner.

Bignonia capreolata.—We now come to a species having ten-
drils of a different type : but first for the internodes. A young
shoot made three large revolutions, following the sun, at an
average rate of 2h. 23m. The stem is thin and flexible, and I have
seen one make four regular spiral turns round a thin upright stick,
ascending, of course, from right to left, and therefore in a reversed
direction compared with the first-described species; but after-
wards, from the interference of the tendrils, it ascended either
straight up the stick or in an irregular spire. These tendrils are
highly remarkable. In a young plant they were about 24 inches
in length, and much branched, the five chief branches apparently
representing two pairs of leaflets and a terminal one; each branch
is bifid or more commonly trifid toward its extremity, with all the
points blunt but distinctly hooked. A tendril when lightly rub-
bed bends to that side, and subsequently becomes straight again ;
but a loop of thread weighing 4th of a grain produced no effect.
The terminal branches of a tendril twice became in 10m. slightly
eurved when touching a stick; and in 30 m. the tips curled quite
round the stick: the basal part is less sensitive. The tendrils
revolve in an apparently capricious manner, sometimes not at all,
or very slightly, but at other times they describe large regular
ellipses. J could detect no spontaneous movement in the petioles.

At the same time that the tendrils are revolving more or less
regularly, another remarkable movement first begins ; the tendrils
slowly begin to bend from the light towards the darkest side of the
house. J repeatedly changed the position of my plants, and the
successively formed tendrils always ended by pointing, some little
time after. the revolving movement had quite ceased, to the darkest
side. But when I placed a thick post near a tendril, and between
it and the light, the tendril pointed in that direction, In two in-
stances a pair of leaves stood so that one tendril was directed to-

TEN DRIL-BEARERS. 57

wards the light and the other to the darkest side of the house ; the
latter did not move, but the opposite one bent itself first upwards
and then right over its fellow, so that the two became parallel,
one above the other, both pointing to the dark: I then turned the
plant half round ; and the tendril which had turned over recovered
its original position, and the opposite one, which had not moved
before, now turned right over to the dark side. Lastly, on another
plant, three pairs of tendrils were produced by three shoots at the
same time, and all happened to be differently directed: I placed
the pot in a box open only on one side, and obliquely facing the
light ; in two days all six tendrils pointed with unerring truth to
the darkest corner of the box, though to do this each had to bend
in a different manner. Six tattered flags could not have pointed
more truly from the wind than did these branched tendrils from
the stream of light which entered the box. I left these tendrils
undisturbed for above 24h., and then turned the pot half round ;
but they had now lost the power of movement, so that they could
not any longer avoid the light.

When a tendril has not succeeded, either through its own re-
volving movement or that of the shoot, or by turning towards any
object which intercepts the light, in clasping a support, it bends
vertically downwards and then towards its own stem, which it
seizes together with the supporting stick, if there be one. A little
aid is thus given in keeping the stem secure. If the tendril
seizes nothing, it does not contract spirally, but soon withers away
and drops off. If it does seize an object, all its branches contract
spirally.

I have stated that, after a tendril has come into contact with a
stick, in about half an hour it bends round it; but I repeatedly
observed, as with 2. speciosa and its allies, that it again loosed
the stick: sometimes it seized and loosed the same stick three or
four times. Knowing that the tendrils avoided the light, I gave
them a glass tube blackened within, and a well-blackened zine
plate: the branches curled round the tube and abruptly bent them-
selves round the edges of the zinc plate; but they soon recoiled,
with what I can only call disgust, from these objects, and straight-
ened themselves. I then placed close to a pair of tendrils a post
with extremely rugged bark ; twice the tendrils touched it for an
hour or two, and twice they withdrew ; at last one of the hooked
extremities curled round and firmly seized an excessively minute
projecting point of bark, and then the other branches spread them-

58 MR. DARWIN ON CLIMBING PLANTs.

selves out, following with accuracy every inequality of the sur-
face. I then placed a post without bark, but much fissured, and
the points of the tendrils crawled into all the crevices in a beau-
tiful manner. To my surprise, I observed that the tips of imma-
ture tendrils, with the branches not yet fully separated, likewise
crawled, just like roots, into the minutest crevices. In two or
three days after the tips had thus crawled into the crevices, or
after their hooked ends had seized some minute point, the final
process, now to be described, commenced.

This process I discovered by having accidentally left a piece of
wool near a tendril. I then bound a quantity of flax, moss, and
wool (the wool must not be dyed, for these tendrils are ex-
cessively sensitive to some poisons) loosely round sticks, and placed
them near tendrils. The hooked points soon caught the fibres,
even loosely floating fibres, and now there was no recoiling; on the
contrary, the excitement from the fibres caused the hooks to pene-
trate the fibrous matter and to curl inwards, so that each hook
firmly caught one or two fibres, or a small bundle of them. The
tips and the inner surfaces of the hooks now began to swell, and
in two or three days could be seen to be visibiy enlarged. After
a few more days the hooks were converted into whitish, irregular
balls, rather above the ;4)th of an inch in diameter, and formed of
coarse cellular tissue, which sometimes wholly enveloped and
concealed the hooks themselves. The surfaces of these balls secrete
some viscid resinous matter, to which the fibres of the flax, &c.
adhere. When a fibre has become fastened to the surface, the cel-
lular tissue does not grow directly beneath it, but continues to grow
closely on each side ; so that when several adjoining fibres, though
excessively thin, were caught, so many crests of cellular matter,
each not as thick as a human hair, grew up between them, and
these, arching over on both sides, grew firmly together. As the
whole surface of the ball continues to grow, fresh fibres adhere
and are enveloped ; so that I have seen a little ball with between
fifty and sixty fibres of flax crossing at various angles, all imbedded
more or less deeply. Every gradation in the process could be
seen—some fibres merely sticking to the surface, others lying in
more or less deep furrows, or deeply imbedded, or passing through
the very centre of the cellular ball. The imbedded fibres are
so closely clasped that they cannot be withdrawn. The cellular
outgrowth has such a tendency to unite, that two balls pro-
duced from two branches sometimes grow into a single one.

TENDRIL-BEARERS. 59

On one occasion, when a tendril had eurled round a small stick,
half an inch in diameter, an adhesive disk was formed; but gene-
rally the tendrils can do nothing with smooth sticks or posts. If,
however, the tip of any one branch can curl round the minutest
projecting point, the other branches will form disks, especially if
they can find crevices to crawl into. The tendril quite fails to
attach itself to a brick wall.

I infer that the disks or balls secrete some resinous adhesive
matter, from the adherence of the fibres to them, but more espe-
cially from such fibres becoming loose after immersion in sul-
phuric ether, which likewise removes small, brown, glistening points
that can generally be seen on the surface of the older disks. If
the hooked extremities of the tendrils touch nothing, the cellular
outgrowth, as far as I have seen, never commences ; but tem-
porary contact during a moderate time causes small disks to be
formed. I have seen eight disks developed on one tendril. After
the development of the disks, the tendrils, which now become
spirally contracted, likewise become woody and very strong. A
tendril in this state supported nearly seven ounces, and would
apparently have supported a considerably greater weight had not
the fibres of flax to which the disks were attached yielded.

From the facts above given, I infer that though the tendrils
of this Bignonia can occasionally adhere to smooth cylindrical
sticks and often to rugged bark, yet that they are specially adapted
to climb trees clothed with lichens, mosses, or with Polypodiwm
incanum, which I hear from Professor Asa Gray is the case with
the forest-trees where this Bignonia grows. Finally, it is a highly
remarkable fact that a leaf should become metamorphosed into a
branched organ which turns from the light, and which can by its
extremities either crawl like roots into crevices, or seize hold of
minute projecting points, these extremities subsequently form-
ing cellular masses which envelope by their growth the finest fibres
and secrete an adhesive cement.

Eccremocarpus scaber (Bignoniacee).—Plants in the green-
house, though growing pretty well, showed no spontaneous move-
ments in their shoots or tendrils; but, removed to the hot-house,
the young internodes revolved at rates varying from 3h. 15 m. to
Lh. 13 m.: at this latter unusually quick rate one large circle
was swept; but generally the circles or ellipses were small, and
sometimes the course pursued was extremely irregular. An inter-
node which had made several revolutions would sometimes stand

60 MR. DARWIN ON CLIMBING PLANTS.

quite still for 12 h. or 18 h., and then recommence revolving ; such
strongly marked interruptions in the moyements I have observed
in no other plant.

The leaves bear four leaflets, themselves subdivided, and termi-
nate in a much-branched tendril. The main petiole of the leaf,
whilst young, moves spontaneously by curving itself, and follows
nearly the same irregular course, and at about the same rate, with
the internodes. The movement to and from the stem is naturally
the most conspicuous, and I have seen the chord of the curved
petiole forming an angle of 59° with the stem, and an hour after-
wards an angle of 106°. The two opposite petioles do not move
together, and one is sometimes raised so much as to stand close to
the stem whilst the other is not far from horizontal. The basal part
of the petiole moves less than the distal part. The tendrils, be-
sides being carried by the moving petioles and internodes, them-
selves move spontaneously, and the opposite tendrils occasionally
move in opposite directions. By these several movements of the
young internodes, of the petioles, and of the tendrils, all acting
together, a wider space is swept for a support.

In young plants, the tendrils are about three inches in length :
they bear two lateral and two terminal branches ; and each branch
bifurcates twice, with the tips forming blunt double hooks, having
both points directed to the same side. All the branches are sen-
sitive on all sides; and after being lightly rubbed, or after coming
into contact with a stick, they bend in about 10m. One that be-
came, after a light rub, curved in 10 m., continued bending for
between 3h. and 4h., but subsequently in 8h. or 9h. became
straight again. Tendrils, which have caught nothing, ultimately
contract into an irregular spire, as they do also, only much more
quickly, after clasping a support. In both cases the petiole bear-
ing the leaflets, which at first is straight and inclined a little
upwards, moves downwards and abruptly bends itself in the middle
into a right angle; but this is more plainly seen in L. miniatus
than in Z. scaber. The action of the tendrils in the Kecremo-
carpus is in some respects analogous to that of the tendrils of
Bignonia capreolata; but the whole tendril does not move from
the light, nor do the hooked tips become enlarged into cellular
disks. After the tendrils have come into contact with moderately
thick cylindrical sticks or with rugged bark, the several branches
may be observed slowly to lift themselves up, change their posi-
tion, and again come into contact with them. The object of these

TENDRIL-BEARERS. 61

movements is that the double hooks at the extremities of the
branches, which naturally face in all directions, may be brought
into contact with the wood. I have watched a tendril, which had
bent itself at right angles abruptly round the sharp corner of a
post,neatly bring every single hook into contact with both surfaces.
The appearance suggested the belief, that though the whole tendril
is not sensitive to light, yet that the tips are so, and that they
turn and twist themselves towards any opaque surface. Ultimately
the branches arrange and fit themselves very neatly to all the irre-
gularities of the most rugged bark, so that they resemble in
their irregular course a river with its branches, as engraved on
a map. But when a tendril has thus arranged itself round a
rather thick smooth stick, the subsequent spiral contraction
generally spoils the neat arrangement, and draws the tendril
from its support. So it is, but not in quite so marked a manner,
when a tendril has spread itself over the rugged bark of a thick
trunk; for in this case the spiral contraction of the opposite
branches sometimes draws the opposed hooks firmly to their
supports. Hence we may conclude that these tendrils are not
perfectly adapted to seize smooth moderately thick sticks or rug-
ged bark. When a thin stick or twig is placed near a tendril,
its terminal branches wind quite round it and seize their own
lower branches or main stem; and the stick is thus firmly, but
not neatly, grasped. The extremities of the branches, close to the
little double hooks, have a strong tendency to curl inwards, and
are excited to this movement by contact with the thinnest objects.
This accounts for the tendrils apparently preferring such objects
as excessively thin culms of a grass, or the long flexible bristles
of a brush, or the thin rigid leaves of an Asparagus, all which
objects they seized in an admirable manner; for the tips of
each sub-branch seized one, two, or three of the bristles, for in-
stance, and then the spiral contraction of the several branches
brought all these little parcels close together, so that thirty or
forty bristles were drawn into a single bundle, and afforded an
excellent support.

PorEMontacem.—Oobea scandens.—This is an admirably con-
structed climber. The terminal portion of the petiole, which
forms the tendril, was in one very fine specimen eleven inches in
length, with the basal part bearing two pairs of leaflets, only two
and ahalf inches inlength. The tendril of the Cobea revolves more
rapidly and vigorously than in any other plant observed by me,
with the exception of one Passiflora. It made three fine large,nearly

62 MR. DARWIN ON CLIMBING PLANTS.

circular sweeps, against the sun, each in 1h. 15 m., and two others
in Lh. 20m. andlh. 23m. Sometimes it travels in a much in-
clined position, and sometimes nearly upright. The lower part
moves but little, and the basal portion or petiole, which bears the
leaflets, not at all; nor do the internodes revolve ; so that here we
have the tendril alone moving. With most of the species of
Bignonia and with Eecremocarpus, the internodes, tendrils, and
petioles all revolve. The long, straight, tapering main stem of the
tendril of the Cobea bears alternate branches ; and each branch is
several times divided, with the finer branches as thin as very thin
bristles, extremely flexible, so that they are blown about by a
breath of air, yet strong and highly elastic. The extremity of
each branch is a little flattened, and terminates in a minute double
(but sometimes single) hook, formed of hard, transparent, woody
substance, and as sharp as the finest needle. On the eleven-inch
tendril I counted ninety-four of these beautifully constructed
little hooks. They readily catch soft wood, or gloves, or the skin
of the hands. Excepting these hardened hooks, and excepting
the basal part of the central stem of the tendril, every part of
eyery branch is highly sensitive on all sides to a slight touch, and
bends in a few minutes towards the touched side. By lightly
rubbing several branches on different and opposite sides, the whole
tendril rapidly assumes an extraordinarily crooked shape: these
movements from contact do not interfere with the ordinary re-
volving movement. The branches, after becoming greatly curved
from being touched, straighten themselves at a quicker rate than
in almost any other tendril seen by me, namely, in between half
an hour and an hour. After the tendril has caught any object,
the spiral contraction also begins after an unusually short interval
of time, namely, in about twelve hours.

Before the tendril is mature, the terminal branches cohere and
the hooks are curled closely inwards: at this period no part is sensi-
tive to a touch; but as soon as all the branches have diverged and
the hooks stand out, full sensitiveness is acquired. It is a singular
circumstance that the immature tendril, before becoming sensitive,
begins to revolve at its full velocity : this movement must be use-
less, as the tendril in this state can catch nothing: it is a rare
instance of a want, though only for a short time, of perfect co-
adaptation in the structure and functions of a climbing-plant.
The petiole with the tendril perfectly matured, but with the leaf-
lets still quite small, stands at this period vertically upwards, the
young growing shoot or axis being thrown to one side. The ten-

TENDRIL-BEARERS. 63

dril thus standing vertically up sweeps a circle right above the stem,
and is well adapted to catch some object above, and to favour the
ascent of the plant. The whole leaf, with its tendril, after a short
time, bends downwards to one side, allowing the next succeeding
leaf to become vertical, and ultimately it assumes a horizontal
position ; but, before this has occurred, the tendril, supposing it
to have caught nothing, has lost its powers of movement and has
spirally contracted into an entangled mass. In accordance with
the rapidity of all the movements, their duration is short : in a
plant growing vigorously from being placed in a hot-house, a
tendril only revolved for about 36 hours, counting from the period
when it became sensitive; but during this period it probably
made at least 27 revolutions.

When the branches of a revolving tendril strike against a stick,
they quickly bend round and clasp it; but the little hooks play
an important part, especially if only the extremity of the tendril
be caught, in preventing its being dragged by the rapid revolving
movement away too quickly for its irritability to act. As soon
as a tendril has bent round a smooth stick or a thick rugged post,
or has come into contact with planed wood (for it can at least
temporarily adhere even to so smooth a surface as this), the same
peculiar movements begin in the branchlets as have been described
in those of the Bignonia capreolata and the Eecremocarpus, namely,
the branchlets lift themselves up and down; those, however, which
have their hooks already directed downwards remain in this posi-
tion and secure the tendril, whilst the others twist about till they
arrange themselves in conformity with every irregularity of the
surface, and bring their hooks, originally facing in various direc-
tions, into contact with the wood. The use of the hooks was
shown by giving the tendrils tubes and slips of glass to catch ; for
these, though temporarily seized, were afterwards invariably lost,
either during the arrangement of the branches or when the spiral
contraction ensued.

