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+The Project Gutenberg eBook of The Movement and Habits of Climbing Plants, by Charles Darwin
+
+This eBook is for the use of anyone anywhere in the United States and
+most other parts of the world at no cost and with almost no restrictions
+whatsoever. You may copy it, give it away or re-use it under the terms
+of the Project Gutenberg License included with this eBook or online at
+www.gutenberg.org. If you are not located in the United States, you
+will have to check the laws of the country where you are located before
+using this eBook.
+
+Title: The Movement and Habits of Climbing Plants
+
+Author: Charles Darwin
+
+Release Date: March 4, 2000 [eBook #2485]
+[Most recently updated: November 5, 2021]
+
+Language: English
+
+Character set encoding: UTF-8
+
+Produced by: David Price
+
+*** START OF THE PROJECT GUTENBERG EBOOK THE MOVEMENT AND HABITS OF CLIMBING PLANTS ***
+
+                          [Picture: Book cover]
+
+
+
+
+
+                              THE MOVEMENTS
+                              AND HABITS OF
+                             CLIMBING PLANTS.
+
+
+                        BY CHARLES DARWIN, F.R.S.
+
+                                * * * * *
+
+                             POPULAR EDITION
+
+                                * * * * *
+
+                                 LONDON:
+                      JOHN MURRAY, ALBEMARLE STREET.
+                                  1906.
+
+
+
+
+PREFACE
+
+
+THIS Essay first appeared in the ninth volume of the ‘Journal of the
+Linnean Society,’ published in 1865.  It is here reproduced in a
+corrected and, I hope, clearer form, with some additional facts.  The
+illustrations were drawn by my son, George Darwin.  Fritz Müller, after
+the publication of my paper, sent to the Linnean Society (Journal, vol.
+ix., p. 344) some interesting observations on the climbing plants of
+South Brazil, to which I shall frequently refer.  Recently two important
+memoirs, chiefly on the difference in growth between the upper and lower
+sides of tendrils, and on the mechanism of the movements of
+twining-plants, by Dr. Hugo de Vries, have appeared in the ‘Arbeiten des
+Botanischen Instituts in Würzburg,’ Heft. iii., 1873.  These memoirs
+ought to be carefully studied by every one interested in the subject, as
+I can here give only references to the more important points.  This
+excellent observer, as well as Professor Sachs, {iv} attributes all the
+movements of tendrils to rapid growth along one side; but, from reasons
+assigned towards the close of my fourth chapter, I cannot persuade myself
+that this holds good with respect to those due to a touch.  In order that
+the reader may know what points have interested me most, I may call his
+attention to certain tendril-bearing plants; for instance, Bignonia
+capreolata, Cobæa, Echinocystis, and Hanburya, which display as beautiful
+adaptations as can be found in any part of the kingdom of nature.  It is,
+also, an interesting fact that intermediate states between organs fitted
+for widely different functions, may be observed on the same individual
+plant of Corydalis claviculata and the common vine; and these cases
+illustrate in a striking manner the principle of the gradual evolution of
+species.
+
+
+
+
+APPENDIX TO PREFACE (1882).
+
+
+SINCE the publication of this Edition two papers by eminent botanists
+have appeared; Schwendener, ‘Das Winden der Pflanzen’ (Monatsberichte der
+Berliner Akademie, Dec. 1881), and J. Sachs, ‘Notiz über Schlingpflanzen’
+(Arbeiten des botanischen Instituts in Würzburg, Bd. ii. p. 719, 1882).
+The view “that the capacity of revolving, on which most climbers depend,
+is inherent, though undeveloped, in almost every plant in the vegetable
+kingdom” (‘Climbing Plants,’ p. 205), has been confirmed by the
+observations on circumnutation since given in ‘The Power of Movement in
+Plants.’
+
+
+
+
+ERRATA.
+
+
+On pp. 28, 32, 40, 53, statements are made with reference to the supposed
+acceleration of the revolving movement towards the light.  It appears
+from the observations given in ‘The Power of Movement in Plants,’ p. 451,
+that these conclusions were drawn from insufficient observations, and are
+erroneous.
+
+
+
+
+THE MOVEMENTS AND HABITS OF CLIMBING PLANTS.
+
+
+CHAPTER I.
+TWINING PLANTS.
+
+
+Introductory remarks—Description of the twining of the Hop—Torsion of the
+stems—Nature of the revolving movement, and manner of ascent—Stems not
+irritable—Rate of revolution in various plants—Thickness of the support
+round which plants can twine—Species which revolve in an anomalous
+manner.
+
+I WAS led to this subject by an interesting, but short paper by Professor
+Asa Gray on the movements of the tendrils of some Cucurbitaceous plants.
+{1a}  My observations were more than half completed before I learnt that
+the surprising phenomenon of the spontaneous revolutions of the stems and
+tendrils of climbing plants had been long ago observed by Palm and by
+Hugo von Mohl, {1b} and had subsequently been the subject of two memoirs
+by Dutrochet. {1c}  Nevertheless, I believe that my observations, founded
+on the examination of above a hundred widely distinct living species,
+contain sufficient novelty to justify me in publishing them.
+
+Climbing plants may be divided into four classes.  First, those which
+twine spirally round a support, and are not aided by any other movement.
+Secondly, those endowed with irritable organs, which when they touch any
+object clasp it; such organs consisting of modified leaves, branches, or
+flower-peduncles.  But these two classes sometimes graduate to a certain
+extent into one another.  Plants of the third class ascend merely by the
+aid of hooks; and those of the fourth by rootlets; but as in neither
+class do the plants exhibit any special movements, they present little
+interest, and generally when I speak of climbing plants I refer to the
+two first great classes.
+
+
+TWINING PLANTS.
+
+
+This is the largest subdivision, and is apparently the primordial and
+simplest condition of the class.  My observations will be best given by
+taking a few special cases.  When the shoot of a Hop (_Humulus lupulus_)
+rises from the ground, the two or three first-formed joints or internodes
+are straight and remain stationary; but the next-formed, whilst very
+young, may be seen to bend to one side and to travel slowly round towards
+all points of the compass, moving, like the hands of a watch, with the
+sun.  The movement very soon acquires its full ordinary velocity.  From
+seven observations made during August on shoots proceeding from a plant
+which had been cut down, and on another plant during April, the average
+rate during hot weather and during the day is 2 hrs. 8 m. for each
+revolution; and none of the revolutions varied much from this rate.  The
+revolving movement continues as long as the plant continues to grow; but
+each separate internode, as it becomes old, ceases to move.
+
+To ascertain more precisely what amount of movement each internode
+underwent, I kept a potted plant, during the night and day, in a
+well-warmed room to which I was confined by illness.  A long shoot
+projected beyond the upper end of the supporting stick, and was steadily
+revolving.  I then took a longer stick and tied up the shoot, so that
+only a very young internode, 1¾ of an inch in length, was left free.
+This was so nearly upright that its revolution could not be easily
+observed; but it certainly moved, and the side of the internode which was
+at one time convex became concave, which, as we shall hereafter see, is a
+sure sign of the revolving movement.  I will assume that it made at least
+one revolution during the first twenty-four hours.  Early the next
+morning its position was marked, and it made a second revolution in 9
+hrs.; during the latter part of this revolution it moved much quicker,
+and the third circle was performed in the evening in a little over 3 hrs.
+As on the succeeding morning I found that the shoot revolved in 2 hrs. 45
+m., it must have made during the night four revolutions, each at the
+average rate of a little over 3 hrs.  I should add that the temperature
+of the room varied only a little.  The shoot had now grown 3½ inches in
+length, and carried at its extremity a young internode 1 inch in length,
+which showed slight changes in its curvature.  The next or ninth
+revolution was effected in 2 hrs. 30 m.  From this time forward, the
+revolutions were easily observed.  The thirty-sixth revolution was
+performed at the usual rate; so was the last or thirty-seventh, but it
+was not completed; for the internode suddenly became upright, and after
+moving to the centre, remained motionless.  I tied a weight to its upper
+end, so as to bow it slightly and thus detect any movement; but there was
+none.  Some time before the last revolution was half performed, the lower
+part of the internode ceased to move.
+
+A few more remarks will complete all that need be said about this
+internode.  It moved during five days; but the more rapid movements,
+after the performance of the third revolution, lasted during three days
+and twenty hours.  The regular revolutions, from the ninth to
+thirty-sixth inclusive, were effected at the average rate of 2 hrs. 31
+m.; but the weather was cold, and this affected the temperature of the
+room, especially during the night, and consequently retarded the rate of
+movement a little.  There was only one irregular movement, which
+consisted in the stem rapidly making, after an unusually slow revolution,
+only the segment of a circle.  After the seventeenth revolution the
+internode had grown from 1¾ to 6 inches in length, and carried an
+internode 1⅞ inch long, which was just perceptibly moving; and this
+carried a very minute ultimate internode.  After the twenty-first
+revolution, the penultimate internode was 2½ inches long, and probably
+revolved in a period of about three hours.  At the twenty-seventh
+revolution the lower and still moving internode was 8⅜, the penultimate
+3½, and the ultimate 2½ inches in length; and the inclination of the
+whole shoot was such, that a circle 19 inches in diameter was swept by
+it.  When the movement ceased, the lower internode was 9 inches, and the
+penultimate 6 inches in length; so that, from the twenty-seventh to
+thirty-seventh revolutions inclusive, three internodes were at the same
+time revolving.
+
+The lower internode, when it ceased revolving, became upright and rigid;
+but as the whole shoot was left to grow unsupported, it became after a
+time bent into a nearly horizontal position, the uppermost and growing
+internodes still revolving at the extremity, but of course no longer
+round the old central point of the supporting stick.  From the changed
+position of the centre of gravity of the extremity, as it revolved, a
+slight and slow swaying movement was given to the long horizontally
+projecting shoot; and this movement I at first thought was a spontaneous
+one.  As the shoot grew, it hung down more and more, whilst the growing
+and revolving extremity turned itself up more and more.
+
+With the Hop we have seen that three internodes were at the same time
+revolving; and this was the case with most of the plants observed by me.
+With all, if in full health, two internodes revolved; so that by the time
+the lower one ceased to revolve, the one above was in full action, with a
+terminal internode just commencing to move.  With _Hoya carnosa_, on the
+other hand, a depending shoot, without any developed leaves, 32 inches in
+length, and consisting of seven internodes (a minute terminal one, an
+inch in length, being counted), continually, but slowly, swayed from side
+to side in a semicircular course, with the extreme internodes making
+complete revolutions.  This swaying movement was certainly due to the
+movement of the lower internodes, which, however, had not force
+sufficient to swing the whole shoot round the central supporting stick.
+The case of another Asclepiadaceous plant, viz., _Ceropegia Gardnerii_,
+is worth briefly giving.  I allowed the top to grow out almost
+horizontally to the length of 31 inches; this now consisted of three long
+internodes, terminated by two short ones.  The whole revolved in a course
+opposed to the sun (the reverse of that of the Hop), at rates between 5
+hrs. 15 m. and 6 hrs. 45 m. for each revolution.  The extreme tip thus
+made a circle of above 5 feet (or 62 inches) in diameter and 16 feet in
+circumference, travelling at the rate of 32 or 33 inches per hour.  The
+weather being hot, the plant was allowed to stand on my study-table; and
+it was an interesting spectacle to watch the long shoot sweeping this
+grand circle, night and day, in search of some object round which to
+twine.
+
+If we take hold of a growing sapling, we can of course bend it to all
+sides in succession, so as to make the tip describe a circle, like that
+performed by the summit of a spontaneously revolving plant.  By this
+movement the sapling is not in the least twisted round its own axis.  I
+mention this because if a black point be painted on the bark, on the side
+which is uppermost when the sapling is bent towards the holder’s body, as
+the circle is described, the black point gradually turns round and sinks
+to the lower side, and comes up again when the circle is completed; and
+this gives the false appearance of twisting, which, in the case of
+spontaneously revolving plants, deceived me for a time.  The appearance
+is the more deceitful because the axes of nearly all twining-plants are
+really twisted; and they are twisted in the same direction with the
+spontaneous revolving movement.  To give an instance, the internode of
+the Hop of which the history has been recorded, was at first, as could be
+seen by the ridges on its surface, not in the least twisted; but when,
+after the 37th revolution, it had grown 9 inches long, and its revolving
+movement had ceased, it had become twisted three times round its own
+axis, in the line of the course of the sun; on the other hand, the common
+Convolvulus, which revolves in an opposite course to the Hop, becomes
+twisted in an opposite direction.
+
+Hence it is not surprising that Hugo von Mohl (p. 105, 108, &c.) thought
+that the twisting of the axis caused the revolving movement; but it is
+not possible that the twisting of the axis of the Hop three times should
+have caused thirty-seven revolutions.  Moreover, the revolving movement
+commenced in the young internode before any twisting of its axis could be
+detected.  The internodes of a young Siphomeris and Lecontea revolved
+during several days, but became twisted only once round their own axes.
+The best evidence, however, that the twisting does not cause the
+revolving movement is afforded by many leaf-climbing and tendril-bearing
+plants (as _Pisum sativum_, _Echinocystis lobata_, _Bignonia capreolata_,
+_Eccremocarpus scaber_, and with the leaf-climbers, _Solanum jasminoides_
+and various species of _Clematis_), of which the internodes are not
+twisted, but which, as we shall hereafter see, regularly perform
+revolving movements like those of true twining-plants.  Moreover,
+according to Palm (pp. 30, 95) and Mohl (p. 149), and Léon, {8}
+internodes may occasionally, and even not very rarely, be found which are
+twisted in an opposite direction to the other internodes on the same
+plant, and to the course of their revolutions; and this, according to
+Léon (p. 356), is the case with all the internodes of a certain variety
+of _Phaseolus multiflorus_.  Internodes which have become twisted round
+their own axes, if they have not ceased to revolve, are still capable of
+twining round a support, as I have several times observed.
+
+Mohl has remarked (p. 111) that when a stem twines round a smooth
+cylindrical stick, it does not become twisted. {9a}  Accordingly I
+allowed kidney-beans to run up stretched string, and up smooth rods of
+iron and glass, one-third of an inch in diameter, and they became twisted
+only in that degree which follows as a mechanical necessity from the
+spiral winding.  The stems, on the other hand, which had ascended
+ordinary rough sticks were all more or less and generally much twisted.
+The influence of the roughness of the support in causing axial twisting
+was well seen in the stems which had twined up the glass rods; for these
+rods were fixed into split sticks below, and were secured above to cross
+sticks, and the stems in passing these places became much twisted.  As
+soon as the stems which had ascended the iron rods reached the summit and
+became free, they also became twisted; and this apparently occurred more
+quickly during windy than during calm weather.  Several other facts could
+be given, showing that the axial twisting stands in some relation to
+inequalities in the support, and likewise to the shoot revolving freely
+without any support.  Many plants, which are not twiners, become in some
+degree twisted round their own axes; {9b} but this occurs so much more
+generally and strongly with twining-plants than with other plants, that
+there must be some connexion between the capacity for twining and axial
+twisting.  The stem probably gains rigidity by being twisted (on the same
+principle that a much twisted rope is stiffer than a slackly twisted
+one), and is thus indirectly benefited so as to be enabled to pass over
+inequalities in its spiral ascent, and to carry its own weight when
+allowed to revolve freely. {10}
+
+I have alluded to the twisting which necessarily follows on mechanical
+principles from the spiral ascent of a stem, namely, one twist for each
+spire completed.  This was well shown by painting straight lines on
+living stems, and then allowing them to twine; but, as I shall have to
+recur to this subject under Tendrils, it may be here passed over.
+
+The revolving movement of a twining plant has been compared with that of
+the tip of a sapling, moved round and round by the hand held some way
+down the stem; but there is one important difference.  The upper part of
+the sapling when thus moved remains straight; but with twining plants
+every part of the revolving shoot has its own separate and independent
+movement.  This is easily proved; for when the lower half or two-thirds
+of a long revolving shoot is tied to a stick, the upper free part
+continues steadily revolving.  Even if the whole shoot, except an inch or
+two of the extremity, be tied up, this part, as I have seen in the case
+of the Hop, Ceropegia, Convolvulus, &c., goes on revolving, but much more
+slowly; for the internodes, until they have grown to some little length,
+always move slowly.  If we look to the one, two, or several internodes of
+a revolving shoot, they will be all seen to be more or less bowed, either
+during the whole or during a large part of each revolution.  Now if a
+coloured streak be painted (this was done with a large number of twining
+plants) along, we will say, the convex surface, the streak will after a
+time (depending on the rate of revolution) be found to be running
+laterally along one side of the bow, then along the concave side, then
+laterally on the opposite side, and, lastly, again on the originally
+convex surface.  This clearly proves that during the revolving movement
+the internodes become bowed in every direction.  The movement is, in
+fact, a continuous self-bowing of the whole shoot, successively directed
+to all points of the compass; and has been well designated by Sachs as a
+revolving nutation.
+
+As this movement is rather difficult to understand, it will be well to
+give an illustration.  Take a sapling and bend it to the south, and paint
+a black line on the convex surface; let the sapling spring up and bend it
+to the east, and the black line will be seen to run along the lateral
+face fronting the north; bend it to the north, the black line will be on
+the concave surface; bend it to the west, the line will again be on the
+lateral face; and when again bent to the south, the line will be on the
+original convex surface.  Now, instead of bending the sapling, let us
+suppose that the cells along its northern surface from the base to the
+tip were to grow much more rapidly than on the three other sides, the
+whole shoot would then necessarily be bowed to the south; and let the
+longitudinal growing surface creep round the shoot, deserting by slow
+degrees the northern side and encroaching on the western side, and so
+round by the south, by the east, again to the north.  In this case the
+shoot would remain always bowed with the painted line appearing on the
+several above specified surfaces, and with the point of the shoot
+successively directed to each point of the compass.  In fact, we should
+have the exact kind of movement performed by the revolving shoots of
+twining plants. {12}
+
+It must not be supposed that the revolving movement is as regular as that
+given in the above illustration; in very many cases the tip describes an
+ellipse, even a very narrow ellipse.  To recur once again to our
+illustration, if we suppose only the northern and southern surfaces of
+the sapling alternately to grow rapidly, the summit would describe a
+simple arc; if the growth first travelled a very little to the western
+face, and during the return a very little to the eastern face, a narrow
+ellipse would be described; and the sapling would be straight as it
+passed to and fro through the intermediate space; and a complete
+straightening of the shoot may often be observed in revolving plants.
+The movement is frequently such that three of the sides of the shoot seem
+to be growing in due order more rapidly than the remaining side; so that
+a semi-circle instead of a circle is described, the shoot becoming
+straight and upright during half of its course.
+
+When a revolving shoot consists of several internodes, the lower ones
+bend together at the same rate, but one or two of the terminal ones bend
+at a slower rate; hence, though at times all the internodes are in the
+same direction, at other times the shoot is rendered slightly serpentine.
+The rate of revolution of the whole shoot, if judged by the movement of
+the extreme tip, is thus at times accelerated or retarded.  One other
+point must be noticed.  Authors have observed that the end of the shoot
+in many twining plants is completely hooked; this is very general, for
+instance, with the Asclepiadaceæ.  The hooked tip, in all the cases
+observed by me, viz. in _Ceropegia_, _Sphærostemma_, _Clerodendron_,
+_Wistaria_, _Stephania_, _Akebia_, and _Siphomeris_, has exactly the same
+kind of movement as the other internodes; for a line painted on the
+convex surface first becomes lateral and then concave; but, owing to the
+youth of these terminal internodes, the reversal of the hook is a slower
+process than that of the revolving movement. {14}  This strongly marked
+tendency in the young, terminal and flexible internodes, to bend in a
+greater degree or more abruptly than the other internodes, is of service
+to the plant; for not only does the hook thus formed sometimes serve to
+catch a support, but (and this seems to be much more important) it causes
+the extremity of the shoot to embrace the support much more closely than
+it could otherwise have done, and thus aids in preventing the stem from
+being blown away during windy weather, as I have many times observed.  In
+_Lonicera brachypoda_ the hook only straightens itself periodically, and
+never becomes reversed.  I will not assert that the tips of all twining
+plants when hooked, either reverse themselves or become periodically
+straight, in the manner just described; for the hooked form may in some
+cases be permanent, and be due to the manner of growth of the species, as
+with the tips of the shoots of the common vine, and more plainly with
+those of _Cissus discolor_—plants which are not spiral twiners.
+
+The first purpose of the spontaneous revolving movement, or, more
+strictly speaking, of the continuous bowing movement directed
+successively to all points of the compass, is, as Mohl has remarked, to
+favour the shoot finding a support.  This is admirably effected by the
+revolutions carried on night and day, a wider and wider circle being
+swept as the shoot increases in length.  This movement likewise explains
+how the plants twine; for when a revolving shoot meets with a support,
+its motion is necessarily arrested at the point of contact, but the free
+projecting part goes on revolving.  As this continues, higher and higher
+points are brought into contact with the support and are arrested; and so
+onwards to the extremity; and thus the shoot winds round its support.
+When the shoot follows the sun in its revolving course, it winds round
+the support from right to left, the support being supposed to stand in
+front of the beholder; when the shoot revolves in an opposite direction,
+the line of winding is reversed.  As each internode loses from age its
+power of revolving, it likewise loses its power of spirally twining.  If
+a man swings a rope round his head, and the end hits a stick, it will
+coil round the stick according to the direction of the swinging movement;
+so it is with a twining plant, a line of growth travelling round the free
+part of the shoot causing it to bend towards the opposite side, and this
+replaces the momentum of the free end of the rope.
+
+All the authors, except Palm and Mohl, who have discussed the spiral
+twining of plants, maintain that such plants have a natural tendency to
+grow spirally.  Mohl believes (p. 112) that twining stems have a dull
+kind of irritability, so that they bend towards any object which they
+touch; but this is denied by Palm.  Even before reading Mohl’s
+interesting treatise, this view seemed to me so probable that I tested it
+in every way that I could, but always with a negative result.  I rubbed
+many shoots much harder than is necessary to excite movement in any
+tendril or in the foot-stalk of any leaf climber, but without any effect.
+I then tied a light forked twig to a shoot of a Hop, a _Ceropegia_,
+_Sphærostemma_, and _Adhatoda_, so that the fork pressed on one side
+alone of the shoot and revolved with it; I purposely selected some very
+slow revolvers, as it seemed most likely that these would profit most
+from possessing irritability; but in no case was any effect produced.
+{16}  Moreover, when a shoot winds round a support, the winding movement
+is always slower, as we shall immediately see, than whilst it revolves
+freely and touches nothing.  Hence I conclude that twining stems are not
+irritable; and indeed it is not probable that they should be so, as
+nature always economizes her means, and irritability would have been
+superfluous.  Nevertheless I do not wish to assert that they are never
+irritable; for the growing axis of the leaf-climbing, but not spirally
+twining, _Lophospermum scandens_ is, certainly irritable; but this case
+gives me confidence that ordinary twiners do not possess any such
+quality, for directly after putting a stick to the _Lophopermum_, I saw
+that it behaved differently from a true twiner or any other leaf-climber.
+{17}
+
+The belief that twiners have a natural tendency to grow spirally,
+probably arose from their assuming a spiral form when wound round a
+support, and from the extremity, even whilst remaining free, sometimes
+assuming this form.  The free internodes of vigorously growing plants,
+when they cease to revolve, become straight, and show no tendency to be
+spiral; but when a shoot has nearly ceased to grow, or when the plant is
+unhealthy, the extremity does occasionally become spiral.  I have seen
+this in a remarkable manner with the ends of the shoots of the
+_Stauntonia_ and of the allied _Akebia_, which became wound up into a
+close spire, just like a tendril; and this was apt to occur after some
+small, ill-formed leaves had perished.  The explanation, I believe, is,
+that in such cases the lower parts of the terminal internodes very
+gradually and successively lose their power of movement, whilst the
+portions just above move onwards and in their turn become motionless; and
+this ends in forming an irregular spire.
+
+When a revolving shoot strikes a stick, it winds round it rather more
+slowly than it revolves.  For instance, a shoot of the _Ceropegia_,
+revolved in 6 hrs., but took 9 hrs. 30 m. to make one complete spire
+round a stick; _Aristolochia gigas_ revolved in about 5 hrs., but took 9
+hrs. 15 m. to complete its spire.  This, I presume, is due to the
+continued disturbance of the impelling force by the arrestment of the
+movement at successive points; and we shall hereafter see that even
+shaking a plant retards the revolving movement.  The terminal internodes
+of a long, much-inclined, revolving shoot of the _Ceropegia_, after they
+had wound round a stick, always slipped up it, so as to render the spire
+more open than it was at first; and this was probably in part due to the
+force which caused the revolutions, being now almost freed from the
+constraint of gravity and allowed to act freely.  With the _Wistaria_, on
+the other hand, a long horizontal shoot wound itself at first into a very
+close spire, which remained unchanged; but subsequently, as the shoot
+twined spirally up its support, it made a much more open spire.  With all
+the many plants which were allowed freely to ascend a support, the
+terminal internodes made at first a close spire; and this, during windy
+weather, served to keep the shoots in close contact with their support;
+but as the penultimate internodes grew in length, they pushed themselves
+up for a considerable space (ascertained by coloured marks on the shoot
+and on the support) round the stick, and the spire became more open. {18}
+
+It follows from this latter fact that the position occupied by each leaf
+with respect to the support depends on the growth of the internodes after
+they have become spirally wound round it.  I mention this on account of
+an observation by Palm (p. 34), who states that the opposite leaves of
+the Hop always stand in a row, exactly over one another, on the same side
+of the supporting stick, whatever its thickness may be.  My sons visited
+a hop-field for me, and reported that though they generally found the
+points of insertion of the leaves standing over each other for a space of
+two or three feet in height, yet this never occurred up the whole length
+of the pole; the points of insertion forming, as might have been
+expected, an irregular spire.  Any irregularity in the pole entirely
+destroyed the regularity of position of the leaves.  From casual
+inspection, it appeared to me that the opposite leaves of _Thunbergia
+alata_ were arranged in lines up the sticks round which they had twined;
+accordingly, I raised a dozen plants, and gave them sticks of various
+thicknesses, as well as string, to twine round; and in this case one
+alone out of the dozen had its leaves arranged in a perpendicular line: I
+conclude, therefore, Palm’s statement is not quite accurate.
+
+The leaves of different twining-plants are arranged on the stem (before
+it has twined) alternately, or oppositely, or in a spire.  In the latter
+case the line of insertion of the leaves and the course of the
+revolutions coincide.  This fact has been well shown by Dutrochet, {19}
+who found different individuals of _Solanum dulcamara_ twining in
+opposite directions, and these had their leaves in each case spirally
+arranged in the same direction.  A dense whorl of many leaves would
+apparently be incommodious for a twining plant, and some authors assert
+that none have their leaves thus arranged; but a twining _Siphomeris_ has
+whorls of three leaves.
+
+If a stick which has arrested a revolving shoot, but has not as yet been
+encircled, be suddenly taken away, the shoot generally springs forward,
+showing that it was pressing with some force against the stick.  After a
+shoot has wound round a stick, if this be withdrawn, it retains for a
+time its spiral form; it then straightens itself, and again commences to
+revolve.  The long, much-inclined shoot of the _Ceropegia_ previously
+alluded to offered some curious peculiarities.  The lower and older
+internodes, which continued to revolve, were incapable, on repeated
+trials, of twining round a thin stick; showing that, although the power
+of movement was retained, this was not sufficient to enable the plant to
+twine.  I then moved the stick to a greater distance, so that it was
+struck by a point 2½ inches from the extremity of the penultimate
+internode; and it was then neatly encircled by this part of the
+penultimate and by the ultimate internode.  After leaving the spirally
+wound shoot for eleven hours, I quietly withdrew the stick, and in the
+course of the day the curled portion straightened itself and recommenced
+revolving; but the lower and not curled portion of the penultimate
+internode did not move, a sort of hinge separating the moving and the
+motionless part of the same internode.  After a few days, however, I
+found that this lower part had likewise recovered its revolving power.
+These several facts show that the power of movement is not immediately
+lost in the arrested portion of a revolving shoot; and that after being
+temporarily lost it can be recovered.  When a shoot has remained for a
+considerable time round a support, it permanently retains its spiral form
+even when the support is removed.
+
+When a tall stick was placed so as to arrest the lower and rigid
+internodes of the _Ceropegia_, at the distance at first of 15 and then of
+21 inches from the centre of revolution, the straight shoot slowly and
+gradually slid up the stick, so as to become more and more highly
+inclined, but did not pass over the summit.  Then, after an interval
+sufficient to have allowed of a semi-revolution, the shoot suddenly
+bounded from the stick and fell over to the opposite side or point of the
+compass, and reassumed its previous slight inclination.  It now
+recommenced revolving in its usual course, so that after a
+semi-revolution it again came into contact with the stick, again slid up
+it, and again bounded from it and fell over to the opposite side.  This
+movement of the shoot had a very odd appearance, as if it were disgusted
+with its failure but was resolved to try again.  We shall, I think,
+understand this movement by considering the former illustration of the
+sapling, in which the growing surface was supposed to creep round from
+the northern by the western to the southern face; and thence back again
+by the eastern to the northern face, successively bowing the sapling in
+all directions.  Now with the _Ceropegia_, the stick being placed to the
+south of the shoot and in contact with it, as soon as the circulatory
+growth reached the western surface, no effect would be produced, except
+that the shoot would be pressed firmly against the stick.  But as soon as
+growth on the southern surface began, the shoot would be slowly dragged
+with a sliding movement up the stick; and then, as soon as the eastern
+growth commenced, the shoot would be drawn from the stick, and its weight
+coinciding with the effects of the changed surface of growth, would cause
+it suddenly to fall to the opposite side, reassuming its previous slight
+inclination; and the ordinary revolving movement would then go on as
+before.  I have described this curious case with some care, because it
+first led me to understand the order in which, as I then thought, the
+surfaces contracted; but in which, as we now know from Sachs and II. de
+Vries, they grow for a time rapidly, thus causing the shoot to bow
+towards the opposite side.
+
+The view just given further explains, as I believe, a fact observed by
+Mohl (p. 135), namely, that a revolving shoot, though it will twine round
+an object as thin as a thread, cannot do so round a thick support.  I
+placed some long revolving shoots of a _Wistaria_ close to a post between
+5 and 6 inches in diameter, but, though aided by me in many ways, they
+could not wind round it.  This apparently was due to the flexure of the
+shoot, whilst winding round an object so gently curved as this post, not
+being sufficient to hold the shoot to its place when the growing surface
+crept round to the opposite surface of the shoot; so that it was
+withdrawn at each revolution from its support.
+
+When a free shoot has grown far beyond its support, it sinks downwards
+from its weight, as already explained in the case of the Hop, with the
+revolving extremity turned upwards.  If the support be not lofty, the
+shoot falls to the ground, and resting there, the extremity rises up.
+Sometimes several shoots, when flexible, twine together into a cable, and
+thus support one another.  Single thin depending shoots, such as those of
+the _Sollya Drummondii_, will turn abruptly backwards and wind up on
+themselves.  The greater number of the depending shoots, however, of one
+twining plant, the _Hibbertia dentata_, showed but little tendency to
+turn upwards.  In other cases, as with the _Cryptostegia grandiflora_,
+several internodes which were at first flexible and revolved, if they did
+not succeed in twining round a support, become quite rigid, and
+supporting themselves upright, carried on their summits the younger
+revolving internodes.
+
+Here will be a convenient place to give a Table showing the direction and
+rate of movement of several twining plants, with a few appended remarks.
+These plants are arranged according to Lindley’s ‘Vegetable Kingdom’ of
+1853; and they have been selected from all parts of the series so as to
+show that all kinds behave in a nearly uniform manner. {24}
+
+
+The Rate of Revolution of various Twining Plants.
+
+(ACOTYLEDONS.)
+
+
+_Lygodium scandens_ (Polypodiaceæ) moves against the sun.
+
+                                      H.      M.
+June 18, 1st circle was made in        6       0
+      18, 2nd                          6      15  (late in evening)
+      19, 3rd                          5      32  (very hot day)
+      19, 4th                          5       0  (very hot day)
+      20, 5th                          6       0
+
+_Lygodium articulatum_ moves against the sun.
+
+                                      H.      M.
+July 19, 1st circle was made in       16      30  (shoot very young)
+      20, 2nd                         15       0
+      21, 3rd                          8       0
+      22, 4th                         10      30
+
+(MONOCOTYLEDONS.)
+
+
+_Ruscus androgynus_ (Liliaceæ), placed in the hot-house, moves against
+the sun.
+
+                                     H.      M.
+May 24, 1st circle was made in        6      14  (shoot very young)
+      25, 2nd                         2      21
+      25, 3rd                         3      37
+      25, 4th                         3      22
+      26, 5th                         2      50
+      27, 6th                         3      52
+      27, 7th                         4      11
+
+_Asparagus_ (unnamed species from Kew) (Liliaceæ) moves against the sun,
+placed in hothouse.
+
+                                      H.      M.
+Dec. 26, 1st circle was made in        5       0
+      27, 2nd                          5      40
+
+_Tamus communis_ (Dioscoreaceæ).  A young shoot from a tuber in a pot
+placed in the greenhouse: follows the sun.
+
+                                      H.      M.
+July, 7, 1st circle was made in        3      10
+      7, 2nd                           2      38
+      8, 3rd                           3       5
+      8, 4th                           2      56
+      8, 5th                           2      30
+      8, 6th                           2      30
+
+_Lapagerea rosea_ (Philesiaceæ), in greenhouse, follows the sun.
+
+                                      H.      M.
+March 9, 1st circle was made in       26      15  (shoot young)
+      10, semicircle                   8      15
+      11, 2nd circle                  11       0
+      12, 3rd                         15      30
+      13, 4th                         14      15
+      16, 5th                          8      40  when placed in the
+                                                  hothouse; but the
+                                                  next day the shoot
+                                                  remained
+                                                  stationary.
+
+_Roxburghia viridiflora_ (Roxburghiaceæ) moves against the sun; it
+completed a circle in about 24 hours.
+
+
+(DICOTYLEDONS.)
+
+
+_Humulus Lupulus_ (Urticaceæ) follows the sun.  The plant was kept in a
+room during warm weather.
+
+                                      H.      M.
+April 9, 2 circles were made in        4      16
+Aug. 13, 3rd circle was                2       0
+      14, 4th                          2      20
+      14, 5th                          2      16
+      14, 6th                          2       2
+      14, 7th                          2       0
+      14, 8th                          2       4
+
+With the Hop a semicircle was performed, in travelling from the light, in
+1 hr. 33 m.; in travelling to the light, in 1 hr. 13 m.; difference of
+rate, 20 m.
+
+_Akebia quinata_ (Lardizabalaceæ), placed in hothouse, moves against the
+sun.
+
+                                       H.      M.
+March 17, 1st circle was made in        4       0  (shoot young)
+      18, 2nd                           1      40
+      18, 3rd                           1      30
+      19, 4th                           1      45
+
+_Stauntonia latifolia_ (Lardizabalaceæ), placed in hothouse, moves
+against the sun.
+
+                                       H.      M.
+March 28, 1st circle was made in        3      30
+      29, 2nd                           3      45
+
+_Sphærostemma marmoratum_ (Schizandraceæ) follows the sun.
+
+                                               H.      M.
+August 5th, 1st circle was made in about       24       0
+      5th, 2nd circle was made in              18      30
+
+_Stephania rotunda_ (Menispermaceæ) moves against the sun.
+
+                                     H.      M.
+May 27, 1st circle was made in        5       5
+      30, 2nd                         7       6
+June 2, 3rd                           5      15
+      3, 4th                          6      28
+
+Thryallis brachystachys (Malpighiaceæ) moves against the sun: one shoot
+made a circle in 12 hrs., and another in 10 hrs. 30 m.; but the next day,
+which was much colder, the first shoot took 10 hrs. to perform only a
+semicircle.
+
+Hibbertia dentata (Dilleniaceæ), placed in the hothouse, followed the
+sun, and made (May 18th) a circle in 7 hrs. 20 m.; on the 19th, reversed
+its course, and moved against the sun, and made a circle in 7 hrs.; on
+the 20th, moved against the sun one-third of a circle, and then stood
+still; on the 26th, followed the sun for two-thirds of a circle, and then
+returned to its starting-point, taking for this double course 11 hrs. 46
+m.
+
+_Sollya Drummondii_ (Pittosporaceæ) moves against the sun kept in
+greenhouse.
+
+                                      H.      M.
+April 4, 1st circle was made in        4      25
+      5, 2nd                           8       0  (very cold day)
+      6, 3rd                           6      25
+      7, 4th                           7       5
+
+_Polygonum dumetorum_ (Polygonaceæ).  This case is taken from Dutrochet
+(p.  299), as I observed, no allied plant: follows the sun.  Three
+shoots, cut off a plant, and placed in water made circles in 3 hrs. 10
+m., 5 hrs. 20 m., and 7 hrs. 15 m.
+
+_Wistaria Chinensis_ (Leguminosæ), in greenhouse, moves against the sun.
+
+                                     H.      M.
+May 13, 1st circle was made in        3       5
+      13, 2nd                         3      20
+      16, 3rd                         2       5
+      24, 4th                         3      21
+      25, 5th                         2      37
+      25, 6th                         2      35
+
+_Phaseolus vulgaris_ (Leguminosæ), in greenhouse, moves against the sun.
+
+                                  H.      M.
+May, 1st circle was made in        2       0
+      2nd                          1      55
+      3rd                          1      55
+
+_Dipladenia urophylla_ (Apocynaceæ) moves against the sun.
+
+                                       H.      M.
+April 18, 1st circle was made in        8       0
+      19, 2nd                           9      15
+      30, 3rd                           9      40
+
+_Dipladenia crassinoda_ moves against the sun.
+
+                                     H.      M.
+May 16, 1st circle was made in        9       5
+July 20, 2nd                          8       0
+      21, 3rd                         8       5
+
+_Ceropegia Gardnerii_ (Asclepiadaceæ) moves against the sun.
+
+                                                            H.      M.
+Shoot very young, 2 inches in         1st circle was         7      55
+length                                performed in
+Shoot still young                     2nd                    7       0
+Long shoot                            3rd                    6      33
+Long shoot                            4th                    5      15
+Long shoot                            5th                    6      45
+
+_Stephanotis floribunda_ (Asclepiadaceæ) moves against the sun and made a
+circle in 6 hrs. 40 m., a second circle in about 9 hrs.
+
+_Hoya carnosa_ (Asclepiadaceæ) made several circles in from 16 hrs. to 22
+hrs. or 24 hrs.
+
+_Ipomæa purpurea_ (Convolvulaceæ) moves against the sun.  Plant placed in
+room with lateral light.
+
+1st circle was made in 2 hrs. 42    Semicircle, from the light in 1
+m.                                  hr. 14 m., to the light 1 hr. 28
+                                    m.: difference 14 m.
+2nd circle was made in 2 hrs. 47    Semicircle, from the light in 1
+m.                                  hr. 17 m., to the light 1 hr. 30
+                                    m.: difference 13 m.
+
+_Ipomæa jucunda_ (Convolvulaceæ) moves against the sun, placed in my
+study, with windows facing the north-east.  Weather hot.
+
+1st circle was made in 5 hrs. 30    Semicircle, from the light in 4
+m.                                  hrs. 30 m., to the light 1 hr. 0
+                                    m.: difference 3 hrs. 30 m.
+2nd circle was made in 5 hrs. 20    Semicircle, from the light in 3
+m.  (Late in afternoon: circle      hrs. 50 m., to the light 1 hr. 30
+completed at 6 hrs. 40 m. P.M.)     m.: difference 2 hrs. 20 m.
+
+We have here a remarkable instance of the power of light in retarding and
+hastening the revolving movement.  (_See_ ERRATA.)
+
+_Convolvulus sepium_ (large-flowered cultivated var.) moves against the
+sun.  Two circles, were made each in 1 hr. 42 m.: difference in
+semicircle from and to the light 14 m.
+
+_Rivea tiliæfolia_ (Convolvulaceæ) moves against the sun, made four
+revolutions in 9 hrs.; so that, on an average, each was performed in 2
+hrs. 15 m.
+
+_Plumbago rosea_ (Plumbaginaceæ) follows the sun.  The shoot did not
+begin to revolve until nearly a yard in height; it then made a fine
+circle in 10 hrs. 45 m.  During the next few days it continued to move,
+but irregularly.  On August 15th the shoot followed, during a period of
+10 hrs. 40 m., a long and deeply zigzag course and then made a broad
+ellipse.  The figure apparently represented three ellipses, each of which
+averaged 3 hrs. 38 m. for its completion.
+
+_Jasminum pauciflorum_, Bentham (Jasminaceæ), moves against the sun.  A
+circle was made in 7 hrs. 15 m., and a second rather more quickly.
+
+_Clerodendrum Thomsonii_ (Verbenaceæ) follows the sun.
+
+                                       H.      M.
+April 12, 1st circle was made in        5      45  (shoot very young)
+      14, 2nd                           3      30
+      18, a semicircle                  5       0  (directly after
+                                                   the plant was
+                                                   shaken on being
+                                                   moved)
+      19, 3rd circle                    3       0
+      20, 4th                           4      20
+
+_Tecoma jasminoides_ (Bignoniaceæ) moves against the sun.
+
+                                       H.      M.
+March 17, 1st circle was made in        6      30
+      19, 2nd                           7       0
+      22, 3rd                           8      30  (very cold day)
+      24, 4th                           6      45
+
+_Thunbergia alata_ (Acanthaceæ) moves against sun.
+
+                                       H.      M.
+April 14, 1st circle was made in        3      20
+      18, 2nd                           2      50
+      18, 3rd                           2      55
+      18, 4th                           3      55  (late in
+                                                   afternoon)
+
+_Adhadota cydonæfolia_ (Acanthaceæ) follows the sun.  A young shoot made
+a semicircle in 24 hrs.; subsequently it made a circle in between 40 hrs.
+and 48 hrs.  Another shoot, however, made a circle in 26 hrs. 30 m.
+
+_Mikania scandens_ (Compositæ) moves against the sun.
+
+                                       H.      M.
+March 14, 1st circle was made in        3      10
+      15, 2nd                           3       0
+      16, 3rd                           3       0
+      17, 4th                           3      33
+April 7, 5th                            2      50
+      7, 6th                            2      40  This circle was
+                                                   made after a
+                                                   copious watering
+                                                   with cold water at
+                                                   47° Fahr.
+
+_Combretum argenteum_ (Combretaceæ) moves against the sun.  Kept in
+hothouse.
+
+                                          H.      M.
+Jan. 24, 1st circle was made in            2      55  Early in
+                                                      morning, when
+                                                      the temperature
+                                                      of the house
+                                                      had fallen a
+                                                      little.
+      24, 2 circles each at an             2      20
+average of
+      25, 4th circle was made in           2      25
+
+_Combretum purpureum_ revolves not quite so quickly as _C. argenteum_.
+
+_Loasa aurantiaca_ (Loasaceæ).  Revolutions variable in their course: a
+plant which moved against the sun.
+
+                                      H.      M.
+June 20, 1st circle was made in        2      37
+      20, 2nd                          2      13
+      20, 3rd                          4       0
+      21, 4th                          2      35
+      22, 5th                          3      26
+      23, 6th                          3       5
+
+Another plant which followed the sun in its revolutions.
+
+                                      H.      M.
+July 11, 1st circle was made in        1      51  Very hot day.
+      11, 2nd                          1      46
+      11, 3rd                          1      41
+      11, 4th                          1      48
+      12, 5th                          2      35
+
+_Scyphanthus elegans_ (Loasaceæ) follows the sun.
+
+                                      H.      M.
+June 13, 1st circle was made in        1      45
+      13, 2nd                          1      17
+      14, 3rd                          1      36
+      14, 4th                          1      59
+      14, 5th                          2       3
+
+_Siphomeris_ or _Lecontea_ (unnamed sp.) (Cinchonaceæ) follows the sun.
+
+                                     H.      M.
+May 25, semicircle was made in       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  Taken from the
+                                                 hothouse, and placed
+                                                 in a room in my
+                                                 house.
+      9, 6th                          8      36
+
+_Manettia bicolor_ (Cinchonaceæ), young plant, follows the sun.
+
+                                     H.      M.
+July 7, 1st circle was made in        6      18
+      8, 2nd                          6      53
+      9, 3rd                          6      30
+
+_Lonicera brachypoda_ (Caprifoliaceæ) follows the sun, kept in a warm
+room in the house.
+
+                                    H.      M.
+April, 1st circle was made in        9      10  (about)
+April, 2nd circle was made in       12      20  (a distinct shoot,
+                                                very young, on same
+                                                plant)
+      3rd                            7      30
+      4th                            8       0  In this latter
+                                                circle, the
+                                                semicircle from the
+                                                light took 5 hrs. 23
+                                                m., and to the light
+                                                2 hrs. 37 min.:
+                                                difference 2 hrs 46
+                                                m.
+
+_Aristolochia gigas_ (Aristolochiaceæ) moves against the sun.
+
+                                      H.      M.
+July 22, 1st circle was made in        8       0  (rather young
+                                                  shoot)
+      23, 2nd                          7      15
+      24, 3rd                          5       0  (about)
+
+In the foregoing Table, which includes twining plants belonging to widely
+different orders, we see that the rate at which growth travels or
+circulates round the axis (on which the revolving movement depends),
+differs much.  As long as a plant remains under the same conditions, the
+rate is often remarkably uniform, as with the Hop, _Mikania_,
+_Phaseolus_, &c.  The Scyphanthus made one revolution in 1 hr. 17 m., and
+this is the quickest rate observed by me; but we shall hereafter see a
+tendril-bearing Passiflora revolving more rapidly.  A shoot of the
+_Akebia quinata_ made a revolution in 1 hr. 30 m., and three revolutions
+at the average rate of 1 hr. 38 m.; a Convolvulus made two revolutions at
+the average of 1 hr. 42 m., and _Phaseolus vulgaris_ three at the average
+of 1 hr. 57 m.  On the other hand, some plants take 24 hrs. for a single
+revolution, and the _Adhadota_ sometimes required 48 hrs.; yet this
+latter plant is an efficient twiner.  Species of the same genus move at
+different rates.  The rate does not seem governed by the thickness of the
+shoots: those of the _Sollya_ are as thin and flexible as string, but
+move more slowly than the thick and fleshy shoots of the _Ruscus_, which
+seem little fitted for movement of any kind.  The shoots of the
+_Wistaria_, which become woody, move faster than those of the herbaceous
+_Ipomoea_ or _Thunbergia_.
+
+We know that the internodes, whilst still very young, do not acquire
+their proper rate of movement; hence the several shoots on the same plant
+may sometimes be seen revolving at different rates.  The two or three, or
+even more, internodes which are first formed above the cotyledons, or
+above the root-stock of a perennial plant, do not move; they can support
+themselves, and nothing superfluous is granted.
+
+A greater number of twiners revolve in a course opposed to that of the
+sun, or to the hands of a watch, than in the reversed course, and,
+consequently, the majority, as is well known, ascend their supports from
+left to right.  Occasionally, though rarely, plants of the same order
+twine in opposite directions, of which Mohl (p. 125) gives a case in the
+Leguminosæ, and we have in the table another in the Acanthaceæ.  I have
+seen no instance of two species of the same genus twining in opposite
+directions, and such cases must be rare; but Fritz Müller {33} states
+that although _Mikania scandens_ twines, as I have described, from left
+to right, another species in South Brazil twines in an opposite
+direction.  It would have been an anomalous circumstance if no such cases
+had occurred, for different individuals of the same species, namely, of
+_Solanum dulcamara_ (Dutrochet, tom. xix. p. 299), revolve and twine in
+two directions: this plant, however; is a most feeble twiner.  _Loasa
+aurantiaca_ (Léon, p. 351) offers a much more curious case: I raised
+seventeen plants: of these eight revolved in opposition to the sun and
+ascended from left to right; five followed the sun and ascended from
+right to left; and four revolved and twined first in one direction, and
+then reversed their course, {34} the petioles of the opposite leaves
+affording a _point d’appui_ for the reversal of the spire.  One of these
+four plants made seven spiral turns from right to left, and five turns
+from left to right.  Another plant in the same family, the _Scyphanthus
+elegans_, habitually twines in this same manner.  I raised many plants of
+it, and the stems of all took one turn, or occasionally two or even three
+turns in one direction, and then, ascending for a short space straight,
+reversed their course and took one or two turns in an opposite direction.
+The reversal of the curvature occurred at any point in the stem, even in
+the middle of an internode.  Had I not seen this case, I should have
+thought its occurrence most improbable.  It would be hardly possible with
+any plant which ascended above a few feet in height, or which lived in an
+exposed situation; for the stem could be pulled away easily from its
+support, with but little unwinding; nor could it have adhered at all, had
+not the internodes soon become moderately rigid.  With leaf-climbers, as
+we shall soon see, analogous cases frequently occur; but these present no
+difficulty, as the stem is secured by the clasping 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
+_Ipomoea jucunda_; but frequently with _Hibbertia dentata_.  This plant
+at first perplexed me much, for I continually observed its long and
+flexible shoots, evidently well fitted for twining, make a whole, or
+half, or quarter circle in one direction and then in an opposite
+direction; consequently, when I placed the shoots near thin or thick
+sticks, or perpendicularly stretched string, they seemed as if constantly
+trying to ascend, but always failed.  I then surrounded the plant with a
+mass of branched twigs; the shoots ascended, and passed through them, but
+several came out laterally, and their depending extremities seldom turned
+upwards as is usual with twining plants.  Finally, I surrounded a second
+plant with many thin upright sticks, and placed it near the first one
+with twigs; and now both had got what they liked, for they twined up the
+parallel sticks, sometimes winding round one and sometimes round several;
+and the shoots travelled laterally from one to the other pot; but as the
+plants grew older, some of the shoots twined regularly up thin upright
+sticks.  Though the revolving movement was sometimes in one direction and
+sometimes in the other, the twining was invariably from left to right;
+{36} so that the more potent or persistent movement of revolution must
+have been in opposition to the course of the sun.  It would appear that
+this _Hibbertia_ is adapted both to ascend by twining, and to ramble
+laterally through the thick Australian scrub.
+
+I have described the above case in some detail, because, as far as I have
+seen, it is rare to find any special adaptations with twining plants, in
+which respect they differ much from the more highly organized
+tendril-bearers.  The _Solanum dulcamara_, as we shall presently see, can
+twine only round stems which are both thin and flexible.  Most twining
+plants are adapted to ascend supports of moderate though of different
+thicknesses.  Our English twiners, as far as I have seen, never twine
+round trees, excepting the honeysuckle (_Lonicera periclymenum_), which I
+have observed twining up a young beech-tree nearly 4½ inches in diameter.
+Mohl (p. 134) found that the _Phaseolus multiflorus_ and _Ipomoea
+purpurea_ could not, when placed in a room with the light entering on one
+side, twine round sticks between 3 and 4 inches in diameter; for this
+interfered, in a manner presently to be explained, with the revolving
+movement.  In the open air, however, the _Phaseolus_ twined round a
+support of the above thickness, but failed in twining round one 9 inches
+in diameter.  Nevertheless, some twiners of the warmer temperate regions
+can manage this latter degree of thickness; for I hear from Dr. Hooker
+that at Kew the _Ruscus androgynus_ has ascended a column 9 inches in
+diameter; and although a _Wistaria_ grown by me in a small pot tried in
+vain for weeks to get round a post between 5 and 6 inches in thickness,
+yet at Kew a plant ascended a trunk above 6 inches in diameter.  The
+tropical twiners, on the other hand, can ascend thicker trees; I hear
+from Drs. Thomson and Hooker that this is the case with the _Butea
+parviflora_, one of the Menispermaceæ, and with some Dalbergias and other
+Leguminosæ. {37}  This power would be necessary for any species which had
+to ascend by twining the large trees of a tropical forest; otherwise they
+would hardly ever be able to reach the light.  In our temperate countries
+it would be injurious to the twining plants which die down every year if
+they were enabled to twine round trunks of trees, for they could not grow
+tall enough in a single season to reach the summit and gain the light.
+
+By what means certain twining plants are adapted to ascend only thin
+stems, whilst others can twine round thicker ones, I do not know.  It
+appeared to me probable that twining plants with very long revolving
+shoots would be able to ascend thick supports; accordingly I placed
+_Ceropegia Gardnerii_ near a post 6 inches in diameter, but the shoots
+entirely failed to wind round it; their great length and power of
+movement merely aid them in finding a distant stem round which to twine.
+The _Sphærostemma marmoratum_ is a vigorous tropical twiner; and as it is
+a very slow revolver, I thought that this latter circumstance might help
+it in ascending a thick support; but though it was able to wind round a
+6-inch post, it could do this only on the same level or plane, and did
+not form a spire and thus ascend.
+
+As ferns differ so much in structure from phanerogamic plants, it may be
+worth while here to show that twining ferns do not differ in their habits
+from other twining plants.  In _Lygodium articulatum_ the two internodes
+of the stem (properly the rachis) which are first formed above the
+root-stock do not move; the third from the ground revolves, but at first
+very slowly.  This species is a slow revolver: but _L. scandens_ made
+five revolutions, each at the average rate of 5 hrs. 45 m.; and this
+represents fairly well the usual rate, taking quick and slow movers,
+amongst phanerogamic plants.  The rate was accelerated by increased
+temperature.  At each stage of growth only the two upper internodes
+revolved.  A line painted along the convex surface of a revolving
+internode becomes first lateral, then concave, then lateral and
+ultimately again convex.  Neither the internodes nor the petioles are
+irritable when rubbed.  The movement is in the usual direction, namely,
+in opposition to the course of the sun; and when the stem twines round a
+thin stick, it becomes twisted on its own axis in the same direction.
+After the young internodes have twined round a stick, their continued
+growth causes them to slip a little upwards.  If the stick be soon
+removed, they straighten themselves, and recommence revolving.  The
+extremities of the depending shoots turn upwards, and twine on
+themselves.  In all these respects we have complete identity with twining
+phanerogamic plants; and the above enumeration may serve as a summary of
+the leading characteristics of all twining plants.
