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Full text of "On the movements and habits of climbing plants"

ON THE 



MOVEMENTS AND HABITS 



OF 



CLIMBING PLANTS. 



/ 



BY 



CHARLES DARWIN, Esq., F.R.S., F.L.S. etc. 




\Fro>n the Journal of the Linnean Society 



LONDON: 

SOLI) AT THE SOCIETY'S APARTMENTS, BURLINGTON HOUSE; 

AND BY 

LONGMAN, GREEN, LONGMAN, ROBERTS & GREEN, 

AND 

WILLIAMS AND NORGATE. 

1SG5. 



ON THE 



MOVEMENTS AND HABITS 



OP 



CLIMBING PLANTS. 



Table of Contents. 



PAGE 

Introduction 1 

Part I. — Sl'IRALLV TWINING PLANTS. 

Axial twisting 5 

Nature of the revolving movement 7 
Purpose oi' the revolving move- 
ment, and manner of the spiral 

ascent 9 

Tahle of the rates of revolution . 11 

Anomalous revolvers .... 21 

Yariat ions in the power of twining 21 

Part II. — Leaf-climbeus. 

Clematis 2G 

Troprcolum 31 

Antirrhincoe 38 

Solanum 41 

Fumariaceae 43 

Cocculus 45 

Gloriosa 45 

Flagellaria 40 

Nepenthes 46 

Summary on Leaf-climbers . . 47 



TAGF. 



Part III. — Tendbil-beaeebs. 

Bignoniacca; 49 

Polemoniacece 61 

Legumiuostt) 65 

Composite 67 

Smilacese 68 

Fumariacere 70 

Cucurbitacea: 73 

Vitacete 79 

Sapindaoesa 87 

Passitloracete 89 

Spiral contraction of tendrils . . 92 
Summary of the nature and ac- 
tion of tendrils 98 

Part IV. — ITook- AND Koot- 
cumrehs; Concluding Kemaeks. 

Hook-climbers 105 

lioot-climbers 105 

Concluding remarks on Climbing- 
plants 107 



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 steins and tendrils of 
climbing plants had been long ago observed by Palm and by 
Hugo von Mohlf, and had subsequently been the subject of two 

* Proc. Amcr. Acad, of Arts and Sciences, vol. iv. Aug. 12, 1858, p. 98. 
t Ludwig 1L Palm, Ueber das YVimlen dor Pflanzen ; Hugo von Mold, Ueber 
den Bau and das Winden der Kankcn mid Schlingpflanzcii, 1827. Palm's 



2 Mil. DARWIN ON CLIMBING PLANTS. 

memoirs by Dutrochet*. Nevertheless I believe that my obseiv 
rations, 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 eacli 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 I. — Spirally 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 (llwmdtis Lwpulus) 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- 
vations 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 bey on d the upper end of the supporting 



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

* "Des Mouvenients n'volutil's spontanea," &c\, ' Coinptes Rendus,' torn. xvii. 
(1843) p. 989 ; "E^cherches sur la Volubility des Tiges," &c, torn. xix. (1844) 
p. 295. 



SPIHAL TWINEES. 



3 



stick, and was steadily revolving. I then took a longer stick and 
tied up the shoot, so that only a very young intcrnode, If of an 
inch in length, was left free ; this was so nearly upright that its 
revolution could not he easily observed ; but it certainly moved, 
and the side of the internode which was at one time convex be- 
came concave, which, as wo shall hereafter see, is a sure sign ot 
the revolving movement. I will assume that it made at least one 
revolution during the first twenty-four hours. Early the next 
morning its position was marked, and it made the second revolu- 
tion in 9 h. ; during the latter part of this revolution it moved much 
quicker, and the third circle was performed in the evening in a 
little over 3 h. As on the succeeding morning I found that the 
shoot revolved in 2 h. 45 m., it must have made during the night 
four revolutions, each at the average rate of B little over 3h. I 
should add that the temperature of the room varied only a little. 
The shoot had now grown 3^ inches in length, and carried at its 
extremity a young internode 1 inch in length, which showed slight 
changes in its curvature. The next or ninth revolution was 
effected in 2 h. 30 m. From this time forward, the revolutions were 
easily observed. The thirty-sixth revolution was performed at 
the usual rate ; so was the last or thirty-seventh, but it was not 
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 2 h. 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. 49 m. After the seventeenth revolution the inter- 
node had grown from 1-| to (5 inches m length, and carried an inter- 
node 1-i inch long, which was just perceptibly moving; and this 
carried a very minute ultimate internode. After the twenty-first 
revolution, the penultimate internode was 2} inches long, and 
probably revolved in a period of about three hours. At the 

b2 



4 MR. DARWIN' OX CLTMBIHG TT.AIS'TS. 

twenty-seventh revolution our lower internode was 8|, the penul- 
timate 3|, and ultimate 2| Laches in length ; and the inclination 
of the whole shoot was such, that a circle 10 inches in diameter 
was swept hy it. When the movement ceased, the lower inter- 
node was 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. Prom 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 5 h. 15 m. and G h. 45 m. for each revolution. Hence, as 
the extreme tip made a circle of above 5 feet (or 62 inches) in dia- 
meter and 1G feet in circumference, the t ip 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; aud it was an interesting 



Sl'TIJAL TWINERS. <> 

spectacle to watch the long shoot sweeping, night and clay, 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, likp 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 mo 
for a time. The appearance is the more deceitful because the 
axes of nearly all twiuing-plants are really twisted; and they are 
twisted in the same direction with the spontaneous revolving 
movement. To give an instance, the internode of the Hop of 
which the history has been recorded was at first, as could be seen 
by the ridges on its surface, not in the least twisted; but when, 
after the 37th revolution, it had grown 9 inches long, and its 
revolving movement had ceased, it had become twisted three 
times round its own axis, in the line of the course of the sun ; on 
1 he other hand, the common Convolvulus, which revolves in an op- 
posite course to the Hop, becomes twisted in an opposite direction. 

J fence it is not surprising that Hugo von Mohl (!S. 105, 108, 
&c.) thought that the twisting of the axis caused the revolving 
movement. 1 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 Lecontca 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 Pisiwi sativum, 
Echinocystis lobata, Bignonia capreolata, Eccrcmoearpus 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 see, revolving 
movements like those of true twining-plants. Moreover, accord- 
ing to Palm (S. 30,95) and Mohl (S. 149), and Loon*, internodes 
may occasionally, and even not very rarely, be found which are 
* Bull. Bot. Soc. do France, torn. v. 1858, p. 33G. 



6 MR. DARWIN 0>' CLIMBIXG PLAXTS. 

twisted in an opposite direction to the other internodes on the 
same plant, and to the course of revolution ; and this, according 
to L6on (p. 35G), is the case with all the internodes of a variety 
of the Phaseolus multijlonts. Internodes which havo become 
twisted round their own axes, it' they have not ceased revolving, 
are still capable of twining, as I have several times observed. 

Mohl has remarked (S. Ill,) 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 steins 
which had twined up the glass rods; for these were fixed in split 
sticks below, and were secured above to cross sticks, and the steins 
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 
training-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 f. 

* Professor Asa Gray has remarked to me, in a letter, that in Thuja occiden- 
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 flvo 
were observed to be twisted in an opposite direction. 

t 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 TWI2TER9. ' 

I bare 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, 
Convolvulus, &c, goes on revolving, but much more slowly ; for 
the internodes, until they have grown to some little length, always 
move slowly. If we look to the one, two, or several internodes 
of a revolving shoot, they will be all seen to be more or less 
bowed either during the whole or during a large part of each 
revolution. Now if a coloured streak lie 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 Bapling Bpring 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 tho 
southern lateral face; ami 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 lomri- 



8 MK. DARWIN ON CLIMBING TLANTP. 

tudinal contracting surface slowly creep round the shoot, desert- 
ing by slow degrees ihe 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 1 wi- 
ning plants. I have spoken in the illustration, for brevity's sake, 
of the cells along each face successively contracting; of course 
iurgcscencc 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 wo suppose 
the southern and then the northern face of the sapling to con- 
tract, the summit woxild describe a simple arc ; if the contraction 
first travelled a very little to the eastern face, and during the 
return a very little to the western face, a narrow ellipse would be 
described; and the sapling would become siraight 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 ihe 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 Asclepiadacca\ The hooked tip, in all the cases which 
I observed, viz. in Ceropegia, Splucrosteina, Clerodendron, Wis- 
taria, Stephania, AJcelia, and SipJiomeris, has exactly the same kind 
of movement as the other revolving internodes ; for a line painted 



SPTR.VL TWIXEES. V 

on Ihc convex surface becomes lateral and then concave; but, 
owing to the youth of these terminal internodes, tbe 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 tbus 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 braclvypoda the hook only straightened 
itself periodically, and never became reversed. Twill not assert 
that the tips of all twining plants, when hooked, move as above 
described; for this position may in some eases 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 Cissns discolor; these 
plants, however, arc 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 Mold 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 ai'rested ; 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. If a man swings a rope round his head, and the end hits a 
stick, it will coil round the stick according to the direction of the 
swinging rope ; so it is with t wining plants, the continued contrac- 
tion or turgeseence 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 Mold, who have discussed the 