The perfect manner in which the branches arrange themselves,
creeping like rootlets over all the inequalities and into any deep
crevice, is quite a pretty sight; for it is perhaps more effec-
tually done than by the tendrils of the former species, and is cer-
tainly more conspicuous, as the upper surfaces of the main stem
and of every branch to the extreme hooks are angular and coloured
green, whilst the lower surfaces are rounded and purple. I was
led to infer, as in the former cases, that light guided these con-
forming moyements of the branches of the tendrils. I made

64 MR. DARWIN ON CLIMBING PLANTS.

many trials with black and white glass and cards to prove it, but
failed from various causes; yet these trials countenanced the
belief. The tendril may be looked at as a leaf split into filaments,
with the segments facing in all directions ; hence, when the reyolv-
ing movement is arrested, so that the light shines on them
steadily in one direction, there is nothing surprising in their
upper surfaces turning towards the light: now this may aid, but
will not account for, the whole movement ; for the segments would
in this case move towards the light as well as turn round to it,
whereas in truth the segments or branches of the tendrils not only
turn their upper surfaces to the light, and their lower surfaces
which bear the hooks to any closely adjoining opaque object (that
is, to the dark), but they actually curve or bend from the light
towards the dark.

When the Cobea grows in the open air, the wind must aid the
extremely flexible tendrils in seizing a support, for I found a mere
breath sufficed to cause the extreme branches of a tendril to catch
by their hooks twigs which they could not have reached by the
revolving movement. It might have been thought that a tendril
thus hooked only by its extremity could not have fairly grasped its
support. But several times I watched cases like the following,
one of which alone I will describe: a tendril caught a thin stick
by the hooks of one of its two extreme branches; though thus
held by the tip, it continued to try to revolve, bowing itself out to
all sides, and thus moving its. branches ; the other extreme branch
soon caught the stick; the first branch then loosed itself, and
then, arranging itself afresh, again caught hold. After a time, from
the continued movement of the tendril, a third branch became
caught by a single extreme hook ; no other branches, as things then
remained, could possibly have touched the stick ; but before long
the main stem, towards its extremity, began just perceptibly to
contract into an open spire, and thus to shorten itself (dragging
the whole shoot towards the stick), and as it continued to try to
revolve, a fourth branch was brought into contact. As the spiral
contraction travelled down the main stem and down the branches
of the tendril, all the lower branches, one after another, were
brought into contact with the stick, and were wound round it and
round their own branches until the whole was tied together in an
inextricable knot round the stick. The branches of a tendril,
though at first so flexible, after having clasped a support for
a time, become rigid and even stronger than they were at first.
Thus the plant is secured to its support in a perfect manner.

TENDRIL-BEARERS. 65

Lxe@uMINnos®.—Piswm sativum.—The common Pea was the sub-
ject of a valuable memoir by Dutrochet*, who discovered that
both the internodes and tendrils revolved in ellipses. The ellipses
are generally very narrow, but sometimes approach to circles: I
several times observed that the longer axis slowly changed its
direction, which is of importance, as the tendril thus sweeps a
much wider circuit. Owing to this change of direction, and
likewise to the movement of the stem towards the light, the
successive irregular ellipses generally form an irregular spire.
I have thought it worth while

to annex a tracing of the course
pursued by the upper inter-
node (the movement of the
tendril being neglected) of a
young plant from 8.40 a.m. to
9.15 pm. The course was

Fig. 6.

Diagram showing the movement
of the upper internodes of the com-
mon Pea, traced on a hemispherical
glass and transferred to paper; re-
duced one-half in size. (Aug. 1st.)

1

traced on a hemispherical glass
placed over the plant, and the
dots with figures give the hours
of observation ; each dot was
joined by a straight line: no
doubt these lines, if the course
had been observed at shorter
intervals, would have been all
curvilinear. The extremity of
the petiole, where the young
tendril arises, was 2 inches
from the glass, so that if a
pencil 2 inches long had been
in imagination affixed to the
petiole, it would have traced
the annexed figure on the
under side of the glass; but
it must be remembered that

Side of room with window.

j i h. m. h. m. m.
the figure is here reduced one- 1. "5 4s, | 9.1 spac. | 18.5 257.
i 2.10 0 10;.9.25> 5 17.5 50 ,,
half. eee - = great: $3) 9” u.3 0” 18.6 25,
: i 4.11 87 , 13.3720 55 O71
sweep towards the light or ie | iss a” 20.7 45 3,
window, the end of the pe- 612% , 1SE EAD: 9h =n on
; FOOD 5 16.5 5 ;, 22.915 5;
tiole swept a space 4 inches 8 130 ,

across in one direction, and 8 inches in another. As a full-
grown tendril is considerably above 2 inches in length, and as the

* Comptes Rendus, tom. xvii. 1843, p. 989.
r

66 MR. DARWIN ON CLIMBING PLANTS.

tendril itself bends and revolves in harmony with the internode,
a considerably wider space than that here specified (and repre-
sented one-half reduced) is swept. Dutrochet observed an ellipse
completed in 1h.20m.; I saw one completed in 1h. 30m. The
direction followed is variable, either with or against the sun.

Dutrochet asserts that the petiole of the leaf spontaneously
moves, a8 well as the young internodes and tendrils; but he
does not say that he secured the internodes; when this was done,
I never detected any movement in the petiole, except to and
from the light.

The tendrils, on the other hand, when the internodes and pe-
tioles were secured, described irregular spires or regular ellipses,
exactly like those made by the internodes. A young tendril, only
14 inch in length, revolved. Dutrochet has shown that when
a plant is placed in a room, so that the light enters laterally, the
internodes travel much quicker to the light than from it: on the
other hand, he asserts that the tendril itself moves from the light
towards the dark side of the room. With due deference to this
great observer, I think he was mistaken, owing to his not having
secured the internodes. I took a young plant with highly sensi-
tive tendrils, and tied the petiole so that the tendril alone could
move; it completed a perfect ellipse in Lh. 30m.; and I then turned
the plant half round, so that the opposite side faced the light, but
this made no change in the direction of the succeeding ellipse.
The next day I watched a plant similarly secured until the tendril
(which was highly sensitive) made an ellipse in a line exactly to
and from the light ; the movement was so great that the tendril
bent itself down at the two ends of its elliptical course into a line
a little beneath the horizon, thus trayelling more than 180 degrees ;
but the curvature was fully as great towards the light as towards
the dark side of the room. I believe Dutrochet was misled by not
having secured the internodes, and by haying observed a plant of
which the internodes and tendrils, from inequality of age, no
longer curved or moved in harmony together.

Dutrochet made no observations on the sensitiveness of the
tendrils; these, whilst young and about an inch in length, with
the leaflets on the petiole only partially expanded, are highly
sensitive; a single light touch with a twig on the inferior or con-
eave surface near the tip caused them quickly to bend, as did
occasionally a loop of thread weighing one-seventh of a grain.
The upper or convex surface is barely or not at all sensitive.
After bending from a touch the tendril straightened itself in

TENDRIL-BEARERS. 67

about two hours, and was ready to act again. As soon as the
tendrils begin to grow old their extremities become hooked, and
they then appear, with their two or three pairs of branches, an
admirable grappling instrument; but this is not really the case,
for at this period the tips have generally quite lost their sensitive-
ness; when hooked on to twigs some were not at all affected, and
others required from 18h. to 24h. to clasp the twigs. Ultimately
the lateral branches of the tendril, but not the middle or main
stem, contract spirally.

Lathyrus aphaca.—As the tendril here replaces the whole leaf
(except occasionally in very young plants), the leaf itself being
replaced in function by the large stipules, it might have been ex-
pected that the tendrils would have been highly organized; this,
however, is not so. They are moderately long, thin, and un-
branched, with their tips slightly curved: they are sensitive whilst
young on all sides, but chiefly on the concave side of the extre-
mity. They have no spontaneous revolving power, but are at first
inclined upwards at an angle of about 45°, then move into a hori-
zontal position, and ultimately bend downwards. The young
internodes, on the other hand, revolve in ellipses, and carry with
them the tendrils: two ellipses were completed, each in nearly
5h.; the longer axes of these two, and of some subsequently
formed ellipses, were directed at about an angle of 45° from the
line of the axis of the previous ellipse. .

Lathyrus grandiflorus.—The plants observed were young, and
not growing vigorously, yet sufficiently so, I think, for my observa-
tions to be trusted, Here we have the rare case of neither inter-
nodes nor tendrils haying any spontaneous revolving power. The
tendrils in vigorous plants are above 4 inches in length, and are
often twice divided into three branches; the tips are curved and
are sensitive on the concave side ; the lower part of the central stem
is hardly at all sensitive. Hence this plant climbs simply by its
tendrils being brought, through the growth of the stem, or the more
efficient aid of the wind, into contact with surrounding objects,
which are then effectually clasped. I may add that the tendrils, or
the internodes, or both, of Vicia sativa spontaneously revolve.

Comeosit2.—Mutisia clematis.—The enormous family of Com-
posite is well known to include very few climbing plants. We
have seen in the Table in the first Part that Jikania is a regular
twiner, and Jutisia is the only genus, as far as I can learn, which
bears tendrils: it is therefore interesting to discover that these
tendrils, though rather less metamorphosed from their primordial

F 2

68 MR. DARWIN ON CLIMBING PLANTS.

foliar nature than most other tendrils, yet display all the ordinary
characteristic movements, both those that are spontaneous and
those excited by contact.

The long leaf bears seven or eight alternate leaflets, and termi-
nates in a tendril which, in a plant of considerable size, was 5
inches in length. It consists generally of three branches, which
evidently represent in a much elongated condition the petioles and
midribs of three leaflets ; for the branches of the tendril are exactly
like the petioles and midribs of the leaflets, being square on the
upper surface, furrowed, and edged with green. Moreover, in the
plant whilst quite young, the green edging to the branches of
the tendrils sometimes expands into narrow lamine or blades.
Each branch is curved a little downwards, and ‘is slightly hooked
at its extremity,

An upper young internode revolved, judging sat three revolu-
tions, at an average rate of 1h. 38m.; it swept ellipses with the
longer axes directed at right angles to each other; the plant, ap-
parently, cannot twine. The petiole which bears the tendril, and
the tendril itself, are both in constant movement. But the move-
ment is slower and much less regularly elliptical than that of the
internodes; it is, apparently, much affected by the light, for the
whole leaf usually sank during the night and rose during the day,
moving in a crooked course to the west. The tips of the tendrils
are highly sensitive on their lower surfaces : one just touched with
a twig became perceptibly curved in 3 m., and another became so
in 5m.; the upper surface is not at all sensitive; the sides are
moderately sensitive, so that two branches rubbed on their ad-
joining sides converged and crossed each other. The petiole of the
leaf and the lower part of the tendril, halfway between the upper
leaflet and the lowest tendril-branch, are not sensitive. A tendril
after curling from a touch became straight again in about 6h., and
was ready to react ; but one that had been so roughly rubbed as
to have coiled into a helix was not perfectly straight after 18h.
The tendrils retain their sensibility to an unusual age; for one
borne by a leaf, with five or six fully developed leaves above it, was
still active. Ifa tendril catches nothing, the tips of its branches,
after a considerable interval of time, spontaneously curl a little
inwards; but if the tendril has clasped some object, the whole
length contracts spirally.

Smitacem.—Smilax aspera, var. maculata.—Aug. St.-Hilaire*
considers the tendrils which rise in pairs from the petiole as

* Lecons de Botanique, &c., 1841, p. 170.

TENDRIL-BEARERS. 69

modified lateral leaflets ; but Mohl (S. 41) ranks them as modified
stipules. These tendrils are from 1} to 13 inch in length, are thin,
and have slightly curved, pointed extremities. They diverge a
little from each other, but stand at first nearly upright. When
lightly rubbed on either side, they slowly bend to that side, and
subsequently become straight again. The back or convex side of a
tendril placed in contact with a stick became just perceptibly
curved in 1h. 20m., but did not completely surround the stick till
48h. had elapsed ; the con-
cave side of another tendril
became considerably curved
in 2h., and fairly clasped the
stick in 5h. As the tendrils
grow old, they diverge more
from each other and slowly
bend towards the stem and
downwards, so that they
project on the opposite side
of the stem to that on which
they arise; they still retain
their sensitiveness, and can
clasp a support placed be-
hind the stem. Owing to
this movement, the plant
can ascend a thin upright
stick, clasping it with the
tendrils which arise from
the leaves placed alternately
on opposite sides of the
stem. Ultimately the two
tendrils belonging to the Smilax aspera.

same petiole, if they do not come into contact with any object,
cross each other (as at B in fig. 7) behind the stem and loosely
clasp it. This movement of the tendrils towards and round the
stem is, to a certain extent, guided by the action of the light ;
for when the plant stood so that one of the two tendrils in
thus slowly moving had to travel towards the light, and the other
from the light, the latter always travelled, as I repeatedly ob-
served, more quickly than its fellow. The tendrils do not con-
tract spirally in any case. Their chance of finding a support
depends on the growth of the plant, on the wind, and on their
own slow backward and downward movement, which is guided, to

Fig. 7.

70 MR, DARWIN ON CLIMBING PLANTS,

a certain extent, by the movement from the light or towards any
dark object ; for neither the internodes nor the tendrils have any
proper revolving movement. From this latter circumstance, from
the slow movements of the tendrils after contact (though their
sensitiveness is retained for an unusual length of time), from their
simple structure and shortness, this plant shows less perfection
in its means of climbing than any other tendril-bearing plant
observed by me. Whilst young and only a few inches in height,
it does not produce any tendrils; and considering that it grows
to only about 8 feet high, that the stem is zigzag, and is furnished,
as well as the petioles, with spines, it is surprising that it should
be provided with tendrils, comparatively inefficient though they
be. The plant might have been left, one would have thought,
to climb by the aid of its spines alone, like our brambles. But,
then, it belongs to a genus some of the species of which are fur-
nished with much longer tendrils; and we may believe that 8.
aspera is endowed with these organs solely from being descended
from progenitors more highly organized in this respect.

FuUMARIACER. — Corydalis claviculata. — According to Mohl
(S. 43), both the leaves and the extremities of the branches
are converted into tendrils. In the specimens examined by
me all the tendrils were certainly foliar, and it is hardly credible
that the same plant should produce tendrils of such widely dif-
ferent homological natures. Nevertheless, from this statement
by Mohl, I have ranked this Corydalis amongst tendril-bearers ;
if classed exclusively by its foliar tendrils, it would be doubtful
whether it ought not to have been placed amongst leaf-climbers,
with its allies, Mwmaria and Adlumia. A large majority of its
so-called tendrils still bear leaflets, though excessively reduced in
size ; some few of them may be properly designated as tendrils, for
they are completely destitute of laminew or blades. Consequently
we here behold a plant in an actual state of transition from a leaf-
climber to a tendril-bearer. Whilst the plant is young, only the
outer leaves, but when full-grown all the leaves, have their extre-
mities more or less perfectly converted into tendrils. I have
examined specimens from one locality alone, viz. Hampshire; and
it is not improbable that plants growing under different conditions
might have their leaves a little more or less changed into true
tendrils,

Whilst the plant is quite young, the first-formed leaves are not
modified in any way, but those next formed haye their terminal
leaflets reduced in size, and soon all the leayes assume the struc-

TENDRIL-BEARERS. Ti

ture represented in the following diagram. This leaf bore nine
leaflets; the lower ones are much subdivided. The terminal
portion of the petiole, about 13 inch in length (above the leaflet
(/) ), is thinner and more elongated than the lower part, and may

Fig. 8.