+
+The power of revolving depends on the general health and vigour of the
+plant, as has been laboriously shown by Palm.  But the movement of each
+separate internode is so independent of the others, that cutting off an
+upper one does not affect the revolutions of a lower one.  When, however,
+Dutrochet cut off two whole shoots of the Hop, and placed them in water,
+the movement was greatly retarded; for one revolved in 20 hrs. and the
+other in 23 hrs., whereas they ought to have revolved in between 2 hrs.
+and 2 hrs. 30 m.  Shoots of the Kidney-bean, cut off and placed in water,
+were similarly retarded, but in a less degree.  I have repeatedly
+observed that carrying a plant from the greenhouse to my room, or from
+one part to another of the greenhouse, always stopped the movement for a
+time; hence I conclude that plants in a state of nature and growing in
+exposed situations, would not make their revolutions during very stormy
+weather.  A decrease in temperature always caused a considerable
+retardation in the rate of revolution; but Dutrochet (tom. xvii. pp. 994,
+996) has given such precise observations on this head with respect to the
+common pea that I need say nothing more.  When twining plants are placed
+near a window in a room, the light in some cases has a remarkable power
+(as was likewise observed by Dutrochet, p. 998, with the pea) on the
+revolving movement, but this differs in degree with different plants;
+thus _Ipomoea jucunda_ made a complete circle in 5 hrs. 30 m.; the
+semicircle from the light taking 4 hrs. 80 m., and that towards the light
+only 1 hr.  _Lonicera brachypoda_ revolved, in a reversed direction to
+the _Ipomoea_, in 8 hrs.; the semicircle from the light taking 5 hrs. 23
+m., and that to the light only 2 hrs. 37 m.  From the rate of revolution
+in all the plants observed by me, being nearly the same during the night
+and the day, I infer that the action of the light is confined to
+retarding one semicircle and accelerating the other, so as not to modify
+greatly the rate of the whole revolution.  This action of the light is
+remarkable, when we reflect how little the leaves are developed on the
+young and thin revolving internodes.  It is all the more remarkable, as
+botanists believe (Mohl, p. 119) that twining plants are but little
+sensitive to the action of light.
+
+I will conclude my account of twining plants by giving a few
+miscellaneous and curious cases.  With most twining plants all the
+branches, however many there may be, go on revolving together; but,
+according to Mohl (p. 4), only the lateral branches of _Tamus
+elephantipes_ twine, and not the main stem.  On the other hand, with a
+climbing species of Asparagus, the leading shoot alone, and not the
+branches, revolved and twined; but it should be stated that the plant was
+not growing vigorously.  My plants of _Combretum argenteum_ and _C.
+purpureum_ made numerous short healthy shoots; but they showed no signs
+of revolving, and I could not conceive how these plants could be
+climbers; but at last _C. argenteum_ put forth from the lower part of one
+of its main branches a thin shoot, 5 or 6 feet in length, differing
+greatly in appearance from the previous shoots, owing to its leaves being
+little developed, and this shoot revolved vigorously and twined.  So that
+this plant produces shoots of two kinds.  With _Periploca Græca_ (Palm,
+p. 43) the uppermost shoots alone twine.  Polygonum convolvulus twines
+only during the middle of the summer (Palm, p. 43, 94); and plants
+growing vigorously in the autumn show no inclination to climb.  The
+majority of Asclepiadaceæ are twiners; but _Asclepias nigra_ only “in
+fertiliori solo incipit scandere subvolubili caule” (Willdenow, quoted
+and confirmed by Palm, p. 41).  _Asclepias vincetoxicum_ does not
+regularly twine, but occasionally does so (Palm, p. 42; Mohl, p. 112)
+when growing under certain conditions.  So it is with two species of
+_Ceropegia_, as I hear from Prof.  Harvey, for these plants in their
+native dry South African home generally grow erect, from 6 inches to 2
+feet in height,—a very few taller specimens showing some inclination to
+curve; but when cultivated near Dublin, they regularly twined up sticks 5
+or 6 feet in height.  Most Convolvulaceæ are excellent twiners; but in
+South Africa _Ipomoea argyræoides_ almost always grows erect and compact,
+from about 12 to 18 inches in height, one specimen alone in Prof.
+Harvey’s collection showing an evident disposition to twine.  On the
+other hand, seedlings raised near Dublin twined up sticks above 8 feet in
+height.  These facts are remarkable; for there can hardly be a doubt that
+in the dryer provinces of South Africa these plants have propagated
+themselves for thousands of generations in an erect condition; and yet
+they have retained during this whole period the innate power of
+spontaneously revolving and twining, whenever their shoots become
+elongated under proper conditions of life.  Most of the species of
+_Phaseolus_ are twiners; but certain varieties of the _P. multiflorus_
+produce (Léon, p. 681) two kinds of shoots, some upright and thick, and
+others thin and twining.  I have seen striking instances of this curious
+case of variability in “Fulmer’s dwarf forcing-bean,” which occasionally
+produced a single long twining shoot.
+
+_Solanum dulcamara_ is one of the feeblest and poorest of twiners: it may
+often be seen growing as an upright bush, and when growing in the midst
+of a thicket merely scrambles up between the branches without twining;
+but when, according to Dutrochet (tom. xix. p. 299), it grows near a thin
+and flexible support, such as the stem of a nettle, it twines round it.
+I placed sticks round several plants, and vertically stretched strings
+close to others, and the strings alone were ascended by twining.  The
+stem twines indifferently to the right or left.  Some others species of
+Solanum, and of another genus, viz. _Habrothamnus_, belonging to the same
+family, are described in horticultural works as twining plants, but they
+seem to possess this faculty in a very feeble degree.  We may suspect
+that the species of these two genera have as yet only partially acquired
+the habit of twining.  On the other hand with _Tecoma radicans_, a member
+of a family abounding with twiners and tendril-bearers, but which climbs,
+like the ivy, by the aid of rootlets, we may suspect that a former habit
+of twining has been lost, for the stem exhibited slight irregular
+movements which could hardly be accounted for by changes in the action of
+the light.  There is no difficulty in understanding how a spirally
+twining plant could graduate into a simple root-climber; for the young
+internodes of _Bignonia Tweedyana_ and of _Hoya carnosa_ revolve and
+twine, but likewise emit rootlets which adhere to any fitting surface, so
+that the loss of twining would be no great disadvantage and in some
+respects an advantage to these species, as they would then ascend their
+supports in a more direct line. {44}
+
+
+
+CHAPTER II.
+LEAF-CLIMBERS.
+
+
+Plants which climb by the aid of spontaneously revolving and sensitive
+petioles—_Clematis_—_Tropæolum_—_Maurandia_, flower-peduncles moving
+spontaneously and sensitive to a
+touch—_Rhodochiton_—_Lophospermum_—internodes sensitive—_Solanum_,
+thickening of the clasped petioles—_Fumaria_—_Adlumia_—Plants which climb
+by the aid of their produced
+midribs—_Gloriosa_—_Flagellaria_—_Nepenthes_—Summary on leaf-climbers.
+
+WE now come to our second class of climbing plants, namely, those which
+ascend by the aid of irritable or sensitive organs.  For convenience’
+sake the plants in this class have been grouped under two sub-divisions,
+namely, leaf-climbers, or those which retain their leaves in a functional
+condition, and tendril-bearers.  But these sub-divisions graduate into
+each other, as we shall see under Corydalis and the Gloriosa lily.
+
+It has long been observed that several plants climb by the aid of their
+leaves, either by their petioles (foot-stalks) or by their produced
+midribs; but beyond this simple fact they have not been described.  Palm
+and Mohl class these plants with those which bear tendrils; but as a leaf
+is generally a defined object, the present classification, though
+artificial, has at least some advantages.  Leaf-climbers are, moreover,
+intermediate in many respects between twiners and tendril-bearers.  Eight
+species of _Clematis_ and seven of _Tropæolum_ were observed, in order to
+see what amount of difference in the manner of climbing existed within
+the same genus; and the differences are considerable.
+
+CLEMATIS.—_C. glandulosa_.—The thin upper internodes revolve, moving
+against the course of the sun, precisely like those of a true twiner, at
+an average rate, judging from three revolutions, of 3 hrs. 48 m.  The
+leading shoot immediately twined round a stick placed near it; but, after
+making an open spire of only one turn and a half, it ascended for a short
+space straight, and then reversed its course and wound two turns in an
+opposite direction.  This was rendered possible by the straight piece
+between the opposed spires having become rigid.  The simple, broad, ovate
+leaves of this tropical species, with their short thick petioles, seem
+but ill-fitted for any movement; and whilst twining up a vertical stick,
+no use is made of them.  Nevertheless, if the footstalk of a young leaf
+be rubbed with a thin twig a few times on any side, it will in the course
+of a few hours bend to that side; afterwards becoming straight again.
+The under side seemed to be the most sensitive; but the sensitiveness or
+irritability is slight compared to that which we shall meet with in some
+of the following species; thus, a loop of string, weighing 1.64 grain
+(106.2 mg.) and hanging for some days on a young footstalk, produced a
+scarcely perceptible effect.  A sketch is here given of two young leaves
+which had naturally caught hold of two thin branches.  A forked twig
+placed so as to press lightly on the under side of a young footstalk
+caused it, in 12 hrs., to bend greatly, and ultimately to such an extent
+that the leaf passed to the opposite side of the stem; the forked stick
+having been removed, the leaf slowly recovered its former position.
+
+ [Picture: Fig. 1.  Clematis glandulosa.  With two young leaves clasping
+             two twigs, with the clasping portions thickened]
+
+The young leaves spontaneously and gradually change their position: when
+first developed the petioles are upturned and parallel to the stem; they
+then slowly bend downwards, remaining for a short time at right angles to
+the stem, and then become so much arched downwards that the blade of the
+leaf points to the ground with its tip curled inwards, so that the whole
+petiole and leaf together form a hook.  They are thus enabled to catch
+hold of any twig with which they may be brought into contact by the
+revolving movement of the internodes.  If this does not happen, they
+retain their hooked shape for a considerable time, and then bending
+upwards reassume their original upturned position, which is preserved
+ever afterwards.  The petioles which have clasped any object soon become
+much thickened and strengthened, as may be seen in the drawing.
+
+_Clematis montana_.—The long, thin petioles of the leaves, whilst young,
+are sensitive, and when lightly rubbed bend to the rubbed side,
+subsequently becoming straight.  They are far more sensitive than the
+petioles of _C. glandulosa_; for a loop of thread weighing a quarter of a
+grain (16.2 mg.) caused them to bend; a loop weighing only one-eighth of
+a grain (8.1 mg.) sometimes acted and sometimes did not act.  The
+sensitiveness extends from the blade of the leaf to the stem.  I may here
+state that I ascertained in all cases the weights of the string and
+thread used by carefully weighing 50 inches in a chemical balance, and
+then cutting off measured lengths.  The main petiole carries three
+leaflets; but their short, sub-petioles are not sensitive.  A young,
+inclined shoot (the plant being in the greenhouse) made a large circle
+opposed to the course of the sun in 4 hrs. 20 m., but the next day, being
+very cold, the time was 5 hrs. 10 m.  A stick placed near a revolving
+stem was soon struck by the petioles which stand out at right angles, and
+the revolving movement was thus arrested.  The petioles then began, being
+excited by the contact, to slowly wind round the stick.  When the stick
+was thin, a petiole sometimes wound twice round it.  The opposite leaf
+was in no way affected.  The attitude assumed by the stem after the
+petiole had clasped the stick, was that of a man standing by a column,
+who throws his arm horizontally round it.  With respect to the stem’s
+power of twining, some remarks will be made under _C. calycina_.
+
+_Clematis Sieboldi_.—A shoot made three revolutions against the sun at an
+average rate of 3 hrs. 11 m.  The power of twining is like that of the
+last species.  Its leaves are nearly similar in structure and in
+function, excepting that the sub-petioles of the lateral and terminal
+leaflets are sensitive.  A loop of thread, weighing one-eighth of a
+grain, acted on the main petiole, but not until two or three days had
+elapsed.  The leaves have the remarkable habit of spontaneously
+revolving, generally in vertical ellipses, in the same manner, but in a
+less degree, as will be described under _C. microphylla_.
+
+_Clematis calycina_.—The young shoots are thin and flexible: one
+revolved, describing a broad oval, in 5 hrs. 30 m., and another in 6 hrs.
+12 m.  They followed the course of the sun; but the course, if observed
+long enough, would probably be found to vary in this species, as well as
+in all the others of the genus.  It is a rather better twiner than the
+two last species: the stem sometimes made two spiral turns round a thin
+stick, if free from twigs; it then ran straight up for a space, and
+reversing its course took one or two turns in an opposite direction.
+This reversal of the spire occurred in all the foregoing species.  The
+leaves are so small compared with those of most of the other species,
+that the petioles at first seem ill-adapted for clasping.  Nevertheless,
+the main service of the revolving movement is to bring them into contact
+with surrounding objects, which are slowly but securely seized.  The
+young petioles, which alone are sensitive, have their ends bowed a little
+downwards, so as to be in a slight degree hooked; ultimately the whole
+leaf, if it catches nothing, becomes level.  I gently rubbed with a thin
+twig the lower surfaces of two young petioles; and in 2 hrs. 30 m. they
+were slightly curved downwards; in 5 hrs., after being rubbed, the end of
+one was bent completely back, parallel to the basal portion; in 4 hrs.
+subsequently it became nearly straight again.  To show how sensitive the
+young petioles are, I may mention that I just touched the under sides of
+two with a little water-colour, which when dry formed an excessively thin
+and minute crust; but this sufficed in 24 hrs. to cause both to bend
+downwards.  Whilst the plant is young, each leaf consists of three
+divided leaflets, which barely have distinct petioles, and these are not
+sensitive; but when the plant is well grown, the petioles of the two
+lateral and terminal leaflets are of considerable length, and become
+sensitive so as to be capable of clasping an object in any direction.
+
+When a petiole has clasped a twig, it undergoes some remarkable changes,
+which may be observed with the other species, but in a less strongly
+marked manner, and will here be described once for all.  The clasped
+petiole in the course of two or three days swells greatly, and ultimately
+becomes nearly twice as thick as the opposite one which has clasped
+nothing.  When thin transverse slices of the two are placed under the
+microscope their difference is conspicuous: the side of the petiole which
+has been in contact with the support, is formed of a layer of colourless
+cells with their longer axes directed from the centre, and these are very
+much larger than the corresponding cells in the opposite or unchanged
+petiole; the central cells, also, are in some degree enlarged, and the
+whole is much indurated.  The exterior surface generally becomes bright
+red.  But a far greater change takes place in the nature of the tissues
+than that which is visible: the petiole of the unclasped leaf is flexible
+and can be snapped easily, whereas the clasped one acquires an
+extraordinary degree of toughness and rigidity, so that considerable
+force is required to pull it into pieces.  With this change, great
+durability is probably acquired; at least this is the case with the
+clasped petioles of _Clematis vitalba_.  The meaning of these changes is
+obvious, namely, that the petioles may firmly and durably support the
+stem.
+
+_Clematis microphylla_, var. _leptophylla_.—The long and thin internodes
+of this Australian species revolve sometimes in one direction and
+sometimes in an opposite one, describing long, narrow, irregular ellipses
+or large circles.  Four revolutions were completed within five minutes of
+the same average rate of 1 hr. 51 m.; so that this species moves more
+quickly than the others of the genus.  The shoots, when placed near a
+vertical stick, either twine round it, or clasp it with the basal
+portions of their petioles.  The leaves whilst young are nearly of the
+same shape as those of _C. viticella_, and act in the same manner like a
+hook, as will be described under that species.  But the leaflets are more
+divided, and each segment whilst young terminates in a hardish point,
+which is much curved downwards and inwards; so that the whole leaf
+readily catches hold of any neighbouring object.  The petioles of the
+young terminal leaflets are acted on by loops of thread weighing ⅛th and
+even 0.0625th of a grain.  The basal portion of the main petiole is much
+less sensitive, but will clasp a stick against which it presses.
+
+The leaves, whilst young, are continually and spontaneously moving
+slowly.  A bell-glass was placed over a shoot secured to a stick, and the
+movements of the leaves were traced on it during several days.  A very
+irregular line was generally formed; but one day, in the course of eight
+hours and three quarters, the figure clearly represented three and a half
+irregular ellipses, the most perfect one of which was completed in 2 hrs.
+35 m.  The two opposite leaves moved independently of each other.  This
+movement of the leaves would aid that of the internodes in bringing the
+petioles into contact with surrounding objects.  I discovered this
+movement too late to be enabled to observe it in the other species; but
+from analogy I can hardly doubt that the leaves of at least _C.
+viticella_, _C. flammula_, and _C. vitalba_ move spontaneously; and,
+judging from _C. Sieboldi_, this probably is the case with _C. montana_
+and _C. calycina_.  I ascertained that the simple leaves of _C.
+glandulosa_ exhibited no spontaneous revolving movement.
+
+_Clematis viticella_, var. _venosa_.—In this and the two following
+species the power of spirally twining is completely lost, and this seems
+due to the lessened flexibility of the internodes and to the interference
+caused by the large size of the leaves.  But the revolving movement,
+though restricted, is not lost.  In our present species a young
+internode, placed in front of a window, made three narrow ellipses,
+transversely to the direction of the light, at an average rate of 2 hrs.
+40 m.  When placed so that the movements were to and from the light, the
+rate was greatly accelerated in one half of the course, and retarded in
+the other, as with twining plants.  The ellipses were small; the longer
+diameter, described by the apex of a shoot bearing a pair of not expanded
+leaves, was only 4⅝ inches, and that by the apex of the penultimate
+internode only 1⅛ inch.  At the most favourable period of growth each
+leaf would hardly be carried to and fro by the movement of the internodes
+more than two or three inches, but, as above stated, it is probable that
+the leaves themselves move spontaneously.  The movement of the whole
+shoot by the wind and by its rapid growth, would probably be almost
+equally efficient as these spontaneous movements, in bringing the
+petioles into contact with surrounding objects.
+
+The leaves are of large size.  Each bears three pairs of lateral leaflets
+and a terminal one, all supported on rather long sub-petioles.  The main
+petiole bends a little angularly downwards at each point where a pair of
+leaflets arises (see fig. 2), and the petiole of the terminal leaflet is
+bent downwards at right angles; hence the whole petiole, with its
+rectangularly bent extremity, acts as a hook.  This hook, the lateral
+petioles being directed a little upwards; forms an excellent grappling
+apparatus, by which the leaves readily become entangled with surrounding
+objects.  If they catch nothing, the whole petiole ultimately grows
+straight.  The main petiole, the sub-petioles, and the three branches
+into which each basi-lateral sub-petiole is generally subdivided, are all
+sensitive.  The basal portion of the main petiole, between the stem and
+the first pair of leaflets, is less sensitive than the remainder; it
+will, however, clasp a stick with which it is left in contact.  The
+inferior surface of the rectangularly bent terminal portion (carrying the
+terminal leaflet), which forms the inner side of the end of the hook, is
+the most sensitive part; and this portion is manifestly best adapted to
+catch a distant support.  To show the difference in sensibility, I gently
+placed loops of string of the same weight (in one instance weighing only
+0.82 of a grain or 53.14 mg.) on the several lateral sub-petioles and on
+the terminal one; in a few hours the latter was bent, but after 24 hrs.
+no effect was produced on the other sub-petioles.  Again, a terminal
+sub-petiole placed in contact with a thin stick became sensibly curved in
+45 m., and in 1 hr. 10 m. moved through ninety degrees; whilst a lateral
+sub-petiole did not become sensibly curved until 3 hrs. 30 m. had
+elapsed.  In all cases, if the sticks are taken away, the petioles
+continue to move during many hours afterwards; so they do after a slight
+rubbing; but they become straight again, after about a day’s interval,
+that is if the flexure has not been very great or long continued.
+
+          [Picture: Fig. 2.  A young leaf of Clematis viticeela]
+
+The graduated difference in the extension of the sensitiveness in the
+petioles of the above-described species deserves notice.  In _C. montana_
+it is confined to the main petiole, and has not spread to the
+sub-petioles of the three leaflets; so it is with young plants of _C.
+calycina_, but in older plants it spreads to the three sub-petioles.  In
+_C. viticella_ the sensitiveness has spread to the petioles of the seven
+leaflets, and to the subdivisions of the basi-lateral sub-petioles.  But
+in this latter species it has diminished in the basal part of the main
+petiole, in which alone it resided in _C. montana_; whilst it has
+increased in the abruptly bent terminal portion.
+
+_Clematis flammula_.—The rather thick, straight, and stiff shoots, whilst
+growing vigorously in the spring, make small oval revolutions, following
+the sun in their course.  Four were made at an average rate of 3 hrs. 45
+m.  The longer axis of the oval, described by the extreme tip, was
+directed at right angles to the line joining the opposite leaves; its
+length was in one case only 1⅜, and in another case 1¾ inch; so that the
+young leaves were moved a very short distance.  The shoots of the same
+plant observed in midsummer, when growing not so quickly, did not revolve
+at all.  I cut down another plant in the early summer, so that by August
+1st it had formed new and moderately vigorous shoots; these, when
+observed under a bell-glass, were on some days quite stationary, and on
+other days moved to and fro only about the eighth of an inch.
+Consequently the revolving power is much enfeebled in this species, and
+under unfavourable circumstances is completely lost.  The shoot must
+depend for coming into contact with surrounding objects on the probable,
+though not ascertained spontaneous movement of the leaves, on rapid
+growth, and on movement from the wind.  Hence, perhaps, it is that the
+petioles have acquired a high degree of sensitiveness as a compensation
+for the little power of movement in the shoots.
+
+The petioles are bowed downwards, and have the same general hook-like
+form as in _C. viticella_.  The medial petiole and the lateral
+sub-petioles are sensitive, especially the much bent terminal portion.
+As the sensitiveness is here greater than in any other species of the
+genus observed by me, and is in itself remarkable, I will give fuller
+details.  The petioles, when so young that they have not separated from
+one another, are not sensitive; when the lamina of a leaflet has grown to
+a quarter of an inch in length (that is, about one-sixth of its full
+size), the sensitiveness is highest; but at this period the petioles are
+relatively much more fully developed than are the blades of the leaves.
+Full-grown petioles are not in the least sensitive.  A thin stick placed
+so as to press lightly against a petiole, having a leaflet a quarter of
+an inch in length, caused the petiole to bend in 3 hrs. 15 m.  In another
+case a petiole curled completely round a stick in 12 hrs. These petioles
+were left curled for 24 hrs., and the sticks were then removed; but they
+never straightened themselves.  I took a twig, thinner than the petiole
+itself, and with it lightly rubbed several petioles four times up and
+down; these in 1 hr. 45 m. became slightly curled; the curvature
+increased during some hours and then began to decrease, but after 25 hrs.
+from the time of rubbing a vestige of the curvature remained.  Some other
+petioles similarly rubbed twice, that is, once up and once down, became
+perceptibly curved in about 2 hrs. 30 m., the terminal sub-petiole moving
+more than the lateral sub-petioles; they all became straight again in
+between 12 hrs. and 14 hrs.  Lastly, a length of about one-eighth of an
+inch of a sub-petiole, was lightly rubbed with the same twig only once;
+it became slightly curved in 3 hrs., remaining so during 11 hrs., but by
+the next morning was quite straight.
+
+The following observations are more precise.  After trying heavier pieces
+of string and thread, I placed a loop of fine string, weighing 1.04 gr.
+(67.4 mg.) on a terminal sub-petiole: in 6 hrs. 40 m. a curvature could
+be seen; in 24 hrs. the petiole formed an open ring round the string; in
+48 hrs. the ring had almost closed on the string, and in 72 hrs. seized
+it so firmly, that some force was necessary for its withdrawal.  A loop
+weighing 0.52 of a grain (33.7 mg.) caused in 14 hrs. a lateral
+sub-petiole just perceptibly to curve, and in 24 hrs. it moved through
+ninety degrees.  These observations were made during the summer: the
+following were made in the spring, when the petioles apparently are more
+sensitive:—A loop of thread, weighing one-eighth of a grain (8.1 mg.),
+produced no effect on the lateral sub-petioles, but placed on a terminal
+one, caused it, after 24 hrs., to curve moderately; the curvature, though
+the loop remained suspended, was after 48 hrs. diminished, but never
+disappeared; showing that the petiole had become partially accustomed to
+the insufficient stimulus.  This experiment was twice repeated with
+nearly the same result.  Lastly, a loop of thread, weighing only
+one-sixteenth of a grain (4.05 mg.) was twice gently placed by a forceps
+on a terminal sub-petiole (the plant being, of course, in a still and
+closed room), and this weight certainly caused a flexure, which very
+slowly increased until the petiole moved through nearly ninety degrees:
+beyond this it did not move; nor did the petiole, the loop remaining
+suspended, ever become perfectly straight again.
+
+When we consider, on the one hand, the thickness and stiffness of the
+petioles, and, on the other hand, the thinness and softness of fine
+cotton thread, and what an extremely small weight one-sixteenth of a
+grain (4.05 mg.) is, these facts are remarkable.  But I have reason to
+believe that even a less weight excites curvature when pressing over a
+broader surface than that acted on by a thread.  Having noticed that the
+end of a suspended string which accidentally touched a petiole, caused it
+to bend, I took two pieces of thin twine, 10 inches in length (weighing
+1.64 gr.), and, tying them to a stick, let them hang as nearly
+perpendicularly downwards as their thinness and flexuous form, after
+being stretched, would permit; I then quietly placed their ends so as
+just to rest on two petioles, and these certainly became curved in 36
+hrs. One of the ends touched the angle between a terminal and lateral
+sub-petiole, and it was in 48 hours caught between them as by a forceps.
+In these cases the pressure, though spread over a wider surface than that
+touched by the cotton thread, must have been excessively slight.
+
+_Clematis vitalba_.—The plants were in pots and not healthy, so that I
+dare not trust my observations, which indicate much similarity in habits
+with _C. flammula_.  I mention this species only because I have seen many
+proofs that the petioles in a state of nature are excited to movement by
+very slight pressure.  For instance, I have found them embracing thin
+withered blades of grass, the soft young leaves of a maple, and the
+flower-peduncles of the quaking-grass or Briza.  The latter are about as
+thick as the hair of a man’s beard, but they were completely surrounded
+and clasped.  The petioles of a leaf, so young that none of the leaflets
+were expanded, had partially seized a twig.  Those of almost all the old
+leaves, even when unattached to any object, are much convoluted; but this
+is owing to their having come, whilst young, into contact during several
+hours with some object subsequently removed.  With none of the
+above-described species, cultivated in pots and carefully observed, was
+there any permanent bending of the petioles without the stimulus of
+contact.  In winter, the blades of the leaves of _C. vitalba_ drop off;
+but the petioles (as was observed by Mohl) remain attached to the
+branches, sometimes during two seasons; and, being convoluted, they
+curiously resemble true tendrils, such as those possessed by the allied
+genus _Naravelia_.  The petioles which have clasped some object become
+much more stiff, hard, and polished than those which have failed in this
+their proper function.
+
+TROPÆOLUM.—I observed _T. tricolorum_, _T. azureum_, _T. pentaphyllum_,
+_T. peregrinum_, _T. elegans_, _T. tuberosum_, and a dwarf variety of, as
+I believe, _T. minus_.
+
+_Tropæolum tricolorum_, var. _grandiflorum_.—The flexible shoots, which
+first rise from the tubers, are as thin as fine twine.  One such shoot
+revolved in a course opposed to the sun, at an average rate, judging from
+three revolutions, of 1 hr. 23 m.; but no doubt the direction of the
+revolving movement is variable.  When the plants have grown tall and are
+branched, all the many lateral shoots revolve.  The stem, whilst young,
+twines regularly round a thin vertical stick, and in one case I counted
+eight spiral turns in the same direction; but when grown older, the stem
+often runs straight up for a space, and, being arrested by the clasping
+petioles, makes one or two spires in a reversed direction.  Until the
+plant grows to a height of two or three feet, requiring about a month
+from the time when the first shoot appears above ground, no true leaves
+are produced, but, in their place, filaments coloured like the stem.  The
+extremities of these filaments are pointed, a little flattened, and
+furrowed on the upper surface.  They never become developed into leaves.
+As the plant grows in height new filaments are produced with slightly
+enlarged tips; then others, bearing on each side of the enlarged medial
+tip a rudimentary segment of a leaf; soon other segments appear, and at
+last a perfect leaf is formed, with seven deep segments.  So that on the
+same plant we may see every step, from tendril-like clasping filaments to
+perfect leaves with clasping petioles.  After the plant has grown to a
+considerable height, and is secured to its support by the petioles of the
+true leaves, the clasping filaments on the lower part of the stem wither
+and drop off; so that they perform only a temporary service.
+
+These filaments or rudimentary leaves, as well as the petioles of the
+perfect leaves, whilst young, are highly sensitive on all sides to a
+touch.  The slightest rub caused them to curve towards the rubbed side in
+about three minutes, and one bent itself into a ring in six minutes; they
+subsequently became straight.  When, however, they have once completely
+clasped a stick, if this is removed, they do not straighten themselves.
+The most remarkable fact, and one which I have observed in no other
+species of the genus, is that the filaments and the petioles of the young
+leaves, if they catch no object, after standing for some days in their
+original position, spontaneously and slowly oscillate a little from side
+to side, and then move towards the stem and clasp it.  They likewise
+often become, after a time, in some degree spirally contracted.  They
+therefore fully deserve to be called tendrils, as they are used for
+climbing, are sensitive to a touch, move spontaneously, and ultimately
+contract into a spire, though an imperfect one.  The present species
+would have been classed amongst the tendril-bearers, had not these
+characters been confined to early youth.  During maturity it is a true
+leaf-climber.
+
+_Tropæolum azureum_.—An upper internode made four revolutions, following
+the sun, at an average rate of 1 hr. 47 m.  The stem twined spirally
+round a support in the same irregular manner as that of the last species.
+Rudimentary leaves or filaments do not exist.  The petioles of the young
+leaves are very sensitive: a single light rub with a twig caused one to
+move perceptibly in 5 m., and another in 6 m.  The former became bent at
+right angles in 15 min., and became straight again in between 5 hrs. and
+6 hrs.  A loop of thread weighing ⅛th of a grain caused another petiole
+to curve.
+
+_Tropæolum pentaphyllum_.—This species has not the power of spirally
+twining, which seems due, not so much to a want of flexibility in the
+stem, as to continual interference from the clasping petioles.  An upper
+internode made three revolutions, following the sun, at an average rate
+of 1 hr. 46 m.  The main purpose of the revolving movement in all the
+species of _Tropæolum_ manifestly is to bring the petioles into contact
+with some supporting object.  The petiole of a young leaf, after a slight
+rub, became curved in 6 m.; another, on a cold day, in 20 m., and others
+in from 8 m. to 10 m.  Their curvature usually increased greatly in from
+15 m. to 20 m., and they became straight again in between 5 hrs. and 6
+hrs., but on one occasion in 3 hrs.  When a petiole has fairly clasped a
+stick, it is not able, on the removal of the stick, to straighten itself.
+The free upper part of one, the base of which had already clasped a
+stick, still retained the power of movement.  A loop of thread weighing
+⅛th of a grain caused a petiole to curve; but the stimulus was not
+sufficient, the loop remaining suspended, to cause a permanent flexure.
+If a much heavier loop be placed in the angle between the petiole and the
+stem, it produces no effect; whereas we have seen with _Clematis montana_
+that the angle between the stem and petiole is sensitive.
+
+_Tropæolum peregrinum_.—The first-formed internodes of a young plant did
+not revolve, resembling in this respect those of a twining plant.  In an
+older plant the four upper internodes made three irregular revolutions,
+in a course opposed to the sun, at an average rate of 1 hr. 48 min.  It
+is remarkable that the average rate of revolution (taken, however, but
+from few observations) is very nearly the same in this and the two last
+species, namely, 1 hr. 47 m., 1 hr. 46 m., and 1 hr. 48 m.  The present
+species cannot twine spirally, which seems mainly due to the rigidity of
+the stem.  In a very young plant, which did not revolve, the petioles
+were not sensitive.  In older plants the petioles of quite young leaves,
+and of leaves as much as an inch and a quarter in diameter, are
+sensitive.  A moderate rub caused one to curve in 10 m., and others in 20
+m.  They became straight again in between 5 hrs. 45 m. and 8 hrs.
+Petioles which have naturally come into contact with a stick, sometimes
+take two turns round it.  After they have clasped a support, they become
+rigid and hard.  They are less sensitive to a weight than in the previous
+species; for loops of string weighing 0.82 of a grain (53.14 mg.), did
+not cause any curvature, but a loop of double this weight (1.64 gr.)
+acted.
+
+_Tropæolum elegans_.—I did not make many observations on this species.
+The short and stiff internodes revolve irregularly, describing small oval
+figures.  One oval was completed in 3 hrs. A young petiole, when rubbed,
+became slightly curved in 17 m.; and afterwards much more so.  It was
+nearly straight again in 8 hrs.
+
+_Tropæolum tuberosum_.—On a plant nine inches in height, the internodes
+did not move at all; but on an older plant they moved irregularly and
+made small imperfect ovals.  These movements could be detected only by
+being traced on a bell-glass placed over the plant.  Sometimes the shoots
+stood still for hours; during some days they moved only in one direction
+in a crooked line; on other days they made small irregular spires or
+circles, one being completed in about 4 hrs.  The extreme points reached
+by the apex of the shoot were only about one or one and a half inches
+asunder; yet this slight movement brought the petioles into contact with
+some closely surrounding twigs, which were then clasped.  With the
+lessened power of spontaneously revolving, compared with that of the
+previous species, the sensitiveness of the petioles is also diminished.
+These, when rubbed a few times, did not become curved until half an hour
+had elapsed; the curvature increased during the next two hours, and then
+very slowly decreased; so that they sometimes required 24 hrs. to become
+straight again.  Extremely young leaves have active petioles; one with
+the lamina only 0.15 of an inch in diameter, that is, about a twentieth
+of the full size, firmly clasped a thin twig.  But leaves grown to a
+quarter of their full size can likewise act.
+
+_Tropæolum minus_ (?).—The internodes of a variety named “dwarf crimson
+Nasturtium” did not revolve, but moved in a rather irregular course
+during the day to the light, and from the light at night.  The petioles,
+when well rubbed, showed no power of curving; nor could I see that they
+ever clasped any neighbouring object.  We have seen in this genus a
+gradation from species such as _T. tricolorum_, which have extremely
+sensitive petioles, and internodes which rapidly revolve and spirally
+twine up a support, to other species such as _T. elegans_ and _T.
+tuberosum_, the petioles of which are much less sensitive, and the
+internodes of which have very feeble revolving powers and cannot spirally
+twine round a support, to this last species, which has entirely lost or
+never acquired these faculties.  From the general character of the genus,
+the loss of power seems the more probable alternative.
+
+In the present species, in _T. elegans_, and probably in others, the
+flower-peduncle, as soon as the seed-capsule begins to swell,
+spontaneously bends abruptly downwards and becomes somewhat convoluted.
+If a stick stands in the way, it is to a certain extent clasped; but, as
+far as I have been able to observe, this clasping movement is independent
+of the stimulus from contact.
+
+ANTIRRHINEÆ.—In this tribe (Lindley) of the Scrophulariaceæ, at least
+four of the seven included genera have leaf-climbing species.
+
+_Maurandia Barclayana_.—A thin, slightly bowed shoot made two
+revolutions, following the sun, each in 3 hrs. 17 min.; on the previous
+day this same shoot revolved in an opposite direction.  The shoots do not
+twine spirally, but climb excellently by the aid of their young and
+sensitive petioles.  These petioles, when lightly rubbed, move after a
+considerable interval of time, and subsequently become straight again.  A
+loop of thread weighing ⅛th of a grain caused them to bend.
+
+_Maurandia semperflorens_.—This freely growing species climbs exactly
+like the last, by the aid of its sensitive petioles.  A young internode
+made two circles, each in 1 hr. 46 min.; so that it moved almost twice as
+rapidly as the last species.  The internodes are not in the least
+sensitive to a touch or pressure.  I mention this because they are
+sensitive in a closely allied genus, namely, Lophospermum.  The present
+species is unique in one respect.  Mohl asserts (p. 45) that “the
+flower-peduncles, as well as the petioles, wind like tendrils;” but he
+classes as tendrils such objects as the spiral flower-stalks of the
+_Vallisneria_.  This remark, and the fact of the flower-peduncles being
+decidedly flexuous, led me carefully to examine them.  They never act as
+true tendrils; I repeatedly placed thin sticks in contact with young and
+old peduncles, and I allowed nine vigorous plants to grow through an
+entangled mass of branches; but in no one instance did they bend round
+any object.  It is indeed in the highest degree improbable that this
+should occur, for they are generally developed on branches which have
+already securely clasped a support by the petioles of their leaves; and
+when borne on a free depending branch, they are not produced by the
+terminal portion of the internode which alone has the power of revolving;
+so that they could be brought only by accident into contact with any
+neighbouring object.  Nevertheless (and this is the remarkable fact) the
+flower-peduncles, whilst young, exhibit feeble revolving powers, and are
+slightly sensitive to a touch.  Having selected some stems which had
+firmly clasped a stick by their petioles, and having placed a bell-glass
+over them, I traced the movements of the young flower-peduncles.  The
+tracing generally formed a short and extremely irregular line, with
+little loops in its course.  A young peduncle 1½ inch in length was
+carefully observed during a whole day, and it made four and a half
+narrow, vertical, irregular, and short ellipses—each at an average rate
+of about 2 hrs. 25 m.  An adjoining peduncle described during the same
+time similar, though fewer, ellipses.  As the plant had occupied for some
+time exactly the same position, these movements could not be attributed
+to any change in the action of the light.  Peduncles, old enough for the
+coloured petals to be just visible, do not move.  With respect to
+irritability, {68} I rubbed two young peduncles (1½ inch in length) a few
+times very lightly with a thin twig; one was rubbed on the upper, and the
+other on the lower side, and they became in between 4 hrs. and 5 hrs.
+distinctly bowed towards these sides; in 24 hrs. subsequently, they
+straightened themselves.  Next day they were rubbed on the opposite
+sides, and they became perceptibly curved towards these sides.  Two other
+and younger peduncles (three-fourths of an inch in length) were lightly
+rubbed on their adjoining sides, and they became so much curved towards
+one another, that the arcs of the bows stood at nearly right angles to
+their previous direction; and this was the greatest movement seen by me.
+Subsequently they straightened themselves.  Other peduncles, so young as
+to be only three-tenths of an inch in length, became curved when rubbed.
+On the other hand, peduncles above 1½ inch in length required to be
+rubbed two or three times, and then became only just perceptibly bowed.
+Loops of thread suspended on the peduncles produced no effect; loops of
+string, however, weighing 0.82 and 1.64 of a grain sometimes caused a
+slight curvature; but they were never closely clasped, as were the far
+lighter loops of thread by the petioles.
+
+In the nine vigorous plants observed by me, it is certain that neither
+the slight spontaneous movements nor the slight sensitiveness of the
+flower-peduncles aided the plants in climbing.  If any member of the
+Scrophulariaceæ had possessed tendrils produced by the modification of
+flower-peduncles, I should have thought that this species of _Maurandia_
+had perhaps retained a useless or rudimentary vestige of a former habit;
+but this view cannot be maintained.  We may suspect that, owing to the
+principle of correlation, the power of movement has been transferred to
+the flower-peduncles from the young internodes, and sensitiveness from
+the young petioles.  But to whatever cause these capacities are due, the
+case is interesting; for, by a little increase in power through natural
+selection, they might easily have been rendered as useful to the plant in
+climbing, as are the flower-peduncles (hereafter to be described) of
+Vitis or Cardiospermum.
+
+_Rhodochiton volubile_.—A long flexible shoot swept a large circle,
+following the sun, in 5 hrs. 30 m.; and, as the day became warmer, a
+second circle was completed in 4 hrs. 10 m.  The shoots sometimes make a
+whole or a half spire round a vertical stick, they then run straight up
+for a space, and afterwards turn spirally in an opposite direction.  The
+petioles of very young leaves about one-tenth of their full size, are
+highly sensitive, and bend towards the side which is touched; but they do
+not move quickly.  One was perceptibly curved in 1 hr. 10 m., after being
+lightly rubbed, and became considerably curved in 5 hrs. 40 m.; some
+others were scarcely curved in 5 hrs. 30 m., but distinctly so in 6 hrs.
+30 m.  A curvature was perceptible in one petiole in between 4 hrs. 30 m.
+and 5 hrs., after the suspension of a little loop of string.  A loop of
+fine cotton thread, weighing one sixteenth of a grain (4.05 mg.), not
+only caused a petiole slowly to bend, but was ultimately so firmly
+clasped that it could be withdrawn only by some little force.  The
+petioles, when coming into contact with a stick, take either a complete
+or half a turn round it, and ultimately increase much in thickness.  They
+do not possess the power of spontaneously revolving.
+
+_Lophospermum scandens_, var. _purpureum_.—Some long, moderately thin
+internodes made four revolutions at an average rate of 3 hrs. 15 m.  The
+course pursued was very irregular, namely, an extremely narrow ellipse, a
+large circle, an irregular spire or a zigzag line, and sometimes the apex
+stood still.  The young petioles, when brought by the revolving movement
+into contact with sticks, clasped them, and soon increased considerably
+in thickness.  But they are not quite so sensitive to a weight as those
+of the _Rhodochiton_, for loops of thread weighing one-eighth of a grain
+did not always cause them to bend.
+
+This plant presents a case not observed by me in any other leaf-climber
+or twiner, {71} namely, that the young internodes of the stem are
+sensitive to a touch.  When a petiole of this species clasps a stick, it
+draws the base of the internode against it; and then the internode itself
+bends towards the stick, which is caught between the stem and the petiole
+as by a pair of pincers.  The internode afterwards straightens itself,
+excepting the part in actual contact with the stick.  Young internodes
+alone are sensitive, and these are sensitive on all sides along their
+whole length.  I made fifteen trials by twice or thrice lightly rubbing
+with a thin twig several internodes; and in about 2 hrs., but in one case
+in 3 hrs., all were bent: they became straight again in about 4 hrs.
+afterwards.  An internode, which was rubbed as often as six or seven
+times, became just perceptibly curved in 1 hr. 15 m., and in 3 hrs. the
+curvature increased much; it became straight again in the course of the
+succeeding night.  I rubbed some internodes one day on one side, and the
+next day either on the opposite side or at right angles to the first
+side; and the curvature was always towards the rubbed side.
+
+According to Palm (p. 63), the petioles of _Linaria cirrhosa_ and, to a
+limited degree, those of _L. elatine_ have the power of clasping a
+support.
+
+SOLANACEÆ.—_Solanum jasminoides_.—Some of the species in this large genus
+are twiners; but the present species is a true leaf-climber.  A long,
+nearly upright shoot made four revolutions, moving against the sun, very
+regularly at an average rate of 3 hrs. 26 m.  The shoots, however,
+sometimes stood still.  It is considered a greenhouse plant; but when
+kept there, the petioles took several days to clasp a stick: in the
+hothouse a stick was clasped in 7 hrs.  In the greenhouse a petiole was
+not affected by a loop of string, suspended during several days and
+weighing 2½ grains (163 mg.); but in the hothouse one was made to curve
+by a loop weighing 1.64 gr. (106.27 mg.); and, on the removal of the
+string, it became straight again.  Another petiole was not at all acted
+on by a loop weighing only 0.82 of a grain (53.14 mg.) We have seen that
+the petioles of some other leaf-climbing plants are affected by
+one-thirteenth of this latter weight.  In this species, and in no other
+leaf-climber seen by me, a full-grown leaf is capable of clasping a
+stick; but in the greenhouse the movement was so extraordinarily slow
+that the act required several weeks; on each succeeding week it was clear
+that the petiole had become more and more curved, until at last it firmly
+clasped the stick.
+
+[Picture: Fig. 3.  Solanum jasminoides, with one of its petioles clasping
+                                 a stick]
+
+The flexible petiole of a half or a quarter grown leaf which has clasped
+an object for three or four days increases much in thickness, and after
+several weeks becomes so wonderfully hard and rigid that it can hardly be
+removed from its support.  On comparing a thin transverse slice of such a
+petiole with one from an older leaf growing close beneath, which had not
+clasped anything, its diameter was found to be fully doubled, and its
+structure greatly changed.  In two other petioles similarly compared, and
+here represented, the increase in diameter was not quite so great.  In
+the section of the petiole in its ordinary state (A), we see a semilunar
+band of cellular tissue (not well shown in the woodcut) differing
+slightly in appearance from that outside it, and including three closely
+approximate groups of dark vessels.  Near the upper surface of the
+petiole, beneath two exterior ridges, there are two other small circular
+groups of vessels.  In the section of the petiole (B) which had clasped
+during several weeks a stick, the two exterior ridges have become much
+less prominent, and the two groups of woody vessels beneath them much
+increased in diameter.  The semilunar band has been converted into a
+complete ring of very hard, white, woody tissue, with lines radiating
+from the centre.  The three groups of vessels, which, though near
+together, were before distinct, are now completely blended.  The upper
+part of this ring of woody vessels, formed by the prolongation of the
+horns of the original semilunar band, is narrower than the lower part,
+and slightly less compact.  This petiole after clasping the stick had
+actually become thicker than the stem from which it arose; and this was
+chiefly due to the increased thickness of the ring of wood.  This ring
+presented, both in a transverse and longitudinal section, a closely
+similar structure to that of the stem.  It is a singular morphological
+fact that the petiole should thus acquire a structure almost identically
+the same with that of the axis; and it is a still more singular
+physiological fact that so great a change should have been induced by the
+mere act of clasping a support. {75}
+
+[Picture: Fig. 4.  Solanum jasminoides.  A. Section of the petiole in its
+    ordinary state.  B. Section of the petiole some weeks after it had
+                   clasped a stick, as shown in fig. 2]
+
+FUMARIACEÆ.—_Fumaria officinalis_.—It could not have been anticipated
+that so lowly a plant as this Fumaria should have been a climber.  It
+climbs by the aid of the main and lateral petioles of its compound
+leaves; and 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 become
+rather thicker and more cylindrical.  On lightly rubbing several petioles
+with a twig, they became perceptibly curved in 1 hr. 15 m., and
+subsequently straightened themselves.  A stick gently placed in the angle
+between two sub-petioles excited them to move, and was almost clasped in
+9 hrs.  A loop of thread, weighing one-eighth of a grain, caused, after
+12 hrs. and before 20 hrs, had elapsed, a considerable curvature; but it
+was never fairly clasped by the petiole.  The young internodes are in
+continual movement, which is considerable in extent, but very irregular;
+a zigzag line, or a spire crossing itself; or a figure of 8 being formed.
+The course during 12 hrs., when traced on a bell-glass, apparently
+represented about four ellipses.  The leaves themselves likewise move
+spontaneously, the main petioles curving themselves in accordance with
+the movements of the internodes; so that when the latter moved to one
+side, the petioles moved to the same side, then, becoming straight,
+reversed their curvature.  The petioles, however, do not move over a wide
+space, as could be seen when a shoot was securely tied to a stick.  The
+leaf in this case followed an irregular course, like that made by the
+internodes.
+
+_Adlumia cirrhosa_.—I raised some plants late in the summer; they formed
+very fine leaves, but threw up no central stem.  The first-formed leaves
+were not sensitive; some of the later ones were so, but only towards
+their extremities, which were thus enabled 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 have been, had it
+grown tall enough to climb.  The tip of one of these basal leaves, whilst
+young, described in 1 hr. 36 m. a narrow ellipse, open at one end, and
+exactly three inches in length; a second ellipse was broader, more
+irregular, and shorter, viz., only 2½ inches in length, and was completed
+in 2 hrs. 2 m.  From the analogy of _Fumaria_ and _Corydalis_, I have no
+doubt that the internodes of Adlumia have the power of revolving.
+
+_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 has been classed amongst
+tendril-bearers.
+
+Besides the plants already described, _Bignonia unguis_ and its close
+allies, though aided by tendrils, have clasping petioles.  According to
+Mohl (p. 40), _Cocculus Japonicus_ (one of the Menispermaceæ) and a fern,
+the _Ophioglossum Japonicum_ (p. 39), climb by their leaf-stalks.
+
+                                * * * * *
+
+We now come to a small section of plants which climb by means of the
+produced midribs or tips of their leaves.
+
+LILIACEÆ.—_Gloriosa Plantii_.—The stem of a half-grown plant continually
+moved, generally describing an irregular spire, but sometimes oval
+figures with the longer axes directed in different lines.  It either
+followed the sun, or moved in an opposite course, and sometimes stood
+still before reversing its direction.  One oval was completed in 3 hrs.
+40 m.; of two horseshoe-shaped figures, one was completed in 4 hrs. 35 m.
+and the other in 3 hrs.  The shoots, in their 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 gets into an inclined position,
+the end bends downwards into a well-formed hook.  This hook is now strong
+and rigid enough to catch any object, and, when caught, to anchor the
+plant and stop the revolving movement.  Its inner surface is sensitive,
+but not in nearly so high a degree as that of the many before-described
+petioles; for a loop of string, weighing 1.64 grain, produced no effect.
+When the hook has caught a thin twig or even a rigid fibre, the point may
+be perceived in from 1 hr. to 3 hrs. to have curled a little inwards;
+and, under favourable circumstances, it curls round and permanently
+seizes an object in from 8 hrs. to 10 hrs.  The hook when first formed,
+before the leaf has bent downwards, is but little sensitive.  If it
+catches hold of nothing, it remains open and sensitive for a long time;
+ultimately the extremity spontaneously and slowly curls inwards, and
+makes a button-like, flat, spiral coil at the end of the leaf.  One leaf
+was watched, and the hook remained open for thirty-three days; but during
+the last week the tip had curled so much inwards that only a very thin
+twig could have been inserted within it.  As soon as the tip has curled
+so much inwards that the hook is converted into a ring, its sensibility
+is lost; but as long as it remains open some sensibility is retained.
+
+Whilst the plant was only about six inches in height, the leaves, four or
+five in number, were broader than those subsequently produced; their soft
+and but little-attenuated tips were not sensitive, and did not form
+hooks; nor did the stem then revolve.  At this early period of growth,
+the plant can support itself; its climbing powers are not required, and
+consequently are not developed.  So again, the leaves on the summit of a
+full-grown flowering plant, which would not require to climb any higher,
+were not sensitive and could not clasp a stick.  We thus see how perfect
+is the economy of nature.
+
+COMMELYNACEÆ.—_Flagellaria Indica_.—From dried specimens it is manifest
+that this plant climbs exactly like the _Gloriosa_.  A young plant 12
+inches in height, and bearing fifteen leaves, had not a single leaf as
+yet produced into a hook or tendril-like filament; nor did the stem
+revolve.  Hence this plant acquires its climbing powers later in life
+than does the _Gloriosa_ lily.  According to Mohl (p. 41), _Uvularia_
+(Melanthaceæ) also climbs like _Gloriosa_.
+
+These three last-named genera are Monocotyledons; but there is one
+Dicotyledon, namely _Nepenthes_, which is ranked by Mohl (p. 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 coiling round any support.  The twisted part becomes
+thicker; but I observed in Mr. Veitch’s hothouse that the stalk often
+takes a turn when not in contact with any object, and that this twisted
+part is likewise thickened.  Two vigorous young plants of _N. lævis_ and
+_N. distillatoria_, in my hothouse, whilst less than a foot in height,
+showed no sensitiveness in their leaves, and had no power of climbing.
+But when _N. lævis_ had grown to a height of 16 inches, there were signs
+of these powers.  The young leaves when first formed stand upright, but
+soon become inclined; at this period they terminate in a stalk or
+filament, with the pitcher at the extremity hardly at all developed.  The
+leaves now exhibited slight spontaneous movements; and when the terminal
+filaments came into contact with a stick, they slowly bent round and
+firmly seized it.  But owing to the subsequent growth of the leaf, this
+filament became after a time quite slack, though still remaining firmly
+coiled round the stick.  Hence it would appear that the chief use of the
+coiling, at least whilst the plant is young, is to support the pitcher
+with its load of secreted fluid.
+
+                                * * * * *
+
+_Summary on Leaf-climbers_.—Plants belonging to eight families are known
+to have clasping petioles, and plants belonging to four families climb by
+the tips of their leaves.  In all the species observed by me, with one
+exception, the young internodes revolve more or less regularly, in some
+cases as regularly as those of a twining plant.  They revolve at various
+rates, in most cases rather rapidly.  Some few can ascend by spirally
+twining round a support.  Differently from most twiners, there is a
+strong tendency in the same shoot to revolve first in one and then in an
+opposite direction.  The object gained by the revolving movement is to
+bring the petioles or the tips of the leaves into contact with
+surrounding objects; and without this aid the plant would be much less
+successful in climbing.  With rare exceptions, the petioles are sensitive
+only whilst young.  They are sensitive on all sides, but in different
+degrees in different plants; and in some species of _Clematis_ the
+several parts of the same petiole differ much in sensitiveness.  The
+hooked tips of the leaves of the _Gloriosa_ are sensitive only on their
+inner or inferior surfaces.  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 (4.05 mg.); and there is
+reason to believe that the rather thick and stiff petioles of _Clematis
+flammula_ are sensitive to even much less weight if spread over a wide
+surface.  The petioles always bend towards the side which is pressed or
+touched, at different rates in different species, 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 accustomed to the stimulus, and either bends no more or
+becomes straight again, the weight still remaining suspended.  Petioles
+which have clasped an 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 throughout their whole
+diameter or on one side alone; they subsequently become stronger and more
+woody, sometimes to a wonderful degree; and in some cases they acquire an
+internal structure like that of the stem or axis.
+
+The young internodes of the _Lophospermum_ as well as the petioles are
+sensitive to a touch, and by their combined movement seize an object.