10 MR. DARWIN OK 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 bond towards 
anv object which they touch. Even before reading Mold's in- 
teresting treatise, this view seemed to me so probable that 1 
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 leaf- 
climber, but without result. I then tied a very light forked twig 
to a shoot of a Hop, a Geropegia, Sphwoetema, and Adha&oda, 
so that the fork pressed on one side alone of the shoot and re- 
volved with it; 1 purposely selected some very slow revolvers, as 
it seemed most likely that these would proiit from possessing irri- 
tability ; but in no case was any etl'ect produced. Moreover, 
when a shoot winds round a support, the movement is always 
slower, as we shall immediately sec, 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 1 do not wish to assert that they 
arc never irritable ; for the growing axis of the leaf-climbing, but 
not spirally twining, Lophospermum scandens is, as we shall here- 
after see, certainly irritable ; but this case gives mo 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 Statmtonia 
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 graduallv 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 TWI>'EHS. 11 

When a revolving shoot strikes a stick, it winds round it rather 
more slowly than it revolves. For instance, a shoot of the Cero- 
pegia took 9h. 30m. to make one complete spire round a stick, 
whilst it revolved in 6 h.; Aristolochia gigas revolved in about 5 h., 
but took 9 h. 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 sec that even shaking 
a plant retards the revolving movement. The terminal internodes 
of a long, much-inclined, revolving shoot of the Qeropegia, 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 verv 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 
seined 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. 84), who states that the opposite leaves of the Hop always 
Btand 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. From casual inspection, it appeared to me that the op- 
posite leaves of Thunhergia alata were arranged in a line up the 
sticks round which they had twined; accordingly 1 raised a 
dozen plants, and gave them sticks of various thicknesses ami 
string to twine round; and in this case one alone out of the 



12 MR. DARWIN ON CLIMBING PLA2JTS. 

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 lias 
twined) either alternately, or oppositely, or in a spire; in this 
latter ease 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 man y 
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 lias 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 Ccropcgia previouslv 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 1h 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 wouud 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. 

* Comptcs Eciidus, 1844, torn. xix. p. 295, and Annales des Soc. Nat. 
3rd scries, Bot., torn. ii. p. 1G3. 



SPIRAL TWINERS. 13 

"When a stick was placed so as to arrest the lower and rigid 
internodes of the Ceropegia at the distance at first of 15 and 
then of 21 inches from the centre of revolution, the 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 Avith 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 internodc 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 movement would go on. I have 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 Yon 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 G 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 their, the 
extremity rises again. Sometimes several shoots, when flexible, 
twine together into a eable, and thus support each other. Singlo 
thin depending shoots, sueh as those of the Solly a Drummondii, 
will turn abruptly baek and wind upwards on themselves. The 
greater number of the depending shoots, however, of one twining 
plant, the ILibbertiu dentata, showed but little tendency to turn 
upwards. In other cases, as with the Cryptostcgia yrandijlora, 
several intcrnodes which at first wen' llexible 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 
Lindlcy'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. 

(ACOTYLEDONS.) 

Lygodium scandens (Polypodiacea 1 ) moves against the sun. 
h. m. 
June 18, 1st circle 6 [mg)- 

„ 18, 2nd „ G 15 (late in even- 
„ 19, 3rd „ 5 32 (very hot day). 

Lygodium artificial!'. at moves against the sun. 



h. m. 
June 19, 4th circle 5 (very hot day). 

„ 20,5th „ G 



h. m. 

July 19, 1st circle 16 30 (shoot very 
„' 20, 2nd „ 15 [young)'. 



hi in. 

July 21, 3rd circle 8 

„ 22,4th „ 10 30 



(Monocotyledons.) 

IZuscus androgynus (Liliacese), placed in the hot-house, moves against the sun. 



h, m. 

Mav 24, 1st circle 6 14 (shoot very 
„ 25,2nd „ 2 21 [young). 
„ 25, 3rd „ 3 37 
„ 25, 4th „ 3 22 



h. in. 

May 2G, 5th circle 2 50 

„ 27, Gth „ 3 52 

„ 27, 7th „ 4 11 



* I am much indebted to Dr. Hooker for having sent me many plants from 
Kew; and to Mr. Yeitch, of the Koyal Exotic Nursery, for having generously 
given me a large collection of tine 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. 



SPIKAL TWINERS. 



15 



(Monocotyledons, continued.) 



Asparagus (unnamed species from Kcw) (Liliacea?) moves against the sun, 
placed in hothouse. h m _ 

Dec. 26, 1st circle 5 

„ 27, 2nd „ 5 40 

Tamus communis (Dioscoreacerc). A young shoot from a potted tuher placed 
in the greenhouse} follows the sun. 

h. m. 
8 10 



July 7, 1st circle .. 
„ 7, 2nd „ .. 
., 8,3rd „ .. 



2 38 

3 5 



July 8, 4th circle 

„ 8,5th „ 

„ 8, 6th „ 



hi m. 

2 56 
2 30 
2 30 



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

li. m. 

March 9, 1st circle 26 15 (shoot young). 

„ 10, semicircle 8 15 

„ 11, 2nd circle 11 

„ 12,3rd „ 15 30 

„ 13,4th „ 11 1 5 

„ 1G, 5th „ 8 40 when placed in the hothouse; but the 

next clay the shoot remained stationary. 

Roxhurgliia virklijiora (Roxburghiaccse) moves against the sun j it travelled 
a circle in about 24 hours. 



(Dicotyledons.) 

Hamulus Ijupulus (Urticacciv) follows the sun. 

!'• tn. li. m. 

April 9, 2 circles 4 16 August 14, 6th circle 2 2 

Aug. 13, 3rd circle 2 „ 14, 7th „ 2 

„ 14,4th „ 2 20 „ 14,8th „ 2 4 

„ 11, 5th „ 2 16 

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

Akelia quinaia (Larclizabalacca?), placed in hothouse, moves against the 
sun. 

hi m. 

March 17, 1st circle 4 (shoot 

„ 18, 2nd „ 1 40 [young). 

Stauntonia lalifoVta (Lardizabalacea?), placed in hothouse, moves against 
the sun. h. m> 

March 28, 1st circle 3 30 

„ 29,2nd „ 3 45 

Spharosfama marmoratvm (Sehizandracece) follows the sun. 

August 5th, 1st circle in about 24 h. ; 2nd circle in 18 h. 30 m. 



March 18, 3rd circle... 


h. in. 
... 1 30 


,. 19,4th „ ... 


... 1 45 



Siephania rotunda (Menispermacese) moves against the sun 
h. in. 

May 27, 1st circle 5 5 

„ 30,2nd „ 7 6 



h. m. 

June 3, 8rd circle 6 15 

h 3, 4th „ 6 28 



1G MR. DARWIN ON CLIMBING-PLANTS. 

(Dicotyledons, continued.) 

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

Jlibbertia dentata (Dilleniacea>), placed in the hothouse, followed the sun, 
and made (May 18th) a circle in 7 h. 20 m.; on the 19th, reversed its course and 
moved against the sun, and made a circle hi 7h.; on the 20th, moved against 
the sun one-third of circle, and then stood still ; on the 2Gth, followed the sun 
for two-thirds of circle, and then returned to its starting-point, taking for this 
double course 11 h. 46 m. 

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

hi m. 



h. m. 

April 4, 1st circle 4 25 fjday.) 
„ 5, 2nd „ 8 (very cold 



April G, 3rd circle 6 25 

„ 7,4th „ 7 5 



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

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



h. 



in. 



May 13, 1st circle 3 5 

„ 13, 2nd „ 3 20 

„ 16,3rd „ 2 5 



h. in. 

May 24, 4th circle 3 21 

„ 25, 5th „ 2 37 

„ 25, 6th „ 2 35 



PJiaseolus vulgaris (Leguminosa;), in greenhouse, moves against the sun. 

hi m. 

May, 1st circle 2 

„ 2nd „ 1 55 

„ 3rd „ 1 55 

Dipladenia urophylla (Apocynacea>) moves against the sun. 

h. in. 

April IS, 1st circle 8 

„ 19,2nd „ 916 

„ 30,3rd „ 9 40 

Dipladenia crassinoda moves against the sun. 

li. m. 

May 16, 1st circle 9 5 

July 20, 2nd „ 8 

n 21,3rd „ 8 5 

Ceropegia Oardnerii (Asclepiadacea:) moves against the sun. 

h. ni. 
bhoot very young, 2 inches in length, 1st circle in 7 55 

Shoot still young 2nd „ 7 

Long shoot 3rd „ G 33 

Long shoot 4th „ 5 15 

Long shoot 5th „ 6 45 

Slephanolisjloribunda (Asclepiadacea) moves against the sun, and made a 
circle in 6 h. 40 in., a second circle in about 9 hours. 



SPIRAL TWINEKS. 17 

(Dicotyledons, continued.) 

Iloya carnosa (Asclepiadaceoe) made several circles in from 16 b. to 22 h. 
or 24 h. 

Convolvulus major (Convolvulacew) moves against the sun. Plant placed in 
room with lateral light. 

t . . , 01 .„ f Semicircle, from light in 111. 14 m., to light 

1st circle ... 2h.42m.-i , , „ ' ,.«/*,. 

I 1 h. 28 m. : difference 14 m. 

2nd circle 2 h 47 m •[ Selllit ' irclc » from 1J g ht in lh - 17 nK > to Vl S ht 
I 1 h. 30 m. : difference 13 m. 

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 14 m. 

Iponueajucunda (Convolvulacea?) moves against the sun, placed in my study, 
with windows facing the north-east. Weather hot. 

t t ■ i ' i on I Semicircle, from light in 4 h. 30 m., to light 

1st circle a h. 30 m < ° ' ° 

I lh. in. : difference 3 h. 30 m. 