Corydalis claviculata.
Leaf-tendril, of natural size.

be considered as the tendril. The leaflets borne by this part are
greatly reduced in size, being, on an average, about the tenth of an
inch in length and very narrow; one small leaflet measured one-
twelfth of an inch in length and one-seventy-fifth in breadth, so that
it was almost microscopically minute. All the reduced leaflets have
branching nerves, and terminate in little spines like the fully de-
veloped leaflets. Every gradation can be traced, until we come to
branchlets (as a and d in the figure) which show no vestige of a
lamina or blade. Occasionally all the terminal branchlets of the
petiole are in this latter condition, and we then have a true tendril.

The several terminal branches of the petiole bearing the much-

72 MR. DARWIN ON CLIMBING PLANTS.

reduced leaflets (a, 6, c,d) are highly sensitive, fora loop of thread
weighing only the one-sixteenth of a grain caused them, in under
4h., to become greatly curved: when the loop was removed, the
petioles straightened themselyes in about the same time. The
petiole (e) was rather less sensitive; and in another specimen, in
which the corresponding petiole bore rather larger leaflets, a loop
of thread weighing one-eighth of a grain did not cause curvature
until 18h. had elapsed. Loops of thread weighing one-fourth of a
grain, left suspended on all the lower petioles (to 7) during several
days, produced no effect. Yet the three petioles f, g, andh are not
quite insensible, for when left in contact with a stick for a day or
two they slowly curled round it. So that the sensibility of the
petiole gradually diminishes from the tendril-like extremities to
the base. The internodes are not at all sensitive, which makes
Mohl’s statement that they are sometimes converted into tendrils
the more surprising, not to say improbable.

The whole leaf, whilst young and sensitive, stands almost ver-
tically upwards, as we have seen is the case with many tendrils.
It is in continual movement, and one that I observed swept
large, though irregular, ellipses, sometimes narrow, sometimes
broad, with their longer axes directed to different points of the
compass, at an average rate of about 2h. for each revolution. The
young internodes also, which bear the revolving leaves, likewise
revolve irregularly in ellipses and spires; so that by these com-
bined movements a considerable space is swept for a support. If
the terminal and attenuated portion of the petiole fails in seizing
any object, it ultimately bends downwards and inwards, and then
soon loses all its irritability and power of movement. This bend-
ing down is of a yery different nature from that which occurs with
the extremities of the young leaves in many species of Clematis;
for these, when thus bent or hooked, first acquire their full degree
of sensitiyeness.

Dicentra thalictrifolia.—In this allied plant the metamorphosis
of the terminal leaflets has been complete, and they are converted
into perfect tendrils. Whilst the plant was young, the ten-
drils appeared like modified branches, so that a distinguished
botanist thought this was their nature ; but in a full-grown plant,
there can be no doubt, as I am assured by Dr. Hooker, that the
tendrils are modified leaves. The tendrils, when of full size, are
above 5 inches in length; they bifurcate twice, thrice, or even
four times; their extremities are hooked, but blunt. All the
branches of the tendrils are sensitive on all sides, but the basal

TENDRIL-BEARERS. 73

portion of the main stem is only slightly sensitive. The terminal
branches lightly rubbed with a twig did not curve until from 30m.
to 42m. had elapsed: they slowly became straight again in between
10h. and 20h. <A loop of thread weighing one-eighth of a grain
plainly caused the thinner branches to curve, as did occasionally
a loop weighing one-sixteenth of a grain; but this latter slight
weight, though left suspended, was not sufficient to cause a per-
manent flexure. The whole leaf with its tendril and the young
upper internode together revolve vigorously and quickly, though
irregularly, and sweep a wide space. The figure traced on a bell-
glass was either an irregular spire or a zigzag line. The nearest
approach to an ellipse was an elongated figure of 8, with one end
a little open; this was completed in 1h. 53m. During a period of
6h. 17m. another shoot made a complex figure, apparently repre-
senting three and a half ellipses. When the lower part of the
petiole bearing the leaflets was securely fastened, the tendril itself
described similar but much smaller figures.

This species climbs well. The tendrils after clasping a stick
become thicker and more rigid; but the blunt hooks do not turn
and adapt themselves to the supporting surface, as is the case in
so perfect a manner with some of the Bignoniacew and the Cobea.
In young plants 2 or 3 feet in height, the tendrils, which are only
half the length of those borne by the same plants when grown
taller, do not contract spirally after clasping a support, but only
become slightly flexuous. Full-sized tendrils, on the other hand,
contract spirally, excepting the thick basal portion. Tendrils
which have caught nothing simply bend downwards and inwards,
like the extremities of the leaves of the Corydalis claviculata.
But in all cases the petiole after a time becomes angularly and
abruptly bent like that of the Hecremocarpus.

Cucursiracem.—The tendrils in this family have been ranked
by several competent judges as modified leaves, stipules, and
branches; or the same tendril as part leaf and part branch. De
Candolle considers the tendrils in two of the tribes as different
in their homological nature*. From facts recently adduced, Mr.
Berkeley thinks that Payer’s view is the most probable, namely,
that the tendril is “a separate portion of the leaf itself” f.

* I am indebted to Prof. Oliver for information on this head. In the
Bulletin de la Société Botanique de France, 1857, there are numerous discus-
sions on the nature of the tendrils in this family.

+ Gardeners’ Chronicle, 1864, p. 721. From the affinity of the Cucurbitaces
to the Passifloracese, it might be argued that the tendrils of the former are

74 MR. DARWIN ON CLIMBING PLANTS.

Echinocystis lobata—I made numerous observations on this
plant (raised from seed sent me by Prof. Asa Gray), for here I
first observed the spontaneous revolving movement of the inter-
nodes and of the tendrils ; and knowing nothing of the nature of
these movements, was infinitely perplexed by the whole case, and
by the false appearance of twisting of the axis. My observations
may now be greatly condensed. I recorded thirty-five revolutions
of the internodes and tendrils ; the slowest rate was 2h., and the
average, with no great fluctuations, was Lh. 40m. for each revolu-
tion. Sometimes I tied the internodes, so that the tendrils alone
moved; at other times I cut off the tendrils whilst very young, so
that the internodes revolved by themselves; but the rate was not
thus affected. The course generally pursued was with the sun, but
often in the opposite direction ; sometimes the movement during
a short time would either stop or be reversed; and this apparently
resulted from the interference of the light, shortly after the plant
was placed close to a window. In one instance, an old tendril,
which had nearly ceased revolving, moved in one direction, whilst
the young tendril above moved in the opposite direction. The
two uppermost internodes alone revolve; as the internodes grow
old, the upper part alone moves. The summit of the upper
internode made an ellipse or circle about 3 inches in diameter,
whilst the tip of the tendril swept a circle 15 or 16 inches in dia-
meter. During the revolving movement the internodes become
successively curved to all points of the compass; and often in
one part of their course they were inclined, together with the
tendril, at about 45° to the horizon, and in another part stood
vertical. There was something in the appearance of the revolving
internodes which continually gave the false impression that their
movement was due to the weight of the long and spontaneously
revolving tendril; but, on suddenly cutting off the tendril with a
sharp scissors, the top of the shoot rose very little, and went on
revolving: this false appearance is apparently due to the inter-
nodes and tendrils all curving and moving harmoniously together.

I repeatedly saw that the revolving tendril, though inclined
during the greater part of its course at an angle of about 45°
(in one case of only 37°) above the horizon, in one part of its
course stiffened and straightened itself from tip to base, and became

modified flower-peduncles, as is certainly the case with the tendrils of Passion-
flowers. Mr. R. Holland (Hardwicke’s ‘ Science-Gossip,’ 1865, p. 105) states
that “a cucumber grew, a few years ago, in my own garden, where one of the
short prickles upon the fruit had grown out into a long curled tendril.”

TENDRIL-BEARERS. 45

nearly or quite vertical. This occurred both when the supporting
internodes were free and when they were tied up; but was perhaps
most conspicuous in the latter case, or when the whole shoot hap-
pened to stand in an inclined position. The tendril forms a very
acute angle with the extremity of the shoot, which projects above
the point where the tendril arises; and the stiffening always oc-
curred as the tendril approached, and had to pass in its revolving
course, the point of difficulty—that is, the projecting extremity of
the shoot. Unless the tendril had the power of thus acting, it
would strike against the extremity of the shoot, and be arrested
by it. As soon as all three branches of the tendril have begun to
stiffen themselves in this remarkable manner, as if by a process of
turgescence, and to rise from an inclined into a vertical position,
the revolving movement becomes more rapid; and as soon as the
tendril has succeeded in passing the extremity of the shoot, its
revolving motion, coinciding with that from gravity, often causes
it to fall into its previously inclined position so quickly, that the
end of the tendril could be distinctly seen travelling like the minute
hand of a gigantic clock.

The tendrils are thin, from 7 to 9 inches in length, with a
pair of short lateral branches rising not far from the base. The
tip is slightly but permanently curved, so as to act to a limited
extent as a hook. The concave side of the tip is highly sensitive
to a touch, but not so the convex side, as was likewise observed
by Mohl (8. 65) with other species of the family. I repeatedly
proved this difference by lightly rubbing four or five times the
convex side of one tendril, and only once or twice the concave side
of another tendril, and the latter alone curled inwards: in a few
hours afterwards, when those which had been rubbed on the con-
cave side had recovered themselves, I reversed the process of
rubbing, and always with a similar result. After touching the con-
cave side, the tip becomes sensibly curved in one or two minutes ;
and subsequently, if the touch has been at all rough, it becomes
coiled into a helix. But this helix will, after a time, uncoil itself,
and be ready to act again. A loop of thin thread only one-sixteenth
of a grain in weight caused a temporary flexure in a tendril. One
of my plants had two shoots near each other, and the tendrils
were repeatedly drawn across each other, but it is a singular fact
that they did not once catch each other. It would appear as if
the tendrils had become habituated to the contact of other tendrils,
for the pressure thus caused would apparently be greater than that
caused by a loop of soft thread weighing only the one-sixteenth

76 MR. DARWIN ON CLIMBING PLANTS.

of a grain. So it would appear that the tendrils are habituated
to drops of water or to rain; for artificial rain made by violently
flirting a wet brush produced not the least effect on them. I
repeatedly rubbed rather roughly the lower part of a tendril,
but never caused any curvature; yet this part is sensitive to
prolonged pressure, for when it came into contact with a stick, it
would slowly bend round it.-

The revolving movement is not stopped by the extremity curl-
ing after having been touched. When one of the lateral branches
of a tendril has firmly clasped any object, the middle branch con-
tinues to revolve. When a stem is bent down and secured, so
that its tendril depends but is left free to move, its previous re-
volving movement is nearly or quite stopped; but it begins to
rise in a vertical plane, and as soon as it has become horizontal
the revolving movement recommences. I tried this four times ;
generally the tendril rose to a horizontal position in an hour or an
hour and a half; but in one case, in which the tendril depended
at an angle of 45° beneath the horizon, the movement took two
hours ; in another half-hour the tendril rose to 28° above the
horizon and recommenced revolving. This upward vertical move-
ment is independent of the action of light, for it took place twice
in the dark, and another time with the light coming in on one side
alone. The movement no doubt is guided by opposition to the force
of gravity, as in the case of the ascent of the plumules of germi-
nating seeds.

A tendril does not long retain its revolving power; as soon as
this ceases, it bends downwards and contracts spirally. But after
the revolving movement has ceased the tip still retains fora short
time its sensitiveness to contact, but this can be of little service to
the plant.

Though the tendril is highly flexible, and though the extremity
travels, under favourable circumstances, at about the rate of an
inch in two minutes and a quarter, yet its sensitiveness to contact
is so great that it hardly ever fails to seize a thin stick placed in
its path. The following case surprised me much: I placed a thin,
smooth, cylindrical stick (and I repeated the experiment seven
times) so far from a tendril, that its extremity could only curl half
or three-quarters round the stick; but I always found in the
course of a few hours afterwards that the tip had managed to
curl twice or even thrice quite round the stick. I at first thought
that this was due to rapid growth; but by coloured points and
measurements I proved that there was no sensible increase of

TENDRIL-BEARERS. V4

length by growth. When a stick, flat on one side, was similarly
placed, the tip of the tendril could not curl beyond the flat surface,
but coiled itself into a helix, which, turning to one side, lay flat
on the little flat surface of wood. In one instance a portion of
tendril three-quarters of an inch in length was thus dragged on
to the flat surface by the coiling in of the helix. But the tendril
thus acquires a very insecure hold, and generally slips off: in one
case alone the helix subsequently uncoiled itself, and the tip then
passed round and clasped the stick. The formation of a helix on
the flat side of a stick apparently shows us that the continued
striving of the tip to curl itself closely inwards gives the force
which drags the tendril round a smooth cylindrical stick. In this
latter case, whilst the tendril was slowly and quite insensibly
crawling onwards, I several times observed through a lens that
the whole surface was not in close contact with the stick; and I can
understand the onward movement only by supposing that it is
slightly vermicular, or that the tip alternately straightens itself a
little and then again curls inwards, thus dragging itself onwards by
an insensibly slow, alternate movement, which may be compared
to that of a strong man suspended by the ends of his fingers to
a horizontal pole, who works his fingers onwards until he can
grasp the pole with the palm of his hand. However this may be,
the fact is certain that a tendril which has caught a round stick by
its extreme point can work itself onwards until it has passed twice
or even thrice round the stick, and has permanently grasped it.
Hanburya Mexicana.—The young internodes and tendrils of this
anomalous member of the family revolve in the same manner and
at about the same rate with the Echinocystis. The stem does not
twine, but can ascend an upright stick by the aid of its tendrils.
The concave tip of the tendril is very sensitive ; after rapidly coil-
ing into a loop from a single touch, it straightened itself in 50m.
The tendril, when in full action, stands vertically up, with the
young projecting extremity of the shoot thrown a little on one
side out of the way; but the tendril bears near its base, on the
inner side, a short branch, which projects out at right angles, like
a spur, with the terminal half bowed a little downwards. Hence,
as the main vertical branch of the tendril revolves, the spur, from its
position and rigidity, cannot pass over the extremity of the shoot in
the same curious manner as do the three branches of the tendril
of the Echinocystis by stiffening themselves at the proper point,
but is pressed laterally against the young shoot in one part of the
revolving course, and in another part is carried only a little

78 MR. DARWIN ON CLIMBING PLANTS,

way from it. Hence the sweep of the lower part of the tendril
of the Hanburya is much restricted. Here a nice case of co-
adaptation comes into play: in all the other tendrils observed by
me the several branches become sensitive at the same period; had
this been the case with the Hanburya, the rectangular spur-like
branch being pressed, during the revolving movement, against the
projecting end of the shoot, would infallibly have seized it in a
highly injurious manner. But the main tendril, after revolving
for a time in a vertical position, spontaneously bends downwards ;
and this, of course, raises the rectangular branch, which itself
also curves upwards; so that by these combined movements the
spur-like branch rises above the projecting end of the shoot, and
can now move freely without touching it ; then, and not until then,
it first becomes sensitive.

The tips of both branches, when they come into contact with a
stick, grasp it like any ordinary tendril. In a few days after-
wards the inferior surface swells and becomes developed into a
cellular layer, which adapts itself closely to the wood, and firmly
adheres to it. This layer is analogous to the adhesive disks
formed by the tips of the tendrils in some species of Bignonia,
but in the Hanbwrya the layer is developed along the terminal
portion of the tendril, sometimes for a length of 14 inch, but not at
the extreme tip. The layer is white, whilst the tendril is green,
and near the tip it could sometimes be seen to be thicker than the
tendril itself; it generally spreads a little beyond the sides of the
tendril, and its edge is fringed with free elongated cells, which
have enlarged globular or retort-shaped heads. This cellular
layer apparently secretes some resinous cement ; for its adhesion
to the wood was not lessened by immersion for 24h. in alcohol or
water, but was quite loosened by the action during the same period
of ether and turpentine. After the tendril has once firmly coiled
itself round a stick, it is dificult to imagine of what use the for-
mation of the adhesive cellular layer can be. Owing to the spiral
contraction, which ensues after a time, whether or not the tendril
has clasped any object, it was never able to remain, excepting in
one instance, in contact with a thick post or a nearly flat surface ;
if it could have become attached to such objects by means of the
adhesive cellular layer, this layer would evidently have been of
service to the plant. I hear from Dr. Hooker that several other
Cucurbitaceous plants have adherent tendrils.