+The flower-peduncles of the _Maurandia semperflorens_ revolve
+spontaneously and are sensitive to a touch, yet are not used for
+climbing.  The leaves of at least two, and probably of most, of the
+species of _Clematis_, of _Fumaria_ and _Adlumia_, spontaneously curve
+from side to side, like the internodes, and are thus better adapted to
+seize distant objects.  The petioles of the perfect leaves of _Tropæolum
+tricolorum_, as well as the tendril-like filaments of the plants whilst
+young, ultimately move towards the stem or the supporting stick, which
+they then clasp.  These petioles and filaments also show some tendency to
+contract spirally.  The tips of the uncaught leaves of the _Gloriosa_, as
+they grow old, contract into a flat spire or helix.  These several facts
+are interesting in relation to true tendrils.
+
+With leaf climbers, as with twining plants, the first internodes which
+rise from the ground do not, at least in the cases observed by me,
+spontaneously revolve; nor are the petioles or tips of the first-formed
+leaves sensitive.  In certain species of _Clematis_, the large size of
+the leaves, together with their habit of revolving, and the extreme
+sensitiveness of their petioles, appear to render the revolving movement
+of the internodes superfluous; and this latter power has consequently
+become much enfeebled.  In certain species of _Tropæolum_, both the
+spontaneous movements of the internodes and the sensitiveness of the
+petioles have become much enfeebled, and in one species have been
+completely lost.
+
+
+
+CHAPTER III.
+TENDRIL-BEARERS.
+
+
+Nature of tendrils—BIGNONIACEÆ, various species of, and their different
+modes of climbing—Tendrils which avoid the light and creep into
+crevices—Development of adhesive discs—Excellent adaptations for seizing
+different kinds of supports.—POLEMONIACEÆ—_Cobæa scandens_ much branched
+and hooked tendrils, their manner of
+action—LEGUMINOSÆ—COMPOSITÆ—SMILACEÆ—_Smilax aspera_, its inefficient
+tendrils—FUMARIACEÆ—_Corydalis claviculata_, its state intermediate
+between that of a leaf-climber and a tendril-bearer.
+
+BY tendrils I mean filamentary organs, sensitive to contact and used
+exclusively for climbing.  By this definition, spines, 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, branches, {84} and perhaps stipules.  Mohl, who
+includes under the name of tendrils various organs having a similar
+external appearance, classes them according to their homological nature,
+as being modified leaves, flower-peduncles, &c.  This would be an
+excellent scheme; but I observe that botanists are by no means unanimous
+on the homological nature of certain tendrils.  Consequently I will
+describe tendril-bearing plants by natural families, following Lindley’s
+classification; and this will in most cases keep those of the same nature
+together.  The species to be described belong to ten families, and will
+be given in the following order:—_Bignoniaceæ_, _Polemoniaceæ_,
+_Leguminosæ_, _Compositæ_, _Smilaceæ_, _Fumariaceæ_, _Cucurbitaceæ_,
+_Vitaceæ_, _Sapindaceæ_, _Passifloraceæ_. {85}
+
+BIGNONIACEÆ.—This family contains many tendril-bearers, some twiners, and
+some root-climbers.  The tendrils always consist of 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 within
+the same genus, and to show what remarkable powers some tendrils possess.
+The species, taken together, afford connecting links between twiners,
+leaf-climbers, tendril-bearers, and root-climbers.
+
+         [Picture: Fig. 5.  Bignonia.  Unnamed species from Kew]
+
+_Bignonia_ (an unnamed species from Kew, closely allied to _B. unguis_,
+but with smaller and rather broader leaves).—A young shoot from a
+cut-down plant made three revolutions against the sun, at an average rate
+of 2 hrs. 6 m.  The stem is thin and flexible; it twined round a slender
+vertical stick, ascending from left to right, as perfectly and as
+regularly as any true twining-plant.  When thus ascending, it makes no
+use of its tendrils or petioles; but when it twined round a rather thick
+stick, and its petioles were brought into contact with it, these curved
+round the stick, showing that they have some degree of irritability.  The
+petioles also exhibit a slight degree of spontaneous movement; for in one
+case they certainly described minute, irregular, vertical ellipses.  The
+tendrils apparently curve themselves spontaneously to the same side with
+the petioles; but from various causes, it was difficult to observe the
+movement of either the tendrils or petioles, in this and the two
+following species.  The tendrils are so closely similar in all respects
+to those of _B. unguis_, that one description will suffice.
+
+_Bignonia unguis_.—The young shoots revolve, but less regularly and less
+quickly than those of the last species.  The stem twines imperfectly
+round a vertical stick, sometimes reversing its direction, in the same
+manner as described in so many leaf-climbers; and this plant though
+possessing tendrils, climbs to a certain extent like a leaf-climber.
+Each leaf consists of a petiole bearing a pair of leaflets, and
+terminates in a tendril, which is formed by the modification of three
+leaflets, and closely resembles that above figured (fig. 5).  But it is a
+little larger, and in a young plant was about half an inch in length.  It
+is curiously like 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 are
+of equal length, and diverging, lie in the same plane.  The toes
+terminate in sharp, hard claws, much curved downwards, like those on a
+bird’s foot.  The petiole of the leaf is sensitive to contact; even a
+small loop of thread suspended for two days caused it to bend upwards;
+but the sub-petioles of the two lateral leaflets are not sensitive.  The
+whole tendril, namely, the tarsus and the three toes, are likewise
+sensitive to contact, especially on their under surfaces.  When a shoot
+grows in the midst of thin branches, the tendrils are soon brought by the
+revolving movement of the internodes into contact with them; and then one
+toe of the tendril or more, commonly all three, bend, and after several
+hours seize fast hold of the twigs, like a bird when perched.  If the
+tarsus of the tendril comes into contact with a twig, it goes on slowly
+bending, until the whole foot is carried quite round, and the toes pass
+on each side of the tarsus and seize it.  In like manner, if the petiole
+comes into contact with a twig, it bends round, carrying the tendril,
+which then seizes its own petiole or that of the opposite leaf.  The
+petioles move spontaneously, and thus, when a shoot attempts to twine
+round an upright stick, those on both sides after a time come into
+contact with it, and are excited to bend.  Ultimately the two petioles
+clasp the stick in opposite directions, and the foot-like tendrils,
+seizing on each other or on their own petioles, fasten the stem to the
+support with surprising security.  The tendrils are thus brought into
+action, if the stem twines round a thin vertical stick; and in this
+respect the present species differs from the last.  Both species use
+their tendrils in the same manner when passing through a thicket.  This
+plant is one of the most efficient climbers which I have observed; 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
+moderately well, though not vigorously, I concluded that the tendrils
+acted only like the hooks on a bramble, and that it was the most feeble
+and inefficient of all climbers!
+
+_Bignonia Tweedyana_.—This species is closely allied to the last, and
+behaves in the same manner; but perhaps twines rather better round a
+vertical stick.  On the same plant, one branch twined in one direction
+and another in an opposite direction.  The internodes in one case made
+two circles, each in 2 hrs. 33 m.  I was enabled to observe the
+spontaneous movements of the petioles better in this than in the two
+preceding species: one petiole described three small vertical ellipses in
+the course of 11 hrs., whilst another moved in an irregular spire.  Some
+little time after a stem has twined round an upright stick, and is
+securely fastened to it by the clasping petioles and tendrils, it emits
+aërial roots from the bases of its leaves; and these roots curve partly
+round and adhere to the stick.  This species of _Bignonia_, therefore,
+combines four different methods of climbing generally characteristic of
+distinct plants, namely, twining, leaf-climbing, tendril-climbing, and
+root-climbing.
+
+In the three foregoing species, when the foot-like tendril has caught an
+object, it continues to grow and thicken, and ultimately becomes
+wonderfully strong, in the same manner as 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, and drops off like a leaf in autumn.  I have
+seen this process of disarticulation in no other tendrils, for these,
+when they fail to catch an object, merely wither away.
+
+_Bignonia venusta_.—The tendrils differ considerably from those of the
+previous species.  The lower part, or tarsus, is four times as long as
+the three toes; these are of equal length and diverge equally, but do not
+lie in the same plane; their tips are bluntly hooked, and the whole
+tendril makes an excellent grapnel.  The tarsus is sensitive on all
+sides; but the three toes are sensitive only on their outer surfaces.
+The sensitiveness is not much developed; for a slight rubbing with a twig
+did not cause the tarsus or the toes to become curved until an hour had
+elapsed, and then only in a slight degree.  Subsequently they
+straightened themselves.  Both the tarsus and toes can seize well hold of
+sticks.  If the stem is secured, the tendrils are seen spontaneously to
+sweep large ellipses; the two opposite tendrils moving independently of
+one another.  I have no doubt, from the analogy of the two following
+allied species, that the petioles also move spontaneously; but they are
+not irritable like those of _B. unguis_ and _B. Tweedyana_.  The young
+internodes sweep large circles, one being completed in 2 hrs. 15 m., and
+a second in 2 hrs. 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 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 completed circle.
+
+The tendrils contract spirally a short time after catching any object;
+those which catch nothing merely bend slowly downwards.  But the whole
+subject of the spiral contraction of tendrils will be discussed after all
+the tendril-bearing species have been described.
+
+_Bignonia littoralis_.—The young internodes revolve in large ellipses.
+An internode bearing immature tendrils made two revolutions, each in 3
+hrs. 50 m.; but when grown older with the tendrils mature, it made two
+ellipses, each at the rate of 2 hrs. 44 m.  This species, unlike the
+preceding, is incapable of twining round a stick: this does not appear to
+be due to any want of flexibility in the internodes or to the action of
+the tendrils, and certainly not to any want of the revolving power; nor
+can I account for the fact.  Nevertheless the plant readily ascends a
+thin upright stick by seizing a point above with its two opposite
+tendrils, which then contract spirally.  If the tendrils seize nothing,
+they do not become spiral.
+
+The species last described, ascended a vertical stick by twining spirally
+and by seizing it alternately with its opposite tendrils, like a sailor
+pulling himself up a rope, hand over hand; the present species pulls
+itself up, like a sailor seizing with both hands together a rope above
+his head.
+
+The tendrils are similar in structure to those of the last species.  They
+continue growing for some time, even after they have clasped an object.
+When fully grown, though borne by a young plant, they are 9 inches in
+length.  The three divergent toes are shorter relatively to the tarsus
+than in the former species; they are blunt at their tips and but slightly
+hooked; they are not quite equal in length, the middle one being rather
+longer than the others.  Their outer surfaces 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 hrs. they became straight again and were
+ready to re-act.  The tarsus, for the space of one inch close to the
+toes, is sensitive, but in a rather less degree than the toes; for the
+latter after a slight rubbing, became curved in about half the time.
+Even the middle part of the tarsus is sensitive to prolonged contact, as
+soon as the tendril has arrived at maturity.  After it has grown old, the
+sensitiveness is confined to the toes, and these are only able to curl
+very slowly round a stick.  A tendril is perfectly ready to act, as soon
+as the three toes have diverged, and at this period their outer surfaces
+first become irritable.  The irritability spreads but little from one
+part when excited to another: thus, when a stick was caught by the part
+immediately beneath the three toes, these seldom clasped it, but remained
+sticking straight out.
+
+The tendrils revolve spontaneously.  The movement begins before the
+tendril is converted into a three-pronged grapnel by the divergence of
+the toes, and before any part has become sensitive; so that the revolving
+movement is useless at this early period.  The movement is, also, now
+slow, two ellipses being completed conjointly in 24 hrs. 18 m.  A mature
+tendril made an ellipse in 6 hrs.; so that it moved much more slowly than
+the internodes.  The ellipses which were swept, both in a vertical and
+horizontal plane, were of large size.  The petioles are not in the least
+sensitive, but revolve like the tendrils.  We thus see that the young
+internodes, the petioles, and the tendrils all continue revolving
+together, but at different rates.  The movements of the tendrils which
+rise opposite one another are quite independent.  Hence, when the whole
+shoot is allowed freely to revolve, nothing can be more intricate than
+the course followed by the extremity of each tendril.  A wide space is
+thus irregularly searched for some object to be grasped.
+
+One other curious point remains to be mentioned.  In the course of a few
+days after the toes have closely clasped a stick, their blunt extremities
+become developed, though not invariably, into irregular disc-like balls
+which have the power of adhering firmly to the wood.  As similar cellular
+outgrowths will be fully described under _B. capreolata_, I will here say
+nothing more about them.
+
+_Bignonia æquinoctialis_, var. _Chamberlaynii_.—The internodes, the
+elongated non-sensitive petioles, and the tendrils all revolve.  The stem
+does not twine, but ascends a vertical stick in the same manner as the
+last species.  The tendrils also resemble those of the last species, but
+are shorter; the three toes are more unequal in length, the two outer
+ones being about one-third shorter and rather thinner than the middle
+toe; but they vary in this respect.  They terminate in small hard points;
+and what is important, cellular adhesive discs are not developed.  The
+reduced size of two of the toes as well as their lessened sensitiveness,
+seem to indicate a tendency to abortion; and on one of my plants the
+first-formed tendrils were sometimes simple, that is, were not divided
+into three toes.  We are thus naturally led to the three following
+species with undivided tendrils:—
+
+_Bignonia speciosa_.—The young shoots revolve irregularly, making narrow
+ellipses, spires or circles, at rates varying from 3 hrs. 30 m. to 4 hrs.
+40 m.; but they show no tendency to twine.  Whilst the plant is young and
+does not require a support, tendrils are not developed.  Those borne by a
+moderately young plant were five inches in length.  They revolve
+spontaneously, as do the short and non-sensitive petioles.  When rubbed,
+they slowly bend to the rubbed side and subsequently straighten
+themselves; but they are not highly sensitive.  There is something
+strange in their behaviour: I repeatedly placed close to them, thick and
+thin, rough and smooth sticks and posts, as well as string suspended
+vertically, but none of these objects were well seized.  After clasping
+an upright stick, they repeatedly loosed it again, and often would not
+seize it at all, or their extremities did not coil closely round.  I have
+observed hundreds of tendrils belonging to various Cucurbitaceous,
+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.  They now seized a thin, upright
+stick horizontally, that is, at a point on their own level, and not some
+way up the stick as in the case of all the previous species.
+Nevertheless, the non-twining stem was enabled by this means to ascend
+the stick.
+
+The extremity of the tendril is almost straight and sharp.  The whole
+terminal portion exhibits a singular habit, which in an animal would be
+called an instinct; for it continually searches for any little crevice or
+hole into which to insert itself.  I had two young plants; and, after
+having observed this habit, I placed near them posts, which had been
+bored by beetles, or had become fissured by 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; in order to effect this the extremity for a length of
+half or quarter of an inch, would often bend 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 hole.  I have also seen a tendril keep its
+point, in one case for 20 hrs. and in another for 36 hrs., in a minute
+hole, and then withdraw it.  Whilst the point is thus temporarily
+inserted, the opposite tendril goes on revolving.
+
+The whole length of a tendril often fits itself closely to any surface of
+wood with which it has come into contact; and I have observed one bent at
+right angles, from having entered a wide and deep fissure, with its apex
+abruptly re-bent and inserted into a minute lateral hole.  After a
+tendril has clasped a stick, it contracts spirally; if it remains
+unattached it hangs straight downwards.  If it has merely adapted itself
+to the inequalities of a thick post, though it has clasped nothing, or if
+it has inserted its apex into some little fissure, this stimulus suffices
+to induce spiral contraction; but the contraction always draws the
+tendril away from the post.  So that in every case these movements, which
+seem so nicely adapted for some purpose, were useless.  On one occasion,
+however, the tip became permanently jammed into a narrow fissure.  I
+fully expected, from the analogy of _B. capreolata_ and _B. littoralis_,
+that the tips would have been developed into adhesive discs; but I could
+never detect even a trace of this process.  There is therefore at present
+something unintelligible about the habits of this plant.
+
+_Bignonia picta_.—This species closely resembles the last in the
+structure and movements of its tendrils.  I also casually examined a fine
+growing plant of the allied _B. Lindleyi_, and this apparently behaved in
+all respects in the same manner.
+
+_Bignonia capreolata_.—We now come to a species having tendrils 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 hrs. 23 m.
+The stem is thin and flexible, and I have seen one make four regular
+spiral turns round a thin upright stick, ascending of course from right
+to left, and therefore in a reversed direction compared with the before
+described species.  Afterwards, from the interference of the tendrils, it
+ascended either straight up the stick or in an irregular spire.  The
+tendrils are in some respects highly remarkable.  In a young plant they
+were about 2½ inches in length and much branched, the five chief branches
+apparently representing two pairs of leaflets and a terminal one.  Each
+branch is, however, bifid or more commonly trifid towards the extremity,
+with the points blunt yet distinctly hooked.  A tendril bends to any side
+which is lightly rubbed, and subsequently becomes straight again; but a
+loop of thread weighing ¼th of a grain produced no effect.  On two
+occasions the terminal branches became slightly curved in 10 m. after
+they had touched a stick; and in 30 m. the tips were curled quite round
+it.  The basal part is less sensitive.  The tendrils revolved in an
+apparently capricious manner, sometimes very slightly or not at all; at
+other times they described large regular ellipses.  I could detect no
+spontaneous movement in the petioles of the leaves.
+
+Whilst the tendrils are revolving more or less regularly, another
+remarkable movement takes place, namely, a slow inclination from the
+light towards the darkest side of the house.  I repeatedly changed the
+position of my plants, and some little time after the revolving movement
+had ceased, the successively formed tendrils always ended by pointing to
+the darkest side.  When I placed a thick post near a tendril, between it
+and the light, the tendril pointed in that direction.  In two instances a
+pair of leaves stood so that one of the two tendrils was directed towards
+the light and the other to the darkest side of the house; the latter did
+not move, but the opposite one bent itself first upwards and then right
+over its fellow, so that the two became parallel, one above the other,
+both pointing to the dark: I then turned the plant half round; and the
+tendril which had turned over recovered its original position, and the
+opposite one which had not before moved, now turned over to the dark
+side.  Lastly, on another plant, three pairs of tendrils were produced at
+the same time by three shoots, and all happened to be differently
+directed: I placed the pot in a box open only on one side, and obliquely
+facing the light; in two days all six tendrils pointed with unerring
+truth to the darkest corner of the box, though to do this each had to
+bend in a different manner.  Six wind-vanes could not have more truly
+shown the direction of the wind, than did these branched tendrils the
+course of the stream of light which entered the box.  I left these
+tendrils undisturbed for above 24 hrs., and then turned the pot half
+round; but they had now lost their power of movement, and could not any
+longer avoid the light.
+
+When a tendril has not succeeded in clasping a support, either through
+its own revolving movement or that of the shoot, or by turning towards
+any object which intercepts the light, 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 seizes an object, all the
+branches contract spirally.
+
+I have stated that after a tendril has come into contact with a stick, it
+bends round it in about half an hour; but I repeatedly observed, as in
+the case of _B. speciosa_ and its allies, that it often again loosed the
+stick; sometimes seizing and loosing the same stick three or four times.
+Knowing that the tendrils avoided the light, I gave them a glass tube
+blackened within, and a well-blackened zinc plate: the branches curled
+round the tube and abruptly bent themselves round the edges of the zinc
+plate; but they soon recoiled from these objects with what I can only
+call disgust, and straightened themselves.  I then placed a post with
+extremely rugged bark close to a pair of tendrils; twice they touched it
+for an hour or two, and twice they withdrew; at last one of the hooked
+extremities curled round and firmly seized an excessively minute
+projecting point of bark, and then the other branches spread themselves
+out, following with accuracy every inequality of the surface.  I
+afterwards placed near the plant a post without bark but much fissured,
+and the points of the tendrils crawled into all the crevices in a
+beautiful manner.  To my surprise, I observed that the tips of the
+immature 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 minute points, the final process, now to be described,
+commenced.
+
+This process I discovered by having accidentally left a piece of wool
+near a tendril; and this led me to bind a quantity of flax, moss, and
+wool loosely round sticks, and to place them near tendrils.  The wool
+must not be dyed, for these tendrils are excessively sensitive to some
+poisons.  The hooked points soon caught hold of the fibres, even loosely
+floating fibres, and now there was no recoiling; on the contrary, the
+excitement caused the hooks to penetrate the fibrous mass and to curl
+inwards, so that each hook caught firmly 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 were visibly enlarged.  After a few
+more days the hooks were converted into whitish, irregular balls, rather
+above the 0.05th of an inch (1.27 mm.) in diameter, 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 cellular 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, adhered firmly
+together.  As the whole surface of the ball continues to grow, fresh
+fibres adhere and are afterwards enveloped; so that I have seen a little
+ball with between fifty and sixty fibres of flax crossing it at various
+angles and all embedded more or less deeply.  Every gradation in the
+process could be followed—some fibres merely sticking to the surface,
+others lying in more or less deep furrows, or deeply embedded, or passing
+through the very centre of the cellular ball.  The embedded fibres are so
+closely clasped that they cannot be withdrawn.  The outgrowing tissue has
+so strong a tendency to unite, that two balls produced by distinct
+tendrils sometimes unite and grow into a single one.
+
+On one occasion, when a tendril had curled round a stick, half an inch in
+diameter, an adhesive disc was formed; but this does not generally occur
+in the case of smooth sticks or posts.  If, however, the tip catches a
+minute projecting point, the other branches form discs, especially if
+they find crevices to crawl into.  The tendrils failed to attach
+themselves to a brick wall.
+
+I infer from the adherence of the fibres to the discs or balls, that
+these secrete some resinous adhesive matter; and more especially from
+such fibres becoming loose if immersed in sulphuric ether.  This fluid
+likewise removes small, brown, glistening points which can generally be
+seen on the surfaces of the older discs.  If the hooked extremities of
+the tendrils do not touch anything, discs, as far as I have seen, are
+never formed; {102} but temporary contact during a moderate time suffices
+to cause their development.  I have seen eight discs formed on the same
+tendril.  After their development the tendrils contract spirally, and
+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 discs were attached
+yielded.
+
+From the facts now given, we may 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 other such productions; and I hear from
+Professor Asa Gray that the _Polypodium incanum_ abounds on the
+forest-trees in the districts of North America where this species of
+Bignonia grows.  Finally, I may remark how singular a fact it is that a
+leaf should be 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
+afterwards forming cellular outgrowths which secrete an adhesive cement,
+and then envelop by their continued growth the finest fibres.
+
+_Eccremocarpus scaber_ (_Bignoniaceæ_).—Plants, though growing pretty
+well in my green-house, showed no spontaneous movements in their shoots
+or tendrils; but when removed to the hot-house, the young internodes
+revolved at rates varying from 3 hrs. 15 m. to 1 hr. 13 m.  One large
+circle was swept at this latter unusually quick rate; but generally the
+circles or ellipses were small, and sometimes the course pursued was
+quite irregular.  An internode, after making several revolutions,
+sometimes stood still for 12 hrs. or 18 hrs., and then recommenced
+revolving.  Such strongly marked interruptions in the movements of the
+internodes I have observed in hardly any other plant.
+
+The leaves bear four leaflets, themselves subdivided, and terminate in
+much-branched tendrils.  The main petiole of the leaf, whilst young,
+moves spontaneously, and follows nearly the same irregular course and at
+about the same rate as the internodes.  The movement to and from the stem
+is the most conspicuous, and I have seen the chord of a curved petiole
+which formed an angle of 59° with the stem, in an hour afterwards making
+an angle of 106°.  The two opposite petioles do not move together, and
+one is sometimes so much raised as to stand close to the stem, whilst the
+other is not far from horizontal.  The basal part of the petiole moves
+less than the distal part.  The tendrils, besides being carried by the
+moving petioles and internodes, themselves move spontaneously; and the
+opposite tendrils occasionally move in opposite directions.  By these
+combined movements of the young internodes, petioles, and tendrils, a
+considerable space is swept in search of a support.
+
+In young plants the tendrils are about three inches in length: they bear
+two lateral and two terminal branches; and each branch bifurcates twice,
+with the tips terminating in blunt double hooks, having both points
+directed to the same side.  All the branches are sensitive on all sides;
+and after being lightly rubbed, or after coming into contact with a
+stick, bend in about 10 m.  One which had become curved in 10 m. after a
+light rub, continued bending for between 3 hrs. and 4 hrs., and became
+straight again in 8 hrs. or 9 hrs.  Tendrils, which have caught nothing,
+ultimately contract into an irregular spire, as they likewise do, only
+much more quickly, after clasping a support.  In both cases the main
+petiole bearing the leaflets, which is at first straight and inclined a
+little upwards, moves downwards, with the middle part bent abruptly into
+a right angle; but this is seen in _E. miniatus_ more plainly than in _E.
+scaber_.  The tendrils in this genus act in some respects like those of
+_Bignonia capreolata_; but the whole does not move from the light, nor do
+the hooked tips become enlarged into cellular discs.  After the tendrils
+have come into contact with a moderately thick cylindrical stick or with
+rugged bark, the several branches may be seen slowly to lift themselves
+up, change their positions, and again come into contact with the
+supporting surface.  The object of these movements is to bring the
+double-hooks at the extremities of the branches, which naturally face in
+all directions, into contact with the wood.  I have watched a tendril,
+half of which had bent itself at right angles round the sharp corner of a
+square post, neatly bring every single hook into contact with both
+rectangular surfaces.  The appearance suggested the belief, that though
+the whole tendril is not sensitive to light, yet that the tips are so,
+and that they turn and twist themselves towards any dark surface.
+Ultimately the branches arrange themselves very neatly to all the
+irregularities 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 wound round a rather thick stick, the subsequent
+spiral contraction generally draws it away and spoils the neat
+arrangement.  So it is, but not in quite so marked a manner, when a
+tendril has spread itself over a large, nearly flat surface of rugged
+bark.  We may therefore conclude that these tendrils are not perfectly
+adapted to seize moderately thick sticks or rugged bark.  If a thin stick
+or twig is placed near a tendril, the terminal branches wind quite round
+it, and then seize their own lower branches or the main stem.  The stick
+is thus firmly, but not neatly, grasped.  What the tendrils are really
+adapted for, appears to be such objects as the thin culms of certain
+grasses, or the long flexible bristles of a brush, or thin rigid leaves
+such as those of the Asparagus, all of which they seize in an admirable
+manner.  This is due to the extremities of the branches close to the
+little hooks being extremely sensitive to a touch from the thinnest
+object, which they consequently curl round and clasp.  When a small
+brush, for instance, was placed near a tendril, the tips of each
+sub-branch seized one, two, or three of the bristles; 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, which afforded an excellent support.
+
+POLEMONIACEÆ.—_Cobæa scandens_.—This is an excellently constructed
+climber.  The tendrils on a fine plant were eleven inches long, with the
+petiole bearing two pairs of leaflets, only two and a half inches in
+length.  They revolve more rapidly and vigorously than those of any other
+tendril-bearer observed by me, with the exception of one kind of
+Passiflora.  Three large, nearly circular sweeps, directed against the
+sun were completed, each in 1 hr. 15 m.; and two other circles in 1 hr.
+20 m. and 1 hr. 23 m.  Sometimes a tendril travels in a much inclined
+position, and sometimes nearly upright.  The lower part moves but little
+and the petiole not at all; nor do the internodes revolve; so that here
+we have the tendril alone moving.  On the other hand, with most of the
+species of _Bignonia_ and the _Eccremocarpus_, the internodes, tendrils,
+and petioles all revolved.  The long, straight, tapering main stem of the
+tendril of the _Cobæa_ bears alternate branches; and each branch is
+several times divided, with the finer branches as thin as very thin
+bristles and extremely flexible, so that they are blown about by a breath
+of air; yet they are strong and highly elastic.  The extremity of each
+branch is a little flattened, and terminates in a minute double (though
+sometimes single) hook, formed of a hard, translucent, woody substance,
+and as sharp as the finest needle.  On a tendril which was eleven inches
+long I counted ninety-four of these beautifully constructed little hooks.
+They readily catch soft wood, or gloves, or the skin of the naked hand.
+With the exception of these hardened hooks, and of the basal part of the
+central stem, every part of every branchlet is highly sensitive on all
+sides to a slight touch, and bends in a few minutes towards the touched
+side.  By lightly rubbing several sub-branches on opposite sides, the
+whole tendril rapidly assumed an extraordinarily crooked shape.  These
+movements from contact do not interfere with the ordinary revolving
+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, spiral contraction likewise begins
+after an unusually short interval of time, namely, in about twelve hours.
+
+Before the tendril is mature, the terminal branchlets cohere, and the
+hooks are curled closely inwards.  At this period no part is sensitive to
+a touch; but as soon as the branches diverge and the hooks stand out,
+full sensitiveness is acquired.  It is a singular circumstance that
+immature tendrils revolve at their full velocity before they become
+sensitive, but in a useless manner, as in this state they can catch
+nothing.  This want of perfect co-adaptation, though only for a short
+time, between the structure and the functions of a climbing-plant is a
+rare event.  A tendril, as soon as it is ready to act, stands, together
+with the supporting petiole, vertically upwards.  The leaflets borne by
+the petiole are at this time quite small, and the extremity of the
+growing stem is bent to one side so as to be out of the way of the
+revolving tendril, which sweeps large circles directly over head.  The
+tendrils thus revolve in a position well adapted for catching objects
+standing above; and by this means the ascent of the plant is favoured.
+If no object is caught, the leaf with its tendril bends downwards and
+ultimately assumes a horizontal position.  An open space is thus left for
+the next succeeding and younger tendril to stand vertically upwards and
+to revolve freely.  As soon as an old tendril bends downwards, it loses
+all power of movement, and contracts spirally into an entangled mass.
+Although the tendrils revolve with unusual rapidity, the movement lasts
+for only a short time.  In a plant placed in the hot-house and growing
+vigorously, a tendril revolved for not longer than 36 hours, counting
+from the period when it first became sensitive; but during this period it
+probably made at least 27 revolutions.
+
+When a revolving tendril strikes against a stick, the branches quickly
+bend round and clasp it.  The little hooks here play an important part,
+as they prevent the branches from being dragged away by the rapid
+revolving movement, before they have had time to clasp the stick
+securely.  This is especially the case when only the extremity of a
+branch has caught hold of a support.  As soon as a tendril has bent a
+smooth stick or a thick rugged post, or has come into contact with planed
+wood (for it can adhere temporarily even to so smooth a surface as this),
+the same peculiar movements may be observed as those described under
+_Bignonia capreolata_ and _Eccremocarpus_.  The branches repeatedly lift
+themselves up and down; those which have their hooks already directed
+downwards remaining in this position and securing the tendril, whilst the
+others twist about until they succeed in arranging themselves in
+conformity with every irregularity of the surface, and in bringing their
+hooks into contact with the wood.  The use of the hooks was well shown by
+giving the tendrils tubes and slips of glass to catch; for these, though
+temporarily seized, were invariably lost, either during the
+re-arrangement of the branches or ultimately when spiral contraction
+ensued.
+
+The perfect manner in which the branches arranged themselves, creeping
+like rootlets over every inequality of the surface and into any deep
+crevice, is a pretty sight; for it is perhaps more effectually performed
+by this than by any other species.  The action is certainly more
+conspicuous, as the upper surfaces of the main stem, as well as of every
+branch to the extreme hooks, are angular and green, whilst the lower
+surfaces are rounded and purple.  I was led to infer, as in former cases,
+that a less amount of light guided these movements of the branches of the
+tendrils.  I made many trials with black and white cards and glass tubes
+to prove it, but failed from various causes; yet these trials
+countenanced the belief.  As a tendril consists of a leaf split into
+numerous segments, there is nothing surprising in all the segments
+turning their upper surfaces towards the light, as soon as the tendril is
+caught and the revolving movement is arrested.  But this will not account
+for the whole movement, for the segments actually bend or curve to the
+dark side besides turning round on their axes so that their upper
+surfaces may face the light.
+
+When the _Cobæa_ grows in the open air, the wind must aid the extremely
+flexible tendrils in seizing a support, for I found that a mere breath
+sufficed to cause the extreme branches to catch hold by their hooks of
+twigs, which they could not have reached by the revolving movement.  It
+might have been thought that a tendril, thus hooked by the extremity of a
+single branch, could not have fairly grasped its support.  But several
+times I watched cases like the following: tendril caught a thin stick by
+the hooks of one of its two extreme branches; though thus held by the
+tip, it still tried to revolve, bowing itself to all sides, and by this
+movement the other extreme branch soon caught the stick.  The first
+branch then loosed itself, and, arranging its hooks, again caught hold.
+After a time, from the continued movement of the tendril, the hooks of a
+third branch caught hold.  No other branches, as the tendril then stood,
+could possibly have touched the stick.  But before long the upper part of
+the main stem began to contract into an open spire.  It thus dragged the
+shoot which bore the tendril towards the stick; and as the tendril
+continually tried to revolve, a fourth branch was brought into contact.
+And lastly, from the spiral contraction travelling down both the main
+stem and the branches, all of them, one after another, were ultimately
+brought into contact with the stick.  They then wound themselves round it
+and round one another, until the whole tendril was tied together in an
+inextricable knot.  The tendrils, though at first quite flexible, after
+having clasped a support for a time, become more rigid and stronger than
+they were at first.  Thus the plant is secured to its support in a
+perfect manner.
+
+LEGUMINOSÆ.—_Pisum sativum_.—The common pea was the subject of a valuable
+memoir by Dutrochet, {111} who discovered that the internodes and
+tendrils revolve 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 wider space.  Owing to this change of direction,
+and likewise to the movement of the stem towards the light, the
+successive irregular ellipses generally form an irregular spire.  I have
+thought it worth while to annex a tracing of the course pursued by the
+upper internode (the movement of the tendril being neglected) of a young
+plant from 8.40 A.M. to 9.15 P.M.  The course was traced on a
+hemispherical glass placed over the plant, and the dots with figures give
+the hours of observation; each dot being joined by a straight line.  No
+doubt all the lines would have been curvilinear if the course had been
+observed at much shorter intervals.  The extremity of the petiole, from
+which the young tendril arose, was two inches from the glass, so that if
+a pencil two inches in length could have been 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 reduced by one-half.  Neglecting
+the first great sweep towards the light from the figure 1 to 2, the end
+of the petiole swept a space 4 inches across in one direction, and 3
+inches in another.  As a full-grown tendril is considerably above two
+inches in length, and as the tendril itself bends and revolves in harmony
+with the internode, a considerably wider space is swept than is here
+represented on a reduced scale.  Dutrochet observed the completion of an
+ellipse in 1 hr. 20 m.; and I saw one completed in 1 hr. 30 m.  The
+direction followed is variable, either with or against the sun.
+
+            [Picture: Fig. 6.  Side of room with window] {113}
+
+Dutrochet asserts that the petioles of the leaves spontaneously revolve,
+as well as the young internodes and tendrils; but he does not say that he
+secured the internodes; when this was done, I could never detect any
+movement in the petiole, except to and from the light.
+
+The tendrils, on the other hand, when the internodes and petioles are
+secured, describe irregular spires or regular ellipses, exactly like
+those made by the internodes.  A young tendril, only 1⅛ of an 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 sensitive tendrils, and tied the petiole so that the tendril alone
+could move; it completed a perfect ellipse in 1 hr. 30 m.; I then turned
+the plant partly round, but this made no change in the direction of the
+succeeding ellipse.  The next day I watched a plant similarly secured
+until the tendril (which was highly sensitive) made an ellipse in a line
+exactly to and from the light; the movement was so great that the tendril
+at the two ends of its elliptical course bent itself 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 no longer
+curved in harmony together, owing to inequality of age.
+
+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 concave surface near the tip caused
+them to bend quickly, as did occasionally a loop of thread weighing
+one-seventh of a grain (9.25 mg.).  The upper or convex surface is barely
+or not at all sensitive.  Tendrils, after bending from a touch,
+straighten themselves in about two hours, and are then ready to act
+again.  As soon as they begin to grow old, the extremities of their two
+or three pairs of branches become hooked, and they then appear to form an
+excellent grappling instrument; but this is not the case.  For at this
+period they have generally quite lost their sensitiveness; and when
+hooked on to twigs, some were not at all affected, and others required
+from 18 hrs. to 24 hrs. before clasping such twigs; nevertheless, they
+were able to utilise the last vestige of irritability owing to their
+extremities being hooked.  Ultimately the lateral branches contract
+spirally, but not the middle or main stem.
+
+_Lathyrus aphaca_.—This plant is destitute of leaves, except during a
+very early age, these being replaced by tendrils, and the leaves
+themselves by large stipules.  It might therefore have been expected that
+the tendrils would have been highly organized, but this is not so.  They
+are moderately long, thin, and unbranched, with their tips slightly
+curved.  Whilst young they are sensitive on all sides, but chiefly on the
+concave side of the extremity.  They have no spontaneous revolving power,
+but are at first inclined upwards at an angle of about 45°, then move
+into a horizontal position, and ultimately bend downwards.  The young
+internodes, on the other hand, revolve in ellipses, and carry with them
+the tendrils.  Two ellipses were completed, each in nearly 5 hrs.; their
+longer axes were directed at about an angle of 45° to the axis of the
+previously made ellipse.
+
+_Lathyrus grandiflorus_.—The plants observed were young and not growing
+vigorously, yet sufficiently so, I think, for my observations to be
+trusted.  If so, we have the rare case of neither internodes nor tendrils
+revolving.  The tendrils of vigorous plants are above 4 inches in length,
+and are often twice divided into three branches; the tips are curved and
+are sensitive on their concave sides; the lower part of the central stem
+is hardly at all sensitive.  Hence this plant appears to climb simply by
+its tendrils being brought, through the growth of the stem, or more
+efficiently by the wind, into contact with surrounding objects, which
+they then clasp.  I may add that the tendrils, or the internodes, or
+both, of _Vicia sativa_ revolve.
+
+COMPOSITÆ.—_Mutisia clematis_.—The immense family of the Compositæ is
+well known to include very few climbing plants.  We have seen in the
+Table in the first chapter that _Mikania scandens_ is a regular twiner,
+and F. Müller informs me that in S. Brazil there is another species which
+is a leaf-climber.  _Mutisia_ is the only genus in the family, as far as
+I can learn, which bears tendrils: it is therefore interesting to find
+that these, though rather less metamorphosed from their primordial foliar
+condition than are most other tendrils, yet display all the ordinary
+characteristic movements, both those that are spontaneous and those which
+are excited by contact.
+
+The long leaf bears seven or eight alternate leaflets, and terminates in
+a tendril which, in a plant of considerable size, was 5 inches in length.
+It consists generally of three branches; and these, although much
+elongated, evidently represent the petioles and midribs of three
+leaflets; for they closely resemble the same parts in an ordinary leaf,
+in being rectangular on the upper surface, furrowed, and edged with
+green.  Moreover, the green edging of the tendrils of young plants
+sometimes expands into a narrow lamina or blade.  Each branch is curved a
+little downwards, and is slightly hooked at the extremity.
+
+A young upper internode revolved, judging from three revolutions, at an
+average rate of 1 hr. 38 m.; it swept ellipses with the longer axes
+directed at right angles to one another; but the plant, apparently,
+cannot twine.  The petioles and the tendrils are both in constant
+movement.  But their movement is slower and much less regularly
+elliptical than that of the internodes.  They appear to be much affected
+by the light, for the whole leaf usually sinks down during the night and
+rises during the day, moving, also, during the day in a crooked course to
+the west.  The tip of the tendril is highly sensitive on the lower
+surface; and one which was just touched with a twig became perceptibly
+curved in 3 m., and another in 5 m.; the upper surface is not at all
+sensitive; the sides are moderately sensitive, so that two branches which
+were rubbed on their inner sides converged and crossed each other.  The
+petiole of the leaf and the lower parts of the tendril, halfway between
+the upper leaflet and the lowest branch, are not sensitive.  A tendril
+after curling from a touch became straight again in about 6 hrs., and was
+ready to re-act; but one that had been so roughly rubbed as to have
+coiled into a helix did not become perfectly straight until after 13 hrs.
+The tendrils retain their sensibility to an unusually late age; for one
+borne by a leaf with five or six fully developed leaves above, was still
+active.  If a tendril catches nothing, after a considerable interval of
+time the tips of the branches curl a little inwards; but if it clasps
+some object, the whole contracts spirally.
+
+                    [Picture: Fig. 7.  Smilax aspera]
+
+SMILACEÆ.—_Smilax aspera_, var. _maculata_.—Aug. St.-Hilaire {118}
+considers that the tendrils, which rise in pairs from the petiole, are
+modified lateral leaflets; but Mohl (p. 41) ranks them as modified
+stipules.  These tendrils are from 1½ to 1¾ inches in length, are thin,
+and have slightly curved, pointed extremities.  They diverge a little
+from each other, and 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 when placed in contact with a
+stick became just perceptibly curved in 1 hr. 20 m., but did not
+completely surround it until 48 hrs. had elapsed; the concave side of
+another became considerably curved in 2 hrs. and clasped a stick in 5
+hrs.  As the pairs of tendrils grow old, one tendril diverges more and
+more from the other, and both slowly bend backwards and downwards, so
+that after a time they project on the opposite side of the stem to that
+from which they arise.  They then still retain their sensitiveness, and
+can clasp a support placed _behind_ the stem.  Owing to this power, the
+plant is able to ascend a thin upright stick.  Ultimately the two
+tendrils belonging to the same petiole, if they do not come into contact
+with any object, loosely cross each other behind the stem, as at B, in
+fig. 7.  This movement of the tendrils towards and round the stem is, to
+a certain extent, guided by their avoidance of the light; for when a
+plant stood so that one of the two tendrils was compelled in thus slowly
+moving to travel towards the light, and the other from the light, the
+latter always moved, as I repeatedly observed, more quickly than its
+fellow.  The tendrils do not contract 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, as we have just
+seen, is guided, to a certain extent, by the avoidance of the light; 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 is a less perfect climber than any other tendril-bearing species
+observed by me.  The plant whilst young and only a few inches in height,
+does not produce any tendrils; and considering that it grows to only
+about 8 feet in height, 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 these are.  The plant
+might have been left, one would have thought, to climb by the aid of its
+spines alone, like our brambles.  As, however, it belongs to a genus,
+some of the species of which are furnished with much longer tendrils, we
+may suspect that it possesses these organs solely from being descended
+from progenitors more highly organized in this respect.
+
+FUMARIACEÆ.—_Corydalis claviculata_.—According to Mohl (p. 43), the
+extremities of the branched stem, as well as the leaves, 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 a widely different homological nature.  Nevertheless,
+from this statement by Mohl, I have ranked this species amongst the
+tendril-bearers; if classed exclusively by its foliar tendrils, it would
+be doubtful whether it ought not to have been placed amongst the
+leaf-climbers, with its allies, _Fumaria_ and _Adlumia_.  A large
+majority of its so-called tendrils still bear leaflets, though
+excessively reduced in size; but some few of them may properly be
+designated as tendrils, for they are completely destitute of laminæ 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
+rather young, only the outer leaves, but when full-grown all the leaves,
+have their extremities converted into more or less perfect 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 structure represented in the
+following drawing.  This leaf bore nine leaflets; the lower ones being
+much subdivided.  The terminal portion of the petiole, about 1½ inch in
+length (above the leaflet _f_), is thinner and more elongated than the
+lower part, and may 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 (2.116
+mm. and 0.339 mm.), so that it was almost microscopically minute.  All
+the reduced leaflets have branching nerves, and terminate in little
+spines, like those of the fully developed leaflets.  Every gradation
+could 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 condition, and we then
+have a true tendril.
+
+ [Picture: Fig. 8.  Corydalis claviculata.  Leaf-tendril of natural size]
+
+The several terminal branches of the petiole bearing the much reduced
+leaflets (_a_, _b_, _c_, _d_) are highly sensitive, for a loop of thread
+weighing only the one-sixteenth of a grain (4.05 mg.) caused them to
+become greatly curved in under 4 hrs.  When the loop was removed, the
+petioles straightened themselves in about the same time.  The petiole
+(_e_) was rather less sensitive; and in another specimen, in which the
+corresponding petiole bore rather larger leaflets, a loop of thread
+weighing one-eighth of a grain did not cause curvature until 18 hrs. had
+elapsed.  Loops of thread weighing one-fourth of a grain, left suspended
+on the lower petioles (_f_ to _l_) during several days, produced no
+effect.  Yet the three petioles _f_, _g_, and _h_ were not quite
+insensible, for when left in contact with a stick for a day or two they
+slowly curled round it.  Thus the sensibility of the petiole gradually
+diminishes from the tendril-like extremity to the base.  The internodes
+of the stem are not at all sensitive, which makes Mohl’s statement that
+they are sometimes converted into tendrils the more surprising, not to
+say improbable.
+
+The whole leaf, whilst young and sensitive, stands almost vertically
+upwards, as we have seen to be the case with many tendrils.  It is in
+continual movement, and one that I observed swept at an average rate of
+about 2 hrs. for each revolution, large, though irregular, ellipses,
+which were sometimes narrow, sometimes broad, with their longer axes
+directed to different points of the compass.  The young internodes,
+likewise revolved irregularly in ellipses or spires; so that by these
+combined movements a considerable space was swept for a support.  If the
+terminal and attenuated portion of a petiole fails to seize any object,
+it ultimately bends downwards and inwards, and soon loses all
+irritability and power of movement.  This bending down differs much in
+nature from that which occurs with the extremities of the young leaves in
+many species of _Clematis_; for these, when thus bent downwards or
+hooked, first acquire their full degree of sensitiveness.
+
+_Dicentra thalictrifolia_.—In this allied plant the metamorphosis of the
+terminal leaflets is complete, and they are converted into perfect
+tendrils.  Whilst the plant is young, the tendrils appear like modified
+branches, and a distinguished botanist thought that they were of this
+nature; but in a full-grown plant there can be no doubt, as I am assured
+by Dr. Hooker, that they are modified leaves.  When of full size, they
+are above 5 inches in length; they bifurcate twice, thrice, or even four
+times; their extremities are hooked and blunt.  All the branches of the
+tendrils are sensitive on all sides, but the basal portion of the main
+stem is only slightly so.  The terminal branches when lightly rubbed with
+a twig became curved in the course of from 30 m. to 42 m., and
+straightened themselves in between 10 hrs. and 20 hrs.  A loop of thread
+weighing one-eighth of a grain plainly caused the thinner branches to
+bend, as did occasionally a loop weighing one-sixteenth of a grain; but
+this latter weight, though left suspended, was not sufficient to cause a
+permanent flexure.  The whole leaf with its tendril, as well as the young
+upper internodes, revolves vigorously and quickly, though irregularly,
+and thus sweeps 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, and
+this was completed in 1 hr. 53 m.  During a period of 6 hrs. 17 m.
+another shoot made a complex figure, apparently representing 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 done in so perfect a manner
+by some Bignoniaceæ and Cobæa.  The tendrils of young plants, two or
+three feet in height, are only half the length of those borne by the same
+plant when grown taller, and they do not contract spirally after clasping
+a support, but only become slightly flexuous.  Full-sized tendrils, on
+the other hand, contract spirally, with the exception of 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 is angularly and
+abruptly bent downwards like that of Eccremocarpus.
+
+
+
+CHAPTER IV.
+TENDRIL-BEARERS—(_continued_).
+
+
+CUCURBITACEÆ.—Homologous nature of the tendrils—_Echinocystis lobata_,
+remarkable movements of the tendrils to avoid seizing the terminal
+shoot—Tendrils not excited by contact with another tendril or by drops of
+water—Undulatory movement of the extremity of the tendril—_Hanburya_,
+adherent discs—VITACÆ—Gradation between the flower-peduncles and tendrils
+of the vine—Tendrils of the Virginian Creeper turn from the light, and,
+after contact, develop adhesive
+discs—SAPINDACEÆ—PASSIFLORACEÆ—_Passiflora gracilis_—Rapid revolving
+movement and sensitiveness of the tendrils—Not sensitive to the contact
+of other tendrils or of drops of water—Spiral contraction of
+tendrils—Summary on the nature and action of tendrils.
+
+CUCURBITACEÆ.—The tendrils in this family have been ranked by competent
+judges as modified leaves, stipules, or branches; or as partly a leaf and
+partly a branch.  De Candolle believes that the tendrils differ in their
+homological nature in two of the tribes. {127a}  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;” but
+much may be said in favour of the belief that it is a modified
+flower-peduncle. {127b}
+
+_Echinocystis lobata_.—Numerous observations were made on this plant
+(raised from seed sent me by Prof. Asa Gray), for the spontaneous
+revolving movements of the internodes and tendrils were first observed by
+me in this case, and greatly perplexed me.  My observations may now be
+much condensed.  I observed thirty-five revolutions of the internodes and
+tendrils; the slowest rate was 2 hrs. and the average rate, with no great
+fluctuations, 1 hr. 40 m.  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 an opposite direction.  Sometimes the movement during a short
+time would either stop or be reversed; and this apparently was due to
+interference from the light, as, for instance, when I placed a plant
+close to a window.  In one instance, an old tendril, which had nearly
+ceased revolving, moved in one direction, whilst a young tendril above
+moved in an opposite course.  The two uppermost internodes alone revolve;
+and as soon as the lower one grows old, only its upper part continues to
+move.  The ellipses or circles swept by the summits of the internodes are
+about three inches in diameter; whilst those swept by the tips of the
+tendrils, are from 15 to 16 inches in diameter.  During the revolving
+movement, the internodes become successively curved to all points of the
+compass; in one part of their course they are often inclined, together
+with the tendrils, at about 45° to the horizon, and in another part stand
+vertically up.  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 cutting off the latter with sharp scissors, the top of
+the shoot rose only a little, and went on revolving.  This false
+appearance is apparently due to the internodes and tendrils all curving
+and moving harmoniously together.
+
+A 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, stiffened and straightened itself from tip to base in a certain
+part of its course, thus becoming nearly or quite vertical.  I witnessed
+this repeatedly; and it occurred both when the supporting internodes were
+free and when they were tied up; but was perhaps most conspicuous in the
+latter case, or when the whole shoot happened to be much inclined.  The
+tendril forms a very acute angle with the projecting extremity of the
+stem or shoot; and the stiffening always occurred as the tendril
+approached, and had to pass over the shoot in its circular course.  If it
+had not possessed and exercised this curious power, it would infallibly
+have struck against the extremity of the shoot and been arrested.  As
+soon as the tendril with its three branches begins to stiffen itself in
+this manner and to rise from an inclined into a vertical position, the
+revolving motion becomes more rapid; and as soon as the tendril has
+succeeded in passing over the extremity of the shoot or point of
+difficulty, its motion, coinciding with that from its weight, often
+causes it to fall into its previously inclined position so quickly, that
+the apex could be 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 and
+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 to be the case with other species
+of the family by Mohl (p. 65).  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 the tendrils which
+had been rubbed on the concave side had straightened themselves, I
+reversed the process of rubbing, and always with the same result.  After
+touching the concave side, the tip becomes sensibly curved in one or two
+minutes; and subsequently, if the touch has been at all rough, it coils
+itself into a helix.  But the helix will, after a time, straighten
+itself, and be again ready to act.  A loop of thin thread only
+one-sixteenth of a grain in weight caused a temporary flexure.  The lower
+part was repeatedly rubbed rather roughly, but no curvature ensued; yet
+this part is sensitive to prolonged pressure, for when it came into
+contact with a stick, it would slowly wind round it.
+
+One of my plants bore two shoots near together, and the tendrils were
+repeatedly drawn across one another, but it is a singular fact that they
+did not once catch each other.  It would appear as if they had become
+habituated to contact of this kind, for the pressure thus caused must
+have been much greater than that caused by a loop of soft thread weighing
+only the one-sixteenth of a grain.  I have, however, seen several
+tendrils of _Bryonia dioica_ interlocked, but they subsequently released
+one another.  The tendrils of the Echinocystis are also habituated to
+drops of water or to rain; for artificial rain made by violently flirting
+a wet brush over them produced not the least effect.
+
+The revolving movement of a tendril is not stopped by the curving of its
+extremity after it has been touched.  When one of the lateral branches
+has firmly clasped an object, the middle branch continues to revolve.
+When a stem is bent down and secured, so that the tendril depends but is
+left free to move, its previous revolving movement is nearly or quite
+stopped; but it soon begins to bend upwards, and as soon as it has become
+horizontal the revolving movement recommences.  I tried this four times;
+the tendril generally rose to a horizontal position in an hour or an hour
+and a half; but in one case, in which a tendril depended at an angle of
+45° beneath the horizon, the uprising took two hours; in half an hour
+afterwards it rose to 23° above the horizon and then recommenced
+revolving.  This upward movement is independent of the action of light,
+for it occurred twice in the dark, and on another occasion the light came
+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
+germinating seeds.
+
+A tendril does not long retain its revolving power; and as soon as this
+is lost, it bends downwards and contracts spirally.  After the revolving
+movement has ceased, the tip still retains for a short time its
+sensitiveness to contact, but this can be of little or no use 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 that the tip managed in the course of a few
+hours to curl twice or even thrice round the stick.  I at first thought
+that this was due to rapid growth on the outside; but by coloured points
+and measurements I proved that there had been no sensible increase of
+length within the time.  When a stick, flat on one side, was similarly
+placed, the tip of the tendril could not curl beyond the flat surface,
+but coiled itself into a helix, which, turning to one side, lay flat on
+the little flat surface of wood.  In one instance a portion of tendril
+three-quarters of an inch in length was thus dragged on to the flat
+surface by the coiling in of the helix.  But the tendril thus acquires a
+very insecure hold, and generally after a time slips off.  In one case
+alone the helix subsequently uncoiled itself, and the tip then passed
+round and clasped the stick.  The formation of the helix on the flat side
+of the 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 observed
+several times through a lens that the whole surface was not in close
+contact with the stick; and I can understand the onward progress only by
+supposing that the movement is slightly undulatory or vermicular, and
+that the tip alternately straightens itself a little and then again curls
+inwards.  It thus drags 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
+with its extreme point, can work itself onwards until it has passed twice
+or even thrice round the stick, and has permanently grasped it.
+
+_Hanburya Mexicana_.—The young internodes and tendrils of this anomalous
+member of the family, revolve in the same manner and at about the same
+rate as those of 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 it had become rapidly coiled into a
+ring owing to a single touch, it straightened itself in 50 m.  The
+tendril, when in full action, stands vertically up, with the projecting
+extremity of the young stem thrown a little on one side, so as to be out
+of the way; but the tendril bears on the inner side, near its base, a
+short rigid branch, which projects out at right angles like a spur, with
+the terminal half bowed a little downwards.  Hence, as the main vertical
+branch revolves, the spur, from its position and rigidity, cannot pass
+over the extremity of the shoot, in the same curious manner as do the
+three branches of the tendril of the _Echinocystis_, namely, by
+stiffening themselves at the proper point.  The spur is therefore pressed
+laterally against the young stem in one part of the revolving course, and
+thus the sweep of the lower part of the main branch is much restricted.