2nd circle 5 h. 20 m. (Late ) . . rt 

ft -i Semicircle, from light m 3 h. oO in., to light 

in afternoon: circle com- > , , „ ' .._ ° _. , 

,_.,.- ,„, , lh. 30 m.: difference 2 h. 20 m. 

pleted at 6 m. 10 h. P.M.J J 

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

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

Plumbago rosea (Pluinbaginaeca>) follows the sun. The shoot did not begin 
to revolve until nearly a yard in height ; it then made a fine circle in 10 b. 45 m. 
During (lie next few days it continued to move, but irregularly. On August 15th 
the shoot followed, during a period of 10b. 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. 

Jasmi num paucijlorum, Bentham (Jasminaceffi), moves against the sun. First 
circle in 7h. 15 m., second circle rather more quickly. 

Clerodendrum Thomsonii (Verbenacca?) follows the sun. 

h. m. 

April 12, 1st circle 5 45 (shoot very young). 

„ 14, 2nd „ 3 30 

„ 18, semicircle 5 (directly after the plant was shaken in 

„ 19, 3rd circle 3 [being moved). 

„ 20, 4th „ 4 20 

Tecoma jasminoides (Bignoniacea)) moves against sun. 

h. m. 
March 17, 1st circle 6 30 

„ 19,2nd „ 7 



h. m. 

March 22, 3rd circle 8 30 (very cold 
„ 24, 4th „ 6 45 [day). 

Tliunbergia alala (Acanthacete) moves against sun. 

h. m. 

April 14, 1st circle 3 20 

„ 18, 2nd „ 2 50 



h. m. 
April 18, 3rd circle 2 55 [noon). 

„ 18, 4th „ 3 55 (late in al'ter- 



Adhadota cydo.urfolia (Acanthacea?) follows the sun. A young shoot made 





18 MR. DARWIN ON CLIMBING PLANTS. 

(Dicotyledons, continued.) 

a semicircle in 24 h. ; subsequently made a circlo in between 40 h. and 48 h. ; sub- 
sequently did not complete a circle in 50 h. Another shoot, however, made a 
circle in 26 h. 30 m. 

Mikania scandens (Composite) moves against the sun. 
h. m. 
March 14, 1st circle 3 10 



)> 


15, 2nd 


h 3 


n 


16, 3rd 


„ 3 


>> 


17, 4th 


„ 3 33 


iri] 


7, 5th 


„ 2 50 




7, 6th 


„ 2 40- 



f This circle was made after a copious intentional 
I watering with cold water at 47° Falir. 

Combretum argenteum (Combretaceaj) moves against the sun. 

~ 5J; f Early in morning, when the tompera- 

an. •, s nee « ^ tureof the house had fallen a little. 

„ 24, 2 circles, each at an "i 2 20 

average of J 2 20 

„ 25, 4th circle 2 25 

Combretum purpurea m revolves not quite so quickly as C. argenteum. 
Loasa aurantiaca (Loasacere). First plant moved against the sun. 



li. m. 



h. m. 



June 20,1st circle 2 37 

„ 20,2nd „ 2 13 

„ 20,3rd „ 4 

Second plant followed the sun. ^. m. 

July 11, 1st circle 1 51 



June 21, 4th circle 2 35 

„ 22,5th „ 3 26 

„ 23,6th „ 3 5 



H ' 2nd » * 46 r Very hot day. 

11,3rd „ 1 41 ■ 



„ 11,4th „ 1 48 

„ 12,5th „ ..'. 2 35 Cool morning. 

Scyphanthus elegans (Loasaccie) follows the sun. 

b< ">■ h. in. 

June 14, 4th circle 1 55) 

„ 14, 5th „ 2 3 



June 13, 1st circle 1 45 

„ 13,2nd „ 1 17 

„ 14, 3rd „ 1 36 



tiiphomeris or Lecontea (unnamed sp.) (Cinchonaceic) follows the sun. 

h. m. 

May 25, semicircle 10 27 (shoot extremely young). 

,, 26, 1st circle 10 15 (shoot still young). 

„ 30,2nd „ 8 55 

June 2, 3rd „ 8 11 

„ 6,4th „ 6 8 

„ 8, 5th „ 7 20 1 Taken from the hothouse and placed 

„ 9, 6th „ 8 36 J in a room in my house. 

Manettia bicolor (Cinchonacea 1 ), young pla)it, follows the sun. 

h. in. 

6 18 

6 53 

6 30 



July 


7, 


1st circle 


)> 


8, 


2nd 


)> 


» 


9, 


3rd 


» 



Sl'IHAL TWlNEItS. 19 

(Dicotyledons, continued.) 
Lonicera brachypoda (Caprifoliacea) follows the sun, in a warn) room in 

the house. . 

h. in. 

April, 1st circle about 9 10 

„ 2nd ,, „ 12 20 (another shoot very young). 

„ 3rd „ „ 7 30 

{In this latter circle, the semicircle from the 
light took 5 h. 23 in., and to the light 
2 h. 37 m. : difference 2 h. 46 m. 

Arislolochia gigas (Aristolochiacere) moves against the sun. 

h. m. 
July 22, 1st circle 8 (rather young shoot) . 

„ 23,2nd „ 7 15 

„ 24, 3rd „ 5 (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 much in rate. As 
long as a plant remains under the same conditions, the rate is 
often remarkably uniform, as we see with the Hop, MiJcania, 
Jfhaseolus, &c. The Scyphanthiis made one revolution in 1 h. 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 1 b. 30m., and 
three revolutions at the average rate of 1 h. 3S m.; a Convolvulus 
made two revolutions at the average of 1 b. 42 m., and Phaseolus 
vidt/aj'is three at the average of 1 h. 57m. On the other hand, some 
plants take 21 h. for a single revolution, and the Adhadota some- 
times required 48 h. ; 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 
Solli/a are as thin and flexible as string, but move slower than the 
thick and fleshy shoots of the liuscus, 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 Ipomcea or Thuiibergia. 
AVc 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 bauds of a watch, than in the reversed 

c2 



20 ME. 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 Leguminosrc, and we have in 
the table another in the Acanthacese. 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 Solatium dulcamara (Dutrochet, torn. xix. p. 299) revolve and 
twine in both directions : this plant, however, is a most feeble 
twiner. Loasa aurantiaca (Leon, 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 
d'appui for the reversal of the spire. One of these four plants 
made seven spiral turns from right to left, and five turns from 
left to right. These individuals of the Loasa are interesting, as 
showing how almost every change is effected most gradually. 
For another plant in the same family, the Scypliantlius 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 intcrnode. Had I not seen 
this case, I should have thought its occurrence most improbable. 
It 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 Ipomcea 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 

* I 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 Hib- 
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 Solatium 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 periclymemtm), which I have observed 
twining up a young beech-tree nearly 4£ inches in diameter. 
Mohl (S. 131) found that the Phaseolus multiflorus and Ipomcea 
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 androgi/nm ascends a column 9 inches in dia- 
meter ; and although ^Wistaria grown by me in a small pot tried in 
vain for weeks to get round a post between 6 and G inches in 



22 MR. DAttWIN ON CLIMIiiNG PLANTS. 

thickness, yet at Kew a plant ascended a trunk above G 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 Btitea parvijlora, one of the Menispcrmacea?, 
and with some Dalbergias and other Leguminosa). 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 Ceropcgia Gavdnerii near a post G 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 Splucro- 
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 theG-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 Lyrjodium 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 L. scandens made five revolutions 
at an average rate of 5 h. 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 20 h. and 
the other in 23 h., whereas they ought to have revolved in between 
2 h. and 2 h. 30 m. 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 (torn. xvii. pp. 994, 990) 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 Iponupa jucv.nda 
(as maybe seen in the table) revolved in 5h. 20 m., the semicircle 
from the light taking 4 h. 30 m., and that towards the light only 
I h. ; Lonicem hrachypoda revolved, in a reversed direction to the 
Ipomcea, in 8 h., the semicircle from the light taking 5 h. 23 m., and 
that to the light only 2 h. 37 m. From the rate of revolution in all 



21 Mil. DARWIN ON CLIMBING PLANT8. 

the plants wliicli 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, as 
botanists have thought (Mohl, S. 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 miscellaneous and curious cases. With most twining plants 
all the branches, bowever many there may be, go on revol vino- 
together ; but, according to Mohl (S. 4), the main stem of Tamus 
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 C. purpurcum made nume- 
rous short healthy shoots ; but they showed no signs of revolv- 
ing, and I could not conceive how these plants could be climbers ; 
but at last C. argenteum put forth from the lower part of one of 
its main branches a thin shoot, 5 or G 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 Grceca (Palm, S. 43) the uppermost shoots alone twine. 
Polygonum convolvulus twines only during the middle of the sum- 
mer (Palm. S. 43, 91) : plants growing vigorously in the autumn 
show no inclination to twine. The majority of Asclepiadacea> are 
twiners ; but Asclepias nigra only " in fertiliori solo incipit scan- 
dere sub volubili caule " (Willdenow, quoted and confirmed by 
Palm, S. 41). Asclepias vincctoxicum does not regularly twine, 
but only occasionally (Palm, S. 42 ; Mohl, S. 112) when growing 
under certain conditions. So it is with two species of Ceropcgia, 
as I hear from Prof. Harvey, for these plants in their native dry 
South African home generally grow erect, from 6 inches to 2 feet 
in height, a very few taller specimens showing some inclination to 
curve ; but when cultivated near Dublin, they regularly twined up 
sticks 5 or 6 feet in height. Most Convolvulaceae are excellent 
twiners ; but Ipoma>a argyrceoides 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-CLIMBEKS. 