Of other Cucurbitacex, I observed in Bryonia dioica, Cucurbita
ovifera, and Cucwmis sativa, that the tendrils were sensitive and

TENDRIL-BEARERS. 79

revolved ; in the latter plant, Dutrochet* saw the movement of
the tendril reversed; but whether the internodes as well as the
tendrils revolve in these several species I did not observe. In
Anguria Warscewiczii, however, the internodes, though thick and
stiff, do revolve: in this plant the lower surface of the tendril,
some time after clasping a stick, produces a coarsely cellular layer
or cushion, fitting the wood, like that formed by the tendril of the
Hanburya; but it was not in the least adhesive. In Zanonia
Indica, which belongs to a different tribe of the family, both the
forked tendrils and the internodes revolved, in periods between
2h. 8m. and 3h. 35 m., moving against the sun.

Viracex.—In this funtly mide in the two following, ey
the Sapindacee and Passifloracer, the tendrils are modified flower-
peduncles ; so that they are axial in their nature. In this respect
they differ from those of all the first described families, but
perhaps not from those of the Cucurbitacer. The homological
nature, however, of a tendril seems to make no difference in its
action.

Vitis vinifera.—The tendril is thick and of great size; one from

Fig. 9.

Tendril of the Vine.
A. Peduncle of tendril. C. Shorter branch.
B. Longer branch, with a scale at its base. D. Petiole of opposite leaf.

a vine not growing vigorously out of doors, measured 16 inches
in length. It consists of a peduncle (A), bearing two branches

* Comptes Rendus, tom. xvii. p. 1005.

80 MR. DARWIN ON CLIMBING PLANTS.

which diverge equally from it. One of the-branches (B) has
a scale at its base, and is always, as far as I have seen, longer
than the other, and very often bifurcates. The several branches
when rubbed become curved, and subsequently straighten them-
selves. After a tendril has clasped any object by its extremity,
it contracts spirally; but this does not occur (Palm, 8. 56) when
no object has been seized. The tendrils move spontaneously from
side to side; and on a very hot day one made two elliptical revo-
lutions at anayerage rate of 2h. 15m. During these movements
a coloured line, painted along the convex surface, became first
lateral and then concave. The separate branches have inde-
pendent movements; after a tendril has spontaneously revolved
for a time, it bends from the light towards the dark: I do not
give this latter statement on my own authority, but on that of
Mohl and Dutrochet; Mohl (S. 77) says that in a vine planted
against a wall the tendrils point towards it, and in a vineyard
generally more or less to the north.

The young internodes spontaneously revolve ; but in hardly any
other plant have I seen so slight a movement. A shoot faced a
window, and I traced its course on the glass during two perfectly
calm and hot days; during ten hours on one day it described a
spire, representing two and a half ellipses. I likewise placed a
bell-glass over a young muscat grape in a hothouse, and it made
three or four extremely minute oval revolutions each day: the
shoot moved less than half an inch from side to side; and had it
not made at least three revolutions during the same day when the
sky was uniformly overcast, I should have attributed the motion
to the varying action of the light. The extremity of the shoot is
more or less bent downwards; but the extremity never reverses
its curvature, as so generally occurs with twining plants.

Various authors (Palm, 8S. 55; Mohl, 8. 45; Lindley, &c.)
believe that the tendrils of the vine are modified flower-peduncles.
I here give a drawing (fig. 10) of the ordinary state of a flower-
peduncle in bud: it consists of the “common peduncle” (A); of
the “ flower-tendril” (B), which is represented as having caught
a twig; and of the “sub-peduncle”’ (C) bearing the flower-buds.
The whole peduncle moves spontaneously, like a true tendril, but
in a less degree, and especially when the sub-peduncle (C) does
not bear many flower-buds. The common peduncle (A) has not
the power of clasping a support, nor has the corresponding part
in the true tendril. ‘The flower-tendril (B) is always longer than
the sub-peduncle (C), and has a scale at its base; it sometimes

TENDRIL-BEARERS. 81

bifurcates, and therefore corresponds in every detail with the
longer scale-bearing branch (B, fig. 9) of the true tendril. It is,
however, inclined backwards from the sub-peduncle (©), or stands
at right angles with it, and is thus adapted to aid in carrying the
future bunch of grapes. The flower-tendril (B), when rubbed,
curves and subsequently straightens itself; and it can, as shown
in the drawing, securely clasp a support. I have seen an object
as soft as a young vine-leaf caught by one.

The lower and naked part of the sub-peduncle (C) is likewise

Fig. 10.

Flower of the Vine.

A. Common Peduncle. C. Sub-Pedunele.
B. Flower-tendril, with a scale at its base. D. Petiole of opposite leaf.

slightly sensitive toa rub, and I have seen it distinctly bent round
a stick and even partly round a leaf with which it had come into
contact. That the sub-peduncle has the same nature as the cor-
responding branch of the ordinary tendril is well shown when it
bears only a few flowers; for in this case it becomes less branched,
increases in length, and gains both in sensitiveness and in the
power of spontaneous movement. I have twice seen sub-peduncles
(C), bearing only from thirty to forty flower-buds, which had be-
G

82 MR, DARWIN ON CLIMBING PLANTS.

come considerably elongated and had completely wound round
sticks, exactly like true tendrils. The whole length of another sub-
peduncle bearing only eleven flower-buds quickly became curved
when slightly rubbed; but even this scanty number of flowers
rendered the stalk less sensitive than the other branch, that is, the
flower-tendril; for the latter after a lighter rub became curved in
a greater degree and more quickly than the sub-peduncle with its
few flowers. I have seen a sub-peduncle thickly covered with
flower-buds, but with one of the higher lateral branchlets bearing
from some cause only two buds, and this one branchlet had become
much elongated and had spontaneously caught hold of an ad-
joining twig; in fact, it formed a little tendril. The increase of
length in the sub-peduncle (C) with the decreasing number of
its flower-buds is a good instance of the law of compensation.
Hence it is that the whole ordinary tendril is longer than the whole
flower-peduncle ; thus, on one and the same plant, the longest
flower-peduncle (measured from the base of the common peduncle
to the tip of the flower-tendril) was 8} inches in length, whilst the
longest tendril was nearly double this length, namely 16 inches.

The gradation from the ordinary state of the flower-peduncle,
as represented in the drawing (fig. 10), to that of the true tendril
(fig. 9) is perfect. We have seen that the sub-peduncle (C), whilst
still bearing from thirty to forty flower-buds, may become some-
what elongated and partially assume all the characters of the
corresponding branch of the true tendril. From this state we can
trace every stage till we come to a full-sized common tendril,
bearing on the branch which corresponds with the sub-peduncle
one single flower-bud! Hence there can be no doubt that the
tendril is a modified flower-peduncle.

Another kind of gradation well deserves notice. The ae
tendril (B, fig. 10) sometimes produces a few flower-buds;
found thirteen and twenty-two on two flower-tendrils on a vine
growing against my house; in this state they retain their charac-
teristic qualities of sensitiveness and spontaneous movement, but
in a somewhat lessened degree. On vines in hothouses, so many
flowers are occasionally produced by the flower-tendrils that a
double bunch of grapes is the result; and this is technically called
by gardeners a “cluster.” In this state the whole bunch of
flowers presents scarcely any resemblance to a tendril; and,
judging from the facts already given, it would probably possess
little power of clasping a support, or of spontaneous movement.
Such flower-peduncles closely resemble in structure those borne

TENDRIL-BEARERS. 83

by the next genus, Cissus. This genus, as we shall immediately
see, produces well-developed tendrils and ordinary bunches of
flowers; but there is no gradation between the two states. If
the genus Vitis were unknown, the boldest believer in the modi-
fication of species would never, I suppose, have surmised that
the same individual plant, at the same period of growth, would
have yielded every possible gradation between ordinary flower-
stalks for the support of the flowers and fruit, and tendrils used
exclusively for climbing. But the vine clearly gives us this case ;
and it seems to me as striking and curious an instance of tran-
sition as can well be conceived.

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:h. 45 m., 4h. 50m., 4h. 45 m., 4h. 80m., and5h. The
same tendril continues revolving during three or four days. The
tendrils are from 33 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 is
bent abruptly downwards; and this position is probably of service
in keeping it out of the way of the revolving tendril.

The two branches whilst young are highly sensitive ; for-l found
a touch with a pencil so gentle as only just to move the tendril
which was borne at the end of a long flexible shoot, sufficed to
cause it to become perceptibly curved in four or five minutes; the
tendril became straight again in rather above one hour. A loop
of soft thread weighing one-seventh of a grain was thrice tried,
and caused the tendrils to become curved in 380 or 40m.: half
this weight produced no effect. The long foot-stalk is much
less sensitive, for slight rubbing produced no effect; but pro-
longed contact with a stick caused it to bend. The two terminal
branches are sensitive on all sides; if a number of tendrils be just
touched on different sides, two branches of the one on their inner
sides, two on their outer sides, or both branches on the same side,
in about a quarter of an hour they present a curiously different
appearance. Ifa branch be touched at the same time with equal
force on opposite sides, both sides are equally stimulated and
there is no movement. At the beginning of my work, and before

a2

84 MR. DARWIN ON CLIMBING PLANTS.

examining this plant, I had observed only those tendrils which
are sensitive on one side, and these when lightly pressed between
the finger and thumb become curved; but on thus pinching many
times the tendrils of this Cissus no curvature ensued, and I was at
first falsely led to infer that they were not at all sensitive to a touch.

Cissus antarcticus.—The tendrils on a young plant were thick
and straight, with the tips a little curved ; when the concave sur-
face was rubbed with some force they very slowly became curved,
and subsequently became straight again. Hence they are much
less sensitive than the tendrils of the last species ; but they made
two revolutions, following the sun, rather more rapidly, viz. in
3h. 30m. and4h. The internodes do not revolve.

Ampelopsis hederacea, or Virginian Creeper—In this plant
also the internodes do not move more than apparently can be
accounted for by the varying action of the light. The tendrils are
from 4 to 5 inches in length; the main stem sends off several
lateral branches, which have their tips curved, as may be seen in
fig. 11, A. They exhibit no true spontaneous revolving move-
ment, but turn, as was long ago observed by Andrew Knight*,
from the light to the dark. I have seen several tendrils move
through an angle of 180° to the dark side of a case in less than
24 hours; but the movement is sometimes very much slower.
The several lateral branches often move independently of each
other, and sometimes irregularly, without any apparent cause.
These tendrils are less sensitive to a touch than any others ob-
served by me: by gentle but repeated rubbings 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 crawled over a large box-tree clasped several of
the branches. But I have repeatedly seen the tendrils come into
contact with sticks, and then withdraw from them. 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

* Trans. Phil. Soc. 1812, p. 314.

TENDRIL-BEARERS. | 85

little disks or cushions, which adhere firmly to the surface. In
one case these tips became slightly swollen in 38 h. after coming
into contact with a brick; in another case they were considerably
swollen in 48h., and in an additional 24h. they were firmly at-
tached to a smooth board; and lastly, the tips of a younger ten-
dril not only swelled but became attached to a stuccoed wall in
42h. These adhesive disks resemble, except in colour and in
being larger, those of Bignonia capreolata. When they were de-
veloped in contact with a ball of tow, fibres were separately enve-
loped, but not in so effective a manner as with B. capreolata.
Disks are never developed, as far as I have seen, without the
stimulus of at least temporary contact with some object. They
are generally first formed on one side of the curved tip, the whole
of which often becomes so much changed, that a line of green unal-
tered tissue can be traced only along the concave surface. When,
however, a tendril has clasped a cylindrical stick, an irregular
yim or disk is formed along the inner surface at some little distance
from the curved tip; this was also observed (S. 71) by Mohl.
The disks consist of enlarged cells, with smooth projecting hemi-
spherical surfaces, coloured red, and at first gorged with fluid (see
section given by Mohl, S. 70), but they ultimately become woody.

As the disks can almost immediately adhere firmly to such
smooth surfaces as planed and painted wood, or to the polished
leaf of the ivy, this alone would render it probable that some
cement is secreted, as has been asserted to be the case (quoted by
Mohl, S. 71) by Malpighi. I removed a number of disks formed
during the previous year from a stuccoed wall, and placed them in
warm water, diluted acetic acid and alcohol during many hours ;
but the attached grains of silex were not loosened: immersion in
sulphuric ether for 24h. much loosened them ; but warmed essen-
tial oils (I tried oil of thyme and peppermint) in the course of a
few hours completely released every atom of stone. This seems.
to prove that some resinous cement is secreted; the quantity
secreted, however, must be small; for when a plant ascended a
thinly whitewashed wall, the disks adhered firmly to the white-
wash; but as the cement never penetrated the thin layer, they
were easily withdrawn, together with little scales of the white-
wash. It must not be supposed that the attachment is by any
means exclusively effected by the cement; for the cellular out-
growth completely envelopes every minute and irregular projec-
tion, and insinuates itself into every crevice.

A tendril which has not become attached to any body, dogs not

86 MR. DARWIN ON CLIMBING PLANTS,

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 equally
distributed to all the attached disks. For a few days after the

Fig. 11.

Ampelopsis hederacea

A. Tendril, with the young leaf.

B. Tendril, several weeks after its attachment to a wall, with the branches
thickened and spirally contracted, and with the extremities developed into
disks. ‘The unattached branches have withered and dropped off.
attachment of the disks, 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 remains firmly
attached to the stem and to the surface of attachment. In the

TENDRIL-BEARERS. 87

accompanying diagram we may compare the differences of a tendril
(B) some weeks after attachment to a wall, with one (A) from the
same plant, fully grown but unattached. That the change in the
nature of the tissues of the tendril, as well as the act of spiral con-
traction, is consequent on the formation of the disks, 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
a whole tendril when unattached. The gain in strength and dura-
bility 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, esti-
mated to be at least ten years old, was still elastic and supported
a weight of exactly two pounds. This tendril had five disk-bearing
branches of equal thickness and of apparently equal strength ; so
that this one tendril, after having been exposed during ten years
to the weather, would have resisted a strain of ten pounds!

SaPINDACEH.—Cardiospermum halicacabum.—In this family, as
in the last, the tendrils are modified flower-peduncles. In our
present plant there are no organs exclusively used for climbing
like ordinary tendrils; but the two lateral branches of the
main flower-peduncle have been converted into a pair of ten-
drils, corresponding with the single “ flower-tendril’’? of the
common vine. The main peduncle is thin, stiff, and from 3
to 44 inches in length. Near the summit, above two little
bracts, it divides into three branches. The middle one divides
and redivides, and bears the flowers; ul-
timately 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 flat-
tened, with the lower clasping surface desti-
tute of hairs. At first they project straight
up; but soon diverging, they spontaneously
curl downwards so as to become symmetri-
cally and elegantly hooked, as represented | Upper part of the
in the diagram. They are now, whilst the ae ee oc
‘flower-buds are still small, ready for action.

The two or three upper young internodes steadily revolve;
those on one plant made two circles, against the course of the sun,

Fig. 12.

C. halicacabun,

88 . MR. DARWIN ON CLIMBING PLANTS.

in 3h. 12m.; in a second plant the same course was followed, and
_ the two were completed in 3h. 41 m.; in a third plant the inter-
nodes followed the sun, and made two circles in 3h. 47m. The
average rate of these six revolutions was 1h. 46m. The stem
shows no tendency to twine spirally round a support; but the
allied tendril-bearing genus Paullinia is said (Mohl, S. 4) to be a
twiner. By the revolving movement, the flower-peduncles, which
stand up above the end of the shoot, are carried round and round ;
but when the internodes were securely tied, the long and thin
peduncles themselves were seen to be in continued and sometimes
rapid movement from side to side. They swept a wide space, but
only occasionally moyed in a moderately regular elliptical course.
By these combined movements one of the two short hooked ten-
drils, 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 sur-
faces only a slight movement was slowly produced. I hooked a
tendril on to a twig; and in Lh. 45 m. it had curved considerably
inwards ; in 2h, 380 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, after the interval
of several days, closely up into a helix. 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. It never contracts
spirally. Such contraction would apparently have been of service
to the plant in climbing ; nevertheless it climbs pretty well with-
out 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 arising close to
them may possibly be of service in preventing these balloons from
being dashed to pieces by the wind. In the hothouse they served
simply for climbing.