+A nice case of co-adaptation here comes into play: in all the other
+tendrils observed by me, the several branches become sensitive at the
+same period: had this been the case with the _Hanburya_, the inwardly
+directed, spur-like branch, from being pressed, during the revolving
+movement, against the projecting end of the shoot, would infallibly have
+seized it in a useless or injurious manner.  But the main branch of the
+tendril, after revolving for a time in a vertical position, spontaneously
+bends downwards; and in doing so, raises the spur-like branch, which
+itself also curves upwards; so that by these combined movements it rises
+above the projecting end of the shoot, and can now move freely without
+touching the shoot; and now it first becomes sensitive.
+
+The tips of both branches, when they come into contact with a stick,
+grasp it like any ordinary tendril.  But in the course of a few days, the
+lower 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 discs formed by the extremities of the
+tendrils of some species of _Bignonia_ and of _Ampelopsis_; but in the
+_Hanburya_ the layer is developed along the terminal inner surface,
+sometimes for a length of 1¾ inches, and not at the extreme tip.  The
+layer is white, whilst the tendril is green, and near the tip it is
+sometimes thicker than the tendril itself; it generally spreads a little
+beyond the sides of the tendril, and 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 an immersion of 24 hrs. in alcohol or
+water, but was quite loosened by a similar immersion in ether or
+turpentine.  After a tendril has once firmly coiled itself round a stick,
+it is difficult to imagine of what use the adhesive cellular layer can
+be.  Owing to the spiral contraction which soon ensues, the tendrils were
+never able to remain, excepting in one instance, in contact with a thick
+post or a nearly flat surface; if they had quickly become attached by
+means of the adhesive layer, this would evidently have been of service to
+the plant.
+
+The tendrils of _Bryonia dioica_, _Cucurbita ovifera_, and _Cucumis
+sativa_ are sensitive and revolve.  Whether the internodes likewise
+revolve I did not observe.  In _Anguria Warscewiczii_, the internodes,
+though thick and stiff, revolve: in this plant the lower surface of the
+tendril, some time after clasping a stick, produces a coarsely cellular
+layer or cushion, which adapts itself closely to the wood, like that
+formed by the tendril of the _Hanburya_; but it is not in the least
+adhesive.  In _Zanonia Indica_, which belongs to a different tribe of the
+family, the forked tendrils and the internodes revolve in periods between
+2 hrs. 8 m. and 3 hrs. 35 m., moving against the sun.
+
+VITACEÆ.—In this family and in the two following, namely, the Sapindacæ
+and Passifloraceæ, the tendrils are modified flower-peduncles; and are
+therefore axial in their nature.  In this respect they differ from all
+those previously described, with the exception, perhaps, of the
+Cucurbitaceæ.  The homological nature, however, of a tendril seems to
+make no difference in its action.
+
+  [Picture: Fig. 9.  Tendril of the Vine.  A.  Peduncle of tendril.  B.
+    Longer Branch, with a scale at its base.  C.  Shorter branch.  D.
+                      Petiole of the opposite leaf]
+
+_Vitis vinifera_.—The tendril is thick and of great length; one from a
+vine growing out of doors and not vigorously, was 16 inches long.  It
+consists of a peduncle (A), bearing two branches which diverge equally
+from it.  One of the branches (B) has a scale at its base; it is always,
+as far as I have seen, longer than the other and often bifurcates.  The
+branches when rubbed become curved, and subsequently straighten
+themselves.  After a tendril has clasped any object with its extremity,
+it contracts spirally; but this does not occur (Palm, p. 56) when no
+object has been seized.  The tendrils move spontaneously from side to
+side; and on a very hot day, one made two elliptical revolutions, at an
+average rate of 2 hrs. 15 m.  During these movements a coloured line,
+painted along the convex surface, appeared after a time on one side, then
+on the concave side, then on the opposite side, and lastly again on the
+convex side.  The two branches of the same tendril have independent
+movements.  After a tendril has spontaneously revolved for a time, it
+bends from the light towards the dark: I do not state this on my own
+authority, but on that of Mohl and Dutrochet.  Mohl (p. 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 revolve spontaneously; but the movement is unusually
+slight.  A shoot faced a window, and I traced its course on the glass
+during two perfectly calm and hot days.  On one of these days it
+described, in the course of ten hours, a spire, representing two and a
+half ellipses.  I also placed a bell-glass over a young Muscat grape in
+the hot-house, and it made each day three or four very small oval
+revolutions; the shoot moving less than half an inch from side to side.
+Had it not made at least three revolutions whilst the sky was uniformly
+overcast, I should have attributed this slight degree of movement to the
+varying action of the light.  The extremity of the stem is more or less
+bent downwards, but it never reverses its curvature, as so generally
+occurs with twining plants.
+
+ [Picture: Fig. 10.  Flower-stalk of the Vine.  A.  Common Peduncle.  B.
+ Flower-tendril.  C.  Sub-Peduncle, bearing the flower-buds.  D.  Petiole
+                          of the opposite leaf]
+
+Various authors (Palm, p. 55; Mohl, p. 45; Lindley, &c.) believe that the
+tendrils of the vine are modified flower-peduncles.  I here give a
+drawing (fig. 10) of the ordinary state of a young flower-stalk: 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 moves spontaneously, like a true
+tendril, but in a less degree; the movement, however, is greater 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
+of a true tendril.  The flower-tendril (B) is always longer than the
+sub-peduncle (C) and has a scale at its base; it sometimes 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.  When
+rubbed, it curves and subsequently straightens itself; and it can, as is
+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 slightly
+sensitive to a rub, and I have seen it 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 corresponding branch of an ordinary tendril,
+is well shown when it bears only a few flowers; for in this case it
+becomes less branched, increases in length, and gains both in
+sensitiveness and in the power of spontaneous movement.  I have twice
+seen sub-peduncles which bore from thirty to forty flower-buds, and which
+had become considerably elongated and were completely wound round sticks,
+exactly like true tendrils.  The whole length of another sub-peduncle,
+bearing only eleven flower-buds, quickly became curved when slightly
+rubbed; but even this scanty number of flowers rendered the stalk less
+sensitive than the other branch, that is, the flower-tendril; for the
+latter after a lighter rub became curved more quickly and in a greater
+degree.  I have seen a sub-peduncle thickly covered with flower-buds,
+with one of its 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 adjoining twig; in fact, it formed a
+little sub-tendril.  The increasing length of the sub-peduncle (C) with
+the decreasing number of the flower-buds is a good instance of the law of
+compensation.  In accordance with this same principle, the true tendril
+as a whole is always longer than the flower-stalk; for instance, on the
+same plant, the longest flower-stalk (measured from the base of the
+common peduncle to the tip of the flower-tendril) was 8½ inches in
+length, whilst the longest tendril was nearly double this length, namely
+16 inches.
+
+The gradations from the ordinary state of a flower-stalk, as represented
+in the drawing (fig. 10), to that of a true tendril (fig. 9) are
+complete.  We have seen that the sub-peduncle (C), whilst still bearing
+from thirty to forty flower-buds, sometimes becomes a little elongated
+and partially assumes all the characters of the corresponding branch of a
+true tendril.  From this state we can trace every stage till we come to a
+full-sized perfect 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.  Flower-tendrils (B, fig.
+10) sometimes produce a few flower-buds.  For instance, on a vine growing
+against my house, there were thirteen and twenty-two flower-buds
+respectively on two flower-tendrils, which still retained their
+characteristic qualities of sensitiveness and spontaneous movement, but
+in a somewhat lessened degree.  On vines in hothouses, so many flowers
+are occasionally produced on 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-stalks closely resemble in structure
+those borne by _Cissus_.  This genus, belonging to the same family of the
+Vitaceæ, produces well-developed tendrils and ordinary bunches of
+flowers; but there are no gradations between the two states.  If the
+genus _Vitis_ had been unknown, the boldest believer in the modification
+of species would never 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 such a case; and it seems to me as striking and curious an instance of
+transition as can well be conceived.
+
+_Cissus discolor_.—The young shoots show no more movement than can be
+accounted for by daily variations in the action of the light.  The
+tendrils, however, revolve with much regularity, following the sun; and,
+in the plants observed by me, swept circles of about 5 inches in
+diameter.  Five circles were completed in the following times:—4 hrs. 45
+m., 4 hrs. 50 m., 4 hrs. 45 m., 4 hrs. 30 m., and 5 hrs. The same tendril
+continues to revolve during three or four days.  The tendrils are from 3½
+to 5 inches in length.  They are formed of a long foot-stalk, bearing two
+short branches, which in old plants again bifurcate.  The two branches
+are not of quite equal length; and as with the vine, the longer one has a
+scale at its base.  The tendril stands vertically upwards; the extremity
+of the shoot being bent abruptly downwards, and this position is probably
+of service to the plant by allowing the tendril to revolve freely and
+vertically.
+
+Both branches of the tendril, whilst young, are highly sensitive.  A
+touch with a pencil, so gentle as only just to move a tendril borne at
+the end of a long flexible shoot, sufficed to cause it to become
+perceptibly curved in four or five minutes.  It became straight again in
+rather above one hour.  A loop of soft thread weighing one-seventh of a
+grain (9.25 mg.) was thrice tried, and each time caused the tendril to
+become curved in 30 or 40 m.  Half this weight produced no effect.  The
+long foot-stalk is much less sensitive, for a slight rubbing produced no
+effect, although prolonged contact with a stick caused it to bend.  The
+two branches are sensitive on all sides, so that they converge if touched
+on their inner sides, and diverge if touched on their outer sides.  If a
+branch be touched at the same time with equal force on opposite sides,
+both sides are equally stimulated and there is no movement.  Before
+examining this plant, I had observed only tendrils which are sensitive on
+one side alone, and these when lightly pressed between the finger and
+thumb become curved; but on thus pinching many times the tendrils of the
+_Cissus_ no curvature ensued, and I falsely inferred at first that they
+were not at all sensitive.
+
+_Cissus antarcticus_.—The tendrils on a young plant were thick and
+straight, with the tips a little curved.  When their concave surfaces
+were rubbed, and it was necessary to do this with some force, they very
+slowly became curved, and subsequently straight again.  They are
+therefore much less sensitive than those of the last species; but they
+made two revolutions, following the sun, rather more rapidly, viz., in 3
+hrs. 30 m. and 4 hrs. The internodes do not revolve.
+
+_Ampelopsis hederacea_ (_Virginian Creeper_).—The internodes apparently
+do not move more than can be accounted for by the varying action of the
+light.  The tendrils are from 4 to 5 inches in length, with the main stem
+sending off several lateral branches, which have their tips curved, as
+may be seen in the upper figure (fig. 11).  They exhibit no true
+spontaneous revolving movement, but turn, as was long ago observed by
+Andrew Knight, {145} from the light to the dark.  I have seen several
+tendrils move in less than 24 hours, through an angle of 180° to the dark
+side of a case in which a plant was placed, but the movement is sometimes
+much slower.  The several lateral branches often move independently of
+one another, and sometimes irregularly, without any apparent cause.
+These tendrils are less sensitive to a touch than any others observed by
+me.  By gentle but repeated rubbing with a twig, the lateral branches,
+but not the main stem, became in the course of three or four hours
+slightly curved; but they seemed to have hardly any power of again
+straightening themselves.  The tendrils of a plant which had crawled over
+a large box-tree clasped several of the branches; but I have repeatedly
+seen that they will withdraw themselves after seizing a stick.  When they
+meet with a flat surface of wood or a wall (and this is evidently what
+they are adapted for), they turn all their branches towards it, and,
+spreading them widely apart, bring their hooked tips laterally into
+contact with it.  In effecting this, the several branches, after touching
+the surface, often rise up, place themselves in a new position, and again
+come down into contact with it.
+
+In the course of about two days after a tendril has arranged its branches
+so as to press on any surface, the curved tips swell, become bright red,
+and form on their under-sides the well-known little discs or cushions
+with which they adhere firmly.  In one case the tips were slightly
+swollen in 38 hrs. after coming into contact with a brick; in another
+case they were considerably swollen in 48 hrs., and in an additional 24
+hrs. were firmly attached to a smooth board; and lastly, the tips of a
+younger tendril not only swelled but became attached to a stuccoed wall
+in 42 hrs.  These adhesive discs resemble, except in colour and in being
+larger, those of _Bignonia capreolata_.  When they were developed in
+contact with a ball of tow, the fibres were separately enveloped, but not
+in so effective a manner as by _B. capreolata_.  Discs are never
+developed, as far as I have seen, without the stimulus of at least
+temporary contact with some object. {146}  They are generally first
+formed on one side of the curved tip, the whole of which often becomes so
+much changed in appearance, that a line of the original green tissue can
+be traced only along the concave surface.  When, however, a tendril has
+clasped a cylindrical stick, an irregular rim or disc is sometimes formed
+along the inner surface at some little distance from the curved tip; this
+was also observed (p. 71) by Mohl.  The discs consist of enlarged cells,
+with smooth projecting hemispherical surfaces, coloured red; they are at
+first gorged with fluid (see section given by Mohl, p. 70), but
+ultimately become woody.
+
+As the discs soon adhere firmly to such smooth surfaces as planed or
+painted wood, or to the polished leaf of the ivy, this alone renders it
+probable that some cement is secreted, as has been asserted to be the
+case (quoted by Mohl, p. 71) by Malpighi.  I removed a number of discs
+formed during the previous year from a stuccoed wall, and left them
+during many hours, in warm water, diluted acetic acid and alcohol; but
+the attached grains of silex were not loosened.  Immersion in sulphuric
+ether for 24 hrs. loosened them much, but warmed essential oils (I tried
+oil of thyme and peppermint) completely released every particle of stone
+in the course of a few hours.  This seems to prove that some resinous
+cement is secreted.  The quantity, however, must be small; for when a
+plant ascended a thinly whitewashed wall, the discs adhered firmly to the
+whitewash; but as the cement never penetrated the thin layer, they were
+easily withdrawn, together with little scales of the whitewash.  It must
+not be supposed that the attachment is effected exclusively by the
+cement; for the cellular outgrowth completely envelopes every minute and
+irregular projection, and insinuates itself into every crevice.
+
+ [Picture: Fig. 11.  Ampelopsis hederacea.  A.  Tendril fully developed,
+ with a young leaf on the opposite side of the stem.  B.  Older tendril,
+several weeks after its attachment to a wall, with the branches thickened
+ and spirally contracted, and with the extremities developed into discs.
+  The unattached branches of this tendril have withered and dropped off]
+
+A tendril which has not become attached to any body, does not contract
+spirally; and in course of a week or two shrinks into the finest thread,
+withers and drops off.  An attached tendril, on the other hand, contracts
+spirally, and thus becomes highly elastic, so that when the main
+foot-stalk is pulled the strain is distributed equally between all the
+attached discs.  For a few days after the attachment of the discs, the
+tendril remains weak and brittle, but it rapidly increases in thickness
+and acquires great strength.  During the following winter it ceases to
+live, but adheres firmly in a dead state both to its own stem and to the
+surface of attachment.  In the accompanying diagram (fig. 11.) we see the
+difference between a tendril (B) some weeks after its attachment to a
+wall, with one (A) from the same plant fully grown but unattached.  That
+the change in the nature of the tissues, as well as the spiral
+contraction, are consequent on the formation of the discs, is well shown
+by any lateral branches which have not become attached; for these in a
+week or two wither and drop off, in the same manner as does the whole
+tendril if unattached.  The gain in strength and durability in a tendril
+after its attachment is something wonderful.  There are tendrils now
+adhering to my house which are still strong, and have been exposed to the
+weather in a dead state for fourteen or fifteen years.  One single
+lateral branchlet of a tendril, estimated to be at least ten years old,
+was still elastic and supported a weight of exactly two pounds.  The
+whole tendril had five disc-bearing branches of equal thickness and
+apparently of equal strength; so that after having been exposed during
+ten years to the weather, it would probably have resisted a strain of ten
+pounds!
+
+SAPINDACEÆ.—_Cardiospermum halicacabum_.—In this family, as in the last,
+the tendrils are modified flower-peduncles.  In the present plant the two
+lateral branches of the main flower-peduncle have been converted into a
+pair of tendrils, corresponding with the single “flower-tendril” of the
+common vine.  The main peduncle is thin, stiff, and from 3 to 4½ inches
+in length.  Near the summit, above two little bracts, it divides into
+three branches.  The middle one divides and re-divides, and bears the
+flowers; ultimately it grows half as long again as the two other modified
+branches.  These latter are the tendrils; they are at first thicker and
+longer than the middle branch, but never become more than an inch in
+length.  They taper to a point and are flattened, with the lower clasping
+surface destitute of hairs.  At first they project straight up; but soon
+diverging, spontaneously curl downwards so as to become symmetrically and
+elegantly hooked, as represented in the diagram.  They are now, whilst
+the flower-buds are still small, ready for action.
+
+    [Picture: Fig. 12.  Cardiospermum halicacabum.  Upper part of the
+                  flower-peduncle with its two tendrils]
+
+The two or three upper internodes, whilst young, steadily revolve; those
+on one plant made two circles, against the course of the sun, in 3 hrs.
+12 m.; in a second plant the same course was followed, and the two
+circles were completed in 3 hrs. 41 m.; in a third plant, the internodes
+followed the sun and made two circles in 3 hrs. 47 m.  The average rate
+of these six revolutions was 1 hr. 46 m.  The stem shows no tendency to
+twine spirally round a support; but the allied tendril-bearing genus
+_Paullinia_ is said (Mohl, p. 4) to be a twiner.  The flower-peduncles,
+which stand up above the end of the shoot, are carried round and round by
+the revolving movement of the internodes; and when the stem is securely
+tied, the long and thin flower-peduncles themselves are seen to be in
+continued and sometimes rapid movement from side to side.  They sweep a
+wide space, but only occasionally revolve in a regular elliptical course.
+By the combined movements of the internodes and peduncles, one of the two
+short hooked tendrils, sooner or later, catches hold of some twig or
+branch, and then it curls round and securely grasps it.  These tendrils
+are, however, but slightly sensitive; for by rubbing their under surface
+only a slight movement is slowly produced.  I hooked a tendril on to a
+twig; and in 1 hr. 45 m. it was curved considerably inwards; in 2 hrs. 30
+m. it formed a ring; and in from 5 to 6 hours from being first hooked, it
+closely grasped the stick.  A second tendril acted at nearly the same
+rate; but I observed one that took 24 hours before it curled twice round
+a thin twig.  Tendrils which have caught nothing, spontaneously curl up
+to a close helix after the interval of several days.  Those which have
+curled round some object, soon become a little thicker and tougher.  The
+long and thin main peduncle, though spontaneously moving, is not
+sensitive and never clasps a support.  Nor does it ever contract
+spirally, {152} although a contraction of this kind apparently would have
+been of service to the plant in climbing.  Nevertheless it climbs pretty
+well without this aid.  The seed-capsules though light, are of enormous
+size (hence its English name of balloon-vine), and as two or three are
+carried on the same peduncle, the tendrils rising close to them may be of
+service in preventing their being dashed to pieces by the wind.  In the
+hothouse the tendrils served simply for climbing.
+
+The position of the tendrils alone suffices to show their homological
+nature.  In two instances one of two tendrils produced a flower at its
+tip; this, however, did not prevent its acting properly and curling round
+a twig.  In a third case both lateral branches which ought to have been
+modified into tendrils, produced flowers like the central branch, and had
+quite lost their tendril-structure.
+
+I have seen, but was not enabled carefully to observe, only one other
+climbing Sapindaceous plant, namely, _Paullinia_.  It was not in flower,
+yet bore long forked tendrils.  So that, _Paullinia_, with respect to its
+tendrils, appears to bear the same relation to _Cardiospermum_ that
+_Cissus_ does to _Vitis_.
+
+PASSIFLORACEÆ.—After reading the discussion and facts given by Mohl (p.
+47) on the nature of the tendrils in this family, no one can doubt that
+they are modified flower-peduncles.  The tendrils and the
+flower-peduncles rise close side by side; and my son, William E. Darwin,
+made sketches for me of their earliest state of development in the hybrid
+_P. floribunda_.  The two organs appear at first as a single papilla
+which gradually divides; so that the tendril appears to be a modified
+branch of the flower-peduncle.  My son found one very young tendril
+surmounted by traces of floral organs, exactly like those on the summit
+of the true flower-peduncle at the same early age.
+
+_Passiflora gracilis_.—This well-named, elegant, annual species differs
+from the other members of the group observed by me, in the young
+internodes having the power of revolving.  It exceeds all the other
+climbing plants which I have examined, in the rapidity of its movements,
+and all tendril-bearers in the sensitiveness of the tendrils.  The
+internode which carries the upper active tendril and which likewise
+carries one or two younger immature internodes, made three revolutions,
+following the sun, at an average rate of 1 hr. 4 m.; it then made, the
+day becoming very hot, three other revolutions at an average rate of
+between 57 and 58 m.; so that the average of all six revolutions was 1
+hr. 1 m.  The apex of the tendril describes elongated ellipses, sometimes
+narrow and sometimes broad, with their longer axes inclined in slightly
+different directions.  The plant can ascend a thin upright stick by the
+aid of its tendrils; but the stem is too stiff for it to twine spirally
+round it, even when not interfered with by the tendrils, these having
+been successively pinched off at an early age.
+
+When the stem is secured, the tendrils are seen to revolve in nearly the
+same manner and at the same rate as the internodes. {154}  The tendrils
+are very thin, delicate, and straight, with the exception of the tips,
+which are a little curved; they are from 7 to 9 inches in length.  A
+half-grown tendril is not sensitive; but when nearly full-grown they are
+extremely sensitive.  A single delicate touch on the concave surface of
+the tip soon caused one to curve; and in 2 minutes it formed an open
+helix.  A loop of soft thread weighing one thirty-second of a grain (2.02
+mg.) placed most gently on the tip, thrice caused distinct curvature.  A
+bent bit of thin platina wire weighing only fiftieth of a grain (1.23
+mg.) twice produced the same effect; but this latter weight, when left
+suspended, did not suffice to cause a permanent curvature.  These trials
+were made under a bell-glass, so that the loops of thread and wire were
+not agitated by the wind.  The movement after a touch is very rapid: I
+took hold of the lower part of several tendrils, and then touched their
+concave tips with a thin twig and watched them carefully through a lens;
+the tips evidently began to bend after the following intervals—31, 25,
+32, 31, 28, 39, 31, and 30 seconds; so that the movement was generally
+perceptible in half a minute after a touch; but on one occasion it was
+distinctly visible in 25 seconds.  One of the tendrils which thus became
+bent in 31 seconds, had been touched two hours previously and had coiled
+into a helix; so that in this interval it had straightened itself and had
+perfectly recovered its irritability.
+
+To ascertain how often the same tendril would become curved when touched,
+I kept a plant in my study, which from being cooler than the hot-house
+was not very favourable for the experiment.  The extremity was gently
+rubbed four or five times with a thin stick, and this was done as often
+as it was observed to have become nearly straight again after having been
+in action; and in the course of 54 hrs. it answered to the stimulus 21
+times, becoming each time hooked or spiral.  On the last occasion,
+however, the movement was very slight, and soon afterwards permanent
+spiral contraction commenced.  No trials were made during the night, so
+that the tendril would perhaps have answered a greater number of times to
+the stimulus; though, on the other hand, from having no rest it might
+have become exhausted from so many quickly repeated efforts.
+
+I repeated the experiment made on the _Echinocystis_, and placed several
+plants of this _Passiflora_ so close together, that their tendrils were
+repeatedly dragged over each other; but no curvature ensued.  I likewise
+repeatedly flirted small drops of water from a brush on many tendrils,
+and syringed others so violently that the whole tendril was dashed about,
+but they never became curved.  The impact from the drops of water was
+felt far more distinctly on my hand than that from the loops of thread
+(weighing one thirty-second of a grain) when allowed to fall on it from a
+height, and these loops, which caused the tendrils to become curved, had
+been placed most gently on them.  Hence it is clear, that the tendrils
+either have become habituated to the touch of other tendrils and drops of
+rain, or that they were from the first rendered sensitive only to
+prolonged though excessively slight pressure of solid objects, with the
+exclusion of that from other tendrils.  To show the difference in the
+kind of sensitiveness in different plants and likewise to show the force
+of the syringe used, I may add that the lightest jet from it instantly
+caused the leaves of a _Mimosa_ to close; whereas the loop of thread
+weighing one thirty-second of a grain, when rolled into a ball and placed
+gently on the glands at the bases of the leaflets of the _Mimosa_, caused
+no action.
+
+_Passiflora punctata_.—The internodes do not move, but the tendrils
+revolve regularly.  A half-grown and very sensitive tendril made three
+revolutions, opposed to the course of the sun, in 3 hrs. 5 m., 2 hrs. 40
+m. and 2 hrs. 50 m.; perhaps it might have travelled more quickly when
+nearly full-grown.  A plant was placed in front of a window, and, as with
+twining stems, the light accelerated the movement of the tendril in one
+direction and retarded it in the other; the semicircle towards the light
+being performed in one instance in 15 m. less time and in a second
+instance in 20 m. less time than that required by the semicircle towards
+the dark end of the room.  Considering the extreme tenuity of these
+tendrils, the action of the light on them is remarkable.  The tendrils
+are long, and, as just stated, very thin, with the tip slightly curved or
+hooked.  The concave side is extremely sensitive to a touch—even a single
+touch causing it to curl inwards; it subsequently straightened itself,
+and was again ready to act.  A loop of soft thread weighing one
+fourteenth of a grain (4.625 mg.) caused the extreme tip to bend; another
+time I tried to hang the same little loop on an inclined tendril, but
+three times it slid off; yet this extraordinarily slight degree of
+friction sufficed to make the tip curl.  The tendril, though so
+sensitive, does not move very quickly after a touch, no conspicuous
+movement being observable until 5 or 10 m. had elapsed.  The convex side
+of the tip is not sensitive to a touch or to a suspended loop of thread.
+On one occasion I observed a tendril revolving with the convex side of
+the tip forwards, and in consequence it was not able to clasp a stick,
+against which it scraped; whereas tendrils revolving with the concave
+side forward, promptly seize any object in their path.
+
+_Passiflora quadrangularis_.—This is a very distinct species.  The
+tendrils are thick, long, and stiff; they are sensitive to a touch only
+on the concave surface towards the extremity.  When a stick was placed so
+that the middle of the tendril came into contact with it, no curvature
+ensued.  In the hothouse a tendril made two revolutions, each in 2 hrs.
+22 m.; in a cool room one was completed in 3 hrs., and a second in 4 hrs.
+The internodes do not revolve; nor do those of the hybrid _P.
+floribunda_.
+
+_Tacsonia manicata_.—Here again the internodes do not revolve.  The
+tendrils are moderately thin and long; one made a narrow ellipse in 5
+hrs. 20 m., and the next day a broad ellipse in 5 hrs. 7 m.  The
+extremity being lightly rubbed on the concave surface, became just
+perceptibly curved in 7 m., distinctly in 10 m., and hooked in 20 m.
+
+We have seen that the tendrils in the last three families, namely, the
+Vitaceæ, Sapindaceæ and Passifloraceæ, are modified flower-peduncles.
+This is likewise the case, according to De Candolle (as quoted by Mohl),
+with the tendrils of _Brunnichia_, one of the Polygonaceæ.  In two or
+three species of _Modecca_, one of the Papayaceæ, the tendrils, as I hear
+from Prof. Oliver, occasionally bear flowers and fruit; so that they are
+axial in their nature.
+
+
+_The Spiral Contraction of Tendrils_.
+
+
+This movement, which shortens the tendrils and renders them elastic,
+commences in half a day, or in a day or two after their extremities have
+caught some object.  There is no such movement in any leaf-climber, with
+the exception of an occasional trace of it in the petioles of _Tropæolum
+tricolorum_.  On the other hand, the tendrils of all tendril-bearing
+plants, contract spirally after they have caught an object with the
+following exceptions.  Firstly, _Corydalis claviculata_, but then this
+plant might be called a leaf-climber.  Secondly and thirdly, _Bignonia
+unguis_ with its close allies, and _Cardiospermum_; but their tendrils
+are so short that their contraction could hardly occur, and would be
+quite superfluous.  Fourthly, _Smilaæ aspera_ offers a more marked
+exception, as its tendrils are moderately long.  The tendrils of
+_Dicentra_, whilst the plant is young, are short and after attachment
+only become slightly flexuous; in older plants they are longer and then
+they contract spirally.  I have seen no other exceptions to the rule that
+tendrils, after clasping with their extremities a support, undergo spiral
+contraction.  When, however, the tendril of a plant of which the stem is
+immovably fixed, catches some fixed object, it does not contract, simply
+because it cannot; this, however, rarely occurs.  In the common Pea the
+lateral branches alone contract, and not the central stem; and with most
+plants, such as the Vine, Passiflora, Bryony, the basal portion never
+forms a spire.
+
+I have said that in _Corydalis claviculata_ the end of the leaf or
+tendril (for this part may be indifferently so called) does not contract
+into a spire.  The branchlets, however, after they have wound round thin
+twigs, become deeply sinuous or zigzag.  Moreover the whole end of the
+petiole or tendril, if it seizes nothing, bends after a time abruptly
+downwards and inwards, showing that its outer surface has gone on growing
+after the inner surface has ceased to grow.  That growth is the chief
+cause of the spiral contraction of tendrils may be safely admitted, as
+shown by the recent researches of H. de Vries.  I will, however, add one
+little fact in support of this conclusion.
+
+If the short, nearly straight portion of an attached tendril of
+_Passiflora gracilis_, (and, as I believe, of other tendrils,) between
+the opposed spires, be examined, it will be found to be transversely
+wrinkled in a conspicuous manner on the outside; and this would naturally
+follow if the outer side had grown more than the inner side, this part
+being at the same time forcibly prevented from becoming curved.  So again
+the whole outer surface of a spirally wound tendril becomes wrinkled if
+it be pulled straight.  Nevertheless, as the contraction travels from the
+extremity of a tendril, after it has been stimulated by contact with a
+support, down to the base, I cannot avoid doubting, from reasons
+presently to be given, whether the whole effect ought to be attributed to
+growth.  An unattached tendril rolls itself up into a flat helix, as in
+the case of Cardiospermum, if the contraction commences at the extremity
+and is quite regular; but if the continued growth of the outer surface is
+a little lateral, or if the process begins near the base, the terminal
+portion cannot be rolled up within the basal portion, and the tendril
+then forms a more or less open spire.  A similar result follows if the
+extremity has caught some object, and is thus held fast.
+
+The tendrils of many kinds of plants, if they catch nothing, contract
+after an interval of several days or weeks into a spire; but in these
+cases the movement takes place after the tendril has lost its revolving
+power and hangs down; it has also then partly or wholly lost its
+sensibility; so that this movement can be of no use.  The spiral
+contraction of unattached tendrils is a much slower process than that of
+attached ones.  Young tendrils which have caught a support and are
+spirally contracted, may constantly be seen on the same stem with the
+much older unattached and uncontracted tendrils.  In the _Echinocystis_ I
+have seen a tendril with the two lateral branches encircling twigs and
+contracted into beautiful spires, whilst the main branch which had caught
+nothing remained for many days straight.  In this plant I once observed a
+main branch after it had caught a stick become spirally flexuous in 7
+hrs., and spirally contracted in 18 hrs.  Generally the tendrils of the
+_Echinocystis_ begin to contract in from 12 hrs. to 24 hrs. after
+catching some object; whilst unattached tendrils do not begin to contract
+until two or three or even more days after all revolving movement has
+ceased.  A full-grown tendril of _Passiflora quadrangularis_ which had
+caught a stick began in 8 hrs. to contract, and in 24 hrs. formed several
+spires; a younger tendril, only two-thirds grown, showed the first trace
+of contraction in two days after clasping a stick, and in two more days
+formed several spires.  It appears, therefore, that the contraction does
+not begin until the tendril 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 formed one complete
+spire.  This first spire was formed towards the basal end, and the
+contraction steadily but slowly progressed towards the apex; but the
+whole was not closely wound up into a spire until 21 days had elapsed
+from the first observation, that is, until 17 days after the tendril had
+grown to its full length.
+
+The spiral contraction of tendrils is quite independent of their power of
+spontaneously revolving, for it occurs in tendrils, such as those of
+_Lathyrus grandiflorus_ and _Ampelopsis hederacea_, which do not revolve.
+It is not necessarily related to the curling of the tips round a support,
+as we see with the Ampelopsis and _Bignonia capreolata_, in which the
+development of adherent discs suffices to cause spiral contraction.  Yet
+in some cases this contraction seems connected with the curling or
+clasping movement, due to contact with a support; for not only does it
+soon follow this act, but the contraction generally begins close to the
+curled extremity, and travels downwards to the base.  If, however, a
+tendril be very slack, the whole length almost simultaneously becomes at
+first flexuous and then spiral.  Again, the tendrils of some few plants
+never contract spirally unless they have first seized hold of some
+object; if they catch nothing they hang down, remaining straight, until
+they wither and drop off: this is the case with the tendrils of Bignonia,
+which consist of modified leaves, and with those of three genera of the
+Vitaceæ, which are modified flower-peduncles.  But in the great majority
+of cases, tendrils which have never come in contact with any object,
+after a time contract spirally.  All these facts taken together, show
+that the act of clasping a support and the spiral contraction of the
+whole length of the tendril, are phenomena not necessarily connected.
+
+The spiral contraction which ensues after a tendril has caught a support
+is of high service to the plant; hence its almost universal occurrence
+with species belonging to 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 stem, after the tendrils have seized some object above, would leave
+it slack, were it not for the spiral contraction which draws up the stem
+as it increases in length.  Thus there is no waste of growth, and the
+stretched stem ascends by the shortest course.  When a terminal branchlet
+of the tendril of Cobæa catches a stick, we have seen how well the spiral
+contraction successively brings the other branchlets, one after the
+other, into contact with the stick, until the whole tendril grasps it in
+an inextricable knot.  When a tendril has caught a yielding object, this
+is sometimes enveloped and still further secured by the spiral folds, as
+I have seen with _Passiflora quadrangularis_; but this action is of
+little importance.
+
+A far more important service rendered by the spiral contraction of the
+tendrils is that they are thus made highly elastic.  As before remarked
+under Ampelopsis, the strain is thus distributed equally between the
+several attached branches; and this renders the whole far stronger than
+it otherwise would be, as the branches cannot break separately.  It is
+this elasticity which protects both branched and simple tendrils from
+being torn away from their supports 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 thick and thin branches were tossed to and fro by the wind, the
+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.
+
+When an unattached 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, although the same side is concave
+from end to end, invariably becomes twisted in one part in one direction,
+and in another part in the opposite direction; the oppositely turned
+spires being separated by a short straight portion.  This curious and
+symmetrical structure has been noticed by several botanists, but has not
+been sufficiently explained. {165}  It occurs without exception with all
+tendrils which after catching an 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 occurred, it will be
+found that the tendril had originally seized some object and had
+afterwards been torn free.  Commonly, all the spires at one end of an
+attached 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 pieces between them; and
+M. Léon has seen seven or eight such alternations.  Whether the spires
+turn once or more than once in opposite directions, there are as many
+turns in the one direction as in the other.  For instance, I gathered ten
+attached tendrils of the Bryony, the longest with 33, and the shortest
+with only 8 spiral turns; and the number of turns in the one direction
+was in every case the same (within one) as in the opposite direction.
+
+     [Picture: Fig. 13.  A caught tendril of Bryonia dioica, spirally
+                    contracted in reserved directions]
+
+The explanation of this curious little fact is not difficult.  I will not
+attempt any geometrical reasoning, but will give only a practical
+illustration.  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, thus imitating the revolving movement of a
+twining plant, and the strings do not become twisted.  But if we hold at
+the same time a stick in our left hand, in such a position that the
+strings become 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 wound round.  I painted a red line on the straight
+internodes of a _Humulus_, _Mikania_, _Ceropegia_, _Convolvulus_, and
+_Phaseolus_, and saw it become twisted as the plant wound round a stick.
+It is possible that the stems of some plants by spontaneously turning on
+their own axes, at the proper rate and in the proper direction, might
+avoid becoming twisted; but I have seen no such case.
+
+In the above illustration, the parallel strings were wound round a stick;
+but this is by no means necessary, for if wound into a hollow coil (as
+can be done with a narrow slip of elastic paper) there is the same
+inevitable twisting of the axis.  When, therefore, a free tendril coils
+itself into a spire, it must either become twisted along its whole length
+(and this never occurs), or the free extremity must turn round as many
+times as there are spires formed.  It was hardly necessary to observe
+this fact; but I did so by affixing little paper vanes to the extreme
+points of the tendrils of _Echinocystis_ and _Passiflora quadrangularis_;
+and as the tendril contracted itself into successive spires, the vane
+slowly revolved.
+
+We can now understand the meaning of the spires being invariably turned
+in opposite directions, in tendrils which from having caught some object
+are fixed at both ends.  Let us suppose a caught tendril to make thirty
+spiral turns all in the same direction; the inevitable result would be
+that it would become twisted thirty times on its own axis.  This twisting
+would not only require considerable force, but, as I know by trial, would
+burst the tendril before the thirty turns were completed.  Such cases
+never really occur; for, as already stated, when a tendril has caught a
+support and is spirally contracted, there are always as many turns in one
+direction as in the other; so that the twisting of the axis in the one
+direction is exactly compensated by the twisting in the opposite
+direction.  We can further see how the tendency is given to make the
+later formed coils opposite 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 perpendicular pencil,
+and this will twist the lower part of the string; and after it has been
+sufficiently twisted, it will be seen to curve itself into an open spire,
+with the curves running in an opposite direction to those round the
+pencil, and consequently with a straight piece of string between the
+opposed 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
+cannot resist giving one other illustration, though superfluous: when a
+haberdasher winds up ribbon for a customer, he does not wind it into a
+single coil; for, if he did, the ribbon would twist itself as many times
+as there were coils; but he winds it into a figure of eight on his thumb
+and little finger, so that he alternately takes turns in opposite
+directions, and thus the ribbon is not twisted.  So it is with tendrils,
+with this sole difference, that they take several consecutive turns in
+one direction and then the same number in an opposite direction; but in
+both cases the self-twisting is avoided.
+
+
+_Summary on the Nature and Action of Tendrils_.
+
+
+With the majority of tendril-bearing plants the young internodes revolve
+in more or less broad ellipses, like those made by twining plants; but
+the figures described, when carefully traced, generally form irregular
+ellipsoidal spires.  The rate of revolution varies from one to five hours
+in different species, and consequently is in some cases 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 direction is
+variable even in the same individual plant.  In _Passiflora_, the
+internodes of only one species have the power of revolving.  The Vine is
+the weakest revolver observed by me, apparently exhibiting only a trace
+of a former power.  In the _Eccremocarpus_ the movement is interrupted by
+many long pauses.  Very few tendril-bearing plants can spirally twine up
+an upright stick.  Although the power of twining has generally been lost,
+either from the stiffness or shortness of the internodes, from the size
+of the leaves, or from some other unknown cause, the revolving movement
+of the stem serves to bring the tendrils into contact with surrounding
+objects.
+
+The tendrils themselves also spontaneously revolve.  The movement begins
+whilst the tendril is young, and is at first slow.  The mature tendrils
+of _Bignonia littoralis_ move much slower than the internodes.
+Generally, the internodes and tendrils revolve together at the same rate;
+in Cissus, Cobæa, and most Passifloræ, the tendrils alone revolve; in
+other cases, as with _Lathyrus aphaca_, only the internodes move,
+carrying with them the motionless tendrils; and, lastly (and this is the
+fourth possible case), neither internodes nor tendrils spontaneously
+revolve, as with _Lathyrus grandiflorus_ and _Ampelopsis_.  In most
+Bignonias, Eccremocarpus Mutisia, and the Fumariaceæ, the internodes,
+petioles and tendrils all move harmoniously together.  In every case the
+conditions of life must be favourable in order that the different parts
+should act in a perfect manner.
+
+Tendrils revolve by the curvature of their whole length, excepting the
+sensitive extremity and the base, which parts do not move, or move but
+little.  The movement is of the same nature as that of the revolving
+internodes, and, from the observations of Sachs and H. de Vries, no doubt
+is due to the same cause, namely, the rapid growth of a longitudinal
+band, which travels round the tendril and successively bows each part to
+the opposite side.  Hence, if a line be painted along that surface which
+happens at the time to be convex, the line becomes first lateral, then
+concave, then lateral, and ultimately again convex.  This experiment can
+be tried only on the thicker tendrils, which are not affected by a thin
+crust of dried paint.  The extremities are often slightly curved or
+hooked, and the curvature of this part is never reversed; in this respect
+they differ from the extremities of twining shoots, which not only
+reverse their curvature, or at least become periodically straight, but
+curve themselves in a greater degree than the lower part.  In most other
+respects a tendril acts as if it were one of several revolving
+internodes, which all move together by successively bending to each point
+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.  With most tendril-bearers the summit of
+the stem or shoot projects above the point from which the tendril arises;
+and it is generally bent to 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, as we have seen with the
+Echinocystis, as soon as the tendril comes in its revolving course to
+this point, it stiffens and straightens itself, and thus rising
+vertically up passes over the obstacle in an admirable manner.
+
+All tendrils are sensitive, but in various degrees, to contact with an
+object, and curve towards the touched side.  With several plants a single
+touch, so slight as only just to move the highly flexible tendril, is
+enough to induce curvature.  _Passiflora gracilis_ possesses the most
+sensitive tendrils which I have observed: a bit of platina wire 0.02 of a
+grain (1.23 mg.) in weight, gently placed on the concave point, caused a
+tendril to become hooked, as did a loop of soft, thin cotton thread
+weighing one thirty-second of a grain (2.02 mg.)  With the tendrils of
+several other plants, loops weighing one sixteenth of a grain (4.05 mg.)
+sufficed.  The point of a tendril of _Passiflora gracilis_ began to move
+distinctly in 25 seconds after a touch, and in many cases after 30
+seconds.  Asa Gray also saw movement in the tendrils of the
+Cucurbitaceous genus, _Sicyos_, in 30 seconds.  The tendrils of some
+other plants, when lightly rubbed, moved in a few minutes; with Dicentra
+in half-an-hour; with Smilax in an hour and a quarter or half; and with
+Ampelopsis still more slowly.  The curling movement consequent on a
+single touch continues to increase for a considerable time, then ceases;
+after a few hours the tendril uncurls itself, and is again ready to act.
+When the tendrils of several kinds of plants were caused to bend by
+extremely light weights suspended on them, they seemed to grow accustomed
+to so slight a stimulus, and straightened themselves, as if the loops had
+been removed.  It makes no difference what sort of object a tendril
+touches, with the remarkable exception of other tendrils and drops of
+water, as was observed with the extremely sensitive-tendrils of
+_Passiflora gracilis_ and of the _Echinocystis_.  I have, however, seen
+tendrils of the Bryony which had temporarily caught other tendrils, and
+often in the case of the vine.
+
+Tendrils of which the extremities are permanently and slightly curved,
+are sensitive only on the concave surface; other tendrils, such as those
+of the Cobæa (though furnished with horny hooks directed to one side) and
+those of _Cissus discolor_, are sensitive on all sides.  Hence the
+tendrils of this latter plant, when stimulated by a touch of equal force
+on opposite sides, did not bend.  The inferior and lateral surfaces of
+the tendrils of _Mutisia_ are sensitive, but not the upper surface.  With
+branched tendrils, the several branches act alike; but in the _Hanburya_
+the lateral spur-like branch does not acquire (for excellent reasons
+which have been explained) its sensitiveness nearly so soon as the main
+branch.  With most tendrils the lower or basal part is either not at all
+sensitive, or sensitive only to prolonged contact.  We thus see that the
+sensitiveness of tendrils is a special and localized capacity.  It is
+quite independent of the power of spontaneously revolving; for the
+curling of the terminal portion from touch does not in the least
+interrupt the former movement.  In _Bignonia unguis_ and its close
+allies, the petioles of the leaves, as well as the tendrils, are
+sensitive to a touch.
+
+Twining plants when they come into contact with a stick, curl round it
+invariably in the direction of their revolving movement; but tendrils
+curl indifferently to either side, in accordance with the position of the
+stick and the side which is first touched.  The clasping movement of the
+extremity is apparently not steady, but undulatory or vermicular in its
+nature, as may be inferred from the curious manner in which the tendrils
+of the Echinocystis slowly crawled round a smooth stick.
+
+As with a few exceptions tendrils spontaneously revolve, it may be
+asked,—why have they been endowed with sensitiveness?—why, when they come
+into contact with a stick, do they not, like twining plants, spirally
+wind round it?  One reason may be that they are in most cases so flexible
+and thin, that when brought into contact with any object, they would
+almost certainly yield and be dragged onwards by the revolving movement.
+Moreover, the sensitive extremities have no revolving power as far as I
+have observed, and could not by this means curl round a support.  With
+twining plants, on the other hand, the extremity spontaneously bends more
+than any other part; and this is of high importance for the ascent of the
+plant, as may be seen on a windy day.  It is, however, possible that the
+slow movement of the basal and stiffer parts of certain tendrils, which
+wind round sticks placed in their path, may be analogous to that of
+twining plants.  But I hardly attended sufficiently to this point, and it
+would have been difficult to distinguish between a movement due to
+extremely dull irritability, from the arrestment of the lower part,
+whilst the upper part continued to move onwards.
+
+Tendrils which are only three-fourths grown, and perhaps even at an
+earlier age, but not whilst extremely young, have the power of revolving
+and of grasping any object which they touch.  These two capacities are
+generally acquired at about the same period, and both fail when the
+tendril is full grown.  But in _Cobæa_ and _Passiflora punctata_ the
+tendrils begin to revolve in a useless manner, before they have become
+sensitive.  In the Echinocystis they retain their sensitiveness for some
+time after they have ceased to revolve and after they have sunk
+downwards; in this position, even if they were able to seize an object,
+such power would be of no service in supporting the stem.  It is a rare
+circumstance thus to detect any superfluity or imperfection in the action
+of tendrils—organs which are so excellently adapted for the functions
+which they have to perform; but we see that they are not always 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 or retarded, in
+moving to or from the light; others, as with the Pea, seem indifferent to
+its action; others move steadily from the light to the dark, and this
+aids them in an important manner in finding a support.  For instance, the
+tendrils of _Bignonia capreolata_ bend from the light to the dark as
+truly as a wind-vane from the wind.  In the Eccremocarpus the extremities
+alone twist and turn about so as to bring their finer branches and hooks
+into close contact with any dark surface, or into crevices and holes.
+
+A short time after a tendril has caught a support, it contracts with some
+rare exceptions into a spire; but the manner of contraction and the
+several important advantages thus gained have been discussed so lately,
+that nothing need here be repeated on the subject.  Tendrils soon after
+catching a support grow much stronger and thicker, and sometimes more
+durable to a wonderful degree; and this shows how much their internal
+tissues must be changed.  Occasionally it is the part which is wound
+round a support which chiefly becomes thicker and stronger; I have seen,
+for instance, this part of a tendril of _Bignonia æquinoctialis_ twice as
+thick and rigid as the free basal part.  Tendrils which have caught
+nothing soon shrink and wither; but in some species of Bignonia they
+disarticulate and fall off like leaves in autumn.
+
+                                * * * * *
+
+Any one who had not closely observed tendrils of many kinds would
+probably infer that their action was uniform.  This is the case with the
+simpler kinds, which simply curl round an object of moderate thickness,
+whatever its nature may be. {176}  But the genus Bignonia shows us what
+diversity of action there may be between the tendrils of closely allied
+species.  In all the nine species observed by me, the young internodes
+revolve vigorously; the tendrils also revolve, but in some of the species
+in a very feeble manner; and lastly the petioles of nearly all revolve,
+though with unequal power.  The petioles of three of the species, and the
+tendrils of all are sensitive to contact.  In the first-described
+species, the tendrils resemble in shape a bird’s foot, and they are of no
+service to the stem in spirally ascending a thin upright stick, but they
+can seize firm hold of a twig or branch.  When the stem twines round a
+somewhat thick stick, a slight degree of sensitiveness possessed by the
+petioles is brought into play, and the whole leaf together with the
+tendril winds round it.  In _B. unguis_ the petioles are more sensitive,
+and have greater power of movement than those of the last species; they
+are able, together with the tendrils, to wind inextricably round a thin
+upright stick; but the stem does not twine so well.  _B. Tweedyana_ has
+similar powers, but in addition, emits aërial roots which adhere to the
+wood.  In _B. venusta_ the tendrils are converted into elongated
+three-pronged grapnels, which move spontaneously in a conspicuous manner;
+the petioles, however, have lost their sensitiveness.  The stem of this
+species can twine round an upright stick, and is aided in its ascent by
+the tendrils seizing the stick alternately some way above and then
+contracting spirally.  In _B. littoralis_ the tendrils, petioles, and
+internodes, all revolve spontaneously.  The stem, however, cannot twine,
+but ascends an upright stick by seizing it above with both tendrils
+together, which then contract into a spire.  The tips of these tendrils
+become developed into adhesive discs.  _B. speciosa_ possesses similar
+powers of movement as the last species, but it cannot twine round a
+stick, though it can ascend by clasping the stick horizontally with one
+or both of its unbranched tendrils.  These tendrils continually insert
+their pointed ends into minute crevices or holes, but as they are always
+withdrawn by the subsequent spiral contraction, the habit seems to us in
+our ignorance useless.  Lastly, the stem of _B. capreolata_ twines
+imperfectly; the much-branched tendrils revolve in a capricious manner,
+and bend from the light to the dark; their hooked extremities, even
+whilst immature, crawl into crevices, and, when mature, seize any thin
+projecting point; in either case they develop adhesive discs, and these
+have the power of enveloping the finest fibres.
+
+In the allied Eccremocarpus the internodes, petioles, and much-branched
+tendrils all spontaneously revolve together.  The tendrils do not as a
+whole turn from the light; but their bluntly-hooked extremities arrange
+themselves neatly on any surface with which they come into contact,
+apparently so as to avoid the light.  They act best when each branch
+seizes a few thin stems, like the culms of a grass, which they afterwards
+draw together into a solid bundle by the spiral contraction of all the
+branches.  In Cobæa the finely-branched tendrils alone revolve; the
+branches terminate in sharp, hard, double, little hooks, with both points
+directed to the same side; and these turn by well-adapted movements to
+any object with which they come into contact.  The tips of the branches
+also crawl into dark crevices or holes.  The tendrils and internodes of
+Ampelopsis have little or no power of revolving; the tendrils are but
+little sensitive to contact; their hooked extremities cannot seize thin
+objects; they will not even clasp a stick, unless in extreme need of a
+support; but they turn from the light to the dark, and, spreading out
+their branches in contact with any nearly flat surface, develop discs.
+These adhere by the secretion of some cement to a wall, or even to a
+polished surface; and this is more than the discs of the _Bignonia
+capreolata_ can effect.
+
+The rapid development of these adherent discs is one of the most
+remarkable peculiarities possessed by any tendrils.  We have seen that
+such discs are formed by two species of Bignonia, by Ampelopsis, and,
+according to Naudin, {179} by the Cucurbitaceous genus _Peponopsis
+adhærens_.  In Anguria 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; whilst in Hanburya a similar layer is
+adherent.  The growth of these cellular out-growths depends, (except in
+the case of the _Haplolophium_ and of one species of Ampelopsis,) on the
+stimulus from contact.  It is a singular fact that three families, so
+widely distinct as the Bignoniaceæ, Vitaceæ, and Cucurbitaceæ, should
+possess species with tendrils having this remarkable power.
+
+                                * * * * *
+
+Sachs attributes all the movements of tendrils to rapid growth on the
+side opposite to that which becomes concave.  These movements consist of
+revolving nutation, the bending to and from the light, and in opposition
+to gravity, those caused by a touch, and spiral contraction.  It is rash
+to differ from so great an authority, but I cannot believe that one at
+least of these movements—curvature from a touch—is thus caused. {180}  In
+the first place it may be remarked that the movement of nutation differs
+from that due to a touch, in so far that in some cases the two powers are
+acquired by the same tendril at different periods of growth; and the
+sensitive part of the tendril does not seem capable of nutation.  One of
+my chief reasons for doubting whether the curvature from a touch is the
+result of growth, is the extraordinary rapidity of the movement.  I have
+seen the extremity of a tendril of _Passiflora gracilis_, after being
+touched, distinctly bent in 25 seconds, and often in 30 seconds; and so
+it is with the thicker tendril of Sicyos.  It appears hardly credible
+that their outer surfaces could have actually grown in length, which
+implies a permanent modification of structure, in so short a time.  The
+growth, moreover, on this view must be considerable, for if the touch has
+been at all rough the extremity is coiled in two or three minutes into a
+spire of several turns.
+
+When the extreme tip of the tendril of Echinocystis caught hold of a
+smooth stick, it coiled itself in a few hours (as described at p. 132)
+twice or thrice round the stick, apparently by an undulatory movement.
+At first I attributed this movement to the growth of the outside; black
+marks were therefore made, and the interspaces measured, but I could not
+thus detect any increase in length.  Hence it seems probable in this case
+and in others, that the curvature of the tendril from a touch depends on
+the contraction of the cells along the concave side.  Sachs himself
+admits {181} that “if the growth which takes place in the entire tendril
+at the time of contact with a support is small, a considerable
+acceleration occurs on the convex surface, but in general there is no
+elongation on the concave surface, or there may even be a _contraction_;
+in the case of a tendril of Cucurbita this contraction amounted to nearly
+one-third of the original length.”  In a subsequent passage Sachs seems
+to feel some difficulty in accounting for this kind of contraction.  It
+must not however be supposed from the foregoing remarks that I entertain
+any doubt, after reading De Vries’ observations, about the outer and
+stretched surfaces of attached tendrils afterwards increasing in length
+by growth.  Such increase seems to me quite compatible with the first
+movement being independent of growth.  Why a delicate touch should cause
+one side of a tendril to contract we know as little as why, on the view
+held by Sachs, it should lead to extraordinarily rapid growth of the
+opposite side.  The chief or sole reason for the belief that the
+curvature of a tendril when touched is due to rapid growth, seems to be
+that tendrils lose their sensitiveness and power of movement after they
+have grown to their full length; but this fact is intelligible, if we
+bear in mind that all the functions of a tendril are adapted to drag up
+the terminal growing shoot towards the light.  Of what use would it be,
+if an old and full-grown tendril, arising from the lower part of a shoot,
+were to retain its power of clasping a support?  This would be of no use;
+and we have seen with tendrils so many instances of close adaptation and
+of the economy of means, that we may feel assured that they would acquire
+irritability and the power of clasping a support at the proper
+age—namely, youth—and would not uselessly retain such power beyond the
+proper age.