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 condi- 
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 Phascolus are twiners ; but certain varieties 
of the P. multijlorus produce (Leon, p. 681) two kinds of shoots, 
some upright and thick, and others thin and twining. I have 
seen striking instances of this curious case of variability 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 
(torn. 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, 
sec 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. Habrotliamnus, of the same family 
of Solanacese, 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 Tecoma 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 Tieecdyana and of Hoya car?iosa revolve 
and twine, and likewise emit rootlets which adhere to any fitting 
surface. 

Part II. — Leaf-cltmbebs. 
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 



2G 



MR. DA 11 WIN ON CLIMBING PLANTS. 



and Mold class these plants with those which bear tendrils ; but 
as a leaf is generally a defined object, the present classification 
has, at least, some plaiu 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 Tropocolum in order to discover what 
amount of difference there may be within the same genus ; and 
the differences, as we shall see, are considerable. 

Clematis. — C. glandulosa, — The thin upper internodes revolve, 
moving against the course of the sun, precisely like those of a 
true twiner, at an average rate, judging from three revolutions, 
of 3 h. 48 m. The leading shoot immediately twined round a stick 
placed near it ; but, after making an open spire of only one turn 
and a half, it ascended for a short space straight, and then 
reversed its 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 bo the most 
sensitive ; but the sensitiveness or irritability is but slight corn- 



Fig. 1. 



pared to that which we shall meet 
with in some of the following spe- 
cies ; for a loop of string, weighing 
1G4 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 12 h., 
to bend greatly, and ultimately to Clematis glandulosa, with two 
i nt Lii. i J l young leaves clasping twigs, with 

such an extent that the leal passed tho cla8ping portions thickened. 
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 
1 line at right angles to the stem, and then become so much arched 
downwards that the blade of the leaf points to the ground witli 
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 origiual upturned position, which is 
retained ever afterwards. The young leaves, being hooked, are 
thus enabled to catch twngs 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 4 h. 20 m., but the next day, being 
very cold, the time was 5 h. 10 m. A stick 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 rate of 3 h. 11 m. The pow r er of twining is like 
that of the last species. Its leaves are nearly similar, except that 

* Our English grain equalg nearly, (55 milligrammes. 



t 






28 MR. DARWrN OX CLTM15INO 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 O. micro- 
phylla. 

Clematis calycina. — The young shoots are thin and flexible ; 
one revolved, describing a broad oval, in 5 h. 30 m., and another in 
6h. 12 m. : 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 is a 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 2 h. 30m. 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 4 h. 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 21 h. 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. &> 

all. The clasped petiole in the courso 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 micropliylla, var. leptaphylla. — 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 \t\\ 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. DAKWl> OB OUMBITfQ I'LANTS. 

gular line was generally lbnned ; but one day, in the eourse 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 2 h. 35 m. 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 C. viticella, C.flammula, and C. vitalba move spontaneously ; 
and, judging from C. Sieboldi, this probably is the case with C. 
montana and C. calycina. I ascertained that the simple leaves of 
C. glandulosa exhibited no spontaneous revolving movement. 

Clematis viticella, var. venosa. — In this and the two following 
species the power of spirally twining is completely lost, and this 
seems due to the lessened flexibility of the internodes and to the 
interference caused by the large size of the leaves. But the 
revolving movement, though restricted, is not lost. In our 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 2 h. 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 4f inches, and that by the apex of the 
penultimato internode only \\ 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 arc 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 vitieella. 
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 - S2 of a grain) on the several lateral and 
on the terminal sub-petioles; in a few hours the latter were bent, 
but after 21 h. no effect was produced on any of the lateral petioles. 
Again, a terminal sub-petiole placed in contact witli a thin stick 
became sensibly curved in 45 m., and in 1 h. 10 m. had moved 
through ninety degrees, whereas a lateral petiole did not become 
sensibly curved until 3 h. 30 m. 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 MIL DAEWIN ON CLIMBING PLANTS. 

of C. calycina ; but in older plants it has spread to the three sub- 
petioles. Iu 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. Four were made 
at an average rate of 3 h. 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 14 } 
and in another case If inch ; so that the young leaves arc moved a 
very short distance. The shoots of tho same plant observed in 
midsummer, when growing not so quickly, did not revolve at all. 
I cut down another plant in tho 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 clays 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 sec, 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 lamina) 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 3 h. 15 m. ; in another case a 
petiole curled completely round a stick in 12 h. These petioles 



LEAF-CLI.MBEHS. 33 

were left curled for 24 h., 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. 30 m., a 
terminal sub-petiole moving more than a lateral sub-petiole ; they 
became quite straight again in between 12 h. and 14 h. 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 3 h., 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, 1 placed a loop of 
string, weighing 101 gr., on a terminal petiole : in 6 h. 40 m. a cur- 
vature could be seen ; in 21 h. the petiole formed an open ring 
round the string ; in 48 h. the ring had almost closed on the string, 
and in 72 h. 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 14 h., but after 2 1 h. 
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 24 h., 
a moderate curvature in it ; the curvature, though the loop re- 
mained suspended, was after 48 h. 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 : bevond 
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- 



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 TG4 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 36 h. 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.—bly plants in pots were not healthy ; so that 
I dare not trust my observations, which indicated much similarity 
in habits with C.flammtda. 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. For instance, 
I found petioles which had clasped thin withered blades of grass, 
the soft young leaves 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 oft' ; 
but the petioles (as was also observed by Mohl) remain, some- 
times during two seasons, attached to the branches ; and, being 
convoluted, 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. 

Trop^OLUM. — I observed T. tricolorum, T. azureum, T. penta- 



LEAF-CLIMBBBS. 35 

phgllum, T. peregrinum, T. elegans, T. tuberosum, and a dwarf 

variety of, as I believe, T. minus. 

Tropceolum tricolorum, var. grandijlorum. — 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 1 h. 23 m. ; 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 
lias 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 plaut 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 leases, 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 

D 2 



36 MIJ. DAKWIX OX CLIMBING PLANTS. 

clasp either their own stem or the support ing 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 laminae, 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. 

Tropcsolwm azurcum. — 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 veiy sensitive : a single very light rub with a 
twig caused one to move perceptibly in 5 m., and another in G m. ; 
the former petiole became bent at right angles in 15 m., and 
became straight again in between 5 h. and 6 h. A loop of thread 
weighing £th of a grain caused a petiole to curve. 

Tropeeolum pentaphyllum. — The 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 6 m. ; another, on a cold day, in 20 m. ; but others generally in 
from 8m. to 10m.: the curvature usually increased greatly in from 
15 m. to 20m. The petioles became straight again in between 5h. 
and 6 h., and on one occasion in 3 h. 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 1th of a grain certainly caused a petiole 
to curve ; but the stimulus was not sufficient, the loop remaining 
suspended, to cause a perm ancnt flexure. If a 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. 

Tropacolum 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 1 h. 48 m. It is remarkable how nearly the 
same the average rate of revolution (taken, however, but from few 



LEAF-CLIMBERS. 37 

observations) is iu this and the two last species, namely, 1 h. 47m., 
1 h. 46 m, and lh. 48 m. 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, ihe petioles were not 
sensitive. In older plants the petioles of quite young leaves, and 
of leaves as much as an inch and a quarter in diameter, are sensi- 
tive. A moderate rub caused one to curve in 10 m., 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 an} r curvature, whilst a loop of 
double this weight (IGlgr.) did act. 

Tropceolum elegans. — I did not make many observations on this 
species. The short and stiff internodes revolve irregularly, and 
describe extremely small oval 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 S h. 

Tropceolum 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 veiy small imperfect ovals. These movements could 
be detected only by being traced on a bell-glass placed over the 
plant. Sometimes the shoots stood still for hours; during some 
days they moved only in one direction in a crooked line ; on 
other days they made small irregular spires or circles, one being 
completed in about 4 h. The movement of the apex of the shoot, 
from extreme point to point of the oval, was only about one inch or 
one and a 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 very 
slowly decreased ; so that the petioles sometimes required 24 h. 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. 

Twpa'ohim minus (?).— The internodes of a variety named 



38 MB. DARWIN o.N (IJMIHXli 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. AVe have seen in this genus a gradation 
from species such as T. tricolorum, which have exquisitely sensi- 
tive petioles, and intcrnodes which have rapid revolving powers 
and can spirally twine up a support, to other species, such as 
T. eleaans and T. tuberosum, the petioles of which arc much loss 
sensitive, and the intcrnodes 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 gemis, the loss of power seems 
the more probable alternative. 

In this species and in T. 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. 

Antireiiineje. — In this tribe (Lindlcy) of the Scrophulariacea?, 
at least four of the seven included genera have leaf-climbing 
species. 

Maurandia JBarcIai/ana. — A thin, slightly bowed shoot made two 
revolutions, following the sun, each in 3 h. 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 ^th 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. 46 m. ; 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- 
neria. Nevertheless this remark, and the well-known fact that 
the flower-peduncles of this Maurandia are ilexuous, led me care- 



LEAF-CLIMBERS. 89 

fully to examine them. They never act as tendrils : I repeatedly 
placed thin sticks in contact with young and old peduncles, and 
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 2 h. 25 m. j 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 (1^ 
inch in length), one on the upper side and the other on tho 
lower side, and they became in between 4 h. and 5 h. plainly bowed 
towards the rubbed sides ; in 2-4 h. 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 arcs 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 l£ 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 Mil DAUWIX OX CLIMHIN'G TLANTS. 

duced no eftect ; but loops of string weighing -82 and TG4 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 Serophulariacere 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, Lophospermam, the young inter- 
nodes, as we shall sec, are sensitive. By whatever means the 
peduncles of this Maurandia 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 Vifis and Cardiospermum, 
as will hereafter be described. 