The position of the tendrils alone suffices to show their homo-
logical nature ; but in two instances one of the tendrils produced
at its tip a flower ; this, however, did not prevent the tendril act-
ing properly and curling round a twig. Ina third case the two
lateral branches which ought to have existed as tendrils, both’
produced flowers like the central branch, and had quite lost their
tendril-structure.

TENDRIL-BEARERS. 89

I have only seen, but was not enabled carefully to observe, one
other climbing Sapindaceous plant, namely Paullinia. It was not in
flower, yet thus it bore fine long forked tendrils, differing from
Cardiospermum. So that, in its tendrils, Pawllinia apparently bears
the same relation to Cardiospermum that Cissus does to Vitis.

PassIFLORACE®.—After reading the discussion and facts given
by Mohl (S. 47) on the nature of the tendrils in this family, no
one can doubt that they are modified flower-peduncles. The ten-
drils and true flower-peduncles rise close side by side; and my
son, Mr. W. E. Darwin, made sketches for me of their earliest
state of development in the hybrid P. floribunda. The two organs
at first appear as a single papilla which gradually divides; so that
I presume the tendril is a modified branch of a single 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 other climbing plants in the rapidity of its movements, and all
tendril-bearers in the sensitiveness of its tendrils. The internode
which carries the upper active tendril and which likewise carries
one or two young immature internodes, made three revolutions,
following the sun, at an average rate of 1h. 4m.; it then made,
the day becoming very hot, three other revolutions at an average
rate of between 57 and 58m.; so that the average rate of all six
revolutions was Lh. lm. The apex of the tendril described
ellipses, sometimes narrow and long, sometimes broad and long,
with their longer axes inclined in slightly different directions.
The plant can ascend a thin upright stick by the aid of its ten-
drils; but the stem is too stiff for it to twine spirally round a
stick, even when not interfered with by the tendrils, which had
been successively pinched off at an early age.

When the stem was secured, the tendrils were seen to re-
volve in nearly the same manner and at the same rate as the
internodes. 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 was not sen-
sitive ; but when nearly full-grown they are extremely sensitive.
A single delicate touch on the concave surface of the tip soon
caused it to curve, and in two minutes it formed an open helix.
A. loop of soft thread weighing =};nd of a grain (equal to only two

90 MR. DARWIN ON CLIMBING PLANTS.

millegrammes) placed most gently on the tip, thrice plainly caused
it to curve; as twice did a bent bit of thin platina wire weighing
oth of a grain ;. but this latter weight, when left suspended, did
not suffice to cause 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
with a thin twig their concave tips, and watched them carefully
through a lens; the tips plainly began to bend in the following
times—31, 25, 32, 31, 28, 89, 31, and 80 seconds; so that the
movement was generally perceptible in half a minute after the
touch, but once plainly in 25 seconds. One of the tendrils which
thus became bent in 81 seconds had been touched two hours pre-
viously and had coiled into a helix; thus in this interval it had
straightened itself and had perfectly recovered its sensibility.

I repeated the experiment made on the Echinocystis, and placed
several plants of this Passiflora so close together that the 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 on my hand was felt far more
plainly than that from the loops of thread (weighing =;nd of a
grain) when allowed to fall on it; and these loops, which caused
the tendrils to become curved, had been placed most gently on
them. Hence it is clear, either that the tendrils are habituated to
the touch of other tendrils and to that of drops of rain, or that
they are sensitive only to prolonged though excessively slight
pressure. 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 ;4nd
of a grain, when rolled intoa ball and gently placed on the glands
at the bases of the leaflets of the Mimosa, caused no action. Had
I space, I could advance much more striking cases in plants both
belonging to the same family, of one being excessively sensitive to
the lightest pressure if prolonged, but not to a brief impact; and
of another plant equally sensitive to impact, but not to slight
though prolonged pressure.

Passiflora punctata—The internodes do not move; but the
tendrils regularly revolve. One that was about half-grown and
very sensitive made three revolutions, opposed to the course of

TENDRIL-BEARERS. 91

the sun, in 8h. 5m., 2h.40m., and 2h.50m.; perhaps it
might have travelled more quickly when nearly full-grown. The
plant was placed in front of a window, and I ascertained that,
as with twining stems so with these tendrils, the light accelerated
the movement in one direction and retarded it in the other,
the semicircle towards the light being performed in one instance
in 15 m., 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 straightens
itself, and is again ready to act. A loop of soft thread weighing
7;th of a grain caused the extreme tip to bend; at 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 fric-
tion sufficed to make the tip curl. The tendril, though so sensi-
tive, does not move very quickly after a touch, no conspicuous
change being observable until 5 or 10 m. had elapsed. The con-
vex side of the tip is not sensitive to a touch or to a suspended
loop of thread. In one instance I observed a tendril revolving
with the convex side of the tip forwards, and on coming into con-
tact with a stick it merely scraped up and past the obstacle and
was not able to clasp it; whereas tendrils revolving with the
concave side of their tips 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 towards the extremity and on the concave surface.
When a stick was so placed that the middle of the tendril came
into contact with it, no curvature ensued. In the hothouse a
tendril made two revolutions each in 2h. 22m.; in my cooler
study one was completed in 3h., and a second in 4h. The inter-
nodes 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 h. 20 m., and the next day a broad ellipse in 5h. 7 m.
The extremity being lightly rubbed on the concave surface, be-
came just perceptibly curved in 7 m., clearly curved in 10 m., and
hooked in 20 m.

We have seen that the tendrils in the last three families, namely

92 MR. DARWIN ON CLIMBING PLANTS.

the Vitacew, Sapindacer, and Passifloracer, 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
Polygonacee. In two or three species of Modecca, one of the
Papayaceex, the tendrils, as I hear from Prof. Oliver, occasionally
bear flowers and fruit ; so that at least they are axial in their nature.

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 Zropeolum tricolorum.
On the other hand, it occurs with all tendrils after they have seized
some object, with the few following exceptions,—namely Corydalis
elaviculata, but then this plant might still be called a leaf-climber ;
Bignonia unguis and its close allies, and the Oardiospermum ; though
these tendrils are so short that the contraction could hardly take
place, and would be quite superfluous; and Smilax aspera, the
tendrils of which, though rather short, offer a more marked excep-
tion. In the Dicentra, whilst young, the tendrils are short and do
not contract spirally, but only become slightly flexuous ; the longer
tendrils, however, borne by older plants contract spirally. I have
seen no other exceptions to the rule that all tendrils, after clasp-
ing by their extremities a support, contract spirally. When, how-
ever, the tendril of any plant of which the stem happens to be
immoveably fixed, catches some fixed object, it does not contract,
simply because it cannot; this, however, rarely occurs. In the
common Pea only the lateral branches, and not the central stem
of the tendril, contract; and with most plants, such as the
Vine, Passiflora, Bryony, the basal portion never contracts into a
spire.

I have said that in Corydalis claviculata the end of the leaf or
the tendril (for this part may be indifferently thus designated) does
not contract into a spire. The branchlets, however, of the ten-
dril, after they have wound round thin twigs, become deeply
sinuous or zigzag; and this may be the first indication of the
process of spiral contraction. Moreover the whole end of the
petiole or tendril, if it seizes nothing, ultimately bends abruptly
downwards and inwards, showing that its inferior surface con-
tracts ; and this may be confidently looked at as the first indica-
tion of the power of spiral contraction. For with all true ten-
drils when they contract spirally, it is the lower surface, as Mohl
(S. 52) has remarked, which contracts. If the inferior surface of

TENDRIL-BEARERS. 93

the extremity of a free tendril were to contract quite regularly,
it would roll itself up into a flat helix, as occurs with the Cardio-
spermum ; but if it were to contract in the least on one side, or
if the basal portion were first to contract (as does occur), the
long free extremity could not be rolled up within the basal part,
or if the tip were held during the contraction, as when a tendril
has caught some object,—in all these cases the inevitable result
would be the formation not of a helix, but of a spire, such as
free and caught tendrils form in the act of contraction.

Tendrils of many kinds of plants, if they catch nothing, con-
tract after an interval of several days or weeks into a close spire ;
but in these cases the movement takes place after the tendril
has lost its revolving power and has partly or wholly lost its sen-
sibility, and hangs downwards; this, as we shall presently see,
is a quite useless movement. The spiral contraction of unat-
tached tendrils is a much slower process than that of attached
tendrils: young tendrils which have caught a support and are
spirally contracted may be constantly seen on the same stem with
much older tendrils, unattached and uncontracted. In the Echi-
nocystis I have seen a tendril with the two lateral branches
clasped to twigs and contracted into beautiful spires, whilst the
main branch which had caught nothing remained for many days
afterwards uncontracted. In this plant I once observed a main
branch after it had caught a stick become spirally flexuous in 7 h.,
and spirally contracted in 18h. Generally the tendrils of the
Echinocystis begin to contract in from 12h. to 24h. after catching
something; whilst its unattached tendrils do not begin to con-
tract until two or three or even more days have elapsed after the
revolving movement has ceased. I will give one other case: a
full-grown tendril of Passiflora quadrangularis which had caught
a stick began in 8h. to contract, and in 24h. several spires were
formed ; a younger tendril, only two-thirds grown, showed the first
trace of contraction in two days after clasping a stick, and in two
additional days had formed several spires; hence, apparently, the
contraction does not begin in a tendril until it is grown to nearly
its full length. Another young tendril of about the same age
and length as the last did not catch any object; it acquired its
full length in four days; in six additional days it first became
flexuous, and in two more days had formed one complete spire.
This first spire was formed towards the basal end of the tendril,
and the contraction steadily but slowly progressed towards the
apex ; but the whole was not closely wound up until 21 days had

94 MR, DARWIN ON CLIMBING PLANTS.

elapsed from the first observation, that is until 17 days after the
tendril was fully grown.

The best proof of the intimate connexion between the spiral
contraction of a tendril and the previous act of clasping a support,
is afforded by those tendrils which, when caught, invariably
contract into a spire, whilst as long as they remain unattached
they continue straight, though dependent, and thus wither and
drop off. The tendrils of Bignonia, which are modified leaves,
thus behave, as do the tendrils of the three genera of Vitacee,
and these are modified flower-peduncles. The tendrils, however, of
Eceremocarpus, which is allied to Bignonia, contract spirally even
when they have caught nothing. The uncaught tendrils of the
Cardiospermum, and to a certain extent those of the Mutisia, roll
themselves up not into a spire, but into a helix.

The spiral contraction which ensues after a tendril has caught
a support is of high service to all tendril-bearing plants; hence
its almost universal occurrence with plants of widely different
orders. When a shoot is inclined and its tendril has caught an
object above, the spiral contraction drags up the shoot. When
the shoot is upright, the growth of the internodes, subsequently
to the tendrils having seized some object above, would slacken the
stem were it not for the spiral contraction, which draws up the
internodes as they increase in length. Thus there is no waste of
growth, and the stretched stem ascends by the shortest course.
We have seen in the Cobe@a, when a terminal branchlet of the
tendril has caught a stick, how well the spiral contraction of its
branches successively brings them one after the other into contact
with the stick, until the whole tendril has grasped it in an inex-
tricable knot. When a tendril has caught a yielding object, this
is sometimes enveloped and still further secured by the spiral
folds, as I have seen with Passiflora quadrangularis ; but this action
is of little importance.

A far more important service rendered by the spiral contraction
is that the tendrils are thus made highly elastic. As was pre-
viously remarked under Ampelopsis, the strain is thus equally
distributed to the several attached branches of a branched tendril ;
and this must render the whole tendril far stronger, as branch
after branch cannot separately break. It is this elasticity which
saves both branched and simple tendrils from being torn away
during stormy weather. I have more than once gone on purpose
during a gale to watch a Bryony growing in an exposed hedge,
with its tendrils attached to the surrounding bushes ; and as the

TENDRIL-BEARERS. 95

thick or thin branches were tossed to and fro by the wind, the
attached tendrils, had they not been excessively elastic, would
instantly have been torn off and the plant thrown prostrate. But
as it was, the Bryony safely rode out the gale, like a ship with .
two anchors down, and with a long range of cable ahead to serve
as a spring as she surges to the storm.

With respect to the exciting cause of the spiral contraction,
little can be said. After reading Prof. Oliver’s interesting paper *
on the hygroscopic contraction of legumes, I allowed a number of
different kinds of tendrils to dry slowly, but no spiral contraction
ensued; nor did this occur with the tendrils of the Bryony when
placed in water, diluted alcohol, and syrup of sugar. We know
that the act of clasping a support leads to a change in the
nature of their tissues; and we call this a vital action, and so
we must call the spiral contraction. The contraction is not
related to the spontaneous revolving power, for it occurs in ten-
drils, such as those of Lathyrus grandiflorus and Ampelopsis
hederacea, which do not revolve. It is not necessarily related
to the curling of the tips round a support, as we see in the
case of the Ampelopsis and Bignonia capreolata, in which the
development of the adherent disks suffices to induce the con-
traction. Yet it certainly seems to stand in some close relation
to the curling or clasping movement due to contact with a
support ; for not only does it soon follow this act, but the spiral
contraction generally begins close to the curled extremity, and
travels down towards the base,asif the whole tendril tried to imitate
the movement of its extremity. If, however, a tendril be very
slack, the whole length seems to become almost simultaneously
at first flexuous and then spiral. The spiral contraction of a
tendril when unattached cannot serve any of the useful ends
just described ; it does not occur with many kinds of tendrils
which contract when attached ; and when it does occur, it super-
venes, as we have seen, only after a considerable interval of time.
It may almost be likened to certain instinctive or habitual move-
ments performed by animals under circumstances rendering them
manifestly useless.

When an uncaught tendril contracts spirally, the spire always
runs in the same direction from tip to base. A tendril, on the
other hand, which has caught a support by its extremity, inva-
riably becomes twisted in one part in one direction, and in another
part in the opposite direction ; the oppositely turned spires being

* Trans. Linn. Soc. vol. xxiv. 1864, p. 415.

96 MR. DARWIN ON CLIMBING PLANTS.

separated by short straight portions. This curious and symmetrical
structure has been noticed by several botanists, but has not been

Fig. 13.

A caught tendril of Bryonia dioica, spirally contracted in reversed directions.

explained*, It occurs without exception with all tendrils which
after catching any object contract spirally, but is of course most
conspicuous in the longer tendrils ; it never occurs with uncaught
tendrils ; and when this appears to have happened, it will be found
that the tendril had originally seized some object and had after-
wards been torn free. Commonly all the spires at one end of a
caught tendril run in one direction, and all those at the other end
in the opposite direction, with a single short straight portion in
the middle; but I have seen a tendril with the spires alternately
turning five times in opposite directions, with straight portions
between them; and M. Léon has seen seven or eight such alter-
nations. Whether the spires turn several times in opposite di-
rections, or only once, there are as many turns in the one direction
as in the other. For instance, I gathered ten long and short
caught tendrils of the Bryony, the longest with 38, and the
shortest with only 8 spiral turns ; and the number of turns in one
direction was in every case the same (within one) as in the oppo-
site direction.

The explanation of this curious little fact is not difficult ; I will
not attempt any geometrical reasoning, but will give only prac-
tical illustrations. In doing this, I shall first have to allude to a
point which was almost passed over when treating of Twining-
plants. If we hold in our left hand a bundle of parallel strings,
we can with our right hand turn these round and round, and
imitate the revolving movement of a twining plant, and the strings
do not become twisted. But if we now at the same time hold a
stick in our left hand, in such a position that the strings become

* See M. Isid. Léon in Bull. Soc. Bot. de France, tom. v. 1858, p. 680.