+
+
+
+CHAPTER V.
+HOOK AND ROOT-CLIMBERS.—CONCLUDING REMARKS.
+
+
+Plants climbing by the aid of hooks, or merely scrambling over other
+plants—Root-climbers, adhesive matter secreted by the rootlets—General
+conclusions with respect to climbing plants, and the stages of their
+development.
+
+_Hook-Climbers_.—In my introductory remarks, I stated that, besides the
+two first great classes of climbing plants, namely, those which twine
+round a support, and those endowed with irritability enabling them to
+seize hold of objects by means of their petioles or tendrils, there are
+two other classes, hook-climbers and root-climbers.  Many plants,
+moreover, as Fritz Müller has remarked, {183} climb or scramble up
+thickets in a still more simple fashion, without any special aid,
+excepting that their leading shoots are generally long and flexible.  It
+may, however, be suspected from what follows, that these shoots in some
+cases tend to avoid the light.  The few hook-climbers which I have
+observed, namely, _Galium aparine_, _Rubus australis_, and some climbing
+Roses, exhibit no spontaneous revolving movement.  If they had possessed
+this power, and had been capable of twining, they would have been placed
+in the class of Twiners; for some twiners are furnished with spines or
+hooks, which aid them in their ascent.  For instance, the Hop, which is a
+twiner, has reflexed hooks as large as those of the _Galium_; some other
+twiners have stiff reflexed hairs; and _Dipladenia_ has a circle of blunt
+spines at the bases of its leaves.  I have seen only one tendril-bearing
+plant, namely, _Smilax aspera_, which is furnished with reflexed spines;
+but this is the case with several branch-climbers in South Brazil and
+Ceylon; and their branches graduate into true tendrils.  Some few plants
+apparently depend solely on their hooks for climbing, and yet do so
+efficiently, as certain palms in the New and Old Worlds.  Even some
+climbing Roses will ascend the walls of a tall house, if covered with a
+trellis.  How this is effected I know not; for the young shoots of one
+such Rose, when placed in a pot in a window, bent irregularly towards the
+light during the day and from the light during the night, like the shoots
+of any common plant; so that it is not easy to understand how they could
+have got under a trellis close to the wall. {184}
+
+_Root-climbers_.—A good many plants come under this class, and are
+excellent climbers.  One of the most remarkable is the _Marcgravia
+umbellata_, the stem of 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 it puts 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 produces free branches
+with rounded stems, clad with sharp-pointed leaves, wonderfully different
+in appearance from those borne by the stem as long as it remains
+adherent.  This surprising difference in the leaves, I have also observed
+in a plant of _Marcgravia dubia_ in my hothouse.  Root-climbers, as far
+as I have seen, namely, the Ivy (_Hedera heliæ_), _Ficus repens_, and _F.
+barbatus_, have no power of movement, not even from the light to the
+dark.  As previously stated, the _Hoya carnosa_ (Asclepiadaceæ) is a
+spiral twiner, and likewise adheres by rootlets even to a flat wall.  The
+tendril-bearing _Bignonia Tweedyana_ emits roots, which curve half round
+and adhere to thin sticks.  The _Tecoma radicans_ (Bignoniaceæ), which is
+closely allied to many spontaneously revolving species, climbs by
+rootlets; nevertheless, its young shoots apparently move about more than
+can be accounted for by the varying action of the light.
+
+I have not closely observed many root-climbers, but can give one curious
+fact.  _Ficus repens_ climbs up a wall just like Ivy; and when the young
+rootlets are made to press lightly on slips of glass, they emit after
+about a week’s interval, as I observed several times, minute drops of
+clear fluid, not in the least milky like that exuded from a wound.  This
+fluid is slightly viscid, but cannot be drawn out into threads.  It has
+the remarkable property of not soon drying; a drop, about the size of
+half a pin’s head, was slightly spread out on glass, and I scattered on
+it some minute grains of sand.  The glass was left exposed in a drawer
+during hot and dry weather, and if the fluid had been water, it would
+certainly have dried in a few minutes; but it remained fluid, closely
+surrounding each grain of sand, during 128 days: how much longer it would
+have remained I cannot say.  Some other rootlets were left in contact
+with the glass for about ten days or a fortnight, and the drops of
+secreted fluid were now rather larger, and so viscid that they could be
+drawn out into threads.  Some other rootlets were left in contact during
+twenty-three days, and these were firmly cemented to the glass.  Hence we
+may conclude that the rootlets first secrete a slightly viscid fluid,
+subsequently absorb the watery parts, (for we have seen that the fluid
+will not dry by itself,) 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 very much less volatile by
+what it had dissolved.
+
+As the bisulphide of carbon has a strong power of softening indurated
+caoutchouc, I soaked in it during a short time several rootlets of a
+plant which had grown up a plaistered wall; and I then found many
+extremely thin threads of transparent, not viscid, excessively elastic
+matter, precisely like caoutchouc, attached to two sets of rootlets on
+the same branch.  These threads proceeded from the bark of the rootlet at
+one end, and at the other end were firmly attached to particles of silex
+or mortar from the wall.  There could be no mistake in this observation,
+as I played with the threads for a long time under the microscope,
+drawing them out with my dissecting-needles and letting them spring back
+again.  Yet I looked repeatedly at other rootlets similarly treated, and
+could never again discover these elastic threads.  I therefore infer that
+the branch in question must have been slightly moved from the wall at
+some critical period, whilst the secretion was in the act of drying,
+through the absorption of its watery parts.  The genus _Ficus_ abounds
+with caoutchouc, and we may conclude from the facts just given that this
+substance, at first in solution and ultimately modified into an unelastic
+cement, {187} is used by the _Ficus repens_ to cement its rootlets to any
+surface which it ascends.  Whether 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 the _Marcgravia dubia_
+can adhere firmly to smooth painted wood.
+
+_Vanilla aromatica_ emits aërial roots a foot in length, which point
+straight down to the ground.  According to Mohl (p. 49), these crawl into
+crevices, and when they meet with a thin support, wind round it, as do
+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 a
+little to that side, in the course of about a day, and adhered by their
+rootlets to the wood; but they did not bend quite round the sticks, and
+afterwards they re-pursued their downward course.  It is probable that
+these slight movements of the roots are due to the quicker growth of the
+side exposed to the light, in comparison with the other side, and not
+because the roots are sensitive to contact in the same manner as true
+tendrils.  According to Mohl, the rootlets of certain species of
+_Lycopodium_ act as tendrils. {188}
+
+
+_Concluding Remarks on Climbing Plants_.
+
+
+Plants become climbers, in order, as it may be presumed, to reach the
+light, and to expose a large surface of their leaves to its action and to
+that of the free air.  This is effected by climbers with 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 so many climbing plants in all quarters
+of the world, belonging to so many different orders.  These plants have
+been arranged under four classes, disregarding those which merely
+scramble over bushes without any special aid.  Hook-climbers are the
+least efficient of all, at least in our temperate countries, and can
+climb only in the midst of an entangled mass of vegetation.
+Root-climbers are excellently adapted to ascend naked faces of rock or
+trunks of trees; when, however, they climb trunks 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 require
+long-continued and close contact with a steady surface in order to
+adhere.  The two great classes of twiners and of plants with sensitive
+organs, namely, leaf-climbers and tendril-bearers taken together, far
+exceed in number and in the perfection of their mechanism the climbers of
+the two first classes.  Those which have the power of spontaneously
+revolving and of grasping objects with which they come in contact, easily
+pass from branch to branch, and securely ramble over a wide, sun-lit
+surface.
+
+The divisions containing twining plants, leaf-climbers, and
+tendril-bearers graduate to a certain extent into one another, and nearly
+all have the same remarkable power of spontaneously revolving.  Does this
+gradation, it may be asked, indicate that plants belonging to one
+subdivision have actually passed during the lapse of ages, or can pass,
+from one state to the other?  Has, for instance, any tendril-bearing
+plant assumed its present structure without having previously existed as
+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 exception, revolve in exactly the same manner
+as twiners; some few can still twine well, and many others in an
+imperfect manner.  Several leaf-climbing genera are closely allied to
+other genera which are simple twiners.  It should also be observed, that
+the possession of leaves with sensitive petioles, and with the consequent
+power of clasping an object, would be of comparatively little use to a
+plant, unless associated with revolving internodes, by which the leaves
+are brought into contact with a support; although no doubt a scrambling
+plant would be apt, as Professor Jaeger has remarked, to rest on other
+plants by its leaves.  On the other hand, revolving internodes, without
+any other aid, suffice to give the power of climbing; so that it seems
+probable that leaf-climbers were in most cases at first twiners, and
+subsequently became capable of grasping a support; and this, as we shall
+presently see, is a great additional advantage.
+
+From analogous reasons, it is probable that all tendril-bearers were
+primordially twiners, that is, are the descendants of plants having this
+power and habit.  For the internodes of the majority revolve; and, in a
+few species, the flexible stem still retains the capacity of spirally
+twining round an upright stick.  Tendril-bearers have undergone much more
+modification than leaf-climbers; hence it is not surprising that their
+supposed primordial habits of revolving and twining have been more
+frequently lost or modified than in the case of leaf-climbers.  The three
+great tendril-bearing families in which this loss has occurred in the
+most marked manner, are the Cucurbitaceæ, Passifloraceæ, and Vitaceæ.  In
+the first, the internodes revolve; but I have heard of no twining form,
+with the exception (according to Palm, p. 29. 52) of _Momordica
+balsamina_, and this is only an imperfect twiner.  In the two other
+families I can hear of no twiners; and the internodes rarely have the
+power of revolving, this power being confined to the tendrils.  The
+internodes, however, of _Passiflora gracilis_ have the 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 has been retained by some
+members of all the larger tendril-bearing groups.
+
+On the view here given, it may be asked, Why have the species which were
+aboriginally twiners been converted in so many groups into leaf-climbers
+or tendril-bearers?  Of what advantage has this 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 tendrils or sensitive petioles,
+as some species of Bignonia, Clematis, and Tropæolum, it can readily be
+observed how incomparably better they grasp an upright stick than do
+simple twiners.  Tendrils, from possessing this power of grasping an
+object, can be made long and thin; so that little organic matter is
+expended in their development, and yet they sweep a wide circle in search
+of a support.  Tendril-bearers can, from their first growth, ascend along
+the outer branches of any neighbouring bush, and they are thus always
+fully exposed to the light; twiners, on the contrary, are best fitted to
+ascend bare stems, and generally have to start in the shade.  Within tall
+and dense tropical forests, twining plants would probably 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 thick trunks, whereas this can be affected by
+tendril-bearers if the trunks are branched or bear twigs, and by some
+species if the bark is rugged.
+
+The advantage gained by climbing is to reach the light and free air with
+as little expenditure of organic matter as possible; now, with twining
+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, on the other hand, which had ascended to the same height by the
+aid of its tendrils, was but little longer than the height reached.  That
+this saving of the stem is really an advantage to climbing plants, I
+infer from the species that still twine but are aided by clasping
+petioles or tendrils, generally making more open spires than those made
+by simple twiners.  Moreover, the plants thus aided, after taking one or
+two turns in one direction, generally 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 have been possible; and they do this with safety, as they
+secure themselves at intervals by their clasping petioles or tendrils.
+
+We have seen that tendrils consist of various organs in a modified state,
+namely, leaves, flower-peduncles, branches, and perhaps stipules.  With
+respect to leaves, the evidence of their modification is ample.  In young
+plants of Bignonia the lower leaves often remain quite unchanged, whilst
+the upper ones have their terminal leaflets converted into perfect
+tendrils; in _Eccremocarpus_ I have seen a single lateral branch of a
+tendril replaced by a perfect leaflet; 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 kinds of tendrils; he will wish to learn, as far as is
+possible, by what actual steps leaves, flower-peduncles, &c., have had
+their functions wholly changed, and have come to serve merely as
+prehensile organs.
+
+In the whole group of leaf-climbers abundant evidence has been given that
+an organ, still subserving the functions of a leaf, may become sensitive
+to a touch, and thus grasp an adjoining object.  With several
+leaf-climbers the true leaves spontaneously revolve; and their petioles,
+after clasping a support grow thicker and stronger.  We thus see that
+leaves may acquire all the leading and characteristic qualities of
+tendrils, namely, sensitiveness, spontaneous movement, and subsequently
+increased strength.  If their blades or laminæ were to abort, they would
+form true tendrils.  And of this process of abortion we can follow every
+step, until no trace of the original nature of the tendril is left.  In
+_Mutisia clematis_, the tendril, in shape and colour, closely resembles
+the petiole of one of the ordinary leaves, together with the midribs of
+the leaflets, but vestiges of the laminæ are still occasionally retained.
+In four genera of the Fumariaceæ we can follow the whole process of
+transformation.  The terminal leaflets of the leaf-climbing _Fumaria
+officinalis_ are not smaller than the other leaflets; those of the
+leaf-climbing _Adlumia cirrhosa_ are greatly reduced; those of _Corydalis
+claviculata_ (a plant which may indifferently be called a leaf-climber or
+a tendril-bearer) are either reduced to microscopical dimensions or have
+their blades wholly aborted, so that this plant is actually in a state of
+transition; and, finally, in the _Dicentra_ the tendrils are perfectly
+characterized.  If, therefore, we could behold at the same time all the
+progenitors of _Dicentra_, we should almost certainly see a series like
+that now exhibited by the above-named three genera.  In _Tropæolum
+tricolorum_ we have another kind of passage; for the leaves which are
+first formed on the young stems are entirely destitute of laminæ, and
+must be called tendrils, whilst the later formed leaves have
+well-developed laminæ.  In all cases the acquirement of sensitiveness by
+the mid-ribs of the leaves appears to stand in some close relation with
+the abortion of their laminæ or blades.
+
+On the view here given, leaf-climbers were primordially twiners, and
+tendril-bearers (when formed of modified leaves) were primordially
+leaf-climbers.  The latter, therefore, are intermediate in nature between
+twiners and tendril-bearers, and ought to be related to both.  This is
+the case: thus the several leaf-climbing species of the Antirrhineæ, of
+Solanum, Cocculus, and Gloriosa, have within the same family and even
+within the same genus, relatives which are twiners.  In the genus
+Mikania, there are leaf-climbing and twining species.  The leaf-climbing
+species of Clematis are very closely allied to the tendril-bearing
+Naravelia.  The Fumariaceæ include closely allied genera which are
+leaf-climbers and tendril-bearers.  Lastly, a species of Bignonia is at
+the same time both a leaf-climber and a tendril-bearer; and other closely
+allied species are twiners.
+
+Tendrils of another kind consist of modified flower-peduncles.  In this
+case we likewise have many interesting transitional states.  The common
+Vine (not to mention the _Cardiospermum_) gives us every possible
+gradation between a perfectly developed tendril and a flower-peduncle
+covered with flowers, yet furnished with a branch, forming the
+flower-tendril.  When the latter itself bears a few flowers, as we know
+sometimes is the case, and still retains the power of clasping a support,
+we see an early condition of all those tendrils which have been formed by
+the modification of flower-peduncles.
+
+According to Mohl and others, some tendrils consist of modified branches:
+I have not observed any such cases, and know nothing of their
+transitional states, but these have been fully described by Fritz Müller.
+The genus Lophospermum also shows us how such a transition is possible;
+for its branches spontaneously revolve and are sensitive to contact.
+Hence, if the leaves on some of the branches of the Lophospermum were to
+abort, these branches would be converted into true tendrils.  Nor is
+there anything improbable in certain branches alone being thus modified,
+whilst others remained unaltered; for we have seen with certain varieties
+of _Phaseolus_, that some of the branches are thin, flexible, and twine,
+whilst other branches on the same plant are stiff and have no such power.
+
+If we inquire how a petiole, a branch or flower-peduncle first became
+sensitive to a touch, and acquired the power of bending towards the
+touched side, we get no certain answer.  Nevertheless an observation by
+Hofmeister {197} well deserves attention, namely, that the shoots and
+leaves of all plants, whilst young, move after being shaken.  Kerner also
+finds, as we have seen, that the flower-peduncles of a large number of
+plants, if shaken or gently rubbed bend to this side.  And it is young
+petioles and tendrils, whatever their homological nature may be, which
+move on being touched.  It thus appears that climbing plants have
+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 further inquire how the stems, petioles, tendrils, and
+flower-peduncles of climbing plants first acquired their power of
+spontaneously 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 moving, both spontaneously and from
+various stimulants, is far more common with plants, than is generally
+supposed to be the case by those who have not attended to the subject.  I
+have given one remarkable instance, namely that of the _Maurandia
+semperflorens_, the young flower-peduncles of which spontaneously revolve
+in very small circles, and bend when gently rubbed to the touched side;
+yet this plant certainly does not profit by these two feebly developed
+powers.  A rigorous examination of other young plants would probably show
+slight spontaneous movements in their stems, petioles or peduncles, as
+well as sensitiveness to a touch. {198}  We see at least that the
+_Maurandia_ might, by a little augmentation of the powers which it
+already possesses, come first to grasp a support by its flower-peduncles,
+and then, by the abortion of some of its flowers (as with _Vitis_ or
+_Cardiospermum_), acquire perfect tendrils.
+
+There is one other interesting point which deserves notice.  We have seen
+that some tendrils owe their origin to modified leaves, and others to
+modified flower-peduncles; so that some are foliar and others axial in
+their nature.  It might therefore have been expected that they would have
+presented some difference in function.  This is not the case.  On the
+contrary, they present the most complete identity in their several
+characteristic powers.  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.  Both are either attracted or repelled by the light.
+The latter property is seen in the foliar tendrils of _Bignonia
+capreolata_ and in the axial tendrils of _Ampelopsis_.  The tips of the
+tendrils in these two plants become, after contact, enlarged into discs,
+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 that the petiole of _Solanum jasminoides_,
+after it has clasped a support, assumes one of the most characteristic
+features of the axis, namely, a closed ring of woody vessels, we can
+hardly avoid asking, whether the difference between foliar and axial
+organs can be of so fundamental a nature as is generally supposed? {199}
+
+We have attempted to trace some of the stages in the genesis of climbing
+plants.  But, during the endless fluctuations of the conditions of life
+to which all organic beings have been exposed, it might be 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 their native country never twine, but reassume this
+habit when cultivated in England, we have a case in point.  In the
+leaf-climbing _Clematis flammula_, and in the tendril-bearing Vine, we
+see no loss in the power of climbing, but only a remnant of the 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
+Bignoniaceæ, we see a last and doubtful trace of the power of revolving.
+
+With respect to the abortion of tendrils, certain cultivated varieties of
+_Cucurbita pepo_ have, according to Naudin, {200} either quite lost these
+organs or bear semi-monstrous representatives of them.  In my limited
+experience, I have met with only one apparent instance 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, according to analogy, a tendril ought to have existed, a small
+pointed filament projects, about a third of an inch in length, and which
+is probably the rudiment of a tendril.  This may be the more safely
+inferred, as in young and unhealthy specimens of other tendril-bearing
+plants similar rudiments may occasionally be observed.  In the bean these
+filaments are variable in shape, as is so frequently the case with
+rudimentary organs; they are either cylindrical, or foliaceous, or are
+deeply furrowed on the upper surface.  They have not retained any vestige
+of the power of revolving.  It is a curious fact, that many of these
+filaments, when foliaceous, have on their lower surfaces, dark-coloured
+glands like those on the stipules, which excrete a sweet fluid; so that
+these rudiments have been feebly utilized.
+
+One other analogous case, though hypothetical, is worth giving.  Nearly
+all the species of _Lathyrus_ possesses tendrils; but _L. nissolia_ is
+destitute of them.  This plant has leaves, which must have struck
+everyone with surprise who has noticed them, for they are quite unlike
+those of all common papilionaceous plants, and resemble those of a grass.
+In another species, _L. aphaca_, the tendril, which is not highly
+developed (for it is unbranched, and has no spontaneous revolving-power),
+replaces the leaves, the latter being replaced in function by large
+stipules.  Now if we suppose the tendrils of _L. aphaca_ to become
+flattened and foliaceous, like the little rudimentary tendrils of the
+bean, and the large stipules to become at the same time reduced in size,
+from not being any longer wanted, 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 serving to sum up the foregoing views on the origin
+of tendril-bearing plants, that _L. nissolia_ is probably descended from
+a plant which was primordially a twiner; this then became a leaf-climber,
+the leaves being afterwards converted by degrees into tendrils, with the
+stipules greatly increased in size through the law of compensation. {202}
+After a time the tendrils lost their branches and became simple; they
+then lost their revolving-power (in which state they would have resembled
+the tendrils of the existing _L. aphaca_), and afterwards losing their
+prehensile power and becoming foliaceous would no longer be thus
+designated.  In this last stage (that of the existing _L. nissolia_) the
+former tendrils would reassume their original function of leaves, and the
+stipules which were recently much developed being no longer wanted, would
+decrease in size.  If species become modified in the course of ages, as
+almost all naturalists now admit, we may conclude that _L. nissolia_ has
+passed through a series of changes, in some degree like those here
+indicated.
+
+The most interesting point in the natural history of climbing plants is
+the various kinds of movement which they display in manifest relation to
+their wants.  The most different organs—stems, branches,
+flower-peduncles, petioles, mid-ribs of the leaf and leaflets, and
+apparently aërial roots—all possess this power.
+
+The first action of a tendril is to place itself in a proper position.
+For instance, the tendril of Cobæa first rises vertically up, with its
+branches divergent and with the terminal hooks turned outwards; the young
+shoot at the extremity of the stem is at the same time bent to one side,
+so as to be out of the way.  The young leaves of Clematis, on the other
+hand, prepare for action by temporarily curving themselves downwards, so
+as to serve as grapnels.
+
+Secondly, if a twining plant or a tendril gets by any accident into an
+inclined position, it soon bends upwards, though secluded from the light.
+The guiding stimulus no doubt is the attraction of gravity, as Andrew
+Knight showed to be the case with germinating plants.  If a shoot of any
+ordinary 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 downward-bent shoot reverses
+its curvature; but if the stolen of a strawberry, which has no tendency
+to grow upwards, be thus treated, it will curve downwards in the
+direction of, instead of in opposition to, the force of gravity.  As with
+the strawberry, so it is generally with the twining shoots of the
+_Hibbertia dentata_, which climbs laterally from bush to bush; for these
+shoots, if placed in a position inclined downwards, 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 the incurvation which causes them to
+revolve, so that their revolving movement is often accelerated or
+retarded in travelling to or from the light.  On the other hand, in a few
+instances tendrils bend towards the dark.
+
+Fourthly, we have the spontaneous revolving movement which is independent
+of any outward stimulus, but is contingent on the youth of the part, and
+on vigorous health; and this again of course depends on a proper
+temperature and other favourable conditions of life.
+
+Fifthly, tendrils, whatever their homological nature may be, and the
+petioles or tips of the leaves of leaf-climbers, and apparently certain
+roots, all have the power of movement when touched, and bend quickly
+towards the touched side.  Extremely slight pressure often suffices.  If
+the pressure be not permanent, the part in question straightens itself
+and is again ready to bend on being touched.
+
+Sixthly, and lastly, tendrils, soon after clasping a support, but not
+after a mere temporary curvature, contract spirally.  If they have not
+come into contact with any object, they ultimately contract spirally,
+after ceasing to revolve; but in this case the movement is useless, and
+occurs only after a considerable lapse of time.
+
+With respect to the means by which these various movements are effected,
+there can be little doubt from the researches of Sachs and H. de Vries,
+that they are due to unequal growth; but from the reasons already
+assigned, I cannot believe that this explanation applies to the rapid
+movements from a delicate touch.
+
+Finally, climbing plants are sufficiently numerous to form a conspicuous
+feature in the vegetable kingdom, more especially in tropical forests.
+America, which so abounds with arboreal animals, as Mr. Bates remarks,
+likewise abounds according to Mohl and Palm with climbing plants; and of
+the tendril-bearing plants examined by me, the highest developed kinds
+are natives of this grand continent, namely, the several species of
+_Bignonia_, _Eccremocarpus_, _Cobæa_, and _Ampelopsis_.  But even in the
+thickets of our temperate regions the number of climbing species and
+individuals is considerable, as will be found by counting them.  They
+belong to many and widely different orders.  To gain some rude 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 have added many more), all those families in Lindley’s
+‘Vegetable Kingdom’ which include twiners, leaf-climbers, or
+tendril-bearers.  Lindley divides Phanerogamic plants into fifty-nine
+Alliances; of these, no less than thirty-five include climbing plants of
+the above kinds, hook and root-climbers being excluded.  To these a few
+Cryptogamic plants must be added.  When we reflect on the wide separation
+of these plants in the series, and when we know that in some of the
+largest, well-defined orders, such as the Compositæ, Rubiaceæ,
+Scrophulariaceæ, Liliaceæ, &c., species in only two or three genera have
+the power of climbing, the conclusion is forced on our minds that the
+capacity of revolving, 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 be said
+that plants acquire and display this power only when it is of some
+advantage to them; this being of comparatively rare occurrence, as they
+are affixed to the ground, and food is brought to them by the air 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
+it self.  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 tendrils or internodes, or both, spontaneously revolve with a steady
+motion.  The tendril strikes some object, and quickly curls round and
+firmly grasps it.  In the course of some hours it contracts into a spire,
+dragging up the stem, and forming an excellent spring.  All movements now
+cease.  By growth the tissues soon become wonderfully strong and durable.
+The tendril has done its work, and has done it in an admirable manner.
+
+
+
+FOOTNOTES.
+
+
+{iv}  An English translation of the ‘Lehrbuch der Botanik’ by Professor
+Sachs, has recently (1875), appeared under the title of ‘Text-Book of
+Botany,’ and this is a great boon to all lovers of natural science in
+England.
+
+{1a}  ‘Proc. Amer. Acad. of Arts and Sciences,’ vol. iv. Aug. 12, 1858,
+p. 98.
+
+{1b}  Ludwig H. Palm, ‘Ueber das Winden der Pflanzen;’ Hugo von Mohl,
+‘Ueber den Bau und des Winden der Ranken und Schlingpflanzen,’ 1827.
+Palm’s Treatise was published only a few weeks before Mohl’s.  See also
+‘The Vegetable Cell’ (translated by Henfrey), by H. von Mohl, p. 147 to
+end.
+
+{1c}  “Des Mouvements révolutife Respontanés,” &c., ‘Comptes Rendus,’
+tom. xvii. (1843) p. 989; “Recherches sur la Volubilité des Tiges,” &c.,
+tom. xix. (1844) p. 295.
+
+{8}  ‘Bull. Bot Soc. de France,’ tom. v. 1858, p. 356.
+
+{9a}  This whole subject has been ably discussed and explained by H. de
+Vries, ‘Arbeiten des Bot. Instituts in Würzburg,’ Heft iii. pp. 331, 336.
+See also Sachs (‘Text-Book of Botany,’ English translation, 1875, p.
+770), who concludes “that torsion is the result of growth continuing in
+the outer layers after it has ceased or begun to cease in the inner
+layers.”
+
+{9b}  Professor Asa Gray has remarked to me, in a letter, that in _Thuja
+occidentalis_ the twisting of the bark is very conspicuous.  The twist is
+generally to the right of the observer; but, in noticing about a hundred
+trunks, four or five were observed to be twisted in an opposite
+direction.  The Spanish chestnut is often much twisted: there is an
+interesting article on this subject in the ‘Scottish Farmer,’ 1865, p.
+833.
+
+{10}  It is well known that the stems of many plants occasionally become
+spirally twisted in a monstrous manner; and after my paper was read
+before the Linnean Society, Dr. Maxwell Masters 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 what I have said about the twisting of stems, which have twined
+round rugged supports; but does not preclude the twisting being of
+service to the plant by giving greater rigidity to the stem.
+
+{12}  The view that the revolving movement or nutation of the stems of
+twining plants is due to growth is that advanced by Sachs and H. de
+Vries; and the truth of this view is proved by their excellent
+observations.
+
+{14} The mechanism by which the end of the shoot remains hooked appears
+to be a difficult and complex problem, discussed by Dr. H. de Vries
+(ibid. p. 337): he concludes that “it depends on the relation between the
+rapidity of torsion and the rapidity of nutation.”
+
+{16}  Dr. H. de Vries also has shown (ibid. p. 321 and 325) by a better
+method than that employed by me, that the stems of twining plants are not
+irritable, and that the cause of their winding up a support is exactly
+what I have described.
+
+{17}  Dr. H. de Vries states (ibid. p. 322) that the stem of Cuscuta is
+irritable like a tendril.
+
+{18}  See Dr. H. de Vries (ibid.  p. 324) on this subject.
+
+{19}  Comptes Rendus, 1844, tom. xix. p. 295, and Annales des Sc. Nat 3rd
+series, Bot., tom. ii. p. 163.
+
+{24}  I am much indebted to Dr. Hooker for having sent me many plants
+from Kew; and to Mr. Veitch, of the Royal Exotic Nursery, for having
+generously given me a collection of fine specimens of climbing plants.
+Professor Asa Gray, Prof. Oliver, and Dr. Hooker have afforded me, as on
+many previous occasions, much information and many references.
+
+{33}  Journal of the Linn. Soc. (Bot.) vol. ix. p. 344.  I shall have
+occasion often to quote this interesting paper, in which he corrects or
+confirms various statements made by me.
+
+{34}  I raised nine plants of the hybrid _Loasa Herbertii_, and six of
+these also reversed their spire in ascending a support.
+
+{36}  In another genus, namely Davilla, belonging to the same family with
+Hibbertia, Fritz Müller says (ibid. p. 349) that “the stem twines
+indifferently from left to right, or from right to left; and I once saw a
+shoot which ascended a tree about five inches in diameter, reverse its
+course in the same manner as so frequently occurs with Loasa.”
+
+{37}  Fritz Müller states (ibid. p. 349) that he saw on one occasion in
+the forests of South Brazil a trunk about five feet in circumference
+spirally ascended by a plant, apparently belonging to the Menispermaceæ.
+He adds in his letter to me that most of the climbing plants which there
+ascend thick trees, are root-climbers; some being tendril-bearers.
+
+{44}  Fritz Müller has published some interesting facts and views on the
+structure of the wood of climbing plants in ‘Bot. Zeitung,’ 1866, pp. 57,
+66.
+
+{68}  It appears from A. Kerner’s interesting observations, that the
+flower-peduncles of a large number of plants are irritable, and bend when
+they are rubbed or shaken: Die Schutzmittel des Pollens, 1873, p. 34.
+
+{71}  I have already referred to the case of the twining stem of Cuscuta,
+which, according to H. de Vries (ibid. p. 322) is sensitive to a touch
+like a tendril.
+
+{75}  Dr. Maxwell Masters informs me that in almost all petioles which
+are cylindrical, such as those bearing peltate leaves, the woody vessels
+form a closed ring; semilunar bands of vessels being confined to petioles
+which are channelled along their upper surfaces.  In accordance with this
+statement, it may be observed that the enlarged and clasped petiole of
+the _Solanum_, with its closed ring of woody vessels, has become more
+cylindrical than it was in its original unclasped condition.
+
+{84}  Never having had the opportunity of examining tendrils produced by
+the modification of branches, I spoke doubtfully about them in this essay
+when originally published.  But since then Fritz Müller has described
+(Journal of Linn. Soc. vol. ix. p. 344) many striking cases in South
+Brazil.  In speaking of plants which climb by the aid of their branches,
+more or less modified, he states that the following stages of development
+can be traced: (1.) Plants supporting themselves simply by their branches
+stretched out at right angles—for example, _Chiococca_.  (2.) Plants
+clasping a support with their unmodified branches, as with _Securidaca_.
+(3.) Plants climbing by the extremities of their branches which appear
+like tendrils, as is the case according to Endlicher with _Helinus_.
+(4.) Plants with their branches much modified and temporarily converted
+into tendrils, but which may be again transformed into branches, as with
+certain Papilionaceous plants.  (5.) Plants with their branches forming
+true tendrils, and used exclusively for climbing—as with _Strychnos_ and
+_Caulotretus_.  Even the unmodified branches become much thickened when
+they wind round a support.  I may add that Mr. Thwaites sent me from
+Ceylon a specimen of an Acacia which had climbed up the trunk of a rather
+large tree, by the aid of tendril-like, curved or convoluted branchlets,
+arrested in their growth and furnished with sharp recurved hooks.
+
+{85}  As far as I can make out, the history of our knowledge of tendrils
+is as follows:—We have seen that Palm and von Mohl observed about the
+same time the singular phenomenon of the spontaneous revolving movement
+of twining-plants.  Palm (p. 58), I presume, observed likewise the
+revolving movement 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 common pea.  Mohl first discovered that tendrils
+are 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 their movement.
+Professor Asa Gray, in a paper already quoted, first noticed the extreme
+sensitiveness and rapidity of the movements of the tendrils of certain
+Cucurbitaceous plants.
+
+{102}  Fritz Müller states (ibid. p. 348) that in South Brazil the trifid
+tendrils of Haplolophium, (one of the Bignoniaceæ) without having come
+into contact with any object, terminate in smooth shining discs.  These,
+however, after adhering to any object, sometimes become considerably
+enlarged.
+
+{111}  Comptes Rendus, tom. xvii. 1843, p. 989.
+
+{113}  Diagram showing the movement of the upper internode of the common
+Pea, traced on a hemispherical glass, and transferred to paper; reduced
+one-half in size (Aug. 1st)
+
+No.        H.        M.
+      1       8      46 A.M.
+      2      10            0
+      3      11            0
+      4      11           37
+      5      12       7 P.M.
+      6      12           30
+      7       1            0
+      8       1           30
+      9       1           44
+     10       2           25
+     11       3            0
+     12       3           30
+     13       3           48
+     14       4           40
+     15       5            5
+     16       5           25
+     17       5           50
+     18       6           25
+     19       7            0
+     20       7           45
+     21       8           30
+     22       9           15
+
+{118} ‘Leçons de Botanique,’ &c., 1841, p. 170.
+
+{127a}  I am indebted to Prof. Oliver for information on this head.  In
+the Bulletin de la Société Botanique de France, 1857, there are numerous
+discussions on the nature of the tendrils in this family.
+
+{127b}  ‘Gardeners’ Chronicle,’ 1864, p. 721.  From the affinity of the
+Cucurbitaceæ to the Passifloraceæ, it might be argued that the tendrils
+of the former are modified flower-peduncles, as is certainly the case
+with those of Passion flowers.  Mr. R. Holland (Hardwicke’s
+‘Science-Gossip,’ 1865, p. 105) states that “a cucumber grew, a few years
+ago in my own garden, where one of the short prickles upon the fruit had
+grown out into a long, curled tendril.”
+
+{145}  Trans. Phil. Soc. 1812, p. 314.
+
+{146}  Dr. M’Nab remarks (Trans. Bot. Soc. Edinburgh, vol xi. p. 292)
+that the tendrils of _Amp. Veitchii_ bear small globular discs before
+they have came into contact with any object; and I have since observed
+the same fact.  These discs, however, increase greatly in size, if they
+press against and adhere to any surface.  The tendrils, therefore, of one
+species of _Ampelopsis_ require the stimulus of contact for the first
+development of their discs, whilst those of another species do not need
+any such stimulus.  We have seen an exactly parallel case with two
+species of _Bignoniaceæ_.
+
+{152}  Fritz Müller remarks (ibid. p. 348) that a related genus,
+Serjania, differs from Cardiospermum in bearing only a single tendril;
+and that the common peduncle contracts spirally, when, as frequently
+happens, the tendril has clasped the plant’s own stem.
+
+{154}  Prof. Asa Gray informs me that the tendrils of _P. sicyoides_
+revolve even at a quicker rate than those of _P. gracilis_; four
+revolutions were completed (the temperature varying from 88 degrees-92
+degrees Fahr.) in the following times, 40 m., 45 m., 38½ m., and 46 m.
+One half-revolution was performed in 15 m.
+
+{165}  See M. Isid. Léon in Bull. Soc. Bot. de France, tom. v. 1858, p.
+650.  Dr. H. de Vries points out (p. 306) that I have overlooked, in the
+first edition of this essay, the following sentence by Mohl: “After a
+tendril has caught a support, it begins in some days to wind into a
+spire, which, since the tendril is made fast at both extremities, must of
+necessity be in some places to the right, in others to the left.”  But I
+am not surprised that this brief sentence, without any further
+explanation did not attract my attention.
+
+{176}  Sachs, however (‘Text-Book of Botany,’ Eng. Translation, 1875, p.
+280), has shown that which I overlooked, namely, that the tendrils of
+different species are adapted to clasp supports of different thicknesses.
+He further shows that after a tendril has clasped a support it
+subsequently tightens its hold.
+
+{179}  Annales des Sc. Nat. Bot. 4th series, tom. xii. p. 89.
+
+{180}  It occurred to me that the movement of notation and that from a
+touch might be differently affected by anæsthetics, in the same manner as
+Paul Bert has shown to be the case with the sleep-movements of Mimosa and
+those from a touch.  I tried the common pea and _Passiflora gracilis_,
+but I succeeded only in observing that both movements were unaffected by
+exposure for 1½ hrs. to a rather large dose of sulphuric ether.  In this
+respect they present a wonderful contrast with Drosera, owing no doubt to
+the presence of absorbent glands in the latter plant.
+
+{181}  Text-Book of Botany, 1875, p. 779.
+
+{183} Journal of Linn. Soc. vol. ix. p. 348.  Professor G. Jaeger has
+well remarked (‘In Sachen Darwin’s, insbesondere contra Wigand,’ 1874, p.
+106) that it is highly characteristic of climbing plants to produce thin,
+elongated, and flexible stems.  He further remarks that plants growing
+beneath other and taller species or trees, are naturally those which
+would be developed into climbers; anti such plants, from stretching
+towards the light, and from not being much agitated by the wind, tend to
+produce long, thin and flexible shoots.
+
+{184}  Professor Asa Gray has explained, as it would appear, this
+difficulty in his review (American Journal of Science, vol. xl. Sept.
+1865, p. 282) of the present work.  He has observed that the strong
+summer shoots of the Michigan rose (_Rosa setigera_) are strongly
+disposed to push into dark crevices and away from the light, so that they
+would be almost sure to place themselves under a trellis.  He adds that
+the lateral shoots, made on the following spring emerged from the trellis
+as they sought the light.
+
+{187}  Mr. Spiller has recently shown (Chemical Society, Feb. 16, 1865),
+in a paper on the oxidation of india-rubber or caoutchouc, that this
+substance, when exposed in a fine state of division to the air, gradually
+becomes converted into brittle, resinous matter, very similar to
+shell-lac.
+
+{188}  Fritz Müller informs me that he saw in the forests of South Brazil
+numerous black strings, from some lines to nearly an inch in diameter,
+winding spirally round the trunks of gigantic trees.  At first sight he
+thought that they were the stems of twining plants which were thus
+ascending the trees: but he afterwards found that they were the aërial
+roots of a Philodendron which grew on the branches above.  These roots
+therefore seem to be true twiners, though they use their powers to
+descend, instead of to ascend like twining plants.  The aërial roots of
+some other species of Philodendron hang vertically downwards, sometimes
+for a length of more than fifty feet.
+
+{197}  Quoted by Cohn, in his remarkable memoir, “Contractile Gewebe im
+Pflanzenreiche,” ‘Abhandl. der Schlesischen Gesell.  1861, Heft i. s. 35.
+
+{198}  Such slight spontaneous movements, I now find, have been for some
+time known to occur, for instance with the flower-stems of _Brassica
+napus_ and with the leaves of many plants: Sachs’ ‘Text-Book of Botany’
+1875, pp. 766, 785.  Fritz Müller also has shown in relation to our
+present subject (‘Jenaischen Zeitschrift,’ Bd. V. Heft 2, p. 133) that
+the stems, whilst young, of an Alisma and of a Linum are continually
+performing slight movements to all points of the compass, like those of
+climbing plants.
+
+{199}  Mr. Herbert Spencer has recently argued (‘Principles of Biology,’
+1865, p. 37 et seq.) with much force that there is no fundamental
+distinction between the foliar and axial organs of plants.
+
+{200}  Annales des Sc. Nat. 4th series, Bot. tom. vi. 1856, p. 31.
+
+{202}  Moquin-Tandon (Eléments de Tératologie. 1841, p. 156) gives the
+case of a monstrous bean, in which a case of compensation of this nature
+was suddenly effected; for the leaves completely disappeared and the
+stipules grew to an enormous size.
+
+
+
+
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+<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of The Movement and Habits of Climbing Plants, by Charles Darwin</div>
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+This eBook is for the use of anyone anywhere in the United States and
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+<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: The Movement and Habits of Climbing Plants</div>
+<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Charles Darwin</div>
+<div style='display:block; margin:1em 0'>Release Date: March 4, 2000 [eBook #2485]<br />
+[Most recently updated: November 5, 2021]</div>
+<div style='display:block; margin:1em 0'>Language: English</div>
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+<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: David Price</div>
+<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE MOVEMENT AND HABITS OF CLIMBING PLANTS ***</div>
+
+<p style="text-align: center">
+<a href="images/coverb.jpg">
+<img alt=
+"Book cover"
+title=
+"Book cover"
+ src="images/covers.jpg" />
+</a></p>
+<h1>THE MOVEMENTS<br />
+AND HABITS OF<br />
+CLIMBING PLANTS.</h1>
+<p style="text-align: center"><span class="smcap">By</span>
+CHARLES DARWIN, F.R.S.</p>
+
+<div class="gapspace">&nbsp;</div>
+<p style="text-align: center"><b>POPULAR EDITION</b></p>
+
+<div class="gapspace">&nbsp;</div>
+<p style="text-align: center">LONDON:<br />
+JOHN MURRAY, ALBEMARLE STREET.<br />
+1906.</p>
+
+<h2>PREFACE</h2>
+
+<p><span class="smcap">This</span> Essay first appeared in the
+ninth volume of the &lsquo;Journal of the Linnean Society,&rsquo;
+published in 1865. It is here reproduced in a corrected
+and, I hope, clearer form, with some additional facts. The
+illustrations were drawn by my son, George Darwin. Fritz
+Müller, after the publication of my paper, sent to the
+Linnean Society (Journal, vol. ix., p. 344) some interesting
+observations on the climbing plants of South Brazil, to which I
+shall frequently refer. Recently two important memoirs,
+chiefly on the difference in growth between the upper and lower
+sides of tendrils, and on the mechanism of the movements of
+twining-plants, by Dr. Hugo de Vries, have appeared in the
+&lsquo;Arbeiten des Botanischen Instituts in
+Würzburg,&rsquo; Heft. iii., 1873. These memoirs ought
+to be carefully studied by every one interested in the subject,
+as I can here give only references to the more important
+points. This excellent observer, as well as Professor
+Sachs, <a name="citationiv"></a><a href="#footnoteiv"
+class="citation">[iv]</a> attributes all the movements of
+tendrils to rapid growth along one side; but, from reasons
+assigned towards the close of my fourth chapter, I cannot
+persuade myself that this holds good with respect to those due to
+a touch. In order that the reader may know what points have
+interested me most, I may call his attention to certain
+tendril-bearing plants; for instance, Bignonia capreolata,
+Cobæa, Echinocystis, and Hanburya, which display as
+beautiful adaptations as can be found in any part of the kingdom
+of nature. It is, also, an interesting fact that
+intermediate states between organs fitted for widely different
+functions, may be observed on the same individual plant of
+Corydalis claviculata and the common vine; and these cases
+illustrate in a striking manner the principle of the gradual
+evolution of species.</p>
+
+<h2>APPENDIX TO PREFACE (1882).</h2>
+
+<p><span class="smcap">Since</span> the publication of this
+Edition two papers by eminent botanists have appeared;
+Schwendener, &lsquo;Das Winden der Pflanzen&rsquo;
+(Monatsberichte der Berliner Akademie, Dec. 1881), and J. Sachs,
+&lsquo;Notiz über Schlingpflanzen&rsquo; (Arbeiten des
+botanischen Instituts in Würzburg, Bd. ii. p. 719,
+1882). The view &ldquo;that the capacity of revolving, on
+which most climbers depend, is inherent, though undeveloped, in
+almost every plant in the vegetable kingdom&rdquo;
+(&lsquo;Climbing Plants,&rsquo; p. 205), has been confirmed by
+the observations on circumnutation since given in &lsquo;The
+Power of Movement in Plants.&rsquo;</p>
+
+<h2>ERRATA.</h2>
+
+<p>On pp. 28, 32, 40, 53, statements are made with reference to
+the supposed acceleration of the revolving movement towards the
+light. It appears from the observations given in &lsquo;The
+Power of Movement in Plants,&rsquo; p. 451, that these
+conclusions were drawn from insufficient observations, and are
+erroneous.</p>
+
+<h2>THE MOVEMENTS AND HABITS OF CLIMBING PLANTS.</h2>
+
+<h3>CHAPTER I.<br />
+<span class="smcap">Twining Plants</span>.</h3>
+
+<p class="gutsumm">Introductory remarks&mdash;Description of the
+twining of the Hop&mdash;Torsion of the stems&mdash;Nature of the
+revolving movement, and manner of ascent&mdash;Stems not
+irritable&mdash;Rate of revolution in various
+plants&mdash;Thickness of the support round which plants can
+twine&mdash;Species which revolve in an anomalous manner.</p>
+
+<p>I <span class="smcap">was</span> led to this subject by an
+interesting, but short paper by Professor Asa Gray on the
+movements of the tendrils of some Cucurbitaceous plants. <a
+name="citation1a"></a><a href="#footnote1a"
+class="citation">[1a]</a> My observations were more than
+half completed before I learnt that the surprising phenomenon of
+the spontaneous revolutions of the stems and tendrils of climbing
+plants had been long ago observed by Palm and by Hugo von Mohl,
+<a name="citation1b"></a><a href="#footnote1b"
+class="citation">[1b]</a> and had subsequently been the subject
+of two memoirs by Dutrochet. <a name="citation1c"></a><a
+href="#footnote1c" class="citation">[1c]</a> Nevertheless,
+I believe that my observations, founded on the examination of
+above a hundred widely distinct living species, contain
+sufficient novelty to justify me in publishing them.</p>
+
+<p>Climbing plants may be divided into four classes. First,
+those which twine spirally round a support, and are not aided by
+any other movement. Secondly, those endowed with irritable
+organs, which when they touch any object clasp it; such organs
+consisting of modified leaves, branches, or
+flower-peduncles. But these two classes sometimes graduate
+to a certain extent into one another. Plants of the third
+class ascend merely by the aid of hooks; and those of the fourth
+by rootlets; but as in neither class do the plants exhibit any
+special movements, they present little interest, and generally
+when I speak of climbing plants I refer to the two first great
+classes.</p>
+<h4><span class="smcap">Twining Plants</span>.</h4>
+<p>This is the largest subdivision, and is apparently the
+primordial and simplest condition of the class. My
+observations will be best given by taking a few special
+cases. When the shoot of a Hop (<i>Humulus lupulus</i>)
+rises from the ground, the two or three first-formed joints or
+internodes are straight and remain stationary; but the
+next-formed, whilst very young, may be seen to bend to one side
+and to travel slowly round towards all points of the compass,
+moving, like the hands of a watch, with the sun. The
+movement very soon acquires its full ordinary velocity.
+From seven observations made during August on shoots proceeding
+from a plant which had been cut down, and on another plant during
+April, the average rate during hot weather and during the day is
+2 hrs. 8 m. for each revolution; and none of the revolutions
+varied much from this rate. The revolving movement
+continues as long as the plant continues to grow; but each
+separate internode, as it becomes old, ceases to move.</p>
+
+<p>To ascertain more precisely what amount of movement each
+internode underwent, I kept a potted plant, during the night and
+day, in a well-warmed room to which I was confined by
+illness. A long shoot projected beyond the upper end of the
+supporting stick, and was steadily revolving. I then took a
+longer stick and tied up the shoot, so that only a very young
+internode, 1&frac34; of an inch in length, was left free.
+This was so nearly upright that its revolution could not be
+easily observed; but it certainly moved, and the side of the
+internode which was at one time convex became concave, which, as
+we shall hereafter see, is a sure sign of the revolving
+movement. I will assume that it made at least one
+revolution during the first twenty-four hours. Early the
+next morning its position was marked, and it made a second
+revolution in 9 hrs.; during the latter part of this revolution
+it moved much quicker, and the third circle was performed in the
+evening in a little over 3 hrs. As on the succeeding
+morning I found that the shoot revolved in 2 hrs. 45 m., it must
+have made during the night four revolutions, each at the average
+rate of a little over 3 hrs. I should add that the
+temperature of the room varied only a little. The shoot had
+now grown 3&frac12; inches in length, and carried at its
+extremity a young internode 1 inch in length, which showed slight
+changes in its curvature. The next or ninth revolution was
+effected in 2 hrs. 30 m. From this time forward, the
+revolutions were easily observed. The thirty-sixth
+revolution was performed at the usual rate; so was the last or
+thirty-seventh, but it was not completed; for the internode
+suddenly became upright, and after moving to the centre, remained
+motionless. I tied a weight to its upper end, so as to bow
+it slightly and thus detect any movement; but there was
+none. Some time before the last revolution was half
+performed, the lower part of the internode ceased to move.</p>
+
+<p>A few more remarks will complete all that need be said about
+this internode. It moved during five days; but the more
+rapid movements, after the performance of the third revolution,
+lasted during three days and twenty hours. The regular
+revolutions, from the ninth to thirty-sixth inclusive, were
+effected at the average rate of 2 hrs. 31 m.; but the weather was
+cold, and this affected the temperature of the room, especially
+during the night, and consequently retarded the rate of movement
+a little. There was only one irregular movement, which
+consisted in the stem rapidly making, after an unusually slow
+revolution, only the segment of a circle. After the
+seventeenth revolution the internode had grown from 1&frac34; to
+6 inches in length, and carried an internode 1&#8542; 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&frac12; inches long, and probably
+revolved in a period of about three hours. At the
+twenty-seventh revolution the lower and still moving internode
+was 8&#8540;, the penultimate 3&frac12;, and the ultimate
+2&frac12; inches in length; and the inclination of the whole
+shoot was such, that a circle 19 inches in diameter was swept by
+it. When the movement ceased, the lower internode was 9
+inches, and the penultimate 6 inches in length; so that, from the
+twenty-seventh to thirty-seventh revolutions inclusive, three
+internodes were at the same time revolving.</p>
+
+<p>The lower internode, when it ceased revolving, became upright
+and rigid; but as the whole shoot was left to grow unsupported,
+it became after a time bent into a nearly horizontal position,
+the uppermost and growing internodes still revolving at the
+extremity, but of course no longer round the old central point of
+the supporting stick. From the changed position of the
+centre of gravity of the extremity, as it revolved, a slight and
+slow swaying movement was given to the long horizontally
+projecting shoot; and this movement I at first thought was a
+spontaneous one. As the shoot grew, it hung down more and
+more, whilst the growing and revolving extremity turned itself up
+more and more.</p>
+
+<p>With the Hop we have seen that three internodes were at the
+same time revolving; and this was the case with most of the
+plants observed by me. With all, if in full health, two
+internodes revolved; so that by the time the lower one ceased to
+revolve, the one above was in full action, with a terminal
+internode just commencing to move. With <i>Hoya
+carnosa</i>, on the other hand, a depending shoot, without any
+developed leaves, 32 inches in length, and consisting of seven
+internodes (a minute terminal one, an inch in length, being
+counted), continually, but slowly, swayed from side to side in a
+semicircular course, with the extreme internodes making complete
+revolutions. This swaying movement was certainly due to the
+movement of the lower internodes, which, however, had not force
+sufficient to swing the whole shoot round the central supporting
+stick. The case of another Asclepiadaceous plant, viz.,
+<i>Ceropegia Gardnerii</i>, is worth briefly giving. I
+allowed the top to grow out almost horizontally to the length of
+31 inches; this now consisted of three long internodes,
+terminated by two short ones. The whole revolved in a
+course opposed to the sun (the reverse of that of the Hop), at
+rates between 5 hrs. 15 m. and 6 hrs. 45 m. for each
+revolution. The extreme tip thus made a circle of above 5
+feet (or 62 inches) in diameter and 16 feet in circumference,
+travelling at the rate of 32 or 33 inches per hour. The
+weather being hot, the plant was allowed to stand on my
+study-table; and it was an interesting spectacle to watch the
+long shoot sweeping this grand circle, night and day, in search
+of some object round which to twine.</p>
+
+<p>If we take hold of a growing sapling, we can of course bend it
+to all sides in succession, so as to make the tip describe a
+circle, like that performed by the summit of a spontaneously
+revolving plant. By this movement the sapling is not in the
+least twisted round its own axis. I mention this because if
+a black point be painted on the bark, on the side which is
+uppermost when the sapling is bent towards the holder&rsquo;s
+body, as the circle is described, the black point gradually turns
+round and sinks to the lower side, and comes up again when the
+circle is completed; and this gives the false appearance of
+twisting, which, in the case of spontaneously revolving plants,
+deceived me for a time. The appearance is the more
+deceitful because the axes of nearly all twining-plants are
+really twisted; and they are twisted in the same direction with
+the spontaneous revolving movement. To give an instance,
+the internode of the Hop of which the history has been recorded,
+was at first, as could be seen by the ridges on its surface, not
+in the least twisted; but when, after the 37th revolution, it had
+grown 9 inches long, and its revolving movement had ceased, it
+had become twisted three times round its own axis, in the line of
+the course of the sun; on the other hand, the common Convolvulus,
+which revolves in an opposite course to the Hop, becomes twisted
+in an opposite direction.</p>
+
+<p>Hence it is not surprising that Hugo von Mohl (p. 105, 108,
+&amp;c.) thought that the twisting of the axis caused the
+revolving movement; but it is not possible that the twisting of
+the axis of the Hop three times should have caused thirty-seven
+revolutions. Moreover, the revolving movement commenced in
+the young internode before any twisting of its axis could be
+detected. The internodes of a young Siphomeris and Lecontea
+revolved during several days, but became twisted only once round
+their own axes. The best evidence, however, that the
+twisting does not cause the revolving movement is afforded by
+many leaf-climbing and tendril-bearing plants (as <i>Pisum
+sativum</i>, <i>Echinocystis lobata</i>, <i>Bignonia
+capreolata</i>, <i>Eccremocarpus scaber</i>, and with the
+leaf-climbers, <i>Solanum jasminoides</i> and various species of
+<i>Clematis</i>), of which the internodes are not twisted, but
+which, as we shall hereafter see, regularly perform revolving
+movements like those of true twining-plants. Moreover,
+according to Palm (pp. 30, 95) and Mohl (p. 149), and
+Léon, <a name="citation8"></a><a href="#footnote8"
+class="citation">[8]</a> internodes may occasionally, and even
+not very rarely, be found which are twisted in an opposite
+direction to the other internodes on the same plant, and to the
+course of their revolutions; and this, according to Léon
+(p. 356), is the case with all the internodes of a certain
+variety of <i>Phaseolus multiflorus</i>. Internodes which
+have become twisted round their own axes, if they have not ceased
+to revolve, are still capable of twining round a support, as I
+have several times observed.</p>
+
+<p>Mohl has remarked (p. 111) that when a stem twines round a
+smooth cylindrical stick, it does not become twisted. <a
+name="citation9a"></a><a href="#footnote9a"
+class="citation">[9a]</a> Accordingly I allowed
+kidney-beans to run up stretched string, and up smooth rods of
+iron and glass, one-third of an inch in diameter, and they became
+twisted only in that degree which follows as a mechanical
+necessity from the spiral winding. The stems, on the other
+hand, which had ascended ordinary rough sticks were all more or
+less and generally much twisted. The influence of the
+roughness of the support in causing axial twisting was well seen
+in the stems which had twined up the glass rods; for these rods
+were fixed into split sticks below, and were secured above to
+cross sticks, and the stems in passing these places became much
+twisted. As soon as the stems which had ascended the iron
+rods reached the summit and became free, they also became
+twisted; and this apparently occurred more quickly during windy
+than during calm weather. Several other facts could be
+given, showing that the axial twisting stands in some relation to
+inequalities in the support, and likewise to the shoot revolving
+freely without any support. Many plants, which are not
+twiners, become in some degree twisted round their own axes; <a
+name="citation9b"></a><a href="#footnote9b"
+class="citation">[9b]</a> but this occurs so much more generally
+and strongly with twining-plants than with other plants, that
+there must be some connexion between the capacity for twining and
+axial twisting. The stem probably gains rigidity by being
+twisted (on the same principle that a much twisted rope is
+stiffer than a slackly twisted one), and is thus indirectly
+benefited so as to be enabled to pass over inequalities in its
+spiral ascent, and to carry its own weight when allowed to
+revolve freely. <a name="citation10"></a><a href="#footnote10"
+class="citation">[10]</a></p>
+
+<p>I have alluded to the twisting which necessarily follows on
+mechanical principles from the spiral ascent of a stem, namely,
+one twist for each spire completed. This was well shown by
+painting straight lines on living stems, and then allowing them
+to twine; but, as I shall have to recur to this subject under
+Tendrils, it may be here passed over.</p>
+
+<p>The revolving movement of a twining plant has been compared
+with that of the tip of a sapling, moved round and round by the
+hand held some way down the stem; but there is one important
+difference. The upper part of the sapling when thus moved
+remains straight; but with twining plants every part of the
+revolving shoot has its own separate and independent
+movement. This is easily proved; for when the lower half or
+two-thirds of a long revolving shoot is tied to a stick, the
+upper free part continues steadily revolving. Even if the
+whole shoot, except an inch or two of the extremity, be tied up,
+this part, as I have seen in the case of the Hop, Ceropegia,
+Convolvulus, &amp;c., goes on revolving, but much more slowly;
+for the internodes, until they have grown to some little length,
+always move slowly. If we look to the one, two, or several
+internodes of a revolving shoot, they will be all seen to be more
+or less bowed, either during the whole or during a large part of
+each revolution. Now if a coloured streak be painted (this
+was done with a large number of twining plants) along, we will
+say, the convex surface, the streak will after a time (depending
+on the rate of revolution) be found to be running laterally along
+one side of the bow, then along the concave side, then laterally
+on the opposite side, and, lastly, again on the originally convex
+surface. This clearly proves that during the revolving
+movement the internodes become bowed in every direction.