Hhodochiton volubile. — Along flexible shoot swept a large circle, 
following the sun, in 5 h. 30 m. ; and, as the day became warmer, a 
second circle in 4 h. 10 m. 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 1 h. 10 m., and became consider- 
ably arched in 5 h. 40m. after the rubbing; some other petioles, 
after being rubbed, were scarcely curved in 5 h. 30 m., but in Gh. 
30 m. 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 



LKAF-CLrMHKKS. 41 

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. 

Lophospcrmum scandens, var. purpureum. — Some long, mode- 
rately thin internodes made four revolutions at an average rate of 
3 h. 15 m. 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 ffliothcliiton, 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 interuode 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 4 h., subsequently. An internode, which was rubbed as 
much as six or seven times with a twig, became just perccptibly 
curved in 1 h. lo m., and subsequently in 3 h. 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- 
vat ure was always towards the rubbed side. 

According to Palm (S. 63), the petioles of Zmaria cirrhosa and, 
to a limited degree, those of L. 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 revolutions, moving against the sun, very 



42 



MR. BAttWTX ON CLIMB-INO PLANTS. 



regularly at an average rate of 3h. 26 m. 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 7 h. In the greenhouse a 

Fig. 3. 




Solatium jasminoutes, with one of its leaves clasping a stick. 

petiole was not affected by a loop of string, suspended during 
several days and weighing 2| grains ; in the hothouse one 
was made to curve by a loop weighing 1G1< (and, on the 
removal of the string, became straight again), but was not at 
all affected by another loop weighing '82 of a grain. "Wo 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 that the 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 lias 
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-CLIM1JERS. 



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. 
Solatium jasminoides. 








B 

A. Section of a petiole. 

B. Section of a petiole some weeks after it had clasped a stick, as shown in 
fig. 3. 

semilunar hand 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 have 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 *. 

Fumabtaceje. — Fiwiaria officinalis. — It could not have been 

* Dr. Maxwell Masters informs me that in most, or all, petioles whicli 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 aro 
channelled along their upper surfaces. In accordance with this statement, it 



44 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 lb. 15m., 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 12 h. 
and before 20 h. had elapsed, a considerable curvature ; but the 
petiole never fairly clasped the thread. The young intemodes 
arc 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 12 h., being traced 
on a bell-glass, apparently represented about four ellipses. The 
leaves themselves also move spontaneously, the main petiole curv- 
ing itself in accordance with the movement of the intemodes ; 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 intemodes. 

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. 36 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 2| inches in length, and was com- 
pleted in 2h. 2 m. From analogy with Fumaria and Corydalis, I 
have no doubt that the intemodes have the power of revolving. 

may be observed that the enlarged and clasped petiole of the Solatium, with its 
closed ring of woody vessels, has become much more cylindrical than it was in 
its original unclasped condition. 



LEAF-CLIMUEKS. 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 Menispermaeea>) and a fern, the 
Ojjhioglossum 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. 

G-lokiosa. — G. Plant ii (Liliaeese). — The stem of a half- 
grown plant continually moved, generally describing an irregular 
spire, but sometimes ovals, with the longer axes running in differ- 
ent directions. It cither followed the sun, or moved in an oppo- 
site course, and sometimes stood still before reversing its course. 
One oval was completed in 3h. 40 m.; of two horseshoe-shaped 
figures, one was completed in 4 h. 35 m. and the other in 3 h. 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, and, 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 In. to 3h. to have 
curled a little inwards ; and, under favourable circumstances, in 
from 8 h. to 10 h. it finally 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, and makes a 
button-like, flat, spiral coil at the end of the leaf. One leaf was 



46 MU. DAHWIN ON CLIMBINU PLANTS. 

watched, and the hook remained open for thirty-throe days ; hut 
during the last week the tip had curled inwards so much that at 
last only a very thin twig could have heen 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. 

Flaqellaria Indica (Commelynacea>). — From dried specimens 
it is manifest that this plant climbs exactly like Oloriosa. 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 Glariosa lily. According to Mold 
(S. 41), Uvularia (Mclanthaceae) climbs like Qloriosa. 

These three last-named genera are all Monocotyledons ; but 
there is one Dicotyledon, namely Nepenthes, which is ranked 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 I 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 N. Icevis and AT. 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 N. Icevis had grown to a height of 1G 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 



I,KAF-CMMBERS. 



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-cli?nbers.— Plants belonging to eight families 
are known to have 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 Glariosa are sensitive only on their 
inner or inferior surface. The petioles are sensitive to a 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 stifl' petioles of Clematis 
jlammula 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 elapsed 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 MB. DARWIN OX CUM IUNU PLANTS. 

The young internodes of the Lophospcrmum are sensitive as well 
as the petioles, and by their combined movement seize any object. 
The flower-peduncles of the Maurandia sanpei-jlorcns 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 
Tropcrolum 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 Tro- 
pceolum 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 III. — Tendril-bearing 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 wdl in most, or in all, cases keep those of the same homo- 



TENDKIL-BEAREKS. 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: — Bignoniacece, Polemoniaccce, Leguminosce, Composites, Smi- 
lacece, FumariacecB, CucurUtacecc, Vitacece, Sapindacece, Passijlo- 
raceae. 

Bionontace.'-e. — 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 Fig. 5f. 

plant made three revolutions against the 
sun, at an average rate of 2 h. 6 m. 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 

, , , . , ... ., * . Bignonia, unnamed 

brought into contact with it, these curved species from Kew. 

round the stfiek, showing that they have 

some degree of irritability. The petioles also exhibit a slight 

* As far as I can make out, the history of our knowledge on tendrils is as 
follows :— Wc have seen that Palm and Von Mold observed about the same 
time the singular phenomenon of the spontaneous revolving movement of 
t wining-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. Mold 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 not iced 
theextreme sensitiveness and rapidity of movements in the tendrils of certain 
Cucurbit aceous plants. 

t This and the following drawings, from which the woodcuts have been en- 
graved, were carefully made I'm- me from living plants by my sen Mr. George 
If. Darwin. 




50 MR. DAKWXN OX 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. 

Birjnonia 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 



TENDKIL-BEAUERS. 51 

caused still further bending ; so that ultimately both petioles 
clasped the stick in opposite directions, and the foot-like 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 vigorous^, 
I concluded that the tendrils acted only like the hooks on a 
bramble, and that this was the most feeble and inefficient 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 case made two circles, each in 2 h. 33 m. I was 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 aerial 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 imcaught they soon wither away. 

Bignonia venusta, — The tendrils are here considerably modified 

e 2 



52 MR. DAltWTN ON C'TJMMNO 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 not lie 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 sensif tve 
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. TicrcJi/ana. The young internodes 
also sweep fine large circles, one being completed in 2h. 16m., 
and a second in 2 h. 55 m. 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. 

Birjnonia Wtoralis. — The young internodes revolve in fine large 
ellipses. An internodc bearing immature tendrils made two revo- 
lutions, each in 3 h. 50 m. ; but when grown older, with the tendrils 
mature, two ellipses were performed, each at the rate of 2 h. 44 m. 
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 poAver ; nor can I 



TENDIilL-BEAKERS. 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. Bignotiia 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 
arc 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 4 m. 
and greatly curved in 7 m. ; in 7 h. 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 rubbiug this part required about twice as long a 
1 ime 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 24 h. is m. When the tendril was mature, an ellipse was per- 
formed in G h. ; 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. 



54 MR. DARWIN ON CI.IMIilXli 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 
lime, go on revolving together, but at different rates. Moreover, 
the movements of the opposite petioles and tendrils are quit© 
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 have 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. caprcolata, I will here say nothing more about 
them. 

Bignoiiia (cquinoctialis, var. Chamherlaijnii. — 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 
3 h. 30 m. to 4 h. 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-BEAKEKS. 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- 
bitaceous, Passifloraceous, and Leguminous plants, and never saw 
one behave in this 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; fortius 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. DAIIWIN ON CLIMBING PLANTS. 

fissure. I fully expected, from the analogy of B. caprcolata and 
B. littoral is, 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 having lost the power 
of forming adhesive disks. 

Bignonia picta.—-1\\\s species closely resembles the last in the 
structure and movements of its tendrils. I casually examined a 
fine growing plant of the allied B. Lindlcyi, 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 2 h. 23 m. The stem is thin and flexible, and I ha\ e 
seen one make four regular spiral turns round a thin upright st irk, 
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 1\ 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 \\\\ of a grain produced no effect. 
The terminal branches of a tendril twice became in 10 m. slightly 
curved 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. I could detect no spontaneous movement in the pel ioles. 

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. I 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- 



TENDBIL-BEAHERS. 57 

wards the liglit and the oilier to the darkest side of the house ; the 
latter did not move, hut 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 
liglit; 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 liglit which entered the box. I left these tendrils 
undisturbed for above 2-i h., 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 JB. speciosa and its allies, that it again loosed 
the stick : sometimes it seized and loosed the same stick three or 
four limes. Knowing that the tendrils avoided the light, I gave 
them a glass tube blackened within, and a well-blackened zinc 
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 cm-led round and (irmly sci/.cd an excessively minute 
projecting point of hark, and then the other branches spread them- 



58 MR. BAItWIN ON CLIMBING PLANTS. 

selves out, following with accuracy every inequality of the sur- 
face. I then placed a post without hark, hut 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 
firmlv 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 visibly enlarged. After 
a few more days the hooks were converted into whitish, irregular 
balls, rather above the -^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-sorae 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 he withdrawn. The cellular 
outgrowth has such a tendency to unite, that two halls pro- 
duced from two branches sometimes grow into a single one. 