TENDRIL-BEARERS. 97

spirally turned round it, they will inevitably become twisted.
Hence a straight coloured line, painted along the internodes of a
twining plant before it has wound round a support, becomes
twisted or spiral after it has so wound round. I painted a red
line on the straight internodes of a Humulus, Mikania, Ceropegia,
Convolvulus, and Phaseolus, and saw it become twisted as the
plant wound round a stick. It is possible that the stems of some
plants by spontaneously turning on their own axes, at the proper
rate and in the proper direction, might avoid becoming twisted ;
but I have seen no such case.

In the above illustration, the parallel strings were wound round
a stick; but this is by no means necessary, for if wound into a
hollow coil (as can be done with a narrow slip of elastic paper)
there is the same inevitable twisting of the axis. Hence when a
tendril, which is free at its end, coils itself into a spire, it must
either become twisted along its whole length (and this is a case
which I have never seen), or the free extremity must turn round
as many times as there are spires formed. It was hardly neces-
sary to observe this fact; but I did so by affixing little paper
vanes to the extreme points of the tendrils of the Lchinocystis and
Passiflora quadrangularis ; and as the tendril contracted itself into
suecessive spires, the vane slowly revolved.

We can now understand the meaning of the spires being in-
variably turned in opposite directions in those tendrils which,
having caught some object, are thus fixed at both ends. Let us
suppose a caught tendril to make thirty spiral turns in one direc-
tion; the inevitable result will be that it will become thirty times
twisted on its own axis. This twisting not only would require
considerable force, but, as I know by trial, would burst the ten-
dril before the thirty turns were completed. Such a case never
really occurs ; for, as already stated, when a tendril has caught a
support and has spirally contracted, there are always as many
turns in one direction as in the other ; so that the twisting of the
axis in the one direction is exactly compensated by that in the
other. We ean further see how the tendency is given to make coils
in an opposite direction to those, whether turned to the right or to
the left, which are first made. Take a piece of string, and let it
hang down with the lower end fixed to the floor; then wind the
upper end (holding the string quite loosely) spirally round a per-
pendicular pencil, and this will twist the lower part of the string ;
after it has been sufficiently twisted, it will be seen to curve itself
into an open spire, with the curves running in an opposite direc-

i

98 MRE. DARWIN ON CLIMBING PLANTS.

tion to those round the pencil, and consequently with a straight
piece of string between the opposite spires. In short, we have
given to the string the regular spiral arrangement of a tendril
caught at both ends. ‘The spiral contraction generally begins at
the extremity which has clasped a support; and these first-formed
spires give a twist to the axis of the tendril, which necessarily
inclines the basal part into an opposite spiral curvature. I can-
not resist giving one other illustration, though superfluous: when
a haberdasher winds up ribbon for a customer, he does not wind
it into a single coil; for, if he did, the ribbon would twist itself as
many times as there were coils; but he winds it into a figure of
eight on his thumb and little finger, so that he alternately takes
turns in opposite directions, and thus the ribbon is not twisted.
So it is with tendrils, with this sole difference, that they take
several consecutive turns in one direction and then the same
number in an opposite direction ; but in both cases the self-twist-
ing is equally avoided.

Summary on the Nature and Action of Tendrils—In the con-
cluding remarks I shall have to allude to some points which may
be here passed over. In the majority of tendril-bearing genera
the young internodes revolve in more or less broad ellipses, like
those made by twining plants; but the figures described, when
carefully traced, generally form irregular ellipsoidal spires. . The
rate of revolution in different plants varies from one to five hours,
and consequently in some cases is more rapid than with any
twining plant, and is never so slow as with those many twiners,
which take more than five hours for each revolution. The direc-
tion is variable even in the same individual plant. In Passiflora,
the internodes of only one of the species have the power of re-
yolving. The Vine is the weakest revolver observed by me, appa-
rently exhibiting only a trace of a former power. In the Leeremo-
carpus the movement is interrupted by many long pauses. Some,
but very few, tendril-bearing plants can spirally twine up an up-
right stick. Although the twining-power has generally been lost
by tendril-bearers, either from the stiffness or shortness of the
internodes, from the size of the leaves, or from other unknown
causes, the revolving movement well serves to bring the tendrils
into contact with surrounding objects.

The tendrils also have the power of revolving in the same manner
and generally at the same rate with the internodes. The move-
ment begins whilst the tendril is young, but is at first slow. In
Bignonia littoralis eyen the mature tendrils moved much slower

TENDRIL-BEARERS. 99

than the internodes. In all cases the conditions of life must be
favourable for the perfect action of the tendrils. Generally both
internodes and tendrils revolve together; in other cases, as in
Cissus, Cobea, and most Passiflore, the tendrils alone revolve; in
other cases, as with Lathyrus aphaca, the internodes alone move,
carrying with them the motionless tendrils; and, lastly (and this
is the fourth possible case), neither internodes nor tendrils spon-
taneously revolve, as with Lathyrus grandiflorus and the Ampe-
lopsis. In most Bignonias, in the Eecremocarpus, Mutisia, and
the Fumariacee, the petioles as well as the tendrils, together with
the internodes, all spontaneously move together.

The tendrils revolve by the curvature of their whole length,
excepting the extremity and excepting the base, which parts do
not move, or move but little. The movement is of the same nature
as that of the revolving internodes. Hence, if a line be painted
along that surface which at the time happens to be convex, the
line becomes first lateral and then concave, and ultimately again
convex. This experiment can be tried only on the thicker ten-
drils, which are not affected by a thin crust of dried paint. The
extremities, however, of the tendrils, which so often are slightly
curved or hooked, never reverse their curvature; and in this
respect they differ from the extremities of the shoots of twining
plants, which not only reverse their curvature, or at least become
periodically straight, but curve in a greater degree than the lower
portions. But, in fact, the tendril answers to the upper internode
of the several revolving internodes of a twining plant; and in
the former part of this paper it was explained how the several
internodes move together by the whole successively curving to all
points of the compass. There is, however, in many cases this
unimportant difference, that the curving tendril is separated from
the curving internode by a rigid petiole. There is also another
difference, namely, that the summit of the shoot, which in itself
has no power of revolving, projects above the point from which
the tendril arises; but the summit of the shoot is generally
thrown on one side, so as to be out of the way of the revolutions
swept by the tendril. In those plants in which the terminal
shoot is not sufficiently out of the way, the tendril, as we have
seen with the Hchinocystis, as soon as it comes in its revolving
course to this point, stiffens and straightens itself, Bad, rising
up vertically, passes over the obstacle.

All tendrils are sensitive, but in very various degrees, to con-
tact with any object, and curve towards the touched side. With

* H 2

100 MR. DARWIN ON CLIMBING PLANTS.

several plants a single touch, so slight as only just to move the
highly flexible tendril, is enough to induce curvature. Passiflora
gracilis has the most sensitive tendrils which I have seen: a bit
of platina wire ;;th of a grain in weight, gently placed on the
concave point, caused two tendrils to become hooked, as did (and
this perhaps is a better proof of sensitiveness) a loop of soft, thin
cotton thread weighing ,);nd of a grain, or about two milli-
grammes. With the tendrils of several other plants, loops weigh-
ing jth of a grain sufficed. The point of the tendril of the Pas-
siflora gracilis distinctly began to move in 25 seconds after a
touch. Asa Gray saw movement in the tendrils of the Cucurbi-
taceous genus, Sicyos, in 30 seconds. ‘The tendrils of some other
plants, when lightly rubbed, move in a few minutes; in the
Dicentra in half-an-hour ; in the Smilav in an hour and a quarter
or a half; and in the Ampelopsis still more slowly. The curling
movement consequent on a single touch continues to increase for
a considerable time, then ceases ; after a few hours the tendril
uncurls itself, and is again ready for action. When very light
weights were suspended on tendrils of several plants and caused
them to curve, these seemed to become accustomed to so slight a
stimulus, and straightened themselves, as if the loops had been
removed. It makes no difference, as far as I have seen, what sort
of object a tendril touches, with the remarkable exception of drops
of water in the case of the extremely sensitive tendrils of Passiflora
gracilis and of the Echinocystis ; hence we are led to infer that
they have become habituated to showers of rain. As I made no
observations with this view on other tendrils, | cannot say whether
there are more cases of this adaptation. Moreover adjoining ten-
drils rarely catch each other, as we have seen with the Lchinocystis
and Passiflora, though I have seen this occur with the Bryony.
Tendrils of which the extremities are slightly curved or bowed
are sensitive only on the concave surface ; other tendrils, such as
those of the Cobea (though furnished with minute horny hooks)
and those of Cissus discolor, are sensitive on all sides. Hence
the tendril of this latter plant, when stimulated by a touch of
equal force on opposite sides, does not bend. In the tendril of
the Mutisia the inferior and lateral surfaces are sensitive, but not
the upper surface. With branched tendrils, the several branches
all act alike; but in the Hanburya the lateral spur-like branch
does not acquire (for a reason which has been explained) its sen-
sitiveness nearly so soon as the main branch. The lower or basal

part of many tendrils is either not at all sensitive or sensitive only
°

TENDRIL-BEARERS. 101

_ to prolonged contact. Hence we see that the sensitiveness of ten-
drils is a special and localized capacity, quite independent of the
power of spontaneously moving; for the curling of the terminal
portion from a touch does not in the least interrupt the sponta-
neous revolving movement of the lower part. In Bignonia unguis
and its close allies the petioles of the leaves, as well as the ten-
drils, are sensitive to a touch.

Twining plants when they come into contact with a stick, curl
round it invariably in the direction of their revolving movement ;
but tendrils curl indifferently to either side, in accordance with
the position of the stick and the side which is first touched. The
clasping-movement of the extremity apparently is not steady, but
vermicular in its nature, as may be inferred from the manner in
which the tendrils of the Echinocystis slowly crawled round a
smooth stick.

As with a few exceptions tendrils spontaneously revolve, it may
be asked, Why are they endowed with sensitiveness ?—why, when
they come into contact with a stick, do they not, like a twining
plant, spirally wind round it? One reason may be that in most
cases they are so flexible and thin that, when brought into contact
with a stick, they would yield, and their revolving movement
would not be arrested; they would thus be dragged onwards and
away from the stick. Moreover the sensitive extremities haye no
revolving power, and could not by this means curl round any
object. With twining plants, on the other hand, the extremity
of the shoot spontaneously bends more than any other part; and
this is of high importance to the ascending power of the plant, as
may be seen on a windy day. It is, however, possible that the slow
movement of the basal and stiffer parts of certain tendrils, which
wind round sticks placed in their course, may be analogous to that
of twining plants. I doubt this; but I hardly attended sufli-
ciently to this point, and it would be difficult to distinguish
between a movement due to extremely dull sensitiveness and that
resulting from the arrestment of the lower part together with
the continued movement of the terminal part of a tendril.

Tendrils which are only three-fourths grown, and perhaps
even when younger, but not whilst extremely young, have the
power of revolving and of grasping any object which they may
touch. These two capacities generally commence at about the
same period, and fail when the tendril is full grown. But in
the Cobea and Passiflora punctata the tendrils began revolving
in’ a quite useless manner, before they became sensitive. In

102 MR. DARWIN ON CLIMBING PLANTS.

the Echinocystis they retained their sensitiveness for some time
after they had ceased revolving and had drooped downwards ; in
this position, even if they should seize any object, they could be
of little or no use in supporting the stem. It is a rare cireum-
stance thus to be able to detect any imperfection or superfluity
in tendrils—organs which are so admirably adapted for the func-
tions which they have to perform ; but we see that they are not
always absolutely perfect, and it would be rash to assume that any
existing tendril has reached the utmost limit of perfection.

Some tendrils have their revolving motion accelerated and
retarded in moving to and from the light; others, as with the
Pea, seem indifferent to its action ; others move from the light to
the dark, and this aids them in an important manner in finding a
support. In Bignonia capreolata the tendrils bend from the light
to the dark, like a banner from the wind. In the Cobea and
Eccremocarpus the extremities alone twist and turn about, so as
to bring their finer branches and hooks into close contact with
any surface, or into dark crevices and holes, This latter movement
is one of the best adapted exhibited by tendrils.

A short time after a tendril (with some rare exceptions) has
caught a support, it contracts spirally ; but the manner of con-
traction and the several important advantages thus gained have
been so lately discussed, that nothing need be here said on the
subject. Again, tendrils soon after catching a support grow
much stronger and thicker, and sometimes in a wonderful degree
durable; and all this shows how much their internal tissues must
change. Tendrils which have caught nothing soon shrink and
wither ; in some species of Bignonia they disarticulate and fall off
like leaves in autumn.

Any one who did not closely study tendrils of various kinds
would probably infer that their action would always be uniform.
This is the case with most kinds of tendrils, of which the extre-
mities simply curl round objects of any moderate degree of thick-
ness, and of various shapes or natures. But Bignonia shows us
what diversity of action there may be in the tendrils of even
closely allied species. In all the nine species of this genus ob-
served by me the young internodes revolved vigorously ; as did the
petioles of nearly all, but in very unequal degrees ; in three of the
species the petioles were sensitive to contact; the tendrils of all
are sensitive to contact, and likewise revolve, but in some of the
species in a very feeble manner. In the first-described unnamed
species, the tendrils, in shape like a bird’s foot, are of no service

TENDRIL-BEARERS., 1038

when the stem spirally ascends a thin upright stick, but they can
seize any twig or branch lying beneath them ; but when the stem
spirally ascends a somewhat thicker stick, a slight degree of sensi-
tiveness in the petioles is brought into play, and they wind their
tendrils round the stick. In B. wnguisand B. Tweedyana the sen-
sitiveness, as well as the power of movement, in the petioles is
greatly augmented ; and the tendrils and petioles are thus inex-
tricably wound together round thin upright sticks ; but the stem,
in consequence, does not twine so well: B. Tweedyana, in addition,
emits aérial roots which adhere to the stick. In B. venusta the
tendrils have lost the bird’s-foot structure, and are converted into
long three-pronged grapnels ; these exhibit a conspicuous power of
spontaneous movement; the petioles, however, have lost their
sensitiveness. The stem can spirally twine round an upright stick,
and is aided in its ascent by the tendrils alternately seizing the
stick some way above and then spirally contracting. In this and
all the following species the tendrils spirally contract after seizing
any object. In B. littoralis and B. Chamberlaynii the tendrils, which
have the same structure as in B. venusta, and the non-sensitive
petioles and the internodes all spontaneously revolve. The stem,
however, cannot spirally twine, but ascends an upright stick by
both tendrils, seizing it above. In B. littoralis the tips of the
tendrils become developed into adhesive disks. In B. speciosa and
B. picta we have similar powers of movement, but the plant cannot
spirally twine round a stick; it can, however, ascend by clasping
it with one or both of its unbranched tendrils, on their own level ;
and these exhibit the strange, apparently useless, habit of con-
tinually inserting their pointed ends into minute crevices and
holes. In B. capreolata the stem twines in an imperfect manner ;
the much-branched tendrils revolve in a capricious manner, and
they have the power of bending in a conspicuous manner from
the light to the dark; their hooked extremities, even whilst im-
mature, crawl into any crevice, or, when mature, seize any thin
projecting point; in both cases they develope adhesive disks,
which have the power of enveloping by growth the finest fibres.
In the allied Eeeremocarpus the internodes, petioles, and ten-
drils all spontaneously revolve together ; its much-branched ten-
drils resemble those of Bignonia capreolata, but they do not turn
from the light ; and their bluntly hooked extremities, which arrange
themselves so neatly to any surface, do not form adhesive disks ;
they act best when each seizes a few thin stems, like the culms of
a grass, which they afterwards draw together by their spiral con-

104 MR. DARWIN ON CLIMBING PLANTS.

traction into a firm bundle. In the Oobea the tendrils alone
revolve; these are divided into many fine branches, terminating
in sharp little hooks, which crawl into crevices, and are turned by
an excellently adapted movement to any object that is seized. In
the Ampelopsis, on the other hand, there is little or no power of
revolving in any part: the branched tendrils are but little sen-
sitive to contact ; their hooked extremities cannot seize any thin
object ; they will not even clasp a stick, unless in extreme need
of a support; but they turn from the light to the dark, and,
spreading out their branches in contact with any nearly flat sur-
face, the disks are developed. These can adhere, by the secretion
of some cement, to a wall, or even to a polished surface ; and this
is more than the disks of the Bignonia capreolata can effect.