+The movement is, in fact, a continuous self-bowing of the whole
+shoot, successively directed to all points of the compass; and
+has been well designated by Sachs as a revolving nutation.</p>
+
+<p>As this movement is rather difficult to understand, it will be
+well to give an illustration. Take a sapling and bend it to
+the south, and paint a black line on the convex surface; let the
+sapling spring up and bend it to the east, and the black line
+will be seen to run along the lateral face fronting the north;
+bend it to the north, the black line will be on the concave
+surface; bend it to the west, the line will again be on the
+lateral face; and when again bent to the south, the line will be
+on the original convex surface. Now, instead of bending the
+sapling, let us suppose that the cells along its northern surface
+from the base to the tip were to grow much more rapidly than on
+the three other sides, the whole shoot would then necessarily be
+bowed to the south; and let the longitudinal growing surface
+creep round the shoot, deserting by slow degrees the northern
+side and encroaching on the western side, and so round by the
+south, by the east, again to the north. In this case the
+shoot would remain always bowed with the painted line appearing
+on the several above specified surfaces, and with the point of
+the shoot successively directed to each point of the
+compass. In fact, we should have the exact kind of movement
+performed by the revolving shoots of twining plants. <a
+name="citation12"></a><a href="#footnote12"
+class="citation">[12]</a></p>
+
+<p>It must not be supposed that the revolving movement is as
+regular as that given in the above illustration; in very many
+cases the tip describes an ellipse, even a very narrow
+ellipse. To recur once again to our illustration, if we
+suppose only the northern and southern surfaces of the sapling
+alternately to grow rapidly, the summit would describe a simple
+arc; if the growth first travelled a very little to the western
+face, and during the return a very little to the eastern face, a
+narrow ellipse would be described; and the sapling would be
+straight as it passed to and fro through the intermediate space;
+and a complete straightening of the shoot may often be observed
+in revolving plants. The movement is frequently such that
+three of the sides of the shoot seem to be growing in due order
+more rapidly than the remaining side; so that a semi-circle
+instead of a circle is described, the shoot becoming straight and
+upright during half of its course.</p>
+
+<p>When a revolving shoot consists of several internodes, the
+lower ones bend together at the same rate, but one or two of the
+terminal ones bend at a slower rate; hence, though at times all
+the internodes are in the same direction, at other times the
+shoot is rendered slightly serpentine. The rate of
+revolution of the whole shoot, if judged by the movement of the
+extreme tip, is thus at times accelerated or retarded. One
+other point must be noticed. Authors have observed that the
+end of the shoot in many twining plants is completely hooked;
+this is very general, for instance, with the
+Asclepiadaceæ. The hooked tip, in all the cases
+observed by me, viz. in <i>Ceropegia</i>,
+<i>Sphærostemma</i>, <i>Clerodendron</i>, <i>Wistaria</i>,
+<i>Stephania</i>, <i>Akebia</i>, and <i>Siphomeris</i>, has
+exactly the same kind of movement as the other internodes; for a
+line painted on the convex surface first becomes lateral and then
+concave; but, owing to the youth of these terminal internodes,
+the reversal of the hook is a slower process than that of the
+revolving movement. <a name="citation14"></a><a
+href="#footnote14" class="citation">[14]</a> This strongly
+marked tendency in the young, terminal and flexible internodes,
+to bend in a greater degree or more abruptly than the other
+internodes, is of service to the plant; for not only does the
+hook thus formed sometimes serve to catch a support, but (and
+this seems to be much more important) it causes the extremity of
+the shoot to embrace the support much more closely than it could
+otherwise have done, and thus aids in preventing the stem from
+being blown away during windy weather, as I have many times
+observed. In <i>Lonicera brachypoda</i> the hook only
+straightens itself periodically, and never becomes
+reversed. I will not assert that the tips of all twining
+plants when hooked, either reverse themselves or become
+periodically straight, in the manner just described; for the
+hooked form may in some cases be permanent, and be due to the
+manner of growth of the species, as with the tips of the shoots
+of the common vine, and more plainly with those of <i>Cissus
+discolor</i>&mdash;plants which are not spiral twiners.</p>
+
+<p>The first purpose of the spontaneous revolving movement, or,
+more strictly speaking, of the continuous bowing movement
+directed successively to all points of the compass, is, as Mohl
+has remarked, to favour the shoot finding a support. This
+is admirably effected by the revolutions carried on night and
+day, a wider and wider circle being swept as the shoot increases
+in length. This movement likewise explains how the plants
+twine; for when a revolving shoot meets with a support, its
+motion is necessarily arrested at the point of contact, but the
+free projecting part goes on revolving. As this continues,
+higher and higher points are brought into contact with the
+support and are arrested; and so onwards to the extremity; and
+thus the shoot winds round its support. When the shoot
+follows the sun in its revolving course, it winds round the
+support from right to left, the support being supposed to stand
+in front of the beholder; when the shoot revolves in an opposite
+direction, the line of winding is reversed. As each
+internode loses from age its power of revolving, it likewise
+loses its power of spirally twining. If a man swings a rope
+round his head, and the end hits a stick, it will coil round the
+stick according to the direction of the swinging movement; so it
+is with a twining plant, a line of growth travelling round the
+free part of the shoot causing it to bend towards the opposite
+side, and this replaces the momentum of the free end of the
+rope.</p>
+
+<p>All the authors, except Palm and Mohl, who have discussed the
+spiral twining of plants, maintain that such plants have a
+natural tendency to grow spirally. Mohl believes (p. 112)
+that twining stems have a dull kind of irritability, so that they
+bend towards any object which they touch; but this is denied by
+Palm. Even before reading Mohl&rsquo;s interesting
+treatise, this view seemed to me so probable that I tested it in
+every way that I could, but always with a negative result.
+I rubbed many shoots much harder than is necessary to excite
+movement in any tendril or in the foot-stalk of any leaf climber,
+but without any effect. I then tied a light forked twig to
+a shoot of a Hop, a <i>Ceropegia</i>, <i>Sphærostemma</i>,
+and <i>Adhatoda</i>, so that the fork pressed on one side alone
+of the shoot and revolved with it; I purposely selected some very
+slow revolvers, as it seemed most likely that these would profit
+most from possessing irritability; but in no case was any effect
+produced. <a name="citation16"></a><a href="#footnote16"
+class="citation">[16]</a> Moreover, when a shoot winds
+round a support, the winding movement is always slower, as we
+shall immediately see, than whilst it revolves freely and touches
+nothing. Hence I conclude that twining stems are not
+irritable; and indeed it is not probable that they should be so,
+as nature always economizes her means, and irritability would
+have been superfluous. Nevertheless I do not wish to assert
+that they are never irritable; for the growing axis of the
+leaf-climbing, but not spirally twining, <i>Lophospermum
+scandens</i> is, certainly irritable; but this case gives me
+confidence that ordinary twiners do not possess any such quality,
+for directly after putting a stick to the <i>Lophopermum</i>, I
+saw that it behaved differently from a true twiner or any other
+leaf-climber. <a name="citation17"></a><a href="#footnote17"
+class="citation">[17]</a></p>
+
+<p>The belief that twiners have a natural tendency to grow
+spirally, probably arose from their assuming a spiral form when
+wound round a support, and from the extremity, even whilst
+remaining free, sometimes assuming this form. The free
+internodes of vigorously growing plants, when they cease to
+revolve, become straight, and show no tendency to be spiral; but
+when a shoot has nearly ceased to grow, or when the plant is
+unhealthy, the extremity does occasionally become spiral. I
+have seen this in a remarkable manner with the ends of the shoots
+of the <i>Stauntonia</i> and of the allied <i>Akebia</i>, which
+became wound up into a close spire, just like a tendril; and this
+was apt to occur after some small, ill-formed leaves had
+perished. The explanation, I believe, is, that in such
+cases the lower parts of the terminal internodes very gradually
+and successively lose their power of movement, whilst the
+portions just above move onwards and in their turn become
+motionless; and this ends in forming an irregular spire.</p>
+
+<p>When a revolving shoot strikes a stick, it winds round it
+rather more slowly than it revolves. For instance, a shoot
+of the <i>Ceropegia</i>, revolved in 6 hrs., but took 9 hrs. 30
+m. to make one complete spire round a stick; <i>Aristolochia
+gigas</i> revolved in about 5 hrs., but took 9 hrs. 15 m. to
+complete its spire. This, I presume, is due to the
+continued disturbance of the impelling force by the arrestment of
+the movement at successive points; and we shall hereafter see
+that even shaking a plant retards the revolving movement.
+The terminal internodes of a long, much-inclined, revolving shoot
+of the <i>Ceropegia</i>, after they had wound round a stick,
+always slipped up it, so as to render the spire more open than it
+was at first; and this was probably in part due to the force
+which caused the revolutions, being now almost freed from the
+constraint of gravity and allowed to act freely. With the
+<i>Wistaria</i>, on the other hand, a long horizontal shoot wound
+itself at first into a very close spire, which remained
+unchanged; but subsequently, as the shoot twined spirally up its
+support, it made a much more open spire. With all the many
+plants which were allowed freely to ascend a support, the
+terminal internodes made at first a close spire; and this, during
+windy weather, served to keep the shoots in close contact with
+their support; but as the penultimate internodes grew in length,
+they pushed themselves up for a considerable space (ascertained
+by coloured marks on the shoot and on the support) round the
+stick, and the spire became more open. <a
+name="citation18"></a><a href="#footnote18"
+class="citation">[18]</a></p>
+
+<p>It follows from this latter fact that the position occupied by
+each leaf with respect to the support depends on the growth of
+the internodes after they have become spirally wound round
+it. I mention this on account of an observation by Palm (p.
+34), who states that the opposite leaves of the Hop always stand
+in a row, exactly over one another, on the same side of the
+supporting stick, whatever its thickness may be. My sons
+visited a hop-field for me, and reported that though they
+generally found the points of insertion of the leaves standing
+over each other for a space of two or three feet in height, yet
+this never occurred up the whole length of the pole; the points
+of insertion forming, as might have been expected, an irregular
+spire. Any irregularity in the pole entirely destroyed the
+regularity of position of the leaves. From casual
+inspection, it appeared to me that the opposite leaves of
+<i>Thunbergia alata</i> were arranged in lines up the sticks
+round which they had twined; accordingly, I raised a dozen
+plants, and gave them sticks of various thicknesses, as well as
+string, to twine round; and in this case one alone out of the
+dozen had its leaves arranged in a perpendicular line: I
+conclude, therefore, Palm&rsquo;s statement is not quite
+accurate.</p>
+
+<p>The leaves of different twining-plants are arranged on the
+stem (before it has twined) alternately, or oppositely, or in a
+spire. In the latter case the line of insertion of the
+leaves and the course of the revolutions coincide. This
+fact has been well shown by Dutrochet, <a
+name="citation19"></a><a href="#footnote19"
+class="citation">[19]</a> who found different individuals of
+<i>Solanum dulcamara</i> twining in opposite directions, and
+these had their leaves in each case spirally arranged in the same
+direction. A dense whorl of many leaves would apparently be
+incommodious for a twining plant, and some authors assert that
+none have their leaves thus arranged; but a twining
+<i>Siphomeris</i> has whorls of three leaves.</p>
+
+<p>If a stick which has arrested a revolving shoot, but has not
+as yet been encircled, be suddenly taken away, the shoot
+generally springs forward, showing that it was pressing with some
+force against the stick. After a shoot has wound round a
+stick, if this be withdrawn, it retains for a time its spiral
+form; it then straightens itself, and again commences to
+revolve. The long, much-inclined shoot of the
+<i>Ceropegia</i> previously alluded to offered some curious
+peculiarities. The lower and older internodes, which
+continued to revolve, were incapable, on repeated trials, of
+twining round a thin stick; showing that, although the power of
+movement was retained, this was not sufficient to enable the
+plant to twine. I then moved the stick to a greater
+distance, so that it was struck by a point 2&frac12; inches from
+the extremity of the penultimate internode; and it was then
+neatly encircled by this part of the penultimate and by the
+ultimate internode. After leaving the spirally wound shoot
+for eleven hours, I quietly withdrew the stick, and in the course
+of the day the curled portion straightened itself and recommenced
+revolving; but the lower and not curled portion of the
+penultimate internode did not move, a sort of hinge separating
+the moving and the motionless part of the same internode.
+After a few days, however, I found that this lower part had
+likewise recovered its revolving power. These several facts
+show that the power of movement is not immediately lost in the
+arrested portion of a revolving shoot; and that after being
+temporarily lost it can be recovered. When a shoot has
+remained for a considerable time round a support, it permanently
+retains its spiral form even when the support is removed.</p>
+
+<p>When a tall stick was placed so as to arrest the lower and
+rigid internodes of the <i>Ceropegia</i>, at the distance at
+first of 15 and then of 21 inches from the centre of revolution,
+the straight shoot slowly and gradually slid up the stick, so as
+to become more and more highly inclined, but did not pass over
+the summit. Then, after an interval sufficient to have
+allowed of a semi-revolution, the shoot suddenly bounded from the
+stick and fell over to the opposite side or point of the compass,
+and reassumed its previous slight inclination. It now
+recommenced revolving in its usual course, so that after a
+semi-revolution it again came into contact with the stick, again
+slid up it, and again bounded from it and fell over to the
+opposite side. This movement of the shoot had a very odd
+appearance, as if it were disgusted with its failure but was
+resolved to try again. We shall, I think, understand this
+movement by considering the former illustration of the sapling,
+in which the growing surface was supposed to creep round from the
+northern by the western to the southern face; and thence back
+again by the eastern to the northern face, successively bowing
+the sapling in all directions. Now with the
+<i>Ceropegia</i>, the stick being placed to the south of the
+shoot and in contact with it, as soon as the circulatory growth
+reached the western surface, no effect would be produced, except
+that the shoot would be pressed firmly against the stick.
+But as soon as growth on the southern surface began, the shoot
+would be slowly dragged with a sliding movement up the stick; and
+then, as soon as the eastern growth commenced, the shoot would be
+drawn from the stick, and its weight coinciding with the effects
+of the changed surface of growth, would cause it suddenly to fall
+to the opposite side, reassuming its previous slight inclination;
+and the ordinary revolving movement would then go on as
+before. I have described this curious case with some care,
+because it first led me to understand the order in which, as I
+then thought, the surfaces contracted; but in which, as we now
+know from Sachs and II. de Vries, they grow for a time rapidly,
+thus causing the shoot to bow towards the opposite side.</p>
+
+<p>The view just given further explains, as I believe, a fact
+observed by Mohl (p. 135), namely, that a revolving shoot, though
+it will twine round an object as thin as a thread, cannot do so
+round a thick support. I placed some long revolving shoots
+of a <i>Wistaria</i> close to a post between 5 and 6 inches in
+diameter, but, though aided by me in many ways, they could not
+wind round it. This apparently was due to the flexure of
+the shoot, whilst winding round an object so gently curved as
+this post, not being sufficient to hold the shoot to its place
+when the growing surface crept round to the opposite surface of
+the shoot; so that it was withdrawn at each revolution from its
+support.</p>
+
+<p>When a free shoot has grown far beyond its support, it sinks
+downwards from its weight, as already explained in the case of
+the Hop, with the revolving extremity turned upwards. If
+the support be not lofty, the shoot falls to the ground, and
+resting there, the extremity rises up. Sometimes several
+shoots, when flexible, twine together into a cable, and thus
+support one another. Single thin depending shoots, such as
+those of the <i>Sollya Drummondii</i>, will turn abruptly
+backwards and wind up on themselves. The greater number of
+the depending shoots, however, of one twining plant, the
+<i>Hibbertia dentata</i>, showed but little tendency to turn
+upwards. In other cases, as with the <i>Cryptostegia
+grandiflora</i>, several internodes which were at first flexible
+and revolved, if they did not succeed in twining round a support,
+become quite rigid, and supporting themselves upright, carried on
+their summits the younger revolving internodes.</p>
+
+<p>Here will be a convenient place to give a Table showing the
+direction and rate of movement of several twining plants, with a
+few appended remarks. These plants are arranged according
+to Lindley&rsquo;s &lsquo;Vegetable Kingdom&rsquo; of 1853; and
+they have been selected from all parts of the series so as to
+show that all kinds behave in a nearly uniform manner. <a
+name="citation24"></a><a href="#footnote24"
+class="citation">[24]</a></p>
+
+<h4>The Rate of Revolution of various Twining Plants.</h4>
+
+<h5>(<span class="smcap">Acotyledons</span>.)</h5>
+
+<p><i>Lygodium scandens</i> (Polypodiaceæ) moves against
+the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>June 18, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, 2nd</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p>(late in evening)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;19, 3rd</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">32</p>
+</td>
+<td><p>(very hot day)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;19, 4th</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>(very hot day)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;20, 5th</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Lygodium articulatum</i> moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>July 19, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">16</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>(shoot very young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;20, 2nd</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;21, 3rd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;22, 4th</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<h5>(<span class="smcap">Monocotyledons</span>.)</h5>
+<p><i>Ruscus androgynus</i> (Liliaceæ), placed in the
+hot-house, moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>May 24, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">14</p>
+</td>
+<td><p>(shoot very young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;25, 2nd</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">21</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;25, 3rd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">37</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;25, 4th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">22</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;26, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">50</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;27, 6th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">52</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;27, 7th</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">11</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Asparagus</i> (unnamed species from Kew) (Liliaceæ)
+moves against the sun, placed in hothouse.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>Dec. 26, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;27, 2nd</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">40</p>
+</td>
+</tr>
+</table>
+<p><i>Tamus communis</i> (Dioscoreaceæ). A young
+shoot from a tuber in a pot placed in the greenhouse: follows the
+sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>July, 7, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;7, 2nd</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">38</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8, 3rd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8, 4th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">56</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8, 6th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+</table>
+<p><i>Lapagerea rosea</i> (Philesiaceæ), in greenhouse,
+follows the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>March 9, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">26</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p>(shoot young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;10, semicircle</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11, 2nd circle</p>
+</td>
+<td><p style="text-align: right">11</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;12, 3rd</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;13, 4th</p>
+</td>
+<td><p style="text-align: right">14</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;16, 5th</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">40</p>
+</td>
+<td><p>when placed in the hothouse; but the next day the shoot
+remained stationary.</p>
+</td>
+</tr>
+</table>
+<p><i>Roxburghia viridiflora</i> (Roxburghiaceæ) moves
+against the sun; it completed a circle in about 24 hours.</p>
+<h5>(<span class="smcap">Dicotyledons</span>.)</h5>
+<p><i>Humulus Lupulus</i> (Urticaceæ) follows the
+sun. The plant was kept in a room during warm weather.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>April 9, 2 circles were made in</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">16</p>
+</td>
+</tr>
+<tr>
+<td><p>Aug. 13, 3rd circle was</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 4th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">16</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 6th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 7th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 8th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+</tr>
+</table>
+<p>With the Hop a semicircle was performed, in travelling from
+the light, in 1 hr. 33 m.; in travelling to the light, in 1 hr.
+13 m.; difference of rate, 20 m.</p>
+
+<p><i>Akebia quinata</i> (Lardizabalaceæ), placed in
+hothouse, moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>March 17, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>(shoot young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, 2nd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">40</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, 3rd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;19, 4th</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Stauntonia latifolia</i> (Lardizabalaceæ), placed in
+hothouse, moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>March 28, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;29, 2nd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+</tr>
+</table>
+<p><i>Sphærostemma marmoratum</i> (Schizandraceæ)
+follows the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>August 5th, 1st circle was made in about</p>
+</td>
+<td><p style="text-align: right">24</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5th, 2nd circle was
+made in</p>
+</td>
+<td><p style="text-align: right">18</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+</table>
+<p><i>Stephania rotunda</i> (Menispermaceæ) moves against
+the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>May 27, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;30, 2nd</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+</tr>
+<tr>
+<td><p>June 2, 3rd</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3, 4th</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">28</p>
+</td>
+</tr>
+</table>
+<p>Thryallis brachystachys (Malpighiaceæ) moves against the
+sun: one shoot made a circle in 12 hrs., and another in 10 hrs.
+30 m.; but the next day, which was much colder, the first shoot
+took 10 hrs. to perform only a semicircle.</p>
+
+<p>Hibbertia dentata (Dilleniaceæ), placed in the hothouse,
+followed the sun, and made (May 18th) a circle in 7 hrs. 20 m.;
+on the 19th, reversed its course, and moved against the sun, and
+made a circle in 7 hrs.; on the 20th, moved against the sun
+one-third of a circle, and then stood still; on the 26th,
+followed the sun for two-thirds of a circle, and then returned to
+its starting-point, taking for this double course 11 hrs. 46
+m.</p>
+
+<p><i>Sollya Drummondii</i> (Pittosporaceæ) moves against
+the sun kept in greenhouse.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>April 4, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">25</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5, 2nd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>(very cold day)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6, 3rd</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">25</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;7, 4th</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Polygonum dumetorum</i> (Polygonaceæ). This
+case is taken from Dutrochet (p. 299), as I observed, no
+allied plant: follows the sun. Three shoots, cut off a
+plant, and placed in water made circles in 3 hrs. 10 m., 5 hrs.
+20 m., and 7 hrs. 15 m.</p>
+
+<p><i>Wistaria Chinensis</i> (Leguminosæ), in greenhouse,
+moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>May 13, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;13, 2nd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;16, 3rd</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;24, 4th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">21</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;25, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">37</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;25, 6th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">35</p>
+</td>
+</tr>
+</table>
+<p><i>Phaseolus vulgaris</i> (Leguminosæ), in greenhouse,
+moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>May, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2nd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3rd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+</tr>
+</table>
+<p><i>Dipladenia urophylla</i> (Apocynaceæ) moves against
+the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>April 18, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;19, 2nd</p>
+</td>
+<td><p style="text-align: right">9</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;30, 3rd</p>
+</td>
+<td><p style="text-align: right">9</p>
+</td>
+<td><p style="text-align: right">40</p>
+</td>
+</tr>
+</table>
+<p><i>Dipladenia crassinoda</i> moves against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>May 16, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">9</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+<tr>
+<td><p>July 20, 2nd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;21, 3rd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+</table>
+<p><i>Ceropegia Gardnerii</i> (Asclepiadaceæ) moves against
+the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>Shoot very young, 2 inches in length</p>
+</td>
+<td><p>1st circle was performed in</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+</tr>
+<tr>
+<td><p>Shoot still young</p>
+</td>
+<td><p>2nd</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>Long shoot</p>
+</td>
+<td><p>3rd</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">33</p>
+</td>
+</tr>
+<tr>
+<td><p>Long shoot</p>
+</td>
+<td><p>4th</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+</tr>
+<tr>
+<td><p>Long shoot</p>
+</td>
+<td><p>5th</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+</tr>
+</table>
+<p><i>Stephanotis floribunda</i> (Asclepiadaceæ) moves
+against the sun and made a circle in 6 hrs. 40 m., a second
+circle in about 9 hrs.</p>
+
+<p><i>Hoya carnosa</i> (Asclepiadaceæ) made several circles
+in from 16 hrs. to 22 hrs. or 24 hrs.</p>
+
+<p><i>Ipomæa purpurea</i> (Convolvulaceæ) moves
+against the sun. Plant placed in room with lateral
+light.</p>
+<table>
+<tr>
+<td><p>1st circle was made in 2 hrs. 42 m.</p>
+</td>
+<td><p>Semicircle, from the light in 1 hr. 14 m., to the light 1
+hr. 28 m.: difference 14 m.</p>
+</td>
+</tr>
+<tr>
+<td><p>2nd circle was made in 2 hrs. 47 m.</p>
+</td>
+<td><p>Semicircle, from the light in 1 hr. 17 m., to the light 1
+hr. 30 m.: difference 13 m.</p>
+</td>
+</tr>
+</table>
+<p><i>Ipomæa jucunda</i> (Convolvulaceæ) moves
+against the sun, placed in my study, with windows facing the
+north-east. Weather hot.</p>
+<table>
+<tr>
+<td><p>1st circle was made in 5 hrs. 30 m.</p>
+</td>
+<td><p>Semicircle, from the light in 4 hrs. 30 m., to the light 1
+hr. 0 m.: difference 3 hrs. 30 m.</p>
+</td>
+</tr>
+<tr>
+<td><p>2nd circle was made in 5 hrs. 20 m. (Late in
+afternoon: circle completed at 6 hrs. 40 m. <span
+class="GutSmall">P.M.</span>)</p>
+</td>
+<td><p>Semicircle, from the light in 3 hrs. 50 m., to the light 1
+hr. 30 m.: difference 2 hrs. 20 m.</p>
+</td>
+</tr>
+</table>
+<p>We have here a remarkable instance of the power of light in
+retarding and hastening the revolving movement. (<i>See</i>
+<span class="smcap">Errata</span>.)</p>
+
+<p><i>Convolvulus sepium</i> (large-flowered cultivated var.)
+moves against the sun. Two circles, were made each in 1 hr.
+42 m.: difference in semicircle from and to the light 14 m.</p>
+
+<p><i>Rivea tiliæfolia</i> (Convolvulaceæ) moves
+against the sun, made four revolutions in 9 hrs.; so that, on an
+average, each was performed in 2 hrs. 15 m.</p>
+
+<p><i>Plumbago rosea</i> (Plumbaginaceæ) follows the
+sun. The shoot did not begin to revolve until nearly a yard
+in height; it then made a fine circle in 10 hrs. 45 m.
+During the next few days it continued to move, but
+irregularly. On August 15th the shoot followed, during a
+period of 10 hrs. 40 m., a long and deeply zigzag course and then
+made a broad ellipse. The figure apparently represented
+three ellipses, each of which averaged 3 hrs. 38 m. for its
+completion.</p>
+
+<p><i>Jasminum pauciflorum</i>, Bentham (Jasminaceæ), moves
+against the sun. A circle was made in 7 hrs. 15 m., and a
+second rather more quickly.</p>
+
+<p><i>Clerodendrum Thomsonii</i> (Verbenaceæ) follows the
+sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>April 12, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+<td><p>(shoot very young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 2nd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, a semicircle</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>(directly after the plant was shaken on being moved)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;19, 3rd circle</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;20, 4th</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Tecoma jasminoides</i> (Bignoniaceæ) moves against
+the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>March 17, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;19, 2nd</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;22, 3rd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>(very cold day)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;24, 4th</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Thunbergia alata</i> (Acanthaceæ) moves against
+sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>April 14, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, 2nd</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">50</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, 3rd</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;18, 4th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+<td><p>(late in afternoon)</p>
+</td>
+</tr>
+</table>
+<p><i>Adhadota cydonæfolia</i> (Acanthaceæ) follows
+the sun. A young shoot made a semicircle in 24 hrs.;
+subsequently it made a circle in between 40 hrs. and 48
+hrs. Another shoot, however, made a circle in 26 hrs. 30
+m.</p>
+
+<p><i>Mikania scandens</i> (Compositæ) moves against the
+sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>March 14, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;15, 2nd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;16, 3rd</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;17, 4th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">33</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>April 7, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">50</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;7, 6th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">40</p>
+</td>
+<td><p>This circle was made after a copious watering with cold
+water at 47&deg; Fahr.</p>
+</td>
+</tr>
+</table>
+<p><i>Combretum argenteum</i> (Combretaceæ) moves against
+the sun. Kept in hothouse.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>Jan. 24, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+<td><p>Early in morning, when the temperature of the house had
+fallen a little.</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;24, 2 circles each at
+an average of</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;25, 4th circle was
+made in</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">25</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Combretum purpureum</i> revolves not quite so quickly as
+<i>C. argenteum</i>.</p>
+
+<p><i>Loasa aurantiaca</i> (Loasaceæ). Revolutions
+variable in their course: a plant which moved against the
+sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>June 20, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">37</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;20, 2nd</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">13</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;20, 3rd</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;21, 4th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">35</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;22, 5th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">26</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;23, 6th</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+</table>
+<p>Another plant which followed the sun in its revolutions.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>July 11, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">51</p>
+</td>
+<td><p>Very hot day.</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11, 2nd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">46</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11, 3rd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">41</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11, 4th</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">48</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;12, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">35</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Scyphanthus elegans</i> (Loasaceæ) follows the
+sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>June 13, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;13, 2nd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">17</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 3rd</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">36</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 4th</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">59</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14, 5th</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+</tr>
+</table>
+<p><i>Siphomeris</i> or <i>Lecontea</i> (unnamed sp.)
+(Cinchonaceæ) follows the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>May 25, semicircle was made in</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p style="text-align: right">27</p>
+</td>
+<td><p>(shoot extremely young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;26, 1st circle</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p>(shoot still young)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;30, 2nd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">55</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>June 2, 3rd</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">11</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6, 4th</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8, 5th</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+<td><p>Taken from the hothouse, and placed in a room in my
+house.</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;9, 6th</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">36</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+</table>
+<p><i>Manettia bicolor</i> (Cinchonaceæ), young plant,
+follows the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p>July 7, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">18</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8, 2nd</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">53</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;9, 3rd</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+</table>
+<p><i>Lonicera brachypoda</i> (Caprifoliaceæ) follows the
+sun, kept in a warm room in the house.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>April, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">9</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p>(about)</p>
+</td>
+</tr>
+<tr>
+<td><p>April, 2nd circle was made in</p>
+</td>
+<td><p style="text-align: right">12</p>
+</td>
+<td><p style="text-align: right">20</p>
+</td>
+<td><p>(a distinct shoot, very young, on same plant)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3rd</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4th</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>In this latter circle, the semicircle from the light took
+5 hrs. 23 m., and to the light 2 hrs. 37 min.: difference 2 hrs
+46 m.</p>
+</td>
+</tr>
+</table>
+<p><i>Aristolochia gigas</i> (Aristolochiaceæ) moves
+against the sun.</p>
+<table>
+<tr>
+<td><p>&nbsp;</p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: right"><span
+class="GutSmall">M.</span></p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>July 22, 1st circle was made in</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>(rather young shoot)</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;23, 2nd</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p>&nbsp;</p>
+</td>
+</tr>
+<tr>
+<td><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;24, 3rd</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+<td><p>(about)</p>
+</td>
+</tr>
+</table>
+
+<p>In the foregoing Table, which includes twining plants
+belonging to widely different orders, we see that the rate at
+which growth travels or circulates round the axis (on which the
+revolving movement depends), differs much. As long as a
+plant remains under the same conditions, the rate is often
+remarkably uniform, as with the Hop, <i>Mikania</i>,
+<i>Phaseolus</i>, &amp;c. The Scyphanthus made one
+revolution in 1 hr. 17 m., and this is the quickest rate observed
+by me; but we shall hereafter see a tendril-bearing Passiflora
+revolving more rapidly. A shoot of the <i>Akebia
+quinata</i> made a revolution in 1 hr. 30 m., and three
+revolutions at the average rate of 1 hr. 38 m.; a Convolvulus
+made two revolutions at the average of 1 hr. 42 m., and
+<i>Phaseolus vulgaris</i> three at the average of 1 hr. 57
+m. On the other hand, some plants take 24 hrs. for a single
+revolution, and the <i>Adhadota</i> sometimes required 48 hrs.;
+yet this latter plant is an efficient twiner. Species of
+the same genus move at different rates. The rate does not
+seem governed by the thickness of the shoots: those of the
+<i>Sollya</i> are as thin and flexible as string, but move more
+slowly than the thick and fleshy shoots of the <i>Ruscus</i>,
+which seem little fitted for movement of any kind. The
+shoots of the <i>Wistaria</i>, which become woody, move faster
+than those of the herbaceous <i>Ipomoea</i> or
+<i>Thunbergia</i>.</p>
+
+<p>We know that the internodes, whilst still very young, do not
+acquire their proper rate of movement; hence the several shoots
+on the same plant may sometimes be seen revolving at different
+rates. The two or three, or even more, internodes which are
+first formed above the cotyledons, or above the root-stock of a
+perennial plant, do not move; they can support themselves, and
+nothing superfluous is granted.</p>
+
+<p>A greater number of twiners revolve in a course opposed to
+that of the sun, or to the hands of a watch, than in the reversed
+course, and, consequently, the majority, as is well known, ascend
+their supports from left to right. Occasionally, though
+rarely, plants of the same order twine in opposite directions, of
+which Mohl (p. 125) gives a case in the Leguminosæ, and we
+have in the table another in the Acanthaceæ. I have
+seen no instance of two species of the same genus twining in
+opposite directions, and such cases must be rare; but Fritz
+Müller <a name="citation33"></a><a href="#footnote33"
+class="citation">[33]</a> states that although <i>Mikania
+scandens</i> twines, as I have described, from left to right,
+another species in South Brazil twines in an opposite
+direction. It would have been an anomalous circumstance if
+no such cases had occurred, for different individuals of the same
+species, namely, of <i>Solanum dulcamara</i> (Dutrochet, tom.
+xix. p. 299), revolve and twine in two directions: this plant,
+however; is a most feeble twiner. <i>Loasa aurantiaca</i>
+(Léon, p. 351) offers a much more curious case: I raised
+seventeen plants: of these eight revolved in opposition to the
+sun and ascended from left to right; five followed the sun and
+ascended from right to left; and four revolved and twined first
+in one direction, and then reversed their course, <a
+name="citation34"></a><a href="#footnote34"
+class="citation">[34]</a> the petioles of the opposite leaves
+affording a <i>point d&rsquo;appui</i> for the reversal of the
+spire. One of these four plants made seven spiral turns
+from right to left, and five turns from left to right.
+Another plant in the same family, the <i>Scyphanthus elegans</i>,
+habitually twines in this same manner. I raised many plants
+of it, and the stems of all took one turn, or occasionally two or
+even three turns in one direction, and then, ascending for a
+short space straight, reversed their course and took one or two
+turns in an opposite direction. The reversal of the
+curvature occurred at any point in the stem, even in the middle
+of an internode. Had I not seen this case, I should have
+thought its occurrence most improbable. It would be hardly
+possible with any plant which ascended above a few feet in
+height, or which lived in an exposed situation; for the stem
+could be pulled away easily from its support, with but little
+unwinding; nor could it have adhered at all, had not the
+internodes soon become moderately rigid. With
+leaf-climbers, as we shall soon see, analogous cases frequently
+occur; but these present no difficulty, as the stem is secured by
+the clasping petioles.</p>
+
+<p>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 <i>Ipomoea jucunda</i>; but frequently with
+<i>Hibbertia dentata</i>. This plant at first perplexed me
+much, for I continually observed its long and flexible shoots,
+evidently well fitted for twining, make a whole, or half, or
+quarter circle in one direction and then in an opposite
+direction; consequently, when I placed the shoots near thin or
+thick sticks, or perpendicularly stretched string, they seemed as
+if constantly trying to ascend, but always failed. I then
+surrounded the plant with a mass of branched twigs; the shoots
+ascended, and passed through them, but several came out
+laterally, and their depending extremities seldom turned upwards
+as is usual with twining plants. Finally, I surrounded a
+second plant with many thin upright sticks, and placed it near
+the first one with twigs; and now both had got what they liked,
+for they twined up the parallel sticks, sometimes winding round
+one and sometimes round several; and the shoots travelled
+laterally from one to the other pot; but as the plants grew
+older, some of the shoots twined regularly up thin upright
+sticks. Though the revolving movement was sometimes in one
+direction and sometimes in the other, the twining was invariably
+from left to right; <a name="citation36"></a><a
+href="#footnote36" class="citation">[36]</a> so that the more
+potent or persistent movement of revolution must have been in
+opposition to the course of the sun. It would appear that
+this <i>Hibbertia</i> is adapted both to ascend by twining, and
+to ramble laterally through the thick Australian scrub.</p>
+
+<p>I have described the above case in some detail, because, as
+far as I have seen, it is rare to find any special adaptations
+with twining plants, in which respect they differ much from the
+more highly organized tendril-bearers. The <i>Solanum
+dulcamara</i>, as we shall presently see, can twine only round
+stems which are both thin and flexible. Most twining plants
+are adapted to ascend supports of moderate though of different
+thicknesses. Our English twiners, as far as I have seen,
+never twine round trees, excepting the honeysuckle (<i>Lonicera
+periclymenum</i>), which I have observed twining up a young
+beech-tree nearly 4&frac12; inches in diameter. Mohl (p.
+134) found that the <i>Phaseolus multiflorus</i> and <i>Ipomoea
+purpurea</i> could not, when placed in a room with the light
+entering on one side, twine round sticks between 3 and 4 inches
+in diameter; for this interfered, in a manner presently to be
+explained, with the revolving movement. In the open air,
+however, the <i>Phaseolus</i> 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 <i>Ruscus androgynus</i>
+has ascended a column 9 inches in diameter; and although a
+<i>Wistaria</i> grown by me in a small pot tried in vain for
+weeks to get round a post between 5 and 6 inches in thickness,
+yet at Kew a plant ascended a trunk above 6 inches in
+diameter. The tropical twiners, on the other hand, can
+ascend thicker trees; I hear from Drs. Thomson and Hooker that
+this is the case with the <i>Butea parviflora</i>, one of the
+Menispermaceæ, and with some Dalbergias and other
+Leguminosæ. <a name="citation37"></a><a href="#footnote37"
+class="citation">[37]</a> This power would be necessary for
+any species which had to ascend by twining the large trees of a
+tropical forest; otherwise they would hardly ever be able to
+reach the light. In our temperate countries it would be
+injurious to the twining plants which die down every year if they
+were enabled to twine round trunks of trees, for they could not
+grow tall enough in a single season to reach the summit and gain
+the light.</p>
+
+<p>By what means certain twining plants are adapted to ascend
+only thin stems, whilst others can twine round thicker ones, I do
+not know. It appeared to me probable that twining plants
+with very long revolving shoots would be able to ascend thick
+supports; accordingly I placed <i>Ceropegia Gardnerii</i> near a
+post 6 inches in diameter, but the shoots entirely failed to wind
+round it; their great length and power of movement merely aid
+them in finding a distant stem round which to twine. The
+<i>Sphærostemma marmoratum</i> is a vigorous tropical
+twiner; and as it is a very slow revolver, I thought that this
+latter circumstance might help it in ascending a thick support;
+but though it was able to wind round a 6-inch post, it could do
+this only on the same level or plane, and did not form a spire
+and thus ascend.</p>
+
+<p>As ferns differ so much in structure from phanerogamic plants,
+it may be worth while here to show that twining ferns do not
+differ in their habits from other twining plants. In
+<i>Lygodium articulatum</i> the two internodes of the stem
+(properly the rachis) which are first formed above the root-stock
+do not move; the third from the ground revolves, but at first
+very slowly. This species is a slow revolver: but <i>L.
+scandens</i> made five revolutions, each at the average rate of 5
+hrs. 45 m.; and this represents fairly well the usual rate,
+taking quick and slow movers, amongst phanerogamic plants.
+The rate was accelerated by increased temperature. At each
+stage of growth only the two upper internodes revolved. A
+line painted along the convex surface of a revolving internode
+becomes first lateral, then concave, then lateral and ultimately
+again convex. Neither the internodes nor the petioles are
+irritable when rubbed. The movement is in the usual
+direction, namely, in opposition to the course of the sun; and
+when the stem twines round a thin stick, it becomes twisted on
+its own axis in the same direction. After the young
+internodes have twined round a stick, their continued growth
+causes them to slip a little upwards. If the stick be soon
+removed, they straighten themselves, and recommence
+revolving. The extremities of the depending shoots turn
+upwards, and twine on themselves. In all these respects we
+have complete identity with twining phanerogamic plants; and the
+above enumeration may serve as a summary of the leading
+characteristics of all twining plants.</p>
+
+<p>The power of revolving depends on the general health and
+vigour of the plant, as has been laboriously shown by Palm.
+But the movement of each separate internode is so independent of
+the others, that cutting off an upper one does not affect the
+revolutions of a lower one. When, however, Dutrochet cut
+off two whole shoots of the Hop, and placed them in water, the
+movement was greatly retarded; for one revolved in 20 hrs. and
+the other in 23 hrs., whereas they ought to have revolved in
+between 2 hrs. and 2 hrs. 30 m. Shoots of the Kidney-bean,
+cut off and placed in water, were similarly retarded, but in a
+less degree. I have repeatedly observed that carrying a
+plant from the greenhouse to my room, or from one part to another
+of the greenhouse, always stopped the movement for a time; hence
+I conclude that plants in a state of nature and growing in
+exposed situations, would not make their revolutions during very
+stormy weather. A decrease in temperature always caused a
+considerable retardation in the rate of revolution; but Dutrochet
+(tom. xvii. pp. 994, 996) has given such precise observations on
+this head with respect to the common pea that I need say nothing
+more. When twining plants are placed near a window in a
+room, the light in some cases has a remarkable power (as was
+likewise observed by Dutrochet, p. 998, with the pea) on the
+revolving movement, but this differs in degree with different
+plants; thus <i>Ipomoea jucunda</i> made a complete circle in 5
+hrs. 30 m.; the semicircle from the light taking 4 hrs. 80 m.,
+and that towards the light only 1 hr. <i>Lonicera
+brachypoda</i> revolved, in a reversed direction to the
+<i>Ipomoea</i>, in 8 hrs.; the semicircle from the light taking 5
+hrs. 23 m., and that to the light only 2 hrs. 37 m. From
+the rate of revolution in all the plants observed by me, being
+nearly the same during the night and the day, I infer that the
+action of the light is confined to retarding one semicircle and
+accelerating the other, so as not to modify greatly the rate of
+the whole revolution. This action of the light is
+remarkable, when we reflect how little the leaves are developed
+on the young and thin revolving internodes. It is all the
+more remarkable, as botanists believe (Mohl, p. 119) that twining
+plants are but little sensitive to the action of light.</p>
+
+<p>I will conclude my account of twining plants by giving a few
+miscellaneous and curious cases. With most twining plants
+all the branches, however many there may be, go on revolving
+together; but, according to Mohl (p. 4), only the lateral
+branches of <i>Tamus elephantipes</i> twine, and not the main
+stem. On the other hand, with a climbing species of
+Asparagus, the leading shoot alone, and not the branches,
+revolved and twined; but it should be stated that the plant was
+not growing vigorously. My plants of <i>Combretum
+argenteum</i> and <i>C. purpureum</i> made numerous short healthy
+shoots; but they showed no signs of revolving, and I could not
+conceive how these plants could be climbers; but at last <i>C.
+argenteum</i> put forth from the lower part of one of its main
+branches a thin shoot, 5 or 6 feet in length, differing greatly
+in appearance from the previous shoots, owing to its leaves being
+little developed, and this shoot revolved vigorously and
+twined. So that this plant produces shoots of two
+kinds. With <i>Periploca Græca</i> (Palm, p. 43) the
+uppermost shoots alone twine. Polygonum convolvulus twines
+only during the middle of the summer (Palm, p. 43, 94); and
+plants growing vigorously in the autumn show no inclination to
+climb. The majority of Asclepiadaceæ are twiners; but
+<i>Asclepias nigra</i> only &ldquo;in fertiliori solo incipit
+scandere subvolubili caule&rdquo; (Willdenow, quoted and
+confirmed by Palm, p. 41). <i>Asclepias vincetoxicum</i>
+does not regularly twine, but occasionally does so (Palm, p. 42;
+Mohl, p. 112) when growing under certain conditions. So it
+is with two species of <i>Ceropegia</i>, 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,&mdash;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
+Convolvulaceæ are excellent twiners; but in South Africa
+<i>Ipomoea argyræoides</i> almost always grows erect and
+compact, from about 12 to 18 inches in height, one specimen alone
+in Prof. Harvey&rsquo;s collection showing an evident disposition
+to twine. On the other hand, seedlings raised near Dublin
+twined up sticks above 8 feet in height. These facts are
+remarkable; for there can hardly be a doubt that in the dryer
+provinces of South Africa these plants have propagated themselves
+for thousands of generations in an erect condition; and yet they
+have retained during this whole period the innate power of
+spontaneously revolving and twining, whenever their shoots become
+elongated under proper conditions of life. Most of the
+species of <i>Phaseolus</i> are twiners; but certain varieties of
+the <i>P. multiflorus</i> produce (Léon, p. 681) two kinds
+of shoots, some upright and thick, and others thin and
+twining. I have seen striking instances of this curious
+case of variability in &ldquo;Fulmer&rsquo;s dwarf
+forcing-bean,&rdquo; which occasionally produced a single long
+twining shoot.</p>
+
+<p><i>Solanum dulcamara</i> is one of the feeblest and poorest of
+twiners: it may often be seen growing as an upright bush, and
+when growing in the midst of a thicket merely scrambles up
+between the branches without twining; but when, according to
+Dutrochet (tom. xix. p. 299), it grows near a thin and flexible
+support, such as the stem of a nettle, it twines round it.
+I placed sticks round several plants, and vertically stretched
+strings close to others, and the strings alone were ascended by
+twining. The stem twines indifferently to the right or
+left. Some others species of Solanum, and of another genus,
+viz. <i>Habrothamnus</i>, belonging to the same family, are
+described in horticultural works as twining plants, but they seem
+to possess this faculty in a very feeble degree. We may
+suspect that the species of these two genera have as yet only
+partially acquired the habit of twining. On the other hand
+with <i>Tecoma radicans</i>, a member of a family abounding with
+twiners and tendril-bearers, but which climbs, like the ivy, by
+the aid of rootlets, we may suspect that a former habit of
+twining has been lost, for the stem exhibited slight irregular
+movements which could hardly be accounted for by changes in the
+action of the light. There is no difficulty in
+understanding how a spirally twining plant could graduate into a
+simple root-climber; for the young internodes of <i>Bignonia
+Tweedyana</i> and of <i>Hoya carnosa</i> revolve and twine, but
+likewise emit rootlets which adhere to any fitting surface, so
+that the loss of twining would be no great disadvantage and in
+some respects an advantage to these species, as they would then
+ascend their supports in a more direct line. <a
+name="citation44"></a><a href="#footnote44"
+class="citation">[44]</a></p>
+
+<h3>CHAPTER II.<br />
+<span class="smcap">Leaf-Climbers</span>.</h3>
+
+<p class="gutsumm">Plants which climb by the aid of spontaneously
+revolving and sensitive
+petioles&mdash;<i>Clematis</i>&mdash;<i>Tropæolum</i>&mdash;<i>Maurandia</i>,
+flower-peduncles moving spontaneously and sensitive to a
+touch&mdash;<i>Rhodochiton</i>&mdash;<i>Lophospermum</i>&mdash;internodes
+sensitive&mdash;<i>Solanum</i>, thickening of the clasped
+petioles&mdash;<i>Fumaria</i>&mdash;<i>Adlumia</i>&mdash;Plants
+which climb by the aid of their produced
+midribs&mdash;<i>Gloriosa</i>&mdash;<i>Flagellaria</i>&mdash;<i>Nepenthes</i>&mdash;Summary
+on leaf-climbers.</p>
+
+<p><span class="smcap">We</span> now come to our second class of
+climbing plants, namely, those which ascend by the aid of
+irritable or sensitive organs. For convenience&rsquo; sake
+the plants in this class have been grouped under two
+sub-divisions, namely, leaf-climbers, or those which retain their
+leaves in a functional condition, and tendril-bearers. But
+these sub-divisions graduate into each other, as we shall see
+under Corydalis and the Gloriosa lily.</p>
+
+<p>It has long been observed that several plants climb by the aid
+of their leaves, either by their petioles (foot-stalks) or by
+their produced midribs; but beyond this simple fact they have not
+been described. Palm and Mohl class these plants with those
+which bear tendrils; but as a leaf is generally a defined object,
+the present classification, though artificial, has at least some
+advantages. Leaf-climbers are, moreover, intermediate in
+many respects between twiners and tendril-bearers. Eight
+species of <i>Clematis</i> and seven of <i>Tropæolum</i>
+were observed, in order to see what amount of difference in the
+manner of climbing existed within the same genus; and the
+differences are considerable.</p>
+
+<p><span class="smcap">Clematis</span>.&mdash;<i>C.
+glandulosa</i>.&mdash;The thin upper internodes revolve, moving
+against the course of the sun, precisely like those of a true
+twiner, at an average rate, judging from three revolutions, of 3
+hrs. 48 m. The leading shoot immediately twined round a
+stick placed near it; but, after making an open spire of only one
+turn and a half, it ascended for a short space straight, and then
+reversed its course and wound two turns in an opposite
+direction. This was rendered possible by the straight piece
+between the opposed spires having become rigid. The simple,
+broad, ovate leaves of this tropical species, with their short
+thick petioles, seem but ill-fitted for any movement; and whilst
+twining up a vertical stick, no use is made of them.