TENDRIL-BEAftEKS. 59 

On one occasion, when a tendril had curled 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 Polypodium 
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. 

Eccrcmocarpus scaler {Bignoniaceai). — 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 3 h. 15 m. to 
Ih. 13m.: 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 



GO ME. DABWIH ON CLIMBING PLANTS. 

quite still for 12 h. or 18 h., and tlieu recommence revolving ; such 
strongly marked interruptions in the movements 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 10G°. The two opposite petioles do not move 
together, and one is sometimes raised so much as to stand close to 
1 he 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. 

1 1) 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 arc sen- 
sitive on all sides ; and after being lightly rubbed, or after coming 
into contact with a stick, they bend in about 10 m. One that be- 
came, after a light rub, curved in 10 m., continued bending for 
between 3 h. and 4h., but subsequently in 8 h. or 9 h. 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 E. minialus 
than in E. scaler. The action of the tendrils in the Eccrcmo- 
carpus is in some respects analogous to that of the tendrils of 
Biqnonia caprcolaia; but the whole tendril docs not move from 
the light, nor do the hooked fcipa 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 



TENDRTL-BEARERS. Gl 

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 t wist 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. AYHien 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. 

Polemoxiace.e. — Cobaa 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 a half inches in length. The tendril of the Cobaca revolves more 
rapidly and vigorously than in any other plant observed by me, 
with the exception of one Passijlora. It made three fine large, nearly 



G2 MH. DAKWIN ON CUM1UNC. PLANTS. 

circular sweeps, against the sun, eacli in 1 h. 15 m., and two others 
in 1 h. 20 in. and 1 h. 23 m. 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 Eccre-moearpus, the internodes, tendrils, and 
petioles all revolve. The long, straight, tapering main stem of the 
tendril of the Cobcca 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 
every 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- 



TENDIUL-BEATIEKS. G3 

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 3G 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 Bic/nonia caprcolata 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 movements of the branches of the tendrils. I made 



64 mb. DABwnsr ox climbing plants. 

many trials with black and white glass and cards to prove it, but 
tailed 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 revolv- 
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 Cobcca grows in the open air, the wind must aid the 
extremely flexible tendrils in seizing a support, fori 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 havo 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. 



TEXDEIL-BEAKKRS. 



65 



Legumixos.e. — Pisu-m sativum. — The common Pea was the sub- 
ject of a valuable memoir by Dutrochet*, who discovered that 
both the interuodes 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 



Fie:. 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.) 



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 p.ir. The course was 
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 
the figure is here reduced one- 
half. Neglecting the first great- 
sweep towards the light or 
window, the end of the pe- 
tiole swept a space 4 inches »• i 30 
across in one direction, and 3 inches in another, 
grown tendril is considerably above 2 inches in length, and as (Ik 

* Comptes Kcndus, torn. xvii. 1813, p. 989. 




Side of room with window. 



h. m. 

1. 8 46 A.M. 

2. 10 „ 

3. 11 „ 

4. 11 37 „ 

5. 12 7 p.m. 

6. 12 30 „ 
1 „ 



h. m. 
0. 1 66 P.M. 

10. 2 2"> „ 
11.3 „ 

12. 3 30 „ 

13. 3 48 „ 

11. 4 40 „ 
15. 5 5 „ 



h. m. 

18. .". L'-"> l'.M. 
17. 5 50 „ 
is. f, I'.", ., 
lit. 7 0., 

20. 7 45 ,, 

21. 8 30 „ 

22. 9 15 „ 



As a full- 



66 MB. DABWIN 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 lh. 20m. ; I saw one completed in lh. 30m. The 
direction followed is variable, either w;ith or against the sun. 

Dutrochet asserts that the petiole of the leaf spontaneously 
moves, as 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 
1£ 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 lino 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 travelling 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 having 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- 
cave 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 



TENDBIL-BEAREltS. 67 

about two hours, aud 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, aud 
others required from 18 h. to 24 h. to clasp the twigs. Ultimately 
the lateral branches of tho tendril, but not the middle or main 
stem, contract spirally. 

Lathy rus 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 aro moderately long, thin, and un- 
branched, with their tips slightly curved : they are sensitive whilst 
young on all sides, but chiefly on the coucave side of the extre- 
mity. They have no spontaneous revolving power, but arc at first 
inclined upwards at an angle of about 45°, then move into a hori- 
zontal position, and ultimately bend downwards. The young 
iuternodes, 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 yrandijlorus. — The plants observed were young, and 
not growing vigorously, yet sufficiently so, I think, for my observa- 
tions to bo trusted. Here we have the rare case of neither inter- 
nodes nor tendrils having 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. 

CoMPOSiTiE. — 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 Mikania is a regular 
twiner, and Mutisia 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 MB. DABWIN 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 laminae or blades. 
Each branch is curved a little downwards, and is slightly hooked 
at its extremity. 

An upper young intcrnode revolved, judging from three revolu- 
tions, at an average rate of lh. 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 Gh.,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 13 h. 
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. If a 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. 

Smilaceje. — Smilax aspera, var. macuJata. — Aug. St.-IIilaire* 
considers the tendrils which rise in pairs from the petiole as 

* Logons de Botaniquc, &.C., 1841, p. 170. 



TENDIUL-BEAREKS. 



09 



Via. 7. 



modified lateral leaflets ; but Mold (S. 41) ranks them as modified 
stipules. These tendrils are from 1| to 1| 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 Hi. 20m., but did not completely surround the stick till 
48h. had elapsed ; the con- 
cave side of another tendril 
became considerably curved 
in 2 h., and fairly clasped the 
stick in 5 h. 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 aspcra. 



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 



70 MU. DABWTN 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 
he. 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 S. 
aspcra is endowed with these organs solely from being descended 
from progenitors more highly organized in this respect. 

Fumabtacej:. — Coryilalis claviculata. — According to Mob] 
(S. 43), both the leaves and the e\1 ivmities 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 Con/dalis 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, Fumaria 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 lamina) 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 have their terminal 
leaflets reduced in size, and soon all the leaves assume the struc- 



TEKDItlL-BEAKERS. 



71 



ture represented in the following diagram. This leaf bore nine 
leaflets; the lower ones are much subdivided. The terminal 
portion of the petiole, about 1£ 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 1M.ANTS. 

reduced leaflets (a, b, c, d) are highly sensitive, for a loop of thread 
weighing only the one-sixteenth of a grain caused thnn, in under 
4h., to become greatly curved : when the loop was removed, the 
petioles straightened themselves in about the same time. The 
petiole («) 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 /) during several 
days, produced no effect. Yet the three petioles/", g, and A 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 
Mold'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 very 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 sensitiveness. 

Dicentra thalietrifolia. — 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 



TENDTUL-13EAKEUS. 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 lh. 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 Bignoniacea? and the Cobcca. 
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. Pull-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 Eccremocarpus. 

CucUEBiTACEiE. — 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 "t- 

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

t Gardeners' Chronicle, 1864, p. 721. From the aflinity of the Cucurbitacese 
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 thia 
plaut (raised from seed sent me by Prof. Asa Gray), for bere I 
first observed the spontaneous revolving movement of tbe inter- 
nodes and of tbe tendrils ; and knowing nothing of tbe nature of 
tbese movements, was infinitely perplexed by the whole case, and 
by the false appearance of twisting of tbe 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 lb. 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-pcdunclcs, as is certainly the case with the tendrils of Passion- 
flowers. Mr. E. Ilolland (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. 7. r > 

nearly or quite vertical. This occurred both -when the supporting 
iuternodes 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 
fcnrgescence, 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 (S. 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 



7G MR. DARWIN' ON* CI.T.MIUNO PLA3TT8. 

of a grain. So it would appear tlmt 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 eft'ect 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. AVhen 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 23° 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 for a 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 



TEXDKTL-BEAREES. 77 

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 iu 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 thai 
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 tin's 
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 Eclrinocystis 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 conies 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 tho main tendril, after revolving 
for a time in a vertical position, spontaneously bends downwards ; 
and this, of course, raises the rectangular branch, which it sill* 
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 Hanburya the layer is developed along the terminal 
portion of the tendril, sometimes for a length of 1£ 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 21 h. 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 difficult 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 Cucurbitacerc, I observed in Bryonia dioica, Cucurbit a 
ovifera, and Cucumis sativa, that the tendrils were sensitive and 



TENDItlL-BEAKEES. 



79 



revolved ; in the latter plant, Dutroehet* 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 
Anquria 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 
2 h. 8 m. and 3 h. 35 m., moving against the sun. 

Vitace^;. — In this family and in the two following, namely, 
the Sapindaceffi and Passifloracea?, 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 Cucurbitacea>. The homologies! 
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 tho 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 1G inches 
in length. It consists of a peduncle (A), bearing two branches 

* Comptcs Rendus, torn. 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, S. 5(>) 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 an average rate of 2 h. 15 m. 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 dcscrihed 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, S. 55; Mohl, S. 45; Lindley, Mr.) 
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 flowei'-tcndril (B) is always longer than 
the sub-peduncle (C), and has a scale at its base ; it sometimes 



TENDIUL-BEAKEKS. 