The formation and rapid growth of these adherent disks is one
of the most remarkable peculiarities in the structure and functions
of tendrils. We have seen that such disks are formed by two
species of Bignonia, by the Ampelopsis, and, according to Naudin*,
by the Cucurbitaceous genus Peponopsis adherens. Their deve-
lopment, apparently in all cases, depends on the stimulus from
contact. It is not a little singular that three families so widely
distinct as the Bignoniacez, Vitacew, and Cucurbitacez should all
have species bearing tendrils with this same remarkable pecu-
liarity. Most tendrils, after they have clasped any object, rapidly
increase in strength-and thickness throughout their whole length ;
but some tendrils, when wound round a support either by the
middle or the extremity, become swollen at these points in a
remarkable manner; thus I have seen the clasped portion of a
tendril of the Bignonia Chamberlaynii grown twice ds thick as the
free basal portion, and become wonderfully rigid. In the An-
guria the lower surface of the tendril, after it has wound round a
stick, forms a coarsely cellular layer, which closely fits the wood,
but is not adherent ; in the Hanburya a similar layer is developed,
which is adherent; lastly, in the Peponopsis adherent disks are
formed at the tips of the tendrils. These three last-named genera
belong to the Cucurbitaceze, so that, in this one family, we have a
nearly perfect gradation from a common tendril to one that forms
an adherent disk at its tip; the one small step which is wanted is
a tendril in a state between that of the Anguria and Hanburya—
that is, adherent only in a slight degree or occasionally.

Finally, it may be added that America, which so abounds with
arboreal animals, as has lately been insisted on by Mr. Bates,

* Annales des Sc. Nat. Bot. 4th series, tom, xii. p. 89.

HOOK- AND ROOT-CLIMBERS. 105

likewise, according to Mohl and Palm, abounds with climbing
plants; and, of the tendril-bearing plants examined by me, the
most admirably constructed come from this grand continent,
namely, the several species of Bignonia, Eccremocarpus, Cobea,
and Ampelopsis.

Part IV.—HooxK-ciimpers.—Root-ciimBers.—ConcLupIne
REMARKS.

Hook-climbers.—In my introductory remarks, I stated that,
besides the great class of twining plants, with the subordinate
divisions of leaf-climbers and tendril-bearers, there were hook-
and root-climbers. I mention the former only to say that with
the few which I have examined, namely, Galiwm aparine, Rubus
australis, and some climbing Roses, there is no spontaneous re-
volving movement. If indeed they possessed this power, and
were capable of twining, such plants would be placed in the pre-
vious great class: thus the Hop, which is a twiner, has reflexed
hooks as large as those of the Galium; some other twiners have
stiff reflexed hairs; Dipladenia has a circle of blunt spines at the
base of its leaves ; one tendril-bearing plant alone, as far as I have
seen, namely, Smilax aspera, is furnished with spines. Some few
plants, which apparently depend solely on their hooks, are excel-
lent climbers, as certain Palms in the New and Old Worlds. Even
some of the climbing Roses will ascend the walls of a tall house,
if covered with a trellis: how this is effected I know not; for the
young shoots of one such Rose, when placed in a pot in a window,
bent irregularly towards the light during the day and from it
during the night, hke any other plant; so that it is not easy to
understand how the shoots can get under a trellis close to a wall.

Root-climbers.—A good many plants come under this class, and
are excellent climbers. One of the most remarkable is the Marc-
gravia umbellata, which in the tropical forests of South America,
as I hear from Mr. Spruce, grows in a curiously flattened manner
against the trunks of trees, here and there putting forth claspers
(roots), which adhere to the trunk, and, if the latter be slender,
completely embrace it. When this plant has climbed to the light,
it sends out free and rounded branches, clad with sharp-pointed
leaves, wonderfully different in appearance from those borne by
the stem, as long as it is adherent. This surprising difference in
the leaves I have observed in a plant of JZ dubia in my hothouse.
Root-climbers, as far as I have seen, namely, the Ivy (//edera

106 MR. DARWIN ON CLIMBING PLANTS.

helix), Ficus repens, and F. barbatus, have no power of movement,
not even from the light to the dark. As previously stated, the
Hoya carnosa (Asclepiadacee) is a spiral twiner, and can likewise
adhere by rootlets even to a flat wall; the tendril-bearing Big-
nonia Tweedyana emits roots, which curve half round and adhere
to thin sticks. The Tecoma radicans (Bignoniacee), which is
closely allied to many spontaneously revolving species, climbs by
rootlets ; but its young shoots apparently move about rather more
than can be accounted for by the varying action of the light.

I have not closely observed many root-climbers, but can give
one curious little fact. Ficus repens climbs up walls just like Ivy;
when the young rootlets were made to press lightly on slips of
glass, they emitted (and I observed this several times), after about
a week’s interval, minute drops of clear fluid, not in the least
milky like that exuded from a wound. This fluid was slightly viscid,
but could not be drawn out into threads; it had the remarkable
property of not drying. One drop, about the size of half a pin’s
head, I slightly spread out, and scattered on it some minute
grains of sand. The slip of glass was left exposed in a drawer
during hot and dry weather, and, if the fluid had been water, it
would certainly have dried in one or two minutes ; but it remained
fluid, closely surrounding each grain of sand, during 128 days:
how much longer it would have remained I cannot say. Some
other rootlets were left in contact with the glass for about ten
days or a fortnight, and the drops of fluid secreted by them were
rather larger, and so viscid that they could be drawn out into
threads. Some other rootlets were left in contact during twenty-
three days, and these were firmly cemented to the glass. Hence
we may conclude that the rootlets first secrete a slightly viscid
fluid, and that they subsequently absorb (for we have seen that it
will not dry by itself) the watery parts, and ultimately leave a
cement. When the rootlets were torn from the glass, atoms of
yellowish matter were left on it, which were partly dissolved
by a drop of bisulphide of carbon; and this extremely volatile
fluid was rendered, by what it had dissolved, very much less
volatile.

As the bisulphide of carbon has so strong a power of softening
indurated caoutchouc*, I soaked in it during a short time many

* Mr. Spiller has recently shown (Chemical Society, Feb. 16, 1865), in a
paper on the oxidation of india-rubber, that this substance, when exposed to
the air in a fine state of division, gradually becomes converted into brittle,
resinous matter, very similar to shell-lac. :

ROOT-CLIMBERS. 107

rootlets of a plant which had grown up a plaistered wall. Attached
to two sets of rootlets on the same branch, I found very many
extremely thin threads of a transparent, not viscid, excessively
elastic substance, precisely like caoutchouc. These threads, at
one end, proceeded from the bark of the rootlet, and at the other
end were firmly attached to transparent particles of silex and other
hard substances. There could be no mistake in this observation,
for I played with the threads for a long time, under the microscope,
drawing them out with the dissecting-needles and letting them
spring back again. Yet, as I looked repeatedly at other rootlets,
similarly treated, and could never discover these elastic threads,
I infer that the branch had probably been slightly moved from
the wall at some critical period, whilst the fluid secreted from the
rootlets was in the act of drying and of changing its nature
through the absorption of its watery parts. The genus Ficus
abounds with caoutchouc, and from the facts here given we may
infer that this substance, at first in solution and ultimately modi-
fied into an unelastie cement, is used by Ficus repens to cement
its rootlets to any object which it may ascend. Whether most
other plants, which climb by their rootlets, emit any cement I do
not know; but the rootlets of the Ivy, placed against glass, barely
adhered to it, yet secreted a little yellowish matter. I may add,
that the rootlets of MWarcgravia dubia can adhere firmly to smooth
painted wood.

Vanilla aromatica emits aérial roots a foot in length, which
point straight down to the ground. According to Mohl (S. 49),
these crawl into crevices, and, when they meet with a thin sup-
port, wind round it, like tendrils. A plant which I kept was
young, and did not form long roots; but on placing thin sticks in
contact with them, they certainly bent,in the course of abouta day,
a little to that side, and adhered by their rootlets to the wood ;
but they did not bend quite round the sticks, and afterwards they
repursued their downward.course. If these rootlets are really
sensitive to contact and bend to the touched side, in this case
the class of root-climbers blends into that of tendril-bearers.
According to Mohl, the rootlets of certain species of Lycopodium
likewise act as tendrils.

Concluding Remarks.

Plants become climbers, in order, it may be presumed, to reach
the light, and to expose a large surface of leaves to its action
and to that of the free air. This is effected by climbers with

108 MR. DARWIN ON CLIMBING PLANTS.

wonderfully little expenditure of organized matter, in comparison
with trees, which have to support a load of heavy branches by
a massive trunk. Hence, no doubt, it arises that there are in all
quarters of the world so many climbing plants belonging to so
many different orders. These plants have been here classed under
three heads :—Firstly, hook-climbers, which are, at least in our
temperate countries, the least efficient of all, and can climb only
in the midst of an entangled mass of vegetation. Secondly, root-
climbers, which are excellently adapted to ascend naked faces of
rock : when they climb trees, they are compelled to keep much in
the shade ; they cannot pass from branch to branch, and thus cover
the whole summit of a tree, for their rootlets can adhere only by
long-continued and close contact with a steady surface. Thirdly,
the great class of spiral-twiners, with the subordinate divisions of
leaf-climbers and tendril-bearers, which together far exceed in
number and in perfection of mechanism the climbers of the two
previous classes. These plants, by their power of spontaneously
revolving and of grasping objects with which they come in contact,
can easily pass from branch to branch, and securely ramble over a
wide and sun-lit surface.

I have ranked twiners, leaf- and tendril-climbers as subdivisions
of one class, because they graduate into each other, and because
nearly all have the same. remarkable power of spontaneously re-
volving. Does this gradation, it may be asked, indicate that plants
belonging to one subdivision have passed, during the lapse of
ages, or can pass, from one state to the other ; has, for instance, a
tendril-bearing plant assumed its present structure without having
previously existed as either a leaf-climber or a twiner? If we
consider leaf-climbers alone, the idea that they were primordially
twiners is forcibly suggested. The internodes of all, without ex-
ception, revolve in exactly the same manner as twiners ; and some
few can still twine well, and many others in a more or less imper-
fect manner. Several leaf-climbing genera are closely allied to
other genera which are simple twiners. It should be observed,
that the possession by a plant of leaves with their petioles or tips
sensitive, and with the consequent power of clasping any object,
would be of very little use, unless associated with revolving inter-
nodes, by which the leaves could be brought into contact with
surrounding objects. On the other hand, revolving internodes,
without other aid, suffice to give the power of climbing; so that,
unless we suppose that leaf-climbers simultaneously acquired both
capacities, it seems probable that they were at first twiners, and

CONCLUDING REMARKS. 109

subsequently became capable of grasping a support, which, as we
shall presently see, is a great additional advantage.

From analogous reasons, it is probable that tendril-bearing
plants were primordially twiners, that is, are the descendants of
plants having this power and habit. For the internodes of the
majority revolve, like those of twining plants; and, in a very few,
the flexible stem still retains the capacity of spirally twining round
an upright stick. With some the internodes have lost even the
revolving power. ‘Tendril-bearers have undergone much more
modification than leaf-climbers; hence it is not surprising that
their supposed primordial revolving and twining habits have been
lost or modified more frequently than with leaf-climbers. The
three great tendril-bearing families in which this loss has occurred
in the most marked manner are the Cucurbitacex, Passifloraces,
and Vitacee. In the first the internodes revolve ; but I have heard
of no twining form, with the exception (according to Palm, 8. 29.
52) of Momordica balsamina, and this is only an imperfect twiner.
In the other two families I can hear of no twiners; and the inter-
nodes rarely have the power of revolving, this power being confined
to the tendrils ; nevertheless the internodes of Passiflora gracilis
have this power ina perfect manner, and those of the common Vine
in an imperfect degree: so that at least a trace of the supposed
primordial habit is always retained by some members of the larger
tendril-bearing groups.

On the view here given, it may be asked, Why have nearly
all the plants in so many aboriginally twining groups been con-
verted into leaf-climbers or tendril-bearers? Of what advantage
could this have been to them? Why did they not remain simple
twiners? We can see several reasons. It might be an advantage
to a plant to acquire a thicker stem, with short internodes bearing
many or large leaves; and such stems are ill fitted for twining.
Any one who will look during windy weather at twining plants
will see that they are easily blown from their support ; not so with
tendril-bearers or leaf-climbers, for they quickly and firmly grasp
their support by a much more efficient kind of movement. In
those plants which still twine, but at the same time possess ten-
drils or sensitive petioles, as some species of Bignonia, Clematis,
and Tropeolum, we can readily observe how incomparably more
securely they grasp an upright stick than do simple twiners.
From possessing the power of movement on contact, tendrils can
be made very long and thin; so that little organic matter is ex-
pended in their development, and yet a wide circle is swept.

110 MR. DARWIN ON CLIMBING PLANTS.

Tendril-bearers can, from their first growth, ascend along the outer
branches of any neighbouring bush, and thus always keep in the
full light; twiners, on the contrary, are best fitted to ascend bare
stems, and generally have to start in the shade. In dense tropical
forests, with crowded and bare stems, twining plants would pro-
bably succeed better than most kinds of tendril-bearers; but the
majority of twiners, at least in our temperate regions, from the
nature of their revolving movement, cannot ascend a thick trunk,
whereas this can be effected by tendril-bearers, if the trunks carry
many branches or twigs; and in some cases they can ascend by
special means a trunk without branches, but with rugged bark.

The object of all climbing plants is to reach the light and free
air with as little expenditure of organic matter as possible ; now,
with spirally ascending plants, the stem is much longer than is
absolutely necessary; for instance, I measured the stem of a
kidney-bean, which had ascended exactly two feet in height, and
it was three feet in length: the stem of a pea, ascending by its
tendrils, would, on the other hand, have been but little longer
than the height gained. That this saving of stem is really an
advantage to climbing plants I infer from observing that those
that still twine, but are aided by clasping petioles or tendrils,
generally make more open spires than those made by simple
twiners. Moreover, such plants yery generally, as was observed
over and over again with the several leaf-climbers, after taking
one or two turns in one direction, ascend for a space straight, and
then reverse the direction of their spire. By this means they
ascend to a considerably greater height, with the same length of
stem, than would otherwise be possible ; and they can do it with
safety, as they secure themselves at intervals by their clasping
petioles.

We have seen that tendrils consist of various organs in a modified
state, namely, leaves and flower-peduncles, and perhaps branches
and stipules. The position alone generally suffices*to show when
a tendril has been formed from a leaf; and in Bignonia the lower
leaves are often perfect, whilst the upper ones terminate in a ten-
dril in place of a terminal leaflet ; in Hecremocarpus I have seen a
lateral branch of a tendril replaced by a perfect leaflet; and in
Vicia sativa, on the other hand, leaflets are sometimes replaced by
tendril-branches ; and many other such cases could be given. But
he who believes in the slow modification of species will not be
content simply to ascertain the homological nature of different
tendrils; he will wish to learn, as far as possible, by what steps

CONCLUDING REMARKS. 114

parts acting as leaves or as flower-peduncles can have wholly
changed their function, and haye come to serve as prehensile
organs.