+Nevertheless, if the footstalk of a young leaf be rubbed with a
+thin twig a few times on any side, it will in the course of a few
+hours bend to that side; afterwards becoming straight
+again. The under side seemed to be the most sensitive; but
+the sensitiveness or irritability is slight compared to that
+which we shall meet with in some of the following species; thus,
+a loop of string, weighing 1.64 grain (106.2 mg.) and hanging for
+some days on a young footstalk, produced a scarcely perceptible
+effect. A sketch is here given of two young leaves which
+had naturally caught hold of two thin branches. A forked
+twig placed so as to press lightly on the under side of a young
+footstalk caused it, in 12 hrs., to bend greatly, and ultimately
+to such an extent that the leaf passed to the opposite side of
+the stem; the forked stick having been removed, the leaf slowly
+recovered its former position.</p>
+<p style="text-align: center">
+<a href="images/p47b.jpg">
+<img alt=
+"Fig. 1.  Clematis glandulosa.  With two young leaves clasping
+two twigs, with the clasping portions thickened"
+title=
+"Fig. 1.  Clematis glandulosa.  With two young leaves clasping
+two twigs, with the clasping portions thickened"
+ src="images/p47s.jpg" />
+</a></p>
+
+<p>The young leaves spontaneously and gradually change their
+position: when first developed the petioles are upturned and
+parallel to the stem; they then slowly bend downwards, remaining
+for a short time at right angles to the stem, and then become so
+much arched downwards that the blade of the leaf points to the
+ground with its tip curled inwards, so that the whole petiole and
+leaf together form a hook. They are thus enabled to catch
+hold of any twig with which they may be brought into contact by
+the revolving movement of the internodes. If this does not
+happen, they retain their hooked shape for a considerable time,
+and then bending upwards reassume their original upturned
+position, which is preserved ever afterwards. The petioles
+which have clasped any object soon become much thickened and
+strengthened, as may be seen in the drawing.</p>
+
+<p><i>Clematis montana</i>.&mdash;The long, thin petioles of the
+leaves, whilst young, are sensitive, and when lightly rubbed bend
+to the rubbed side, subsequently becoming straight. They
+are far more sensitive than the petioles of <i>C. glandulosa</i>;
+for a loop of thread weighing a quarter of a grain (16.2 mg.)
+caused them to bend; a loop weighing only one-eighth of a grain
+(8.1 mg.) sometimes acted and sometimes did not act. The
+sensitiveness extends from the blade of the leaf to the
+stem. I may here state that I ascertained in all cases the
+weights of the string and thread used by carefully weighing 50
+inches in a chemical balance, and then cutting off measured
+lengths. The main petiole carries three leaflets; but their
+short, sub-petioles are not sensitive. A young, inclined
+shoot (the plant being in the greenhouse) made a large circle
+opposed to the course of the sun in 4 hrs. 20 m., but the next
+day, being very cold, the time was 5 hrs. 10 m. A stick
+placed near a revolving stem was soon struck by the petioles
+which stand out at right angles, and the revolving movement was
+thus arrested. The petioles then began, being excited by
+the contact, to slowly wind round the stick. When the stick
+was thin, a petiole sometimes wound twice round it. The
+opposite leaf was in no way affected. The attitude assumed
+by the stem after the petiole had clasped the stick, was that of
+a man standing by a column, who throws his arm horizontally round
+it. With respect to the stem&rsquo;s power of twining, some
+remarks will be made under <i>C. calycina</i>.</p>
+
+<p><i>Clematis Sieboldi</i>.&mdash;A shoot made three revolutions
+against the sun at an average rate of 3 hrs. 11 m. The
+power of twining is like that of the last species. Its
+leaves are nearly similar in structure and in function, excepting
+that the sub-petioles of the lateral and terminal leaflets are
+sensitive. A loop of thread, weighing one-eighth of a
+grain, acted on the main petiole, but not until two or three days
+had elapsed. The leaves have the remarkable habit of
+spontaneously revolving, generally in vertical ellipses, in the
+same manner, but in a less degree, as will be described under
+<i>C. microphylla</i>.</p>
+
+<p><i>Clematis calycina</i>.&mdash;The young shoots are thin and
+flexible: one revolved, describing a broad oval, in 5 hrs. 30 m.,
+and another in 6 hrs. 12 m. They followed the course of the
+sun; but the course, if observed long enough, would probably be
+found to vary in this species, as well as in all the others of
+the genus. It is a rather better twiner than the two last
+species: the stem sometimes made two spiral turns round a thin
+stick, if free from twigs; it then ran straight up for a space,
+and reversing its course took one or two turns in an opposite
+direction. This reversal of the spire occurred in all the
+foregoing species. The leaves are so small compared with
+those of most of the other species, that the petioles at first
+seem ill-adapted for clasping. Nevertheless, the main
+service of the revolving movement is to bring them into contact
+with surrounding objects, which are slowly but securely
+seized. The young petioles, which alone are sensitive, have
+their ends bowed a little downwards, so as to be in a slight
+degree hooked; ultimately the whole leaf, if it catches nothing,
+becomes level. I gently rubbed with a thin twig the lower
+surfaces of two young petioles; and in 2 hrs. 30 m. they were
+slightly curved downwards; in 5 hrs., after being rubbed, the end
+of one was bent completely back, parallel to the basal portion;
+in 4 hrs. subsequently it became nearly straight again. To
+show how sensitive the young petioles are, I may mention that I
+just touched the under sides of two with a little water-colour,
+which when dry formed an excessively thin and minute crust; but
+this sufficed in 24 hrs. to cause both to bend downwards.
+Whilst the plant is young, each leaf consists of three divided
+leaflets, which barely have distinct petioles, and these are not
+sensitive; but when the plant is well grown, the petioles of the
+two lateral and terminal leaflets are of considerable length, and
+become sensitive so as to be capable of clasping an object in any
+direction.</p>
+
+<p>When a petiole has clasped a twig, it undergoes some
+remarkable changes, which may be observed with the other species,
+but in a less strongly marked manner, and will here be described
+once for all. The clasped petiole in the course of two or
+three days swells greatly, and ultimately becomes nearly twice as
+thick as the opposite one which has clasped nothing. When
+thin transverse slices of the two are placed under the microscope
+their difference is conspicuous: the side of the petiole which
+has been in contact with the support, is formed of a layer of
+colourless cells with their longer axes directed from the centre,
+and these are very much larger than the corresponding cells in
+the opposite or unchanged petiole; the central cells, also, are
+in some degree enlarged, and the whole is much indurated.
+The exterior surface generally becomes bright red. But a
+far greater change takes place in the nature of the tissues than
+that which is visible: the petiole of the unclasped leaf is
+flexible and can be snapped easily, whereas the clasped one
+acquires an extraordinary degree of toughness and rigidity, so
+that considerable force is required to pull it into pieces.
+With this change, great durability is probably acquired; at least
+this is the case with the clasped petioles of <i>Clematis
+vitalba</i>. The meaning of these changes is obvious,
+namely, that the petioles may firmly and durably support the
+stem.</p>
+
+<p><i>Clematis microphylla</i>, var.
+<i>leptophylla</i>.&mdash;The long and thin internodes of this
+Australian species revolve sometimes in one direction and
+sometimes in an opposite one, describing long, narrow, irregular
+ellipses or large circles. Four revolutions were completed
+within five minutes of the same average rate of 1 hr. 51 m.; so
+that this species moves more quickly than the others of the
+genus. The shoots, when placed near a vertical stick,
+either twine round it, or clasp it with the basal portions of
+their petioles. The leaves whilst young are nearly of the
+same shape as those of <i>C. viticella</i>, and act in the same
+manner like a hook, as will be described under that
+species. But the leaflets are more divided, and each
+segment whilst young terminates in a hardish point, which is much
+curved downwards and inwards; so that the whole leaf readily
+catches hold of any neighbouring object. The petioles of
+the young terminal leaflets are acted on by loops of thread
+weighing &#8539;th and even 0.0625th of a grain. The basal
+portion of the main petiole is much less sensitive, but will
+clasp a stick against which it presses.</p>
+
+<p>The leaves, whilst young, are continually and spontaneously
+moving slowly. A bell-glass was placed over a shoot secured
+to a stick, and the movements of the leaves were traced on it
+during several days. A very irregular line was generally
+formed; but one day, in the course of eight hours and three
+quarters, the figure clearly represented three and a half
+irregular ellipses, the most perfect one of which was completed
+in 2 hrs. 35 m. The two opposite leaves moved independently
+of each other. This movement of the leaves would aid that
+of the internodes in bringing the petioles into contact with
+surrounding objects. I discovered this movement too late to
+be enabled to observe it in the other species; but from analogy I
+can hardly doubt that the leaves of at least <i>C. viticella</i>,
+<i>C. flammula</i>, and <i>C. vitalba</i> move spontaneously;
+and, judging from <i>C. Sieboldi</i>, this probably is the case
+with <i>C. montana</i> and <i>C. calycina</i>. I
+ascertained that the simple leaves of <i>C. glandulosa</i>
+exhibited no spontaneous revolving movement.</p>
+
+<p><i>Clematis viticella</i>, var. <i>venosa</i>.&mdash;In this
+and the two following species the power of spirally twining is
+completely lost, and this seems due to the lessened flexibility
+of the internodes and to the interference caused by the large
+size of the leaves. But the revolving movement, though
+restricted, is not lost. In our present species a young
+internode, placed in front of a window, made three narrow
+ellipses, transversely to the direction of the light, at an
+average rate of 2 hrs. 40 m. When placed so that the
+movements were to and from the light, the rate was greatly
+accelerated in one half of the course, and retarded in the other,
+as with twining plants. The ellipses were small; the longer
+diameter, described by the apex of a shoot bearing a pair of not
+expanded leaves, was only 4&#8541; inches, and that by the apex
+of the penultimate internode only 1&#8539; inch. At the
+most favourable period of growth each leaf would hardly be
+carried to and fro by the movement of the internodes more than
+two or three inches, but, as above stated, it is probable that
+the leaves themselves move spontaneously. The movement of
+the whole shoot by the wind and by its rapid growth, would
+probably be almost equally efficient as these spontaneous
+movements, in bringing the petioles into contact with surrounding
+objects.</p>
+
+<p>The leaves are of large size. Each bears three pairs of
+lateral leaflets and a terminal one, all supported on rather long
+sub-petioles. The main petiole bends a little angularly
+downwards at each point where a pair of leaflets arises (see fig.
+2), and the petiole of the terminal leaflet is bent downwards at
+right angles; hence the whole petiole, with its rectangularly
+bent extremity, acts as a hook. This hook, the lateral
+petioles being directed a little upwards; forms an excellent
+grappling apparatus, by which the leaves readily become entangled
+with surrounding objects. If they catch nothing, the whole
+petiole ultimately grows straight. The main petiole, the
+sub-petioles, and the three branches into which each basi-lateral
+sub-petiole is generally subdivided, are all sensitive. The
+basal portion of the main petiole, between the stem and the first
+pair of leaflets, is less sensitive than the remainder; it will,
+however, clasp a stick with which it is left in contact.
+The inferior surface of the rectangularly bent terminal portion
+(carrying the terminal leaflet), which forms the inner side of
+the end of the hook, is the most sensitive part; and this portion
+is manifestly best adapted to catch a distant support. To
+show the difference in sensibility, I gently placed loops of
+string of the same weight (in one instance weighing only 0.82 of
+a grain or 53.14 mg.) on the several lateral sub-petioles and on
+the terminal one; in a few hours the latter was bent, but after
+24 hrs. no effect was produced on the other sub-petioles.
+Again, a terminal sub-petiole placed in contact with a thin stick
+became sensibly curved in 45 m., and in 1 hr. 10 m. moved through
+ninety degrees; whilst a lateral sub-petiole did not become
+sensibly curved until 3 hrs. 30 m. had elapsed. In all
+cases, if the sticks are taken away, the petioles continue to
+move during many hours afterwards; so they do after a slight
+rubbing; but they become straight again, after about a
+day&rsquo;s interval, that is if the flexure has not been very
+great or long continued.</p>
+<p style="text-align: center">
+<a href="images/p54b.jpg">
+<img alt=
+"Fig. 2.  A young leaf of Clematis viticeela"
+title=
+"Fig. 2.  A young leaf of Clematis viticeela"
+ src="images/p54s.jpg" />
+</a></p>
+
+<p>The graduated difference in the extension of the sensitiveness
+in the petioles of the above-described species deserves
+notice. In <i>C. montana</i> it is confined to the main
+petiole, and has not spread to the sub-petioles of the three
+leaflets; so it is with young plants of <i>C. calycina</i>, but
+in older plants it spreads to the three sub-petioles. In
+<i>C. viticella</i> the sensitiveness has spread to the petioles
+of the seven leaflets, and to the subdivisions of the
+basi-lateral sub-petioles. But in this latter species it
+has diminished in the basal part of the main petiole, in which
+alone it resided in <i>C. montana</i>; whilst it has increased in
+the abruptly bent terminal portion.</p>
+
+<p><i>Clematis flammula</i>.&mdash;The rather thick, straight,
+and stiff shoots, whilst growing vigorously in the spring, make
+small oval revolutions, following the sun in their course.
+Four were made at an average rate of 3 hrs. 45 m. The
+longer axis of the oval, described by the extreme tip, was
+directed at right angles to the line joining the opposite leaves;
+its length was in one case only 1&#8540;, and in another case
+1&frac34; inch; so that the young leaves were moved a very short
+distance. The shoots of the same plant observed in
+midsummer, when growing not so quickly, did not revolve at
+all. I cut down another plant in the early summer, so that
+by August 1st it had formed new and moderately vigorous shoots;
+these, when observed under a bell-glass, were on some days quite
+stationary, and on other days moved to and fro only about the
+eighth of an inch. Consequently the revolving power is much
+enfeebled in this species, and under unfavourable circumstances
+is completely lost. The shoot must depend for coming into
+contact with surrounding objects on the probable, though not
+ascertained spontaneous movement of the leaves, on rapid growth,
+and on movement from the wind. Hence, perhaps, it is that
+the petioles have acquired a high degree of sensitiveness as a
+compensation for the little power of movement in the shoots.</p>
+
+<p>The petioles are bowed downwards, and have the same general
+hook-like form as in <i>C. viticella</i>. The medial
+petiole and the lateral sub-petioles are sensitive, especially
+the much bent terminal portion. As the sensitiveness is
+here greater than in any other species of the genus observed by
+me, and is in itself remarkable, I will give fuller
+details. The petioles, when so young that they have not
+separated from one another, are not sensitive; when the lamina of
+a leaflet has grown to a quarter of an inch in length (that is,
+about one-sixth of its full size), the sensitiveness is highest;
+but at this period the petioles are relatively much more fully
+developed than are the blades of the leaves. Full-grown
+petioles are not in the least sensitive. A thin stick
+placed so as to press lightly against a petiole, having a leaflet
+a quarter of an inch in length, caused the petiole to bend in 3
+hrs. 15 m. In another case a petiole curled completely
+round a stick in 12 hrs. These petioles were left curled for 24
+hrs., and the sticks were then removed; but they never
+straightened themselves. I took a twig, thinner than the
+petiole itself, and with it lightly rubbed several petioles four
+times up and down; these in 1 hr. 45 m. became slightly curled;
+the curvature increased during some hours and then began to
+decrease, but after 25 hrs. from the time of rubbing a vestige of
+the curvature remained. Some other petioles similarly
+rubbed twice, that is, once up and once down, became perceptibly
+curved in about 2 hrs. 30 m., the terminal sub-petiole moving
+more than the lateral sub-petioles; they all became straight
+again in between 12 hrs. and 14 hrs. Lastly, a length of
+about one-eighth of an inch of a sub-petiole, was lightly rubbed
+with the same twig only once; it became slightly curved in 3
+hrs., remaining so during 11 hrs., but by the next morning was
+quite straight.</p>
+
+<p>The following observations are more precise. After
+trying heavier pieces of string and thread, I placed a loop of
+fine string, weighing 1.04 gr. (67.4 mg.) on a terminal
+sub-petiole: in 6 hrs. 40 m. a curvature could be seen; in 24
+hrs. the petiole formed an open ring round the string; in 48 hrs.
+the ring had almost closed on the string, and in 72 hrs. seized
+it so firmly, that some force was necessary for its
+withdrawal. A loop weighing 0.52 of a grain (33.7 mg.)
+caused in 14 hrs. a lateral sub-petiole just perceptibly to
+curve, and in 24 hrs. it moved through ninety degrees.
+These observations were made during the summer: the following
+were made in the spring, when the petioles apparently are more
+sensitive:&mdash;A loop of thread, weighing one-eighth of a grain
+(8.1 mg.), produced no effect on the lateral sub-petioles, but
+placed on a terminal one, caused it, after 24 hrs., to curve
+moderately; the curvature, though the loop remained suspended,
+was after 48 hrs. diminished, but never disappeared; showing that
+the petiole had become partially accustomed to the insufficient
+stimulus. This experiment was twice repeated with nearly
+the same result. Lastly, a loop of thread, weighing only
+one-sixteenth of a grain (4.05 mg.) was twice gently placed by a
+forceps on a terminal sub-petiole (the plant being, of course, in
+a still and closed room), and this weight certainly caused a
+flexure, which very slowly increased until the petiole moved
+through nearly ninety degrees: beyond this it did not move; nor
+did the petiole, the loop remaining suspended, ever become
+perfectly straight again.</p>
+
+<p>When we consider, on the one hand, the thickness and stiffness
+of the petioles, and, on the other hand, the thinness and
+softness of fine cotton thread, and what an extremely small
+weight one-sixteenth of a grain (4.05 mg.) is, these facts are
+remarkable. But I have reason to believe that even a less
+weight excites curvature when pressing over a broader surface
+than that acted on by a thread. Having noticed that the end
+of a suspended string which accidentally touched a petiole,
+caused it to bend, I took two pieces of thin twine, 10 inches in
+length (weighing 1.64 gr.), and, tying them to a stick, let them
+hang as nearly perpendicularly downwards as their thinness and
+flexuous form, after being stretched, would permit; I then
+quietly placed their ends so as just to rest on two petioles, and
+these certainly became curved in 36 hrs. One of the ends touched
+the angle between a terminal and lateral sub-petiole, and it was
+in 48 hours caught between them as by a forceps. In these
+cases the pressure, though spread over a wider surface than that
+touched by the cotton thread, must have been excessively
+slight.</p>
+
+<p><i>Clematis vitalba</i>.&mdash;The plants were in pots and not
+healthy, so that I dare not trust my observations, which indicate
+much similarity in habits with <i>C. flammula</i>. I
+mention this species only because I have seen many proofs that
+the petioles in a state of nature are excited to movement by very
+slight pressure. For instance, I have found them embracing
+thin withered blades of grass, the soft young leaves of a maple,
+and the flower-peduncles of the quaking-grass or Briza. The
+latter are about as thick as the hair of a man&rsquo;s beard, but
+they were completely surrounded and clasped. The petioles
+of a leaf, so young that none of the leaflets were expanded, had
+partially seized a twig. Those of almost all the old
+leaves, even when unattached to any object, are much convoluted;
+but this is owing to their having come, whilst young, into
+contact during several hours with some object subsequently
+removed. With none of the above-described species,
+cultivated in pots and carefully observed, was there any
+permanent bending of the petioles without the stimulus of
+contact. In winter, the blades of the leaves of <i>C.
+vitalba</i> drop off; but the petioles (as was observed by Mohl)
+remain attached to the branches, sometimes during two seasons;
+and, being convoluted, they curiously resemble true tendrils,
+such as those possessed by the allied genus
+<i>Naravelia</i>. The petioles which have clasped some
+object become much more stiff, hard, and polished than those
+which have failed in this their proper function.</p>
+
+<p><span class="smcap">Tropæolum</span>.&mdash;I observed
+<i>T. tricolorum</i>, <i>T. azureum</i>, <i>T. pentaphyllum</i>,
+<i>T. peregrinum</i>, <i>T. elegans</i>, <i>T. tuberosum</i>, and
+a dwarf variety of, as I believe, <i>T. minus</i>.</p>
+
+<p><i>Tropæolum tricolorum</i>, var.
+<i>grandiflorum</i>.&mdash;The flexible shoots, which first rise
+from the tubers, are as thin as fine twine. One such shoot
+revolved in a course opposed to the sun, at an average rate,
+judging from three revolutions, of 1 hr. 23 m.; but no doubt the
+direction of the revolving movement is variable. When the
+plants have grown tall and are branched, all the many lateral
+shoots revolve. The stem, whilst young, twines regularly
+round a thin vertical stick, and in one case I counted eight
+spiral turns in the same direction; but when grown older, the
+stem often runs straight up for a space, and, being arrested by
+the clasping petioles, makes one or two spires in a reversed
+direction. Until the plant grows to a height of two or
+three feet, requiring about a month from the time when the first
+shoot appears above ground, no true leaves are produced, but, in
+their place, filaments coloured like the stem. The
+extremities of these filaments are pointed, a little flattened,
+and furrowed on the upper surface. They never become
+developed into leaves. As the plant grows in height new
+filaments are produced with slightly enlarged tips; then others,
+bearing on each side of the enlarged medial tip a rudimentary
+segment of a leaf; soon other segments appear, and at last a
+perfect leaf is formed, with seven deep segments. So that
+on the same plant we may see every step, from tendril-like
+clasping filaments to perfect leaves with clasping
+petioles. After the plant has grown to a considerable
+height, and is secured to its support by the petioles of the true
+leaves, the clasping filaments on the lower part of the stem
+wither and drop off; so that they perform only a temporary
+service.</p>
+
+<p>These filaments or rudimentary leaves, as well as the petioles
+of the perfect leaves, whilst young, are highly sensitive on all
+sides to a touch. The slightest rub caused them to curve
+towards the rubbed side in about three minutes, and one bent
+itself into a ring in six minutes; they subsequently became
+straight. When, however, they have once completely clasped
+a stick, if this is removed, they do not straighten
+themselves. The most remarkable fact, and one which I have
+observed in no other species of the genus, is that the filaments
+and the petioles of the young leaves, if they catch no object,
+after standing for some days in their original position,
+spontaneously and slowly oscillate a little from side to side,
+and then move towards the stem and clasp it. They likewise
+often become, after a time, in some degree spirally
+contracted. They therefore fully deserve to be called
+tendrils, as they are used for climbing, are sensitive to a
+touch, move spontaneously, and ultimately contract into a spire,
+though an imperfect one. The present species would have
+been classed amongst the tendril-bearers, had not these
+characters been confined to early youth. During maturity it
+is a true leaf-climber.</p>
+
+<p><i>Tropæolum azureum</i>.&mdash;An upper internode made
+four revolutions, following the sun, at an average rate of 1 hr.
+47 m. The stem twined spirally round a support in the same
+irregular manner as that of the last species. Rudimentary
+leaves or filaments do not exist. The petioles of the young
+leaves are very sensitive: a single light rub with a twig caused
+one to move perceptibly in 5 m., and another in 6 m. The
+former became bent at right angles in 15 min., and became
+straight again in between 5 hrs. and 6 hrs. A loop of
+thread weighing &#8539;th of a grain caused another petiole to
+curve.</p>
+
+<p><i>Tropæolum pentaphyllum</i>.&mdash;This species has
+not the power of spirally twining, which seems due, not so much
+to a want of flexibility in the stem, as to continual
+interference from the clasping petioles. An upper internode
+made three revolutions, following the sun, at an average rate of
+1 hr. 46 m. The main purpose of the revolving movement in
+all the species of <i>Tropæolum</i> manifestly is to bring
+the petioles into contact with some supporting object. The
+petiole of a young leaf, after a slight rub, became curved in 6
+m.; another, on a cold day, in 20 m., and others in from 8 m. to
+10 m. Their curvature usually increased greatly in from 15
+m. to 20 m., and they became straight again in between 5 hrs. and
+6 hrs., but on one occasion in 3 hrs. When a petiole has
+fairly clasped a stick, it is not able, on the removal of the
+stick, to straighten itself. The free upper part of one,
+the base of which had already clasped a stick, still retained the
+power of movement. A loop of thread weighing &#8539;th of a
+grain caused a petiole to curve; but the stimulus was not
+sufficient, the loop remaining suspended, to cause a permanent
+flexure. If a much heavier loop be placed in the angle
+between the petiole and the stem, it produces no effect; whereas
+we have seen with <i>Clematis montana</i> that the angle between
+the stem and petiole is sensitive.</p>
+
+<p><i>Tropæolum peregrinum</i>.&mdash;The first-formed
+internodes of a young plant did not revolve, resembling in this
+respect those of a twining plant. In an older plant the
+four upper internodes made three irregular revolutions, in a
+course opposed to the sun, at an average rate of 1 hr. 48
+min. It is remarkable that the average rate of revolution
+(taken, however, but from few observations) is very nearly the
+same in this and the two last species, namely, 1 hr. 47 m., 1 hr.
+46 m., and 1 hr. 48 m. The present species cannot twine
+spirally, which seems mainly due to the rigidity of the
+stem. In a very young plant, which did not revolve, the
+petioles were not sensitive. In older plants the petioles
+of quite young leaves, and of leaves as much as an inch and a
+quarter in diameter, are sensitive. A moderate rub caused
+one to curve in 10 m., and others in 20 m. They became
+straight again in between 5 hrs. 45 m. and 8 hrs. Petioles
+which have naturally come into contact with a stick, sometimes
+take two turns round it. After they have clasped a support,
+they become rigid and hard. They are less sensitive to a
+weight than in the previous species; for loops of string weighing
+0.82 of a grain (53.14 mg.), did not cause any curvature, but a
+loop of double this weight (1.64 gr.) acted.</p>
+
+<p><i>Tropæolum elegans</i>.&mdash;I did not make many
+observations on this species. The short and stiff
+internodes revolve irregularly, describing small oval
+figures. One oval was completed in 3 hrs. A young petiole,
+when rubbed, became slightly curved in 17 m.; and afterwards much
+more so. It was nearly straight again in 8 hrs.</p>
+
+<p><i>Tropæolum tuberosum</i>.&mdash;On a plant nine inches
+in height, the internodes did not move at all; but on an older
+plant they moved irregularly and made small imperfect
+ovals. These movements could be detected only by being
+traced on a bell-glass placed over the plant. Sometimes the
+shoots stood still for hours; during some days they moved only in
+one direction in a crooked line; on other days they made small
+irregular spires or circles, one being completed in about 4
+hrs. The extreme points reached by the apex of the shoot
+were only about one or one and a half inches asunder; yet this
+slight movement brought the petioles into contact with some
+closely surrounding twigs, which were then clasped. With
+the lessened power of spontaneously revolving, compared with that
+of the previous species, the sensitiveness of the petioles is
+also diminished. These, when rubbed a few times, did not
+become curved until half an hour had elapsed; the curvature
+increased during the next two hours, and then very slowly
+decreased; so that they sometimes required 24 hrs. to become
+straight again. Extremely young leaves have active
+petioles; one with the lamina only 0.15 of an inch in diameter,
+that is, about a twentieth of the full size, firmly clasped a
+thin twig. But leaves grown to a quarter of their full size
+can likewise act.</p>
+
+<p><i>Tropæolum minus</i> (?).&mdash;The internodes of a
+variety named &ldquo;dwarf crimson Nasturtium&rdquo; did not
+revolve, but moved in a rather irregular course during the day to
+the light, and from the light at night. The petioles, when
+well rubbed, showed no power of curving; nor could I see that
+they ever clasped any neighbouring object. We have seen in
+this genus a gradation from species such as <i>T. tricolorum</i>,
+which have extremely sensitive petioles, and internodes which
+rapidly revolve and spirally twine up a support, to other species
+such as <i>T. elegans</i> and <i>T. tuberosum</i>, the petioles
+of which are much less sensitive, and the internodes of which
+have very feeble revolving powers and cannot spirally twine round
+a support, to this last species, which has entirely lost or never
+acquired these faculties. From the general character of the
+genus, the loss of power seems the more probable alternative.</p>
+
+<p>In the present species, in <i>T. elegans</i>, and probably in
+others, the flower-peduncle, as soon as the seed-capsule begins
+to swell, spontaneously bends abruptly downwards and becomes
+somewhat convoluted. If a stick stands in the way, it is to
+a certain extent clasped; but, as far as I have been able to
+observe, this clasping movement is independent of the stimulus
+from contact.</p>
+
+<p><span class="smcap">Antirrhineæ</span>.&mdash;In this
+tribe (Lindley) of the Scrophulariaceæ, at least four of
+the seven included genera have leaf-climbing species.</p>
+
+<p><i>Maurandia Barclayana</i>.&mdash;A thin, slightly bowed
+shoot made two revolutions, following the sun, each in 3 hrs. 17
+min.; on the previous day this same shoot revolved in an opposite
+direction. The shoots do not twine spirally, but climb
+excellently by the aid of their young and sensitive
+petioles. These petioles, when lightly rubbed, move after a
+considerable interval of time, and subsequently become straight
+again. A loop of thread weighing &#8539;th of a grain
+caused them to bend.</p>
+
+<p><i>Maurandia semperflorens</i>.&mdash;This freely growing
+species climbs exactly like the last, by the aid of its sensitive
+petioles. A young internode made two circles, each in 1 hr.
+46 min.; so that it moved almost twice as rapidly as the last
+species. The internodes are not in the least sensitive to a
+touch or pressure. I mention this because they are
+sensitive in a closely allied genus, namely, Lophospermum.
+The present species is unique in one respect. Mohl asserts
+(p. 45) that &ldquo;the flower-peduncles, as well as the
+petioles, wind like tendrils;&rdquo; but he classes as tendrils
+such objects as the spiral flower-stalks of the
+<i>Vallisneria</i>. This remark, and the fact of the
+flower-peduncles being decidedly flexuous, led me carefully to
+examine them. They never act as true tendrils; I repeatedly
+placed thin sticks in contact with young and old peduncles, and I
+allowed nine vigorous plants to grow through an entangled mass of
+branches; but in no one instance did they bend round any
+object. It is indeed in the highest degree improbable that
+this should occur, for they are generally developed on branches
+which have already securely clasped a support by the petioles of
+their leaves; and when borne on a free depending branch, they are
+not produced by the terminal portion of the internode which alone
+has the power of revolving; so that they could be brought only by
+accident into contact with any neighbouring object.
+Nevertheless (and this is the remarkable fact) the
+flower-peduncles, whilst young, exhibit feeble revolving powers,
+and are slightly sensitive to a touch. Having selected some
+stems which had firmly clasped a stick by their petioles, and
+having placed a bell-glass over them, I traced the movements of
+the young flower-peduncles. The tracing generally formed a
+short and extremely irregular line, with little loops in its
+course. A young peduncle 1&frac12; inch in length was
+carefully observed during a whole day, and it made four and a
+half narrow, vertical, irregular, and short ellipses&mdash;each
+at an average rate of about 2 hrs. 25 m. An adjoining
+peduncle described during the same time similar, though fewer,
+ellipses. As the plant had occupied for some time exactly
+the same position, these movements could not be attributed to any
+change in the action of the light. Peduncles, old enough
+for the coloured petals to be just visible, do not move.
+With respect to irritability, <a name="citation68"></a><a
+href="#footnote68" class="citation">[68]</a> I rubbed two young
+peduncles (1&frac12; inch in length) a few times very lightly
+with a thin twig; one was rubbed on the upper, and the other on
+the lower side, and they became in between 4 hrs. and 5 hrs.
+distinctly bowed towards these sides; in 24 hrs. subsequently,
+they straightened themselves. Next day they were rubbed on
+the opposite sides, and they became perceptibly curved towards
+these sides. Two other and younger peduncles (three-fourths
+of an inch in length) were lightly rubbed on their adjoining
+sides, and they became so much curved towards one another, that
+the arcs of the bows stood at nearly right angles to their
+previous direction; and this was the greatest movement seen by
+me. Subsequently they straightened themselves. Other
+peduncles, so young as to be only three-tenths of an inch in
+length, became curved when rubbed. On the other hand,
+peduncles above 1&frac12; inch in length required to be rubbed
+two or three times, and then became only just perceptibly
+bowed. Loops of thread suspended on the peduncles produced
+no effect; loops of string, however, weighing 0.82 and 1.64 of a
+grain sometimes caused a slight curvature; but they were never
+closely clasped, as were the far lighter loops of thread by the
+petioles.</p>
+
+<p>In the nine vigorous plants observed by me, it is certain that
+neither the slight spontaneous movements nor the slight
+sensitiveness of the flower-peduncles aided the plants in
+climbing. If any member of the Scrophulariaceæ had
+possessed tendrils produced by the modification of
+flower-peduncles, I should have thought that this species of
+<i>Maurandia</i> had perhaps retained a useless or rudimentary
+vestige of a former habit; but this view cannot be
+maintained. We may suspect that, owing to the principle of
+correlation, the power of movement has been transferred to the
+flower-peduncles from the young internodes, and sensitiveness
+from the young petioles. But to whatever cause these
+capacities are due, the case is interesting; for, by a little
+increase in power through natural selection, they might easily
+have been rendered as useful to the plant in climbing, as are the
+flower-peduncles (hereafter to be described) of Vitis or
+Cardiospermum.</p>
+
+<p><i>Rhodochiton volubile</i>.&mdash;A long flexible shoot swept
+a large circle, following the sun, in 5 hrs. 30 m.; and, as the
+day became warmer, a second circle was completed in 4 hrs. 10
+m. The shoots sometimes make a whole or a half spire round
+a vertical stick, they then run straight up for a space, and
+afterwards turn spirally in an opposite direction. The
+petioles of very young leaves about one-tenth of their full size,
+are highly sensitive, and bend towards the side which is touched;
+but they do not move quickly. One was perceptibly curved in
+1 hr. 10 m., after being lightly rubbed, and became considerably
+curved in 5 hrs. 40 m.; some others were scarcely curved in 5
+hrs. 30 m., but distinctly so in 6 hrs. 30 m. A curvature
+was perceptible in one petiole in between 4 hrs. 30 m. and 5
+hrs., after the suspension of a little loop of string. A
+loop of fine cotton thread, weighing one sixteenth of a grain
+(4.05 mg.), not only caused a petiole slowly to bend, but was
+ultimately so firmly clasped that it could be withdrawn only by
+some little force. The petioles, when coming into contact
+with a stick, take either a complete or half a turn round it, and
+ultimately increase much in thickness. They do not possess
+the power of spontaneously revolving.</p>
+
+<p><i>Lophospermum scandens</i>, var.
+<i>purpureum</i>.&mdash;Some long, moderately thin internodes
+made four revolutions at an average rate of 3 hrs. 15 m.
+The course pursued was very irregular, namely, an extremely
+narrow ellipse, a large circle, an irregular spire or a zigzag
+line, and sometimes the apex stood still. The young
+petioles, when brought by the revolving movement into contact
+with sticks, clasped them, and soon increased considerably in
+thickness. But they are not quite so sensitive to a weight
+as those of the <i>Rhodochiton</i>, for loops of thread weighing
+one-eighth of a grain did not always cause them to bend.</p>
+
+<p>This plant presents a case not observed by me in any other
+leaf-climber or twiner, <a name="citation71"></a><a
+href="#footnote71" class="citation">[71]</a> namely, that the
+young internodes of the stem are sensitive to a touch. When
+a petiole of this species clasps a stick, it draws the base of
+the internode against it; and then the internode itself bends
+towards the stick, which is caught between the stem and the
+petiole as by a pair of pincers. The internode afterwards
+straightens itself, excepting the part in actual contact with the
+stick. Young internodes alone are sensitive, and these are
+sensitive on all sides along their whole length. I made
+fifteen trials by twice or thrice lightly rubbing with a thin
+twig several internodes; and in about 2 hrs., but in one case in
+3 hrs., all were bent: they became straight again in about 4 hrs.
+afterwards. An internode, which was rubbed as often as six
+or seven times, became just perceptibly curved in 1 hr. 15 m.,
+and in 3 hrs. the curvature increased much; it became straight
+again in the course of the succeeding night. I rubbed some
+internodes one day on one side, and the next day either on the
+opposite side or at right angles to the first side; and the
+curvature was always towards the rubbed side.</p>
+
+<p>According to Palm (p. 63), the petioles of <i>Linaria
+cirrhosa</i> and, to a limited degree, those of <i>L. elatine</i>
+have the power of clasping a support.</p>
+
+<p><span class="smcap">Solanaceæ</span>.&mdash;<i>Solanum
+jasminoides</i>.&mdash;Some of the species in this large genus
+are twiners; but the present species is a true
+leaf-climber. A long, nearly upright shoot made four
+revolutions, moving against the sun, very regularly at an average
+rate of 3 hrs. 26 m. The shoots, however, sometimes stood
+still. It is considered a greenhouse plant; but when kept
+there, the petioles took several days to clasp a stick: in the
+hothouse a stick was clasped in 7 hrs. In the greenhouse a
+petiole was not affected by a loop of string, suspended during
+several days and weighing 2&frac12; grains (163 mg.); but in the
+hothouse one was made to curve by a loop weighing 1.64 gr.
+(106.27 mg.); and, on the removal of the string, it became
+straight again. Another petiole was not at all acted on by
+a loop weighing only 0.82 of a grain (53.14 mg.) We have seen
+that the petioles of some other leaf-climbing plants are affected
+by one-thirteenth of this latter weight. In this species,
+and in no other leaf-climber seen by me, a full-grown leaf is
+capable of clasping a stick; but in the greenhouse the movement
+was so extraordinarily slow that the act required several weeks;
+on each succeeding week it was clear that the petiole had become
+more and more curved, until at last it firmly clasped the
+stick.</p>
+<p style="text-align: center">
+<a href="images/p73b.jpg">
+<img alt=
+"Fig. 3.  Solanum jasminoides, with one of its petioles clasping
+a stick"
+title=
+"Fig. 3.  Solanum jasminoides, with one of its petioles clasping
+a stick"
+ src="images/p73s.jpg" />
+</a></p>
+
+<p>The flexible petiole of a half or a quarter grown leaf which
+has clasped an object for three or four days increases much in
+thickness, and after several weeks becomes so wonderfully hard
+and rigid that it can hardly be removed from its support.
+On comparing a thin transverse slice of such a petiole with one
+from an older leaf growing close beneath, which had not clasped
+anything, its diameter was found to be fully doubled, and its
+structure greatly changed. In two other petioles similarly
+compared, and here represented, the increase in diameter was not
+quite so great. In the section of the petiole in its
+ordinary state (A), we see a semilunar band of cellular tissue
+(not well shown in the woodcut) differing slightly in appearance
+from that outside it, and including three closely approximate
+groups of dark vessels. Near the upper surface of the
+petiole, beneath two exterior ridges, there are two other small
+circular groups of vessels. In the section of the petiole
+(B) which had clasped during several weeks a stick, the two
+exterior ridges have become much less prominent, and the two
+groups of woody vessels beneath them much increased in
+diameter. The semilunar band has been converted into a
+complete ring of very hard, white, woody tissue, with lines
+radiating from the centre. The three groups of vessels,
+which, though near together, were before distinct, are now
+completely blended. The upper part of this ring of woody
+vessels, formed by the prolongation of the horns of the original
+semilunar band, is narrower than the lower part, and slightly
+less compact. This petiole after clasping the stick had
+actually become thicker than the stem from which it arose; and
+this was chiefly due to the increased thickness of the ring of
+wood. This ring presented, both in a transverse and
+longitudinal section, a closely similar structure to that of the
+stem. It is a singular morphological fact that the petiole
+should thus acquire a structure almost identically the same with
+that of the axis; and it is a still more singular physiological
+fact that so great a change should have been induced by the mere
+act of clasping a support. <a name="citation75"></a><a
+href="#footnote75" class="citation">[75]</a></p>
+<p style="text-align: center">
+<a href="images/p74b.jpg">
+<img alt=
+"Fig. 4.  Solanum jasminoides.  A. Section of the petiole in its
+ordinary state.  B. Section of the petiole some weeks after it
+had clasped a stick, as shown in fig. 2"
+title=
+"Fig. 4.  Solanum jasminoides.  A. Section of the petiole in its
+ordinary state.  B. Section of the petiole some weeks after it
+had clasped a stick, as shown in fig. 2"
+ src="images/p74s.jpg" />
+</a></p>
+
+<p><span class="smcap">Fumariaceæ</span>.&mdash;<i>Fumaria
+officinalis</i>.&mdash;It could not have been anticipated that so
+lowly a plant as this Fumaria should have been a climber.
+It climbs by the aid of the main and lateral petioles of its
+compound leaves; and 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 become rather thicker and more
+cylindrical. On lightly rubbing several petioles with a
+twig, they became perceptibly curved in 1 hr. 15 m., and
+subsequently straightened themselves. A stick gently placed
+in the angle between two sub-petioles excited them to move, and
+was almost clasped in 9 hrs. A loop of thread, weighing
+one-eighth of a grain, caused, after 12 hrs. and before 20 hrs,
+had elapsed, a considerable curvature; but it was never fairly
+clasped by the petiole. The young internodes are in
+continual movement, which is considerable in extent, but very
+irregular; a zigzag line, or a spire crossing itself; or a figure
+of 8 being formed. The course during 12 hrs., when traced
+on a bell-glass, apparently represented about four
+ellipses. The leaves themselves likewise move
+spontaneously, the main petioles curving themselves in accordance
+with the movements of the internodes; so that when the latter
+moved to one side, the petioles moved to the same side, then,
+becoming straight, reversed their curvature. The petioles,
+however, do not move over a wide space, as could be seen when a
+shoot was securely tied to a stick. The leaf in this case
+followed an irregular course, like that made by the
+internodes.</p>
+
+<p><i>Adlumia cirrhosa</i>.&mdash;I raised some plants late in
+the summer; they formed very fine leaves, but threw up no central
+stem. The first-formed leaves were not sensitive; some of
+the later ones were so, but only towards their extremities, which
+were thus enabled 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 have been,
+had it grown tall enough to climb. The tip of one of these
+basal leaves, whilst young, described in 1 hr. 36 m. a narrow
+ellipse, open at one end, and exactly three inches in length; a
+second ellipse was broader, more irregular, and shorter, viz.,
+only 2&frac12; inches in length, and was completed in 2 hrs. 2
+m. From the analogy of <i>Fumaria</i> and <i>Corydalis</i>,
+I have no doubt that the internodes of Adlumia have the power of
+revolving.</p>
+
+<p><i>Corydalis claviculata</i>.&mdash;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 has been classed amongst tendril-bearers.</p>
+
+<p>Besides the plants already described, <i>Bignonia unguis</i>
+and its close allies, though aided by tendrils, have clasping
+petioles. According to Mohl (p. 40), <i>Cocculus
+Japonicus</i> (one of the Menispermaceæ) and a fern, the
+<i>Ophioglossum Japonicum</i> (p. 39), climb by their
+leaf-stalks.</p>
+
+<div class="gapspace">&nbsp;</div>
+<p>We now come to a small section of plants which climb by means
+of the produced midribs or tips of their leaves.</p>
+
+<p><span class="smcap">Liliaceæ</span>.&mdash;<i>Gloriosa
+Plantii</i>.&mdash;The stem of a half-grown plant continually
+moved, generally describing an irregular spire, but sometimes
+oval figures with the longer axes directed in different
+lines. It either followed the sun, or moved in an opposite
+course, and sometimes stood still before reversing its
+direction. One oval was completed in 3 hrs. 40 m.; of two
+horseshoe-shaped figures, one was completed in 4 hrs. 35 m. and
+the other in 3 hrs. The shoots, in their 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 gets into an inclined
+position, the end bends downwards into a well-formed hook.
+This hook is now strong and rigid enough to catch any object,
+and, when caught, to anchor the plant and stop the revolving
+movement. Its inner surface is sensitive, but not in nearly
+so high a degree as that of the many before-described petioles;
+for a loop of string, weighing 1.64 grain, produced no
+effect. When the hook has caught a thin twig or even a
+rigid fibre, the point may be perceived in from 1 hr. to 3 hrs.
+to have curled a little inwards; and, under favourable
+circumstances, it curls round and permanently seizes an object in
+from 8 hrs. to 10 hrs. The hook when first formed, before
+the leaf has bent downwards, is but little sensitive. If it
+catches hold of nothing, it remains open and sensitive for a long
+time; ultimately the extremity spontaneously and slowly curls
+inwards, and makes a button-like, flat, spiral coil at the end of
+the leaf. One leaf was watched, and the hook remained open
+for thirty-three days; but during the last week the tip had
+curled so much inwards that only a very thin twig could have been
+inserted within it. As soon as the tip has curled so much
+inwards that the hook is converted into a ring, its sensibility
+is lost; but as long as it remains open some sensibility is
+retained.</p>
+
+<p>Whilst the plant was only about six inches in height, the
+leaves, four or five in number, were broader than those
+subsequently produced; their soft and but little-attenuated tips
+were not sensitive, and did not form hooks; nor did the stem then
+revolve. At this early period of growth, the plant can
+support itself; its climbing powers are not required, and
+consequently are not developed. So again, the leaves on the
+summit of a full-grown flowering plant, which would not require
+to climb any higher, were not sensitive and could not clasp a
+stick. We thus see how perfect is the economy of
+nature.</p>
+
+<p><span
+class="smcap">Commelynaceæ</span>.&mdash;<i>Flagellaria
+Indica</i>.&mdash;From dried specimens it is manifest that this
+plant climbs exactly like the <i>Gloriosa</i>. A young
+plant 12 inches in height, and bearing fifteen leaves, had not a
+single leaf as yet produced into a hook or tendril-like filament;
+nor did the stem revolve. Hence this plant acquires its
+climbing powers later in life than does the <i>Gloriosa</i>
+lily. According to Mohl (p. 41), <i>Uvularia</i>
+(Melanthaceæ) also climbs like <i>Gloriosa</i>.</p>
+
+<p>These three last-named genera are Monocotyledons; but there is
+one Dicotyledon, namely <i>Nepenthes</i>, which is ranked by Mohl
+(p. 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 coiling
+round any support. The twisted part becomes thicker; but I
+observed in Mr. Veitch&rsquo;s hothouse that the stalk often
+takes a turn when not in contact with any object, and that this
+twisted part is likewise thickened. Two vigorous young
+plants of <i>N. lævis</i> and <i>N. distillatoria</i>, in
+my hothouse, whilst less than a foot in height, showed no
+sensitiveness in their leaves, and had no power of
+climbing. But when <i>N. lævis</i> had grown to a
+height of 16 inches, there were signs of these powers. The
+young leaves when first formed stand upright, but soon become
+inclined; at this period they terminate in a stalk or filament,
+with the pitcher at the extremity hardly at all developed.
+The leaves now exhibited slight spontaneous movements; and when
+the terminal filaments came into contact with a stick, they
+slowly bent round and firmly seized it. But owing to the
+subsequent growth of the leaf, this filament became after a time
+quite slack, though still remaining firmly 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.</p>
+
+<div class="gapspace">&nbsp;</div>
+<p><i>Summary on Leaf-climbers</i>.&mdash;Plants belonging to
+eight families are known to have clasping petioles, and plants
+belonging to four families climb by the tips of their
+leaves. In all the species observed by me, with one
+exception, the young internodes revolve more or less regularly,
+in some cases as regularly as those of a twining plant.
+They revolve at various rates, in most cases rather
+rapidly. Some few can ascend by spirally twining round a
+support. Differently from most twiners, there is a strong
+tendency in the same shoot to revolve first in one and then in an
+opposite direction. The object gained by the revolving
+movement is to bring the petioles or the tips of the leaves into
+contact with surrounding objects; and without this aid the plant
+would be much less successful in climbing. With rare
+exceptions, the petioles are sensitive only whilst young.
+They are sensitive on all sides, but in different degrees in
+different plants; and in some species of <i>Clematis</i> the
+several parts of the same petiole differ much in
+sensitiveness. The hooked tips of the leaves of the
+<i>Gloriosa</i> are sensitive only on their inner or inferior
+surfaces. 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 (4.05 mg.); and
+there is reason to believe that the rather thick and stiff
+petioles of <i>Clematis flammula</i> are sensitive to even much
+less weight if spread over a wide surface. The petioles
+always bend towards the side which is pressed or touched, at
+different rates in different species, 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 accustomed to the stimulus, and either bends no more or
+becomes straight again, the weight still remaining
+suspended. Petioles which have clasped an 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 throughout their whole diameter or on
+one side alone; they subsequently become stronger and more woody,
+sometimes to a wonderful degree; and in some cases they acquire
+an internal structure like that of the stem or axis.</p>
+
+<p>The young internodes of the <i>Lophospermum</i> as well as the
+petioles are sensitive to a touch, and by their combined movement
+seize an object. The flower-peduncles of the <i>Maurandia
+semperflorens</i> revolve spontaneously and are sensitive to a
+touch, yet are not used for climbing. The leaves of at
+least two, and probably of most, of the species of
+<i>Clematis</i>, of <i>Fumaria</i> and <i>Adlumia</i>,
+spontaneously curve from side to side, like the internodes, and
+are thus better adapted to seize distant objects. The
+petioles of the perfect leaves of <i>Tropæolum
+tricolorum</i>, as well as the tendril-like filaments of the
+plants whilst young, ultimately move towards the stem or the
+supporting stick, which they then clasp. These petioles and
+filaments also show some tendency to contract spirally. The
+tips of the uncaught leaves of the <i>Gloriosa</i>, as they grow
+old, contract into a flat spire or helix. These several
+facts are interesting in relation to true tendrils.</p>
+
+<p>With leaf climbers, as with twining plants, the first
+internodes which rise from the ground do not, at least in the
+cases observed by me, spontaneously revolve; nor are the petioles
+or tips of the first-formed leaves sensitive. In certain
+species of <i>Clematis</i>, the large size of the leaves,
+together with their habit of revolving, and the extreme
+sensitiveness of their petioles, appear to render the revolving
+movement of the internodes superfluous; and this latter power has
+consequently become much enfeebled. In certain species of
+<i>Tropæolum</i>, both the spontaneous movements of the
+internodes and the sensitiveness of the petioles have become much
+enfeebled, and in one species have been completely lost.</p>
+
+<h3>CHAPTER III.<br />
+<span class="smcap">Tendril-Bearers</span>.</h3>
+
+<p class="gutsumm">Nature of tendrils&mdash;<span
+class="smcap">Bignoniaceæ</span>, various species of, and
+their different modes of climbing&mdash;Tendrils which avoid the
+light and creep into crevices&mdash;Development of adhesive
+discs&mdash;Excellent adaptations for seizing different kinds of
+supports.&mdash;<span
+class="smcap">Polemoniaceæ</span>&mdash;<i>Cobæa
+scandens</i> much branched and hooked tendrils, their manner of
+action&mdash;<span
+class="smcap">Leguminosæ</span>&mdash;<span
+class="smcap">Compositæ</span>&mdash;<span
+class="smcap">Smilaceæ</span>&mdash;<i>Smilax aspera</i>,
+its inefficient tendrils&mdash;<span
+class="smcap">Fumariaceæ</span>&mdash;<i>Corydalis
+claviculata</i>, its state intermediate between that of a
+leaf-climber and a tendril-bearer.</p>
+
+<p><span class="smcap">By</span> tendrils I mean filamentary
+organs, sensitive to contact and used exclusively for
+climbing. By this definition, spines, 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, branches, <a
+name="citation84"></a><a href="#footnote84"
+class="citation">[84]</a> and perhaps stipules. Mohl, who
+includes under the name of tendrils various organs having a
+similar external appearance, classes them according to their
+homological nature, as being modified leaves, flower-peduncles,
+&amp;c. This would be an excellent scheme; but I observe
+that botanists are by no means unanimous on the homological
+nature of certain tendrils. Consequently I will describe
+tendril-bearing plants by natural families, following
+Lindley&rsquo;s classification; and this will in most cases keep
+those of the same nature together. The species to be
+described belong to ten families, and will be given in the
+following order:&mdash;<i>Bignoniaceæ</i>,
+<i>Polemoniaceæ</i>, <i>Leguminosæ</i>,
+<i>Compositæ</i>, <i>Smilaceæ</i>,
+<i>Fumariaceæ</i>, <i>Cucurbitaceæ</i>,
+<i>Vitaceæ</i>, <i>Sapindaceæ</i>,
+<i>Passifloraceæ</i>. <a name="citation85"></a><a
+href="#footnote85" class="citation">[85]</a></p>
+
+<p><span class="smcap">Bignoniaceæ</span>.&mdash;This
+family contains many tendril-bearers, some twiners, and some
+root-climbers. The tendrils always consist of modified
+leaves. Nine species of <i>Bignonia</i>, selected by
+hazard, are here described, in order to show what diversity of
+structure and action there may be within the same genus, and to
+show what remarkable powers some tendrils possess. The
+species, taken together, afford connecting links between twiners,
+leaf-climbers, tendril-bearers, and root-climbers.</p>
+<p style="text-align: center">
+<a href="images/p86b.jpg">
+<img alt=
+"Fig. 5.  Bignonia.  Unnamed species from Kew"
+title=
+"Fig. 5.  Bignonia.  Unnamed species from Kew"
+ src="images/p86s.jpg" />
+</a></p>
+
+<p><i>Bignonia</i> (an unnamed species from Kew, closely allied
+to <i>B. unguis</i>, but with smaller and rather broader
+leaves).&mdash;A young shoot from a cut-down plant made three
+revolutions against the sun, at an average rate of 2 hrs. 6
+m. The stem is thin and flexible; it twined round a slender
+vertical stick, ascending from left to right, as perfectly and as
+regularly as any true twining-plant. When thus ascending,
+it makes no use of its tendrils or petioles; but when it twined
+round a rather thick stick, and its petioles were brought into
+contact with it, these curved round the stick, showing that they
+have some degree of irritability. The petioles also exhibit
+a slight degree of spontaneous movement; for in one case they
+certainly described minute, irregular, vertical ellipses.
+The tendrils apparently curve themselves spontaneously to the
+same side with the petioles; but from various causes, it was
+difficult to observe the movement of either the tendrils or
+petioles, in this and the two following species. The
+tendrils are so closely similar in all respects to those of <i>B.
+unguis</i>, that one description will suffice.</p>
+
+<p><i>Bignonia unguis</i>.&mdash;The young shoots revolve, but
+less regularly and less quickly than those of the last
+species. The stem twines imperfectly round a vertical
+stick, sometimes reversing its direction, in the same manner as
+described in so many leaf-climbers; and this plant though
+possessing tendrils, climbs to a certain extent like a
+leaf-climber. Each leaf consists of a petiole bearing a
+pair of leaflets, and terminates in a tendril, which is formed by
+the modification of three leaflets, and closely resembles that
+above figured (fig. 5). But it is a little larger, and in a
+young plant was about half an inch in length. It is
+curiously like 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 are of equal length, and diverging, lie in the
+same plane. The toes terminate in sharp, hard claws, much
+curved downwards, like those on a bird&rsquo;s foot. The
+petiole of the leaf is sensitive to contact; even a small loop of
+thread suspended for two days caused it to bend upwards; but the
+sub-petioles of the two lateral leaflets are not sensitive.