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 (C), 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-Peduncle. 

B. Flower-tendril, with a scale at its base. D. Petiole of opposite leaf. 

slightly sensitive to a 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 ease 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, DAHW1X OS OUMBTSQ 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 tbc 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 1G 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. 0) 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. Prom this state we can 
trace every stage till Ave 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 flower- 
tendril (B, fig. 10) sometimes produces a few flower-buds; I 
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 w r ere completed in the following 
times : — i h. 45 m., 4 h. 50 in., 4 h. 45 m., 4 h. 30 m., and 5 h. The 
same tendril continues revolving during three or four days. The 
tendrils are from 3| 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-I 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 30 or 40 m. : 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. If a branch be touched at the same time with equal 
force on opposite sides, both sides are equally stimulated and 
there is no movement. At the beginning of my work, and before 

o 2 



84 MB. DABWIH 0> T 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 1 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 
3 h. 30 m. and A h. The internodes do not revolve. 

Ampeiopsis hederacea, or Virginian Creeper. — In this plant 
also the internodes do not move more than apparently can he 
accounted for by the varying action of the light. The tendrils arc 
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 cftecting 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. 



TENDIUL-BEAItERS. 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 18 h., and in an additional 21 h. 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 
42 h. 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 aline of green unal- 
tered tissue can be traced only along the concave surface. When, 
however, a tendril has clasped a cylindrical stick, an irregular 
rim 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. 11) 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 24 h. 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, does not 



86 



MB. DABWIN 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 bocomes 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 loaf. 

B. Tendril, several weeks after its attaelnnent 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 



TE>-T)1UL-BEAUEHS. 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 ! 

Sapindace^e. — Cardiospcrmum 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 4£ 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 lg ' 
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- halicacabum. 
cally and elegantly hooked, as represented Upper part of the 

ii j- nv. i_-i - ji flower-peduncle with its 

in the diagram. I hey are now, whilst the two tendrils, 
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, 




88 



MR. UA.RWJN 0>* CLIMH1NG PLANTS. 



iu 3 h. 12 m. ; in a second plant the same course was followed, and 
the two were completed in 3 h. 41 m. ; in a third plant the inter- 
nodes followed the sun, and made two circles in 3 h. 47 m. The 
average rate of these six revolutions was 1 h. 40 m. The stem 
sliows no tendency to twine spirally round a support ; hut the 
allied tendril-hearing genus Paullinia is said (Mold, S. 4) to ho a 
twiner. By the revolving movement, the flower-peduncles, which 
stand up ahove the end of the shoot, are carried round and round ; 
but when the internodes were securely tied, the long and thin 
peduncles themselves Avere seen to be in continued and sometimes 
rapid movement from side to side. They swept a wide space, but 
only occasionally moved 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 arc, 
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 1 h. 45 m. it had curved considerably 
inwards ; in 2 h. 30 m. it formed a ring ; and in from 5 to 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 befoi*e it curled twice round a thin twig. Tendrils 
Avhich 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 ol* 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. In a 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 Sapindaeeous plant, namely Paullinia. It was not in 
flower, yet thus it bore fine long forked tendrils, differing from 
Cardiospermum. So that, in its tendrils, Paullinia apparently bears 
the same relation to Cardiospermum that Oissus docs to Vitis. 

Passifloraceje. — 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.Jloribunda. 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 lh. 4 m.; it then made, 
the day becoming very hot, three other revolutions at an average 
rate of between 57 and 58 m. ; so that the average rate of all six 
revolutions was 1 h. 1 m. 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 



MK. DARWIN" OX CLIMBING! PLANTS. 



millegramines) placed most geutly on the tip, thrice plainly caused 
it to curve ; as twice did a bent bit of thin platina wire weighing 
^th 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, 39, 31, and 30 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 31 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 Echinoci/stis, 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 ^nd 
of a grain, when rolled into a 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 intcrnodes 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 



TEND1UL-BEARERS. 91 

the sun, in 3 h. 5 m., 2 h. 40 in., and 2 h. 50 m. ; 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 heing 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 
-jlj-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 2 h. 22 m. ; in my cooler 
study one was completed in 3 h., and a second in 4 h. The inter- 
nodes do not revolve; nor do those of the hybrid P.Jloribunda. 

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 5 h. 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. DAUWIK ON CLIMHIXU PLANTS. 



the Vitaceae, Sapindace®, and Passifloraeerc, arc modified flower- 
peduncles. This is likewise the case, according to De Candolle (as 
quoted hy Mold), with the tendrils of Brunnichia, one of the 
Polygonacea?. In two or three species of Modecoa, one of the 
Papayacea*, the tendrils, as I hear from Prof. Oliver, occasionally 
bear flowers and fruit ; so that at least they are axial in their nat ure. 
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 ofTropeeohtm trivolorwn. 
On the other hand, it occurs with all tendrils after they have seized 
some object, with the few following exceptions, — namely Corydulis 
clavicnlata, but then this plant might still be called a leaf-climber ; 
Bignonia unguis and its close allies, and the Cardiospcrmum ; though 
these tendrils are so short that the contraction could hardly take 
place, and would be quite superfluous; and Smilaa aspera, the 
tendrils of which, though rather short, offer a more marked excep- 
tion. In the Diccntra, 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 havo 
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. 

1 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 



TENDRTT.-BEARERS. 93 

the extremity of a free tendril were to contract quite regularly, 
it would roll itself up into a Hat helix, as occurs with the Cardio- 
tpermum ; 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 18 h. Generally the tendrils of the 
Echinoci/stis begin to contract in from 12 h. to 24 h. 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 Passijlora qnadrangularis which had caught 
a stick began in 8h. to contract, and in 21 h. 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 



J * MR. DAKW1N ON OUMBIKQ 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 Rignonia, which are modified leaves, 
thus behave, as do the tendrils of the three genera of Vitacea?, 
and these are modified flower-peduncles. The tendrils, however, of 
JEccremocarpus, which is allied to Bignonia, contract spirally even 
when they have caught nothing. The uneaught tendrils of the 
Cardiospermum, and to a certain extent those of the Jlfutisia, 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 Cohcva, 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 Passijlora 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 



TKNDTUL-UEAKERS. 05 

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 Latlnjrus grand ijlor us 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 Bic/nonia ccqireolata, in which the 
development of the adherent disks suffices to induce the con- 
traction. Tet 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 basc,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 fiexuous 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. Soo. vol. xxiv. 18G4, p. 415. 



9G ME. DAItWTX ON CL1MHINO PLANTS. 

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

Fig. 13. 





,/^&5& 



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 toi'n free. Commonly all the spires at one end of a 
cailffht 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. Leon has seen seven or eight such alter- 
nations. "Whether the spires turn several limes in opposite di- 
rections, or only once, there are as many turns in the one direction 
as in the other. Tor instance, I gathered ten long and short 
caught tendrils of the Bryony, the longest witli 33, 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. Leon in Bull. Soe. Bot. de France, torn. 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 Stimulus, 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 Echinocystis and 
Passiflora quadrangular is ; and as the tendril contracted itself into 
successive 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 ease never 
really occurs ; for, as already stated, when a tendril has caught a 
support ami has spirally contracted, there arc 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 can 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,* will be seen to curve itself 
into an open spire, with the curves running in an opposite direc- 

n 



98 :MB. D.VUWIN 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 
manv times as there were coils ; but he winds it into a figure of 
eight on his thumb aud 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 interuodes revolve in more or less broad ellipses, like 
those made by twiuing 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 Passijlora, 
the internodes of only one of the species have the power of re- 
volving. The Vine is the weakest revolver observed by me, appa- 
rently exhibiting only a trace of a former power. In the Eccremo- 
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, cither 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 even the mature tendrils moved much slower 



TEXDRIL-BEAKEKS. 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, Cobeca, aud most Passiflorae, the tendrils alone revolve ; in 
other cases, as with Lathyrm 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 grandijlorm and the Ampe- 
lopsis. In most Bignonias, iu the Eccremocarpw, Mutisia, and 
the Fumariacese, 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 intcrnode 
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 Echinocystis, as soon as it comes in its revolving 
course to this point, stiffens and straightens itself, and, 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 

h2 



100 Mtt. 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. Passijlora 
gracilis has the most sensitive tendrils which 1 bare seen: a hit 
of platina wire J^th of a grain in weight, gently placed on the 
concave point, caused two tendrils to Income 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 -}V tu °f a g 1 ':' 1 " sufficed- The point of the tendril of the Pas- 
sijlora gracilis distinctly began to move in 2o 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 
plauts, when lightly rubbed, move in a few minutes ; in the 
Dicentra in half-an-hour ; in the SmUase in an hour and a quarter 
or a half; and in the Ampclopsis 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 1 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 Passijlora 
gracilis and of the Ju-liinocystis ; 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, 1 cannot say whether 
there are more cases of this adaptation. Moreover adjoining ten- 
drils rarely catch each other, as we have seen with the Echinocys lis 
and Passijlora, 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 Coba?a (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, docs 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 aud 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 m 
which the tendrils of the Echinoci/slis 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 have 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 stifter 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 suffi- 
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 tail when the tendril is full grown. But in 
the Cobcea and Passijlora punctata the tendrils began revolving 
in a quite useless manner, before they became sensitive. In 



102 ME. DAEWIN 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 circum- 
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 indiil'erent 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 caprcolata the tendrils bend from the light 
to the dark, like a banner from the wind. In the Coba-a and 
Eceremocarpus 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 
Bubject. 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 olf 
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 tliis 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 