In the whole group of leaf-climbers abundant evidence has been
given that an organ, still subserving its proper function as a leaf,
may become sensitive to a touch, and thus grasp an adjoining ob-
ject. In several leaf-climbers true leaves spontaneously revolve ;
and their petioles, after clasping a support, grow thicker and
stronger. We thus see that true leaves may acquire all the lead-
ing and characteristic qualities of tendrils, namely, sensitiveness,
spontaneous movement, and subsequent thickening and indura-
tion. If their blades or lamine were to abort, they would form
true tendrils. And of this process of abortion we have seen every
stage; for in an ordinary tendril, as in that of the Pea, we can
discover no trace of its primordial nature; in Mutisia clematis,
the tendril, in shape and colour, closely resembles a petiole with
the denuded midribs of its leaflets; and occasionally vestiges of
lamine are retained or reappear. Lastly, in four genera in the
same family of the Fumariacew we see the whole gradation ; for
the terminal leaflets of the leaf-climbing Fwmaria officinalis are not
smaller than the other leaflets ; those of the leaf-climbing Adlumia
cirrhosa are greatly reduced; those of the Corydalis claviculata
(a plant which may indifferently be called a leaf-climber or tendril-
bearer) are either reduced to microscopical dimensions or have
their blades quite aborted, so that this plant is in an actual
state of transition; and, finally, in the Dicentra the tendrils are
perfectly characterized. Hence, if we were to see at the same
time all the progenitors of the Dicentra, we should almost cer-
tainly behold a series like that now exhibited by the above-named
four genera. In Zropeolum tricolorum we have another kind of
passage ; for the leaves which are first formed on the young plant
are entirely destitute of laminew, and must be called tendrils, whilst
the later-formed leaves have well-developed lamin. In all cases,
in the several kinds of leaf-climbers and of tendril-bearers, the
aequirement of sensitiveness by the mid-ribs of the leaves appa-
rently stands in the closest relation with the abortion of their
lamine or blades.

On the view here given, leaf-climbers were primordially twiners,
and tendril-bearers (of the modified leaf division) were primor-
dially leaf-climbers. Hence leaf-climbers are intermediate in
nature between twiners and tendril-bearers, and ought to be
related te both. This is the case: thus the several leaf-climbing

112 MR. DARWIN ON CLIMBING PLANTS.

species of the Antirrhinee, of Solanum, of Cocculus, of Gloriosa
are related to other genera in the same family, or even to other
species in the same genus, which are true twiners. On the
other hand, the leaf-climbing species of Olematis are very closely
allied to the tendril-bearing Naravelia: the Fumariacee include
closely allied genera which are leaf-climbers and tendril-bearers.
Lastly, one species of Bignonia is both a leaf-climber and a tendril-
bearer, and other closely allied species are twiners.

Tendrils of the second great division consist of modified flower-
peduncles. In this case likewise we have many interesting tran-
sitional states. The common Vine (not to mention the Cardio-
spermum) gives us every possible grade from finely developed
tendrils to a bunch of flower-buds, bearing the single usual lateral
flower-tendril. And when the latter itself bears some flowers, as
we know is not rarely the case, and yet retains the power of clasp-
ing a support, we see the primordial state of all those tendrils
which have been formed by the modification of flower-peduneles.

According to Mohland others, some tendrils consist of modified
branches: I have seen no such case, and therefore of course
know nothing of any transitional states, if such occur. But Lo-
phospermum at least shows us that such a transition is possible ;
for its branches spontaneously revolve, and are sensitive to con-
tact. Hence, if the leaves i some of the branches were to abort,
they would be converted into true tendrils. Nor is it soimprobable
as it may at first appear that certain branches alone should become
modified, the others remaining unaltered ; for we have seen with
certain varieties of Phaseolus that some of the branches are thin
and flexible and twine, whilst other branches on the same plant
are stiff and have no such power.

If we inquire how the petiole of a leaf, or the peduncle of a
flower, or a branch first becomes sensitive and acquires the power
of bending towards the touched side, we get no certain answer.
Nevertheless an observation by Hofmeister* well deserves atten-
tion, namely, that the shoots and leaves of all plants, whilst
young, move after being shaken; and it is almost invariably
young petioles and young tendrils, whether formed of modified
leaves or flower-peduncles, which move on being touched; so that
it would appear as if these plants had utilized and perfected a
widely distributed and incipient capacity, which capacity, as
far as we can see, is of no service to ordinary plants. If we

* Quoted by F. Cohn, in his remarkable memoir, “Contractile Gewebe im
Pflanzenreiche,” Abhand. der Schlesichen Gesell. 1861, Heft i. 8. 35.

CONCLUDING REMARKS. 118

further inquire how the stems, petioles, tendrils, and flower-
peduncles of climbing plants first acquired their power of spon-
taneously revolving, or, to speak more accurately, of successively
bending to all points of the compass, we are again silenced, or
at_ most can only remark, that the power of movement, both spon-
taneous and from various stimuli, is far more common with plants,
as we shall presently see, than is generally supposed to be the case
by those who have not attended to the subject. There is, how-
ever, the one remarkable case of the Mawrandia semperflorens, in
which the young flower-peduncles spontaneously revolve in very
small circles, and bend themselves, when gently rubbed, to the
touched side; yet this plant certainly profits in no way by these
two feebly developed powers. A rigorous examination of other
young plants would probably show some slight spontaneous move-
ments in the peduncles and petioles, as well as that sensitiveness
to shaking observed by Hofmeister. We see at least in the Mau-
vandia a plant which might, by a little augmentation of qualities
which it already possesses, come first to grasp a support by its
flower-peduncles (as with Vitis or Cardiospermum) and then, by
the abortion of some of its flowers, acquire perfect tendrils,

There is one interesting point which deserves notice. We have
seen that some tendrils have originated from modified leaves, and
others from modified flower-peduncles; so that some are foliar and
_ others axial in their homological nature. Hence it might have
been expected that they would have presented some difference in
function. This is not the case. On the contrary, they present
the most perfect identity in their several remarkable character-
istics. Tendrils of both kinds spontaneously revolve at about the
same rate. Both, when touched, bend quickly to the touched side,
and afterwards recover themselves and are able to act again. In
both the sensitiveness is either confined to one side or extends all
round the tendril. They are either attracted or repelled by the
light. ‘The latter case is seen in the foliar tendrils of Bignonia
capreolata and in the axial tendrils of the Ampelopsis, both of
which move from the light. The tips of the tendrils in these two
plants become, after contact, enlarged into disks, which are at
first adhesive by the secretion of some cement. Tendrils of both
kinds, soon after grasping a support, contract spirally ; they then
increase greatly in thickness and strength. When we add to
these several points of identity the fact of the petiole of the
Solanum jasminoides assuming the most characteristic feature of
the axis, namely, a closed ring of woody vessels, we can hardly

I

114 MR. DARWIN ON CLIMBING PLANTS.

avoid asking, whether the difference between foliar and axial
organs can be of so fundamental a nature as is generally sup-
posed to be the case*,

We have attempted to trace some of the stages in the genesis
of climbing plants. But, during the endless fluctuations in the
conditions of life to which all organic beings have been exposed,
it might have been expected that some climbing plants would have
lost the habit of climbing. In the cases given of certain South
African plants belonging to great twining families, which in
certain districts of their native country never twine, but reassume
this habit when cultivated in England, we have a case in point.
Tn the leaf-climbing Clematis flammula, and in the tendril-bearing
Vine, we see no loss in the power of climbing, but only a remnant
of that revolving-power which is indispensable to all twiners, and
is So common, as well as so advantageous, to most climbers. In
Tecoma radicans, one of the Bignoniacer, we see a last and
doubtful trace of the revolving-power.

With respect to the abortion of tendrils, certain cultivated
varieties of Cucurbita pepo have, according to Naudint, either
quite lost these organs or bear semi-monstrous representatives of
them. In my limited experience, I have met with only one in-
stance of their natural suppression, namely, in the common Bean.
All the other species of Vicia, I believe, bear tendrils ; but the Bean
is stiff enough to support its own stem, and in this species, at the
end of the petiole where a tendril ought to have arisen, a small
pointed filament is always present, about a third of an inch in
length, and which must be considered as the rudiment of a tendril.
This may be the more safely inferred, because I have seen in
young unhealthy specimens of true tendril-bearing plants similar
rudiments. In the Bean these filaments are variable in shape, as
is so frequently the case with all rudimentary organs, being either
cylindrical, or foliaceous, or deeply furrowed on the upper surface.
It is a rather curious little fact, that many of these filaments
when foliaceous have dark-coloured glands on their lower surfaces,
like those on the stipules, which secrete a sweet fluid; so that
these rudiments have been feebly utilized.

One other analogous case, though hypothetical, is worth giving.
Nearly all the species of Lathyrus possess tendrils; but L. nissolia
is destitute of them. This plant has leaves, which must have

* Mr. Herbert Spencer has recently argued (‘ Principles of Biology,’ 1865,
p. 37 et seg.) with much force that there is no fundamental distinction between
foliar and axial organs in plants.

+ Annales des Sc. Nat. 4th series, Bot. tom. vi. 1856, p. 31.

CONCLUDING REMARKS. 115

struck every one who has noticed them with surprise, for they
are quite unlike those of all common papilionaceous plants, and
resemble those of a grass. In ZL. aphaca the tendril, which is
not highly developed (for it is unbranched, and has no sponta-
neous revolying-power), replaces the leaves, the latter in function
being replaced by the large stipules. Now if we suppose the
tendrils of Z. aphaca to become flattened and foliaceous, like the
littlerudimentary tendrils of the Bean, and the large stipules, not
being any longer wanted, to become at the same time reduced in
size, we should have the exact counterpart of Z. nissolia, and its
curious leaves are at once rendered intelligible to us.

It may be added, as it will serve to sum up the foregoing views
on the origin of tendril-bearing plants, that if these views be
correct, Z. nissolia must be descended from a primordial spirally-
twining plant; that this became a leaf-climber; that first part of
the leaf and then the whole leaf became converted into a tendril,
with the stipules by compensation greatly increased in size*;
that this tendril lost its branches and became simple, then lost its
revolying-power (in which state it would resemble the tendril of
the existing Z. aphaca), and afterwards losing its prehensile power
and becoming foliaceous would no longer be called a tendril. In
this last stage (that of the existing Z. nissolia) the former tendril
would reassume its original function of a leaf, and its lately largely
developed stipules, being no longer wanted, would decrease in size.
If it be true that species become modified in the course of ages,
we may conclude that LZ. nissolia is the result of a long series of
changes, in some degree like those just traced.

The most interesting point in the natural history of climbing
plants is their diverse powers of movement; and this led me on
to their study. The most different organs—the stem, flower-
peduncle, petiole, mid-ribs of the leaf or leaflets, and apparently
aérial roots—all possess this power.

In the first place, the tendrils place themselves in the proper
position for action, standing, for instance in the Cobea, vertically
upwards, with their branches divergent and their hooks turned
outwards, and with the young terminal shoot thrown on one side ;
or, as in Clematis, the young leaves temporarily curve themselves
downwards, so as to serve as grapnels.

* Moquin-Tandon (Eléments de Tératologie, 1841, p. 156) gives the case
of a monstrous Bean, in which a case of compensation of this nature was
suddenly effected ; for the leaves had completely disappeared and the stipules
had grown to an enormous size.

12

116 MR. DARWIN ON CLIMBING PLANTS.

Secondly, if the young shoot of a twining plant, or if a tendril,
be placed in an inclined position, it soon bends upwards, though
completely secluded from the light. The guiding stimulus to this
movement is no doubt the attraction of gravity, as Andrew Knight
showed to be the case with germinating plants. Ifa succulent shoot
of almost any plant be placed in an inclined position in a glass of
water in the dark, the extremity will, in a few hours, bend upwards ;
and if the position of the shoot be then reversed, the now downward-
bent shoot will reverse its curvature; but if the stolon of a Straw-
berry, which has no tendency to grow upwards, be thus treated,
it will curve downwards in the direction of, instead of in opposi-
tion to, the force of gravity. As with the Strawberry, so it is gene-
rally with the twining shoots of the Hibbertia dentata, which climbs
laterally from bush to bush; for these shoots, when bent down-
wards, show little and sometimes no tendency to curve upwards.

Thirdly, climbing plants, like other plants, bend towards the light
by a movement closely analogous to that incurvation which causes
them to revolve. This similarity in the nature of the movement was
well seen when climbing plants were kept in a room, and their first
movements in the morning towards the light, and their subsequent
revolving movements, were traced on a bell-glass. We have also
seen that the movement of a revolving shoot, and in some cases of
a tendril, is retarded or accelerated ‘in travelling from or to the
light. In a few instances tendrils bend in a conspicuous manner
towards the dark. Many authors speak as if the movement of a
plant towards the light was as directly the result of the evapora-
tion or of the oxygenation of the sap in the stem, as the elongation
of a bar of iron from an increase in its temperature. But, seeing
that tendrils are either attracted to or repelled by the light, it is
more probable that their movements are only guided and stimu-
lated by its action, in the same manner as they are guided by the
force of attraction from or towards the centre of gravity.

Fourthly, we have in stems, petioles, flower-peduncles, and
tendrils the spontaneous revolving movement which depends on
no outward stimulus, but is contingent on the youth of the part
and on its vigorous health, which again of course depends on pro-
per temperature and the other conditions of life. This is perhaps
the most interesting of all the movements of climbing plants, be-
cause it is continuous. Very many other plants exhibit sponta-
neous movements, but they generally occur only once during the
life of the plant, as in the movements of the stamens and pistils,
&e., or at intervals of time, as in the so-called sleep of plants.

CONCLUDING REMARKS. 117

Fifthly, we have in the tendrils, whatever their homological
nature may be, in the petioles and tips of the leaves of leaf-
climbers, in the stem in one case, and apparently in the aérial
roots of the Vanilla, movements—often rapid movements—from
contact with any body. Extremely slight pressure suffices to cause
the movement. These several organs, after bending from a touch,
become straight again, and again bend when touched.

Sixthly, and lastly, most tendrils, soon after clasping a support,
but not after a mere temporary curvature, contract spirally. The
stimulus from the act of clasping some object seems to travel
slowly down the whole length of the tendril. Many tendrils,
moreover, ultimately contract spontaneously even if they have
caught no object; but this latter useless movement occurs only
after a considerable lapse of time.

We have seen how diversified are the movements of climbing
plants. These plants are numerous enough to form a conspicuous
feature in the vegetable kingdom; every one has heard that this
is the case in tropical forests; but even in the thickets of our
temperate regions the number of kinds and of individual plants is
considerable, as will be found by counting them. They belong to
many and widely different orders. To gain some crude idea of
their distribution in the vegetable series, I marked, from the lists
given by Mohl and Palm (adding a few myself, and a competent
botanist, no doubt, could add many more), all those families in
‘Lindley’s Vegetable Kingdom’ which include plants in any of
our several subdivisions of twiners, leaf-climbers, and tendril-
bearers; and these (at least, some in each group) all have the
power of spontaneously revolving. Lindley divides Phanerogamic
plants into fifty-nine Alliances ; of these, no less than above half,
namely thirty-five, include climbing plants according to the above
definition, hook- and root-climbers being excluded. To these a
few Cryptogamic plants must be added which climb by revolving.
When we reflect on this wide serial distribution of plants having
this power, and when we know that in some of the largest, well-
defined orders, such as the Composite, Rubiacee, Scrophulari-
acewe, Liliacee, &c., two or three genera alone, out of the host of
genera in each, have this power, the conclusion is forced on our
minds that the capacity of acquiring the revolving-power on which
most climbers depend is inherent, though undeveloped, in almost
every plant in the vegetable kingdom.

It has often been vaguely asserted that plants are distinguished
from animals by not having the power of movement. Tt should rather

118 MR. DARWIN ON CLIMBING PLANTS.

be said that plants acquire and display this power only when it is
of some advantage to them; but that this is of comparatively rare
occurrence, as they are affixed to the ground, and food is brought
to them by the wind and rain. We see how high in the scale of
organization a plant may rise, when we look at one of the more
perfect tendril-bearers. It first places its tendrils ready for action,
as a polypus places its tentacula. If the tendril be displaced,
it is acted on by the force of gravity and rights itself. It is acted
on by the light, and bends towards or from it, or disregards it,
whichever may be most advantageous. During several days the
tendril or internodes, or both, spontaneously revolve with a steady
motion. The tendril strikes some object, and quickly curls round
and firmly grasps it. In the course of some hours it contracts
into a spire, dragging up the stem, and forming an excellent
spring. All movements now cease. By growth the tissues soon
become wonderfully strong and durable. The tendril has done its
work, and done it in an admirable manner.