+The whole tendril, namely, the tarsus and the three toes, are
+likewise sensitive to contact, especially on their under
+surfaces. When a shoot grows in the midst of thin branches,
+the tendrils are soon brought by the revolving movement of the
+internodes into contact with them; and then one toe of the
+tendril or more, commonly all three, bend, and after several
+hours seize fast hold of the twigs, like a bird when
+perched. If the tarsus of the tendril comes into contact
+with a twig, it goes on slowly bending, until the whole foot is
+carried quite round, and the toes pass on each side of the tarsus
+and seize it. In like manner, if the petiole comes into
+contact with a twig, it bends round, carrying the tendril, which
+then seizes its own petiole or that of the opposite leaf.
+The petioles move spontaneously, and thus, when a shoot attempts
+to twine round an upright stick, those on both sides after a time
+come into contact with it, and are excited to bend.
+Ultimately the two petioles clasp the stick in opposite
+directions, and the foot-like tendrils, seizing on each other or
+on their own petioles, fasten the stem to the support with
+surprising security. The tendrils are thus brought into
+action, if the stem twines round a thin vertical stick; and in
+this respect the present species differs from the last.
+Both species use their tendrils in the same manner when passing
+through a thicket. This plant is one of the most efficient
+climbers which I have observed; 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 moderately well, though not vigorously, I concluded that
+the tendrils acted only like the hooks on a bramble, and that it
+was the most feeble and inefficient of all climbers!</p>
+
+<p><i>Bignonia Tweedyana</i>.&mdash;This species is closely
+allied to the last, and behaves in the same manner; but perhaps
+twines rather better round a vertical stick. On the same
+plant, one branch twined in one direction and another in an
+opposite direction. The internodes in one case made two
+circles, each in 2 hrs. 33 m. I was enabled to observe the
+spontaneous movements of the petioles better in this than in the
+two preceding species: one petiole described three small vertical
+ellipses in the course of 11 hrs., whilst another moved in an
+irregular spire. Some little time after a stem has twined
+round an upright stick, and is securely fastened to it by the
+clasping petioles and tendrils, it emits aërial roots from
+the bases of its leaves; and these roots curve partly round and
+adhere to the stick. This species of <i>Bignonia</i>,
+therefore, combines four different methods of climbing generally
+characteristic of distinct plants, namely, twining,
+leaf-climbing, tendril-climbing, and root-climbing.</p>
+
+<p>In the three foregoing species, when the foot-like tendril has
+caught an object, it continues to grow and thicken, and
+ultimately becomes wonderfully strong, in the same manner as 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, and drops off like a leaf in autumn. I have
+seen this process of disarticulation in no other tendrils, for
+these, when they fail to catch an object, merely wither away.</p>
+
+<p><i>Bignonia venusta</i>.&mdash;The tendrils differ
+considerably from those of the previous species. The lower
+part, or tarsus, is four times as long as the three toes; these
+are of equal length and diverge equally, but do not lie in the
+same plane; their tips are bluntly hooked, and the whole tendril
+makes an excellent grapnel. The tarsus is sensitive on all
+sides; but the three toes are sensitive only on their outer
+surfaces. The sensitiveness is not much developed; for a
+slight rubbing with a twig did not cause the tarsus or the toes
+to become curved until an hour had elapsed, and then only in a
+slight degree. Subsequently they straightened
+themselves. Both the tarsus and toes can seize well hold of
+sticks. If the stem is secured, the tendrils are seen
+spontaneously to sweep large ellipses; the two opposite tendrils
+moving independently of one another. I have no doubt, from
+the analogy of the two following allied species, that the
+petioles also move spontaneously; but they are not irritable like
+those of <i>B. unguis</i> and <i>B. Tweedyana</i>. The
+young internodes sweep large circles, one being completed in 2
+hrs. 15 m., and a second in 2 hrs. 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 one of its tendrils, and, if the stick be
+thin, the right&mdash;and left-hand tendrils are alternately
+used. This alternation follows from the stem necessarily
+taking one twist round its own axis for each completed
+circle.</p>
+
+<p>The tendrils contract spirally a short time after catching any
+object; those which catch nothing merely bend slowly
+downwards. But the whole subject of the spiral contraction
+of tendrils will be discussed after all the tendril-bearing
+species have been described.</p>
+
+<p><i>Bignonia littoralis</i>.&mdash;The young internodes revolve
+in large ellipses. An internode bearing immature tendrils
+made two revolutions, each in 3 hrs. 50 m.; but when grown older
+with the tendrils mature, it made two ellipses, each at the rate
+of 2 hrs. 44 m. This species, unlike the preceding, is
+incapable of twining round a stick: this does not appear to be
+due to any want of flexibility in the internodes or to the action
+of the tendrils, and certainly not to any want of the revolving
+power; nor can I account for the fact. Nevertheless the
+plant readily ascends a thin upright stick by seizing a point
+above with its two opposite tendrils, which then contract
+spirally. If the tendrils seize nothing, they do not become
+spiral.</p>
+
+<p>The species last described, ascended a vertical stick by
+twining spirally and by seizing it alternately with its opposite
+tendrils, like a sailor pulling himself up a rope, hand over
+hand; the present species pulls itself up, like a sailor seizing
+with both hands together a rope above his head.</p>
+
+<p>The tendrils are similar in structure to those of the last
+species. They continue growing for some time, even after
+they have clasped an object. When fully grown, though borne
+by a young plant, they are 9 inches in length. The three
+divergent toes are shorter relatively to the tarsus than in the
+former species; they are blunt at their tips and but slightly
+hooked; they are not quite equal in length, the middle one being
+rather longer than the others. Their outer surfaces 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 hrs. they became straight again and were ready to
+re-act. The tarsus, for the space of one inch close to the
+toes, is sensitive, but in a rather less degree than the toes;
+for the latter after a slight rubbing, became curved in about
+half the time. Even the middle part of the tarsus is
+sensitive to prolonged contact, as soon as the tendril has
+arrived at maturity. After it has grown old, the
+sensitiveness is confined to the toes, and these are only able to
+curl very slowly round a stick. A tendril is perfectly
+ready to act, as soon as the three toes have diverged, and at
+this period their outer surfaces first become irritable.
+The irritability spreads but little from one part when excited to
+another: thus, when a stick was caught by the part immediately
+beneath the three toes, these seldom clasped it, but remained
+sticking straight out.</p>
+
+<p>The tendrils revolve spontaneously. The movement begins
+before the tendril is converted into a three-pronged grapnel by
+the divergence of the toes, and before any part has become
+sensitive; so that the revolving movement is useless at this
+early period. The movement is, also, now slow, two ellipses
+being completed conjointly in 24 hrs. 18 m. A mature
+tendril made an ellipse in 6 hrs.; so that it moved much more
+slowly than the internodes. The ellipses which were swept,
+both in a vertical and horizontal plane, were of large
+size. The petioles are not in the least sensitive, but
+revolve like the tendrils. We thus see that the young
+internodes, the petioles, and the tendrils all continue revolving
+together, but at different rates. The movements of the
+tendrils which rise opposite one another are quite
+independent. Hence, when the whole shoot is allowed freely
+to revolve, nothing can be more intricate than the course
+followed by the extremity of each tendril. A wide space is
+thus irregularly searched for some object to be grasped.</p>
+
+<p>One other curious point remains to be mentioned. In the
+course of a few days after the toes have closely clasped a stick,
+their blunt extremities become developed, though not invariably,
+into irregular disc-like balls which have the power of adhering
+firmly to the wood. As similar cellular outgrowths will be
+fully described under <i>B. capreolata</i>, I will here say
+nothing more about them.</p>
+
+<p><i>Bignonia æquinoctialis</i>, var.
+<i>Chamberlaynii</i>.&mdash;The internodes, the elongated
+non-sensitive petioles, and the tendrils all revolve. The
+stem does not twine, but ascends a vertical stick in the same
+manner as the last species. The tendrils also resemble
+those of the last species, but are shorter; the three toes are
+more unequal in length, the two outer ones being about one-third
+shorter and rather thinner than the middle toe; but they vary in
+this respect. They terminate in small hard points; and what
+is important, cellular adhesive discs are not developed.
+The reduced size of two of the toes as well as their lessened
+sensitiveness, seem to indicate a tendency to abortion; and on
+one of my plants the first-formed tendrils were sometimes simple,
+that is, were not divided into three toes. We are thus
+naturally led to the three following species with undivided
+tendrils:&mdash;</p>
+
+<p><i>Bignonia speciosa</i>.&mdash;The young shoots revolve
+irregularly, making narrow ellipses, spires or circles, at rates
+varying from 3 hrs. 30 m. to 4 hrs. 40 m.; but they show no
+tendency to twine. Whilst the plant is young and does not
+require a support, tendrils are not developed. Those borne
+by a moderately young plant were five inches in length.
+They revolve spontaneously, as do the short and non-sensitive
+petioles. When rubbed, they slowly bend to the rubbed side
+and subsequently straighten themselves; but they are not highly
+sensitive. There is something strange in their behaviour: I
+repeatedly placed close to them, thick and thin, rough and smooth
+sticks and posts, as well as string suspended vertically, but
+none of these objects were well seized. After clasping an
+upright stick, they repeatedly loosed it again, and often would
+not seize it at all, or their extremities did not coil closely
+round. I have observed hundreds of tendrils belonging to
+various Cucurbitaceous, 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. They now seized a thin, upright stick
+horizontally, that is, at a point on their own level, and not
+some way up the stick as in the case of all the previous
+species. Nevertheless, the non-twining stem was enabled by
+this means to ascend the stick.</p>
+
+<p>The extremity of the tendril is almost straight and
+sharp. The whole terminal portion exhibits a singular
+habit, which in an animal would be called an instinct; for it
+continually searches for any little crevice or hole into which to
+insert itself. I had two young plants; and, after having
+observed this habit, I placed near them posts, which had been
+bored by beetles, or had become fissured by 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; in order to effect
+this the extremity for a length of half or quarter of an inch,
+would often bend 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 hole. I have also
+seen a tendril keep its point, in one case for 20 hrs. and in
+another for 36 hrs., in a minute hole, and then withdraw
+it. Whilst the point is thus temporarily inserted, the
+opposite tendril goes on revolving.</p>
+
+<p>The whole length of a tendril often fits itself closely to any
+surface of wood with which it has come into contact; and I have
+observed one bent at right angles, from having entered a wide and
+deep fissure, with its apex abruptly re-bent and inserted into a
+minute lateral hole. After a tendril has clasped a stick,
+it contracts spirally; if it remains unattached it hangs straight
+downwards. If it has merely adapted itself to the
+inequalities of a thick post, though it has clasped nothing, or
+if it has inserted its apex into some little fissure, this
+stimulus suffices to induce spiral contraction; but the
+contraction always draws the tendril away from the post. So
+that in every case these movements, which seem so nicely adapted
+for some purpose, were useless. On one occasion, however,
+the tip became permanently jammed into a narrow fissure. I
+fully expected, from the analogy of <i>B. capreolata</i> and
+<i>B. littoralis</i>, that the tips would have been developed
+into adhesive discs; but I could never detect even a trace of
+this process. There is therefore at present something
+unintelligible about the habits of this plant.</p>
+
+<p><i>Bignonia picta</i>.&mdash;This species closely resembles
+the last in the structure and movements of its tendrils. I
+also casually examined a fine growing plant of the allied <i>B.
+Lindleyi</i>, and this apparently behaved in all respects in the
+same manner.</p>
+
+<p><i>Bignonia capreolata</i>.&mdash;We now come to a species
+having tendrils 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 hrs. 23 m. The
+stem is thin and flexible, and I have seen one make four regular
+spiral turns round a thin upright stick, ascending of course from
+right to left, and therefore in a reversed direction compared
+with the before described species. Afterwards, from the
+interference of the tendrils, it ascended either straight up the
+stick or in an irregular spire. The tendrils are in some
+respects highly remarkable. In a young plant they were
+about 2&frac12; inches in length and much branched, the five
+chief branches apparently representing two pairs of leaflets and
+a terminal one. Each branch is, however, bifid or more
+commonly trifid towards the extremity, with the points blunt yet
+distinctly hooked. A tendril bends to any side which is
+lightly rubbed, and subsequently becomes straight again; but a
+loop of thread weighing &frac14;th of a grain produced no
+effect. On two occasions the terminal branches became
+slightly curved in 10 m. after they had touched a stick; and in
+30 m. the tips were curled quite round it. The basal part
+is less sensitive. The tendrils revolved in an apparently
+capricious manner, sometimes very slightly or not at all; at
+other times they described large regular ellipses. I could
+detect no spontaneous movement in the petioles of the leaves.</p>
+
+<p>Whilst the tendrils are revolving more or less regularly,
+another remarkable movement takes place, namely, a slow
+inclination from the light towards the darkest side of the
+house. I repeatedly changed the position of my plants, and
+some little time after the revolving movement had ceased, the
+successively formed tendrils always ended by pointing to the
+darkest side. When I placed a thick post near a tendril,
+between it and the light, the tendril pointed in that
+direction. In two instances a pair of leaves stood so that
+one of the two tendrils was directed towards the light and the
+other to the darkest side of the house; the latter did not move,
+but the opposite one bent itself first upwards and then right
+over its fellow, so that the two became parallel, one above the
+other, both pointing to the dark: I then turned the plant half
+round; and the tendril which had turned over recovered its
+original position, and the opposite one which had not before
+moved, now turned over to the dark side. Lastly, on another
+plant, three pairs of tendrils were produced at the same time by
+three shoots, and all happened to be differently directed: I
+placed the pot in a box open only on one side, and obliquely
+facing the light; in two days all six tendrils pointed with
+unerring truth to the darkest corner of the box, though to do
+this each had to bend in a different manner. Six wind-vanes
+could not have more truly shown the direction of the wind, than
+did these branched tendrils the course of the stream of light
+which entered the box. I left these tendrils undisturbed
+for above 24 hrs., and then turned the pot half round; but they
+had now lost their power of movement, and could not any longer
+avoid the light.</p>
+
+<p>When a tendril has not succeeded in clasping a support, either
+through its own revolving movement or that of the shoot, or by
+turning towards any object which intercepts the light, 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 seizes an object,
+all the branches contract spirally.</p>
+
+<p>I have stated that after a tendril has come into contact with
+a stick, it bends round it in about half an hour; but I
+repeatedly observed, as in the case of <i>B. speciosa</i> and its
+allies, that it often again loosed the stick; sometimes seizing
+and loosing the same stick three or four times. Knowing
+that the tendrils avoided the light, I gave them a glass tube
+blackened within, and a well-blackened zinc plate: the branches
+curled round the tube and abruptly bent themselves round the
+edges of the zinc plate; but they soon recoiled from these
+objects with what I can only call disgust, and straightened
+themselves. I then placed a post with extremely rugged bark
+close to a pair of tendrils; twice they touched it for an hour or
+two, and twice they withdrew; at last one of the hooked
+extremities curled round and firmly seized an excessively minute
+projecting point of bark, and then the other branches spread
+themselves out, following with accuracy every inequality of the
+surface. I afterwards placed near the plant a post without
+bark but much fissured, and the points of the tendrils crawled
+into all the crevices in a beautiful manner. To my
+surprise, I observed that the tips of the immature 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 minute points, the final process, now to
+be described, commenced.</p>
+
+<p>This process I discovered by having accidentally left a piece
+of wool near a tendril; and this led me to bind a quantity of
+flax, moss, and wool loosely round sticks, and to place them near
+tendrils. The wool must not be dyed, for these tendrils are
+excessively sensitive to some poisons. The hooked points
+soon caught hold of the fibres, even loosely floating fibres, and
+now there was no recoiling; on the contrary, the excitement
+caused the hooks to penetrate the fibrous mass and to curl
+inwards, so that each hook caught firmly 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 were
+visibly enlarged. After a few more days the hooks were
+converted into whitish, irregular balls, rather above the 0.05th
+of an inch (1.27 mm.) in diameter, 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, &amp;c.,
+adhere. When a fibre has become fastened to the surface,
+the cellular 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,
+adhered firmly together. As the whole surface of the ball
+continues to grow, fresh fibres adhere and are afterwards
+enveloped; so that I have seen a little ball with between fifty
+and sixty fibres of flax crossing it at various angles and all
+embedded more or less deeply. Every gradation in the
+process could be followed&mdash;some fibres merely sticking to
+the surface, others lying in more or less deep furrows, or deeply
+embedded, or passing through the very centre of the cellular
+ball. The embedded fibres are so closely clasped that they
+cannot be withdrawn. The outgrowing tissue has so strong a
+tendency to unite, that two balls produced by distinct tendrils
+sometimes unite and grow into a single one.</p>
+
+<p>On one occasion, when a tendril had curled round a stick, half
+an inch in diameter, an adhesive disc was formed; but this does
+not generally occur in the case of smooth sticks or posts.
+If, however, the tip catches a minute projecting point, the other
+branches form discs, especially if they find crevices to crawl
+into. The tendrils failed to attach themselves to a brick
+wall.</p>
+
+<p>I infer from the adherence of the fibres to the discs or
+balls, that these secrete some resinous adhesive matter; and more
+especially from such fibres becoming loose if immersed in
+sulphuric ether. This fluid likewise removes small, brown,
+glistening points which can generally be seen on the surfaces of
+the older discs. If the hooked extremities of the tendrils
+do not touch anything, discs, as far as I have seen, are never
+formed; <a name="citation102"></a><a href="#footnote102"
+class="citation">[102]</a> but temporary contact during a
+moderate time suffices to cause their development. I have
+seen eight discs formed on the same tendril. After their
+development the tendrils contract spirally, and 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 discs
+were attached yielded.</p>
+
+<p>From the facts now given, we may 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
+other such productions; and I hear from Professor Asa Gray that
+the <i>Polypodium incanum</i> abounds on the forest-trees in the
+districts of North America where this species of Bignonia
+grows. Finally, I may remark how singular a fact it is that
+a leaf should be 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 afterwards forming cellular outgrowths
+which secrete an adhesive cement, and then envelop by their
+continued growth the finest fibres.</p>
+
+<p><i>Eccremocarpus scaber</i>
+(<i>Bignoniaceæ</i>).&mdash;Plants, though growing pretty
+well in my green-house, showed no spontaneous movements in their
+shoots or tendrils; but when removed to the hot-house, the young
+internodes revolved at rates varying from 3 hrs. 15 m. to 1 hr.
+13 m. One large circle was swept at this latter unusually
+quick rate; but generally the circles or ellipses were small, and
+sometimes the course pursued was quite irregular. An
+internode, after making several revolutions, sometimes stood
+still for 12 hrs. or 18 hrs., and then recommenced
+revolving. Such strongly marked interruptions in the
+movements of the internodes I have observed in hardly any other
+plant.</p>
+
+<p>The leaves bear four leaflets, themselves subdivided, and
+terminate in much-branched tendrils. The main petiole of
+the leaf, whilst young, moves spontaneously, and follows nearly
+the same irregular course and at about the same rate as the
+internodes. The movement to and from the stem is the most
+conspicuous, and I have seen the chord of a curved petiole which
+formed an angle of 59&deg; with the stem, in an hour afterwards
+making an angle of 106&deg;. The two opposite petioles do
+not move together, and one is sometimes so much raised as to
+stand close to the stem, whilst the other is not far from
+horizontal. The basal part of the petiole moves less than
+the distal part. The tendrils, besides being carried by the
+moving petioles and internodes, themselves move spontaneously;
+and the opposite tendrils occasionally move in opposite
+directions. By these combined movements of the young
+internodes, petioles, and tendrils, a considerable space is swept
+in search of a support.</p>
+
+<p>In young plants the tendrils are about three inches in length:
+they bear two lateral and two terminal branches; and each branch
+bifurcates twice, with the tips terminating in blunt double
+hooks, having both points directed to the same side. All
+the branches are sensitive on all sides; and after being lightly
+rubbed, or after coming into contact with a stick, bend in about
+10 m. One which had become curved in 10 m. after a light
+rub, continued bending for between 3 hrs. and 4 hrs., and became
+straight again in 8 hrs. or 9 hrs. Tendrils, which have
+caught nothing, ultimately contract into an irregular spire, as
+they likewise do, only much more quickly, after clasping a
+support. In both cases the main petiole bearing the
+leaflets, which is at first straight and inclined a little
+upwards, moves downwards, with the middle part bent abruptly into
+a right angle; but this is seen in <i>E. miniatus</i> more
+plainly than in <i>E. scaber</i>. The tendrils in this
+genus act in some respects like those of <i>Bignonia
+capreolata</i>; but the whole does not move from the light, nor
+do the hooked tips become enlarged into cellular discs.
+After the tendrils have come into contact with a moderately thick
+cylindrical stick or with rugged bark, the several branches may
+be seen slowly to lift themselves up, change their positions, and
+again come into contact with the supporting surface. The
+object of these movements is to bring the double-hooks at the
+extremities of the branches, which naturally face in all
+directions, into contact with the wood. I have watched a
+tendril, half of which had bent itself at right angles round the
+sharp corner of a square post, neatly bring every single hook
+into contact with both rectangular surfaces. The appearance
+suggested the belief, that though the whole tendril is not
+sensitive to light, yet that the tips are so, and that they turn
+and twist themselves towards any dark surface. Ultimately
+the branches arrange themselves very neatly to all the
+irregularities 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 wound round a rather thick
+stick, the subsequent spiral contraction generally draws it away
+and spoils the neat arrangement. So it is, but not in quite
+so marked a manner, when a tendril has spread itself over a
+large, nearly flat surface of rugged bark. We may therefore
+conclude that these tendrils are not perfectly adapted to seize
+moderately thick sticks or rugged bark. If a thin stick or
+twig is placed near a tendril, the terminal branches wind quite
+round it, and then seize their own lower branches or the main
+stem. The stick is thus firmly, but not neatly,
+grasped. What the tendrils are really adapted for, appears
+to be such objects as the thin culms of certain grasses, or the
+long flexible bristles of a brush, or thin rigid leaves such as
+those of the Asparagus, all of which they seize in an admirable
+manner. This is due to the extremities of the branches
+close to the little hooks being extremely sensitive to a touch
+from the thinnest object, which they consequently curl round and
+clasp. When a small brush, for instance, was placed near a
+tendril, the tips of each sub-branch seized one, two, or three of
+the bristles; 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, which
+afforded an excellent support.</p>
+
+<p><span
+class="smcap">Polemoniaceæ</span>.&mdash;<i>Cobæa
+scandens</i>.&mdash;This is an excellently constructed
+climber. The tendrils on a fine plant were eleven inches
+long, with the petiole bearing two pairs of leaflets, only two
+and a half inches in length. They revolve more rapidly and
+vigorously than those of any other tendril-bearer observed by me,
+with the exception of one kind of Passiflora. Three large,
+nearly circular sweeps, directed against the sun were completed,
+each in 1 hr. 15 m.; and two other circles in 1 hr. 20 m. and 1
+hr. 23 m. Sometimes a tendril travels in a much inclined
+position, and sometimes nearly upright. The lower part
+moves but little and the petiole not at all; nor do the
+internodes revolve; so that here we have the tendril alone
+moving. On the other hand, with most of the species of
+<i>Bignonia</i> and the <i>Eccremocarpus</i>, the internodes,
+tendrils, and petioles all revolved. The long, straight,
+tapering main stem of the tendril of the <i>Cobæa</i> bears
+alternate branches; and each branch is several times divided,
+with the finer branches as thin as very thin bristles and
+extremely flexible, so that they are blown about by a breath of
+air; yet they are strong and highly elastic. The extremity
+of each branch is a little flattened, and terminates in a minute
+double (though sometimes single) hook, formed of a hard,
+translucent, woody substance, and as sharp as the finest
+needle. On a tendril which was eleven inches long I counted
+ninety-four of these beautifully constructed little hooks.
+They readily catch soft wood, or gloves, or the skin of the naked
+hand. With the exception of these hardened hooks, and of
+the basal part of the central stem, every part of every branchlet
+is highly sensitive on all sides to a slight touch, and bends in
+a few minutes towards the touched side. By lightly rubbing
+several sub-branches on opposite sides, the whole tendril rapidly
+assumed an extraordinarily crooked shape. These movements
+from contact do not interfere with the ordinary revolving
+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,
+spiral contraction likewise begins after an unusually short
+interval of time, namely, in about twelve hours.</p>
+
+<p>Before the tendril is mature, the terminal branchlets cohere,
+and the hooks are curled closely inwards. At this period no
+part is sensitive to a touch; but as soon as the branches diverge
+and the hooks stand out, full sensitiveness is acquired. It
+is a singular circumstance that immature tendrils revolve at
+their full velocity before they become sensitive, but in a
+useless manner, as in this state they can catch nothing.
+This want of perfect co-adaptation, though only for a short time,
+between the structure and the functions of a climbing-plant is a
+rare event. A tendril, as soon as it is ready to act,
+stands, together with the supporting petiole, vertically
+upwards. The leaflets borne by the petiole are at this time
+quite small, and the extremity of the growing stem is bent to one
+side so as to be out of the way of the revolving tendril, which
+sweeps large circles directly over head. The tendrils thus
+revolve in a position well adapted for catching objects standing
+above; and by this means the ascent of the plant is
+favoured. If no object is caught, the leaf with its tendril
+bends downwards and ultimately assumes a horizontal
+position. An open space is thus left for the next
+succeeding and younger tendril to stand vertically upwards and to
+revolve freely. As soon as an old tendril bends downwards,
+it loses all power of movement, and contracts spirally into an
+entangled mass. Although the tendrils revolve with unusual
+rapidity, the movement lasts for only a short time. In a
+plant placed in the hot-house and growing vigorously, a tendril
+revolved for not longer than 36 hours, counting from the period
+when it first became sensitive; but during this period it
+probably made at least 27 revolutions.</p>
+
+<p>When a revolving tendril strikes against a stick, the branches
+quickly bend round and clasp it. The little hooks here play
+an important part, as they prevent the branches from being
+dragged away by the rapid revolving movement, before they have
+had time to clasp the stick securely. This is especially
+the case when only the extremity of a branch has caught hold of a
+support. As soon as a tendril has bent a smooth stick or a
+thick rugged post, or has come into contact with planed wood (for
+it can adhere temporarily even to so smooth a surface as this),
+the same peculiar movements may be observed as those described
+under <i>Bignonia capreolata</i> and <i>Eccremocarpus</i>.
+The branches repeatedly lift themselves up and down; those which
+have their hooks already directed downwards remaining in this
+position and securing the tendril, whilst the others twist about
+until they succeed in arranging themselves in conformity with
+every irregularity of the surface, and in bringing their hooks
+into contact with the wood. The use of the hooks was well
+shown by giving the tendrils tubes and slips of glass to catch;
+for these, though temporarily seized, were invariably lost,
+either during the re-arrangement of the branches or ultimately
+when spiral contraction ensued.</p>
+
+<p>The perfect manner in which the branches arranged themselves,
+creeping like rootlets over every inequality of the surface and
+into any deep crevice, is a pretty sight; for it is perhaps more
+effectually performed by this than by any other species.
+The action is certainly more conspicuous, as the upper surfaces
+of the main stem, as well as of every branch to the extreme
+hooks, are angular and green, whilst the lower surfaces are
+rounded and purple. I was led to infer, as in former cases,
+that a less amount of light guided these movements of the
+branches of the tendrils. I made many trials with black and
+white cards and glass tubes to prove it, but failed from various
+causes; yet these trials countenanced the belief. As a
+tendril consists of a leaf split into numerous segments, there is
+nothing surprising in all the segments turning their upper
+surfaces towards the light, as soon as the tendril is caught and
+the revolving movement is arrested. But this will not
+account for the whole movement, for the segments actually bend or
+curve to the dark side besides turning round on their axes so
+that their upper surfaces may face the light.</p>
+
+<p>When the <i>Cobæa</i> grows in the open air, the wind
+must aid the extremely flexible tendrils in seizing a support,
+for I found that a mere breath sufficed to cause the extreme
+branches to catch hold by their hooks of twigs, which they could
+not have reached by the revolving movement. It might have
+been thought that a tendril, thus hooked by the extremity of a
+single branch, could not have fairly grasped its support.
+But several times I watched cases like the following: tendril
+caught a thin stick by the hooks of one of its two extreme
+branches; though thus held by the tip, it still tried to revolve,
+bowing itself to all sides, and by this movement the other
+extreme branch soon caught the stick. The first branch then
+loosed itself, and, arranging its hooks, again caught hold.
+After a time, from the continued movement of the tendril, the
+hooks of a third branch caught hold. No other branches, as
+the tendril then stood, could possibly have touched the
+stick. But before long the upper part of the main stem
+began to contract into an open spire. It thus dragged the
+shoot which bore the tendril towards the stick; and as the
+tendril continually tried to revolve, a fourth branch was brought
+into contact. And lastly, from the spiral contraction
+travelling down both the main stem and the branches, all of them,
+one after another, were ultimately brought into contact with the
+stick. They then wound themselves round it and round one
+another, until the whole tendril was tied together in an
+inextricable knot. The tendrils, though at first quite
+flexible, after having clasped a support for a time, become more
+rigid and stronger than they were at first. Thus the plant
+is secured to its support in a perfect manner.</p>
+
+<p><span class="smcap">Leguminosæ</span>.&mdash;<i>Pisum
+sativum</i>.&mdash;The common pea was the subject of a valuable
+memoir by Dutrochet, <a name="citation111"></a><a
+href="#footnote111" class="citation">[111]</a> who discovered
+that the internodes and tendrils revolve 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 wider space. Owing to this change of
+direction, and likewise to the movement of the stem towards the
+light, the successive irregular ellipses generally form an
+irregular spire. I have thought it worth while to annex a
+tracing of the course pursued by the upper internode (the
+movement of the tendril being neglected) of a young plant from
+8.40 <span class="GutSmall">A.M.</span> to 9.15 <span
+class="GutSmall">P.M.</span> The course was traced on a
+hemispherical glass placed over the plant, and the dots with
+figures give the hours of observation; each dot being joined by a
+straight line. No doubt all the lines would have been
+curvilinear if the course had been observed at much shorter
+intervals. The extremity of the petiole, from which the
+young tendril arose, was two inches from the glass, so that if a
+pencil two inches in length could have been 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
+reduced by one-half. Neglecting the first great sweep
+towards the light from the figure 1 to 2, the end of the petiole
+swept a space 4 inches across in one direction, and 3 inches in
+another. As a full-grown tendril is considerably above two
+inches in length, and as the tendril itself bends and revolves in
+harmony with the internode, a considerably wider space is swept
+than is here represented on a reduced scale. Dutrochet
+observed the completion of an ellipse in 1 hr. 20 m.; and I saw
+one completed in 1 hr. 30 m. The direction followed is
+variable, either with or against the sun.</p>
+<p style="text-align: center">
+<a href="images/p113b.jpg">
+<img alt=
+"Fig. 6.  Side of room with window"
+title=
+"Fig. 6.  Side of room with window"
+ src="images/p113s.jpg" />
+</a> <a name="citation113"></a><a href="#footnote113"
+class="citation">[113]</a></p>
+
+<p>Dutrochet asserts that the petioles of the leaves
+spontaneously revolve, as well as the young internodes and
+tendrils; but he does not say that he secured the internodes;
+when this was done, I could never detect any movement in the
+petiole, except to and from the light.</p>
+
+<p>The tendrils, on the other hand, when the internodes and
+petioles are secured, describe irregular spires or regular
+ellipses, exactly like those made by the internodes. A
+young tendril, only 1&#8539; of an 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
+sensitive tendrils, and tied the petiole so that the tendril
+alone could move; it completed a perfect ellipse in 1 hr. 30 m.;
+I then turned the plant partly round, but this made no change in
+the direction of the succeeding ellipse. The next day I
+watched a plant similarly secured until the tendril (which was
+highly sensitive) made an ellipse in a line exactly to and from
+the light; the movement was so great that the tendril at the two
+ends of its elliptical course bent itself 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 no longer curved in harmony together,
+owing to inequality of age.</p>
+
+<p>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 concave surface near the tip caused them to bend
+quickly, as did occasionally a loop of thread weighing
+one-seventh of a grain (9.25 mg.). The upper or convex
+surface is barely or not at all sensitive. Tendrils, after
+bending from a touch, straighten themselves in about two hours,
+and are then ready to act again. As soon as they begin to
+grow old, the extremities of their two or three pairs of branches
+become hooked, and they then appear to form an excellent
+grappling instrument; but this is not the case. For at this
+period they have generally quite lost their sensitiveness; and
+when hooked on to twigs, some were not at all affected, and
+others required from 18 hrs. to 24 hrs. before clasping such
+twigs; nevertheless, they were able to utilise the last vestige
+of irritability owing to their extremities being hooked.
+Ultimately the lateral branches contract spirally, but not the
+middle or main stem.</p>
+
+<p><i>Lathyrus aphaca</i>.&mdash;This plant is destitute of
+leaves, except during a very early age, these being replaced by
+tendrils, and the leaves themselves by large stipules. It
+might therefore have been expected that the tendrils would have
+been highly organized, but this is not so. They are
+moderately long, thin, and unbranched, with their tips slightly
+curved. Whilst young they are sensitive on all sides, but
+chiefly on the concave side of the extremity. They have no
+spontaneous revolving power, but are at first inclined upwards at
+an angle of about 45&deg;, then move into a horizontal position,
+and ultimately bend downwards. The young internodes, on the
+other hand, revolve in ellipses, and carry with them the
+tendrils. Two ellipses were completed, each in nearly 5
+hrs.; their longer axes were directed at about an angle of
+45&deg; to the axis of the previously made ellipse.</p>
+
+<p><i>Lathyrus grandiflorus</i>.&mdash;The plants observed were
+young and not growing vigorously, yet sufficiently so, I think,
+for my observations to be trusted. If so, we have the rare
+case of neither internodes nor tendrils revolving. The
+tendrils of vigorous plants are above 4 inches in length, and are
+often twice divided into three branches; the tips are curved and
+are sensitive on their concave sides; the lower part of the
+central stem is hardly at all sensitive. Hence this plant
+appears to climb simply by its tendrils being brought, through
+the growth of the stem, or more efficiently by the wind, into
+contact with surrounding objects, which they then clasp. I
+may add that the tendrils, or the internodes, or both, of
+<i>Vicia sativa</i> revolve.</p>
+
+<p><span class="smcap">Compositæ</span>.&mdash;<i>Mutisia
+clematis</i>.&mdash;The immense family of the Compositæ is
+well known to include very few climbing plants. We have
+seen in the Table in the first chapter that <i>Mikania
+scandens</i> is a regular twiner, and F. Müller informs me
+that in S. Brazil there is another species which is a
+leaf-climber. <i>Mutisia</i> is the only genus in the
+family, as far as I can learn, which bears tendrils: it is
+therefore interesting to find that these, though rather less
+metamorphosed from their primordial foliar condition than are
+most other tendrils, yet display all the ordinary characteristic
+movements, both those that are spontaneous and those which are
+excited by contact.</p>
+
+<p>The long leaf bears seven or eight alternate leaflets, and
+terminates in a tendril which, in a plant of considerable size,
+was 5 inches in length. It consists generally of three
+branches; and these, although much elongated, evidently represent
+the petioles and midribs of three leaflets; for they closely
+resemble the same parts in an ordinary leaf, in being rectangular
+on the upper surface, furrowed, and edged with green.
+Moreover, the green edging of the tendrils of young plants
+sometimes expands into a narrow lamina or blade. Each
+branch is curved a little downwards, and is slightly hooked at
+the extremity.</p>
+
+<p>A young upper internode revolved, judging from three
+revolutions, at an average rate of 1 hr. 38 m.; it swept ellipses
+with the longer axes directed at right angles to one another; but
+the plant, apparently, cannot twine. The petioles and the
+tendrils are both in constant movement. But their movement
+is slower and much less regularly elliptical than that of the
+internodes. They appear to be much affected by the light,
+for the whole leaf usually sinks down during the night and rises
+during the day, moving, also, during the day in a crooked course
+to the west. The tip of the tendril is highly sensitive on
+the lower surface; and one which was just touched with a twig
+became perceptibly curved in 3 m., and another in 5 m.; the upper
+surface is not at all sensitive; the sides are moderately
+sensitive, so that two branches which were rubbed on their inner
+sides converged and crossed each other. The petiole of the
+leaf and the lower parts of the tendril, halfway between the
+upper leaflet and the lowest branch, are not sensitive. A
+tendril after curling from a touch became straight again in about
+6 hrs., and was ready to re-act; but one that had been so roughly
+rubbed as to have coiled into a helix did not become perfectly
+straight until after 13 hrs. The tendrils retain their
+sensibility to an unusually late age; for one borne by a leaf
+with five or six fully developed leaves above, was still
+active. If a tendril catches nothing, after a considerable
+interval of time the tips of the branches curl a little inwards;
+but if it clasps some object, the whole contracts spirally.</p>
+<p style="text-align: center">
+<a href="images/p119b.jpg">
+<img alt=
+"Fig. 7.  Smilax aspera"
+title=
+"Fig. 7.  Smilax aspera"
+ src="images/p119s.jpg" />
+</a></p>
+
+<p><span class="smcap">Smilaceæ</span>.&mdash;<i>Smilax
+aspera</i>, var. <i>maculata</i>.&mdash;Aug. St.-Hilaire <a
+name="citation118"></a><a href="#footnote118"
+class="citation">[118]</a> considers that the tendrils, which
+rise in pairs from the petiole, are modified lateral leaflets;
+but Mohl (p. 41) ranks them as modified stipules. These
+tendrils are from 1&frac12; to 1&frac34; inches in length, are
+thin, and have slightly curved, pointed extremities. They
+diverge a little from each other, and 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 when placed in contact with a stick
+became just perceptibly curved in 1 hr. 20 m., but did not
+completely surround it until 48 hrs. had elapsed; the concave
+side of another became considerably curved in 2 hrs. and clasped
+a stick in 5 hrs. As the pairs of tendrils grow old, one
+tendril diverges more and more from the other, and both slowly
+bend backwards and downwards, so that after a time they project
+on the opposite side of the stem to that from which they
+arise. They then still retain their sensitiveness, and can
+clasp a support placed <i>behind</i> the stem. Owing to
+this power, the plant is able to ascend a thin upright
+stick. Ultimately the two tendrils belonging to the same
+petiole, if they do not come into contact with any object,
+loosely cross each other behind the stem, as at B, in fig.
+7. This movement of the tendrils towards and round the stem
+is, to a certain extent, guided by their avoidance of the light;
+for when a plant stood so that one of the two tendrils was
+compelled in thus slowly moving to travel towards the light, and
+the other from the light, the latter always moved, as I
+repeatedly observed, more quickly than its fellow. The
+tendrils do not contract 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, as we have just seen, is guided, to a certain extent, by
+the avoidance of the light; 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 is a less perfect climber than any other
+tendril-bearing species observed by me. The plant whilst
+young and only a few inches in height, does not produce any
+tendrils; and considering that it grows to only about 8 feet in
+height, 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 these
+are. The plant might have been left, one would have
+thought, to climb by the aid of its spines alone, like our
+brambles. As, however, it belongs to a genus, some of the
+species of which are furnished with much longer tendrils, we may
+suspect that it possesses these organs solely from being
+descended from progenitors more highly organized in this
+respect.</p>
+
+<p><span
+class="smcap">Fumariaceæ</span>.&mdash;<i>Corydalis
+claviculata</i>.&mdash;According to Mohl (p. 43), the extremities
+of the branched stem, as well as the leaves, 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 a widely different homological
+nature. Nevertheless, from this statement by Mohl, I have
+ranked this species amongst the tendril-bearers; if classed
+exclusively by its foliar tendrils, it would be doubtful whether
+it ought not to have been placed amongst the leaf-climbers, with
+its allies, <i>Fumaria</i> and <i>Adlumia</i>. A large
+majority of its so-called tendrils still bear leaflets, though
+excessively reduced in size; but some few of them may properly be
+designated as tendrils, for they are completely destitute of
+laminæ 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 rather young, only the
+outer leaves, but when full-grown all the leaves, have their
+extremities converted into more or less perfect 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.</p>
+
+<p>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 structure represented in the following drawing. This
+leaf bore nine leaflets; the lower ones being much
+subdivided. The terminal portion of the petiole, about
+1&frac12; inch in length (above the leaflet <i>f</i>), is thinner
+and more elongated than the lower part, and may 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 (2.116 mm.
+and 0.339 mm.), so that it was almost microscopically
+minute. All the reduced leaflets have branching nerves, and
+terminate in little spines, like those of the fully developed
+leaflets. Every gradation could be traced, until we come to
+branchlets (as <i>a</i> and <i>d</i> in the figure) which show no
+vestige of a lamina or blade. Occasionally all the terminal
+branchlets of the petiole are in this condition, and we then have
+a true tendril.</p>
+<p style="text-align: center">
+<a href="images/p123b.jpg">
+<img alt=
+"Fig. 8.  Corydalis claviculata.  Leaf-tendril of natural size"
+title=
+"Fig. 8.  Corydalis claviculata.  Leaf-tendril of natural size"
+ src="images/p123s.jpg" />
+</a></p>
+
+<p>The several terminal branches of the petiole bearing the much
+reduced leaflets (<i>a</i>, <i>b</i>, <i>c</i>, <i>d</i>) are
+highly sensitive, for a loop of thread weighing only the
+one-sixteenth of a grain (4.05 mg.) caused them to become greatly
+curved in under 4 hrs. When the loop was removed, the
+petioles straightened themselves in about the same time.
+The petiole (<i>e</i>) 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 18 hrs. had elapsed. Loops of thread
+weighing one-fourth of a grain, left suspended on the lower
+petioles (<i>f</i> to <i>l</i>) during several days, produced no
+effect. Yet the three petioles <i>f</i>, <i>g</i>, and
+<i>h</i> were not quite insensible, for when left in contact with
+a stick for a day or two they slowly curled round it. Thus
+the sensibility of the petiole gradually diminishes from the
+tendril-like extremity to the base. The internodes of the
+stem are not at all sensitive, which makes Mohl&rsquo;s statement
+that they are sometimes converted into tendrils the more
+surprising, not to say improbable.</p>
+
+<p>The whole leaf, whilst young and sensitive, stands almost
+vertically upwards, as we have seen to be the case with many
+tendrils. It is in continual movement, and one that I
+observed swept at an average rate of about 2 hrs. for each
+revolution, large, though irregular, ellipses, which were
+sometimes narrow, sometimes broad, with their longer axes
+directed to different points of the compass. The young
+internodes, likewise revolved irregularly in ellipses or spires;
+so that by these combined movements a considerable space was
+swept for a support. If the terminal and attenuated portion
+of a petiole fails to seize any object, it ultimately bends
+downwards and inwards, and soon loses all irritability and power
+of movement. This bending down differs much in nature from
+that which occurs with the extremities of the young leaves in
+many species of <i>Clematis</i>; for these, when thus bent
+downwards or hooked, first acquire their full degree of
+sensitiveness.</p>
+
+<p><i>Dicentra thalictrifolia</i>.&mdash;In this allied plant the
+metamorphosis of the terminal leaflets is complete, and they are
+converted into perfect tendrils. Whilst the plant is young,
+the tendrils appear like modified branches, and a distinguished
+botanist thought that they were of this nature; but in a
+full-grown plant there can be no doubt, as I am assured by Dr.
+Hooker, that they are modified leaves. When of full size,
+they are above 5 inches in length; they bifurcate twice, thrice,
+or even four times; their extremities are hooked and blunt.
+All the branches of the tendrils are sensitive on all sides, but
+the basal portion of the main stem is only slightly so. The
+terminal branches when lightly rubbed with a twig became curved
+in the course of from 30 m. to 42 m., and straightened themselves
+in between 10 hrs. and 20 hrs. A loop of thread weighing
+one-eighth of a grain plainly caused the thinner branches to
+bend, as did occasionally a loop weighing one-sixteenth of a
+grain; but this latter weight, though left suspended, was not
+sufficient to cause a permanent flexure. The whole leaf
+with its tendril, as well as the young upper internodes, revolves
+vigorously and quickly, though irregularly, and thus sweeps 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, and this was completed in 1 hr. 53 m. During a period
+of 6 hrs. 17 m. another shoot made a complex figure, apparently
+representing 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.</p>
+
+<p>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 done
+in so perfect a manner by some Bignoniaceæ and
+Cobæa. The tendrils of young plants, two or three
+feet in height, are only half the length of those borne by the
+same plant when grown taller, and they do not contract spirally
+after clasping a support, but only become slightly
+flexuous. Full-sized tendrils, on the other hand, contract
+spirally, with the exception of the thick basal portion.
+Tendrils which have caught nothing simply bend downwards and
+inwards, like the extremities of the leaves of the <i>Corydalis
+claviculata</i>. But in all cases the petiole after a time
+is angularly and abruptly bent downwards like that of
+Eccremocarpus.</p>
+
+<h3>CHAPTER IV.<br />
+<span class="smcap">Tendril-Bearers</span>&mdash;(<i>continued</i>).</h3>
+
+<p><span
+class="smcap">Cucurbitaceæ</span>.&mdash;Homologous nature
+of the tendrils&mdash;<i>Echinocystis lobata</i>, remarkable
+movements of the tendrils to avoid seizing the terminal
+shoot&mdash;Tendrils not excited by contact with another tendril
+or by drops of water&mdash;Undulatory movement of the extremity
+of the tendril&mdash;<i>Hanburya</i>, adherent discs&mdash;<span
+class="smcap">Vitacæ</span>&mdash;Gradation between the
+flower-peduncles and tendrils of the vine&mdash;Tendrils of the
+Virginian Creeper turn from the light, and, after contact,
+develop adhesive discs&mdash;<span
+class="smcap">Sapindaceæ</span>&mdash;<span
+class="smcap">Passifloraceæ</span>&mdash;<i>Passiflora
+gracilis</i>&mdash;Rapid revolving movement and sensitiveness of
+the tendrils&mdash;Not sensitive to the contact of other tendrils
+or of drops of water&mdash;Spiral contraction of
+tendrils&mdash;Summary on the nature and action of tendrils.</p>
+
+<p><span class="smcap">Cucurbitaceæ</span>.&mdash;The
+tendrils in this family have been ranked by competent judges as
+modified leaves, stipules, or branches; or as partly a leaf and
+partly a branch. De Candolle believes that the tendrils
+differ in their homological nature in two of the tribes. <a
+name="citation127a"></a><a href="#footnote127a"
+class="citation">[127a]</a> From facts recently adduced,
+Mr. Berkeley thinks that Payer&rsquo;s view is the most probable,
+namely, that the tendril is &ldquo;a separate portion of the leaf
+itself;&rdquo; but much may be said in favour of the belief that
+it is a modified flower-peduncle. <a name="citation127b"></a><a
+href="#footnote127b" class="citation">[127b]</a></p>
+
+<p><i>Echinocystis lobata</i>.&mdash;Numerous observations were
+made on this plant (raised from seed sent me by Prof. Asa Gray),
+for the spontaneous revolving movements of the internodes and
+tendrils were first observed by me in this case, and greatly
+perplexed me. My observations may now be much
+condensed. I observed thirty-five revolutions of the
+internodes and tendrils; the slowest rate was 2 hrs. and the
+average rate, with no great fluctuations, 1 hr. 40 m.
+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 an opposite direction. Sometimes the
+movement during a short time would either stop or be reversed;
+and this apparently was due to interference from the light, as,
+for instance, when I placed a plant close to a window. In
+one instance, an old tendril, which had nearly ceased revolving,
+moved in one direction, whilst a young tendril above moved in an
+opposite course. The two uppermost internodes alone
+revolve; and as soon as the lower one grows old, only its upper
+part continues to move. The ellipses or circles swept by
+the summits of the internodes are about three inches in diameter;
+whilst those swept by the tips of the tendrils, are from 15 to 16
+inches in diameter. During the revolving movement, the
+internodes become successively curved to all points of the
+compass; in one part of their course they are often inclined,
+together with the tendrils, at about 45&deg; to the horizon, and
+in another part stand vertically up. 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 cutting off
+the latter with sharp scissors, the top of the shoot rose only a
+little, and went on revolving. This false appearance is
+apparently due to the internodes and tendrils all curving and
+moving harmoniously together.</p>
+
+<p>A revolving tendril, though inclined during the greater part
+of its course at an angle of about 45&deg; (in one case of only
+37&deg;) above the horizon, stiffened and straightened itself
+from tip to base in a certain part of its course, thus becoming
+nearly or quite vertical. I witnessed this repeatedly; and
+it occurred both when the supporting internodes were free and
+when they were tied up; but was perhaps most conspicuous in the
+latter case, or when the whole shoot happened to be much
+inclined. The tendril forms a very acute angle with the
+projecting extremity of the stem or shoot; and the stiffening
+always occurred as the tendril approached, and had to pass over
+the shoot in its circular course. If it had not possessed
+and exercised this curious power, it would infallibly have struck
+against the extremity of the shoot and been arrested. As
+soon as the tendril with its three branches begins to stiffen
+itself in this manner and to rise from an inclined into a
+vertical position, the revolving motion becomes more rapid; and
+as soon as the tendril has succeeded in passing over the
+extremity of the shoot or point of difficulty, its motion,
+coinciding with that from its weight, often causes it to fall
+into its previously inclined position so quickly, that the apex
+could be seen travelling like the minute hand of a gigantic
+clock.</p>
+
+<p>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 and 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 to be the case with other species of the
+family by Mohl (p. 65). 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 the tendrils which had been rubbed on the
+concave side had straightened themselves, I reversed the process
+of rubbing, and always with the same result. After touching
+the concave side, the tip becomes sensibly curved in one or two
+minutes; and subsequently, if the touch has been at all rough, it
+coils itself into a helix. But the helix will, after a
+time, straighten itself, and be again ready to act. A loop
+of thin thread only one-sixteenth of a grain in weight caused a
+temporary flexure. The lower part was repeatedly rubbed
+rather roughly, but no curvature ensued; yet this part is
+sensitive to prolonged pressure, for when it came into contact
+with a stick, it would slowly wind round it.</p>
+
+<p>One of my plants bore two shoots near together, and the
+tendrils were repeatedly drawn across one another, but it is a
+singular fact that they did not once catch each other. It
+would appear as if they had become habituated to contact of this
+kind, for the pressure thus caused must have been much greater
+than that caused by a loop of soft thread weighing only the
+one-sixteenth of a grain. I have, however, seen several
+tendrils of <i>Bryonia dioica</i> interlocked, but they
+subsequently released one another. The tendrils of the
+Echinocystis are also habituated to drops of water or to rain;
+for artificial rain made by violently flirting a wet brush over
+them produced not the least effect.</p>
+
+<p>The revolving movement of a tendril is not stopped by the
+curving of its extremity after it has been touched. When
+one of the lateral branches has firmly clasped an object, the
+middle branch continues to revolve. When a stem is bent
+down and secured, so that the tendril depends but is left free to
+move, its previous revolving movement is nearly or quite stopped;
+but it soon begins to bend upwards, and as soon as it has become
+horizontal the revolving movement recommences. I tried this
+four times; the tendril generally rose to a horizontal position
+in an hour or an hour and a half; but in one case, in which a
+tendril depended at an angle of 45&deg; beneath the horizon, the
+uprising took two hours; in half an hour afterwards it rose to
+23&deg; above the horizon and then recommenced revolving.
+This upward movement is independent of the action of light, for
+it occurred twice in the dark, and on another occasion the light
+came 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 germinating seeds.</p>
+
+<p>A tendril does not long retain its revolving power; and as
+soon as this is lost, it bends downwards and contracts
+spirally. After the revolving movement has ceased, the tip
+still retains for a short time its sensitiveness to contact, but
+this can be of little or no use to the plant.</p>
+
+<p>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 that the tip
+managed in the course of a few hours to curl twice or even thrice
+round the stick. I at first thought that this was due to
+rapid growth on the outside; but by coloured points and
+measurements I proved that there had been no sensible increase of
+length within the time. When a stick, flat on one side, was
+similarly placed, the tip of the tendril could not curl beyond
+the flat surface, but coiled itself into a helix, which, turning
+to one side, lay flat on the little flat surface of wood.
+In one instance a portion of tendril three-quarters of an inch in
+length was thus dragged on to the flat surface by the coiling in
+of the helix. But the tendril thus acquires a very insecure
+hold, and generally after a time slips off. In one case
+alone the helix subsequently uncoiled itself, and the tip then
+passed round and clasped the stick. The formation of the
+helix on the flat side of the 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 observed
+several times through a lens that the whole surface was not in
+close contact with the stick; and I can understand the onward
+progress only by supposing that the movement is slightly
+undulatory or vermicular, and that the tip alternately
+straightens itself a little and then again curls inwards.
+It thus drags 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 with its extreme point,
+can work itself onwards until it has passed twice or even thrice
+round the stick, and has permanently grasped it.</p>
+
+<p><i>Hanburya Mexicana</i>.&mdash;The young internodes and
+tendrils of this anomalous member of the family, revolve in the
+same manner and at about the same rate as those of the
+<i>Echinocystis</i>. 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 it had become
+rapidly coiled into a ring owing to a single touch, it
+straightened itself in 50 m. The tendril, when in full
+action, stands vertically up, with the projecting extremity of
+the young stem thrown a little on one side, so as to be out of
+the way; but the tendril bears on the inner side, near its base,
+a short rigid branch, which projects out at right angles like a
+spur, with the terminal half bowed a little downwards.
+Hence, as the main vertical branch 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 <i>Echinocystis</i>, namely, by stiffening
+themselves at the proper point. The spur is therefore
+pressed laterally against the young stem in one part of the
+revolving course, and thus the sweep of the lower part of the
+main branch is much restricted. A nice case of
+co-adaptation here comes into play: in all the other tendrils
+observed by me, the several branches become sensitive at the same
+period: had this been the case with the <i>Hanburya</i>, the
+inwardly directed, spur-like branch, from being pressed, during
+the revolving movement, against the projecting end of the shoot,
+would infallibly have seized it in a useless or injurious
+manner. But the main branch of the tendril, after revolving
+for a time in a vertical position, spontaneously bends downwards