TEXDBIL-BEARERS. 103 

when the stem spirally ascends a thin upright stick, but they can 
seize any twig or branch lying beneath them j but when the stem 
spirally ascends a somewhat thicker stick, a slight degree of sensi- 
tiveness in the petioles is brought into play, and thej r wind their 
tendrils round the stick. In B. unguis and 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 aerial roots which adhere to the stick. In B. venmta 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 
slide 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. Chamlcrlaynii 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. caprcolaia 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 Eccremocarpm 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 ca'ch seizes a few thin stems, like the culms of 
a grass, which they afterwards draw together by their spiral con- 



101 MR. dakwix OS rm\ri(rNG PIA.HTS. 

traction into a firm bundle. In the Cobcea the tendrils alone 
revolve; these are divided into many fine branches, terminating 
in sharp little hooks, which crawl into crevices, and arc turned by 
an excellently adapted movement to any object thai is seized. In 
the Ampehpsis, on the other hand, there is little or no power of 
revolving in any part: the branched tendrils arc 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 wilh any nearly Hat 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 caprcolata 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 Amp 6 I 'op sis, and, according to Xaudin*, 
by the Cucurbitaceous genus Veponopsis adhwrens. Their deve- 
lopment, apparently in all cases, depends on the stimulus from 
contact. It is not a little singular that three families so widely 
d'.stinct as the Bignoniaee.T. Yitacea*, and CucurbitaceSB 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 cither 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 Chamber} aijnii grown twice as thick as the 
free basal portion, and become wonderfully rigid. In the An- 
garia 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 I/aubiiri/a 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 Cucurbit aceie, 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 llanlnirya — 
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, 
* Annates des So. Nat. Bot. 4th series, torn. xii. p. 89. 



HOOK- AKD ROOT-OLIMJBERS. 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 Biynonia, Eccremocarjnis, Cobcea, 
and Ampelopsis. 

Part IV. — IIOOK-CMMKERS. — RoOT-CLIMHERS. — CONCLUDING 

Remarks. 

Jlook-climbers. — In my introductory remarks, I staled that, 
besides the great class of twining plants, with the subordinate 
divisions of leaf-climbers and tendril-bearers, there w^ere hook- 
and root-climbers. I mention the former only to say that with 
the few which 1 have examined, namely, Galium aparine, Ttubus 
ausfraJift, and some climbing Roses, there is no spontaneous re- 
volving movement. If indeed they possessed tliis 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; Dipladcuia has a circle of blunt spines at the 
base of its leaves; one tendril-bearing plant alone, as far as T have 
seen, namely, Smilas aspera, is furnished with spines. Some few 
plants, which apparently depend solely on their hooks, are excel- 
lent climbers, as certain Palms in the Xewand Old Worlds. Even 
some of the climbing Koscs 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, like any other plant; so that it is not easy to 
understand how the shoots can get under a trellis close to a wall. 

Soot-climbers. — A good many plants come under tin's class, and 
are excellent climbers. One of the most remarkable is the Marc- 
gravia unihcllaia. 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 JIT. dubia in my hothouse. 
Root-climbers, as far as I have seen, namely, the Ivy {JBLedera 



10G ME. DARWIN ON CLIMHING PLANTS. 

helix - ), Ficus repens, and F. bai-hatus, have no power of movement, 
not even from the light to the dark. As previously stated, the 
Hoya carnosa (Aselepiadacea?) is a spiral twiner, andean likewise 
adhere by rootlets even to a flat wall ; the tendril-bearing Big- 
nonia Twcedyana emits roots, which curve half round and adhere 
to thin sticks. The Tecoma radieans (Bignoniacett), which is 
closely allied to many spontaneously revolving species, climbs by 
rootlets ; but its young shoots apparently move about rather more 1 
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 fcnia 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 vise-id, 
but could not be drawn out into threads ; it bad 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 WES 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 caunot 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, aud so viscid that they could be drawn out into 
threads. Some other rootlets were left in contact during twenty- 
three days, and these wen' firmly cemented to the glass. llenee 
we may conclude that the rootlets firsl 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*, 1 soaked in it during a short time many 

* Mr. Spiller has recently shown (Chemical Society, Feb. 16, 18G">), in a 
paper on the oxidation of india-rubber, thai 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. 



KOOT-CLTifBEBS. 107 

rootlets of a plant which had grown up a plaistercd 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. Tet, 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 Fiats 
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 unelastic cement, is used by Fimis repent 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 Mcercgrcmia dubia can adhere firmly to smooth 
painted wood. 

Vanilla aromatica emits aerial 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 about a 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 Lycojwdium 
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 mb. n.uiwix on" cr.TMiuxa 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 
a^es. 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 thai, 
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 sec, is a great additional advantage. 

From analogous reasons, it is probable that tendril-bearing 
plants were primordiallv 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 lew, 
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-elimbers. The 
three great tendril-bearing families in which this loss has occurred 
in the most marked manner are the Cucurbitaee®, Passifloracea?, 
and Vitaceae. In the first the internodes revolve ; but I have heard 
of no twining form, with the exception (according to Palm, S. 25). 
52) of Momordica hahamma, 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 Passijlora gracilis 
have this power in a 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 gz*oups 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 Rignonia, Clematis, 
and Tropccolum, we can readily observe how incomparably more 
seenrely 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 very 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 JEccremocarpus 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. Ill 

parts acting as leaves or as flower-peduncles can have wholly 
changed their function, and have 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 lamina? 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 ran 
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 
lamina? are retained or reappear. Lastly, in four genera in the 
same family of the Fumariacea? we see the whole gradation; for 
the terminal leaflets of the leaf-climbing Fumaria qjjicinalis are not 
smaller than the other leaflets ; those of the leaf-climbing Adhmia 
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 Dlcentra 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 Tropaolum tricolorum we have another kind of 
passage ; for the leaves which arc first formed on the young plant 
are entirely destitute of lamina, and must be called tendrils, whilst 
the later-formed leaves have well-developed lamina?. In all cases, 
in the several, kinds of leaf-climbers and of tendril-bearers, the 
acquirement of sensitiveness by the mid-ribs of the leaves appa- 
rently stands in the closest relation with the abortion of their 
lamina? 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 beiween twiners and tendril-bearers, and ought to be 
related to both. This is the case ; thus the several leaf-climbing 



112 Ml?. DARWIN ON CLIMBING PLANTS. 

species of the Antirrhinece, of Solanwn, of Cocculics, 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 Clematis are very closely 
allied to the tendril-bearing Naravelia : the Fumariacese include 
closely allied genera which are Leaf-climbers and tendril-hearers. 
Lastly, one species of Bignonia is both a Leaf-climber and a tendril- 
bearer t and other closely allied species are twiners. 

Tendrils of the second great division consist of modified flower- 
peduncles. In this case Likewise we have man; interesting tran- 
sitional states. The common Vine (not to mention the Gardio- 
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-peduncles. 

According to Mold and others, some tendrils consist of modified 
branches: 1 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 arc sensitive to con- 
tact. Hence, if the leaves of some of the branches were to abort, 
they would be converted into true tendrils. Nor is it so improbable 
as it may at flrst appear that certain branches alone should become 
modified, the others remaining unaltered; for we have seen with 
certain varieties of Phaseolw 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 Bhoots 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. Colm, in his remarkable memoir, "Contractile Gewcbe im 
Pflanzenreichc," Abhand. dor Schlesiehen Oesell. 1861, Ileft i. S. 35. 



COM 1,1 UI NO HE-MARKS. 113 

further inquire how the stems, petioles, tendrils, and flower- 
pedtmclea 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 Maurandia semperjlorem, 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 Hofmeieter. We see at least in the Mau- 
randia 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 Ampclopsis, 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 
Solatium jasminoides assuming the most characteristic feature of 
the axis, namely, a closed ring of woody vessels, we cnw hardly 

t 



Ill 



mr. oarwin 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. 
In the leaf-climbing Clematis jlammula, 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 Bignoniacese, 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 Naudinf, 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 iilaments 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 Lath yr us 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,' 1805, 
p. 37 et seq.) with much force that there is no fundamental distinction between 
foliar and axial organs in plants. 

t Annates des So. Nat. 4th series, Bot. torn. 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 L. aphaca the tendril, which is 
not highly developed (for it is unbranched, and has no sponta- 
neous revolving-power), replaces the leaves, the latter in function 
being replaced by the large stipules. Now if we suppose the 
tendrils of L. aphaca to become flattened and foliaccous, like the 
little-rudimentary 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 L. 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, L. 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 
revolving-power (in which state it would resemble the tendril of 
the existing L. apliaca), and afterwards losing its prehensile power 
and becoming foliaceous would no longer be called a tendril. In 
this last stage (that of the existing L. 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 L. 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 
aerial roots — all possess this power. 

In the first place, the tendrils place themselves in the proper 
position for action, standing, for instance in the Coba?a, 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 (Elements dc Teratologic, 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. 

i2 



116 HE, DAItAVIX ON CLIMBING IM.AMS. 

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. If a 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 llibhertia 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 1 ho 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, 
&c, or at intervals of time, as in the so-called sleep of plants. 



CONCLUDING ItEMAltKS. 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 aerial 
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 bendiug 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 arc 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, Kubiacea\ Scrophulari- 
ace», Liliace», &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. It should rather 



118 ME. DARWIN' OX CLIMBING P1.A.XTS. 

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 iuternodes, 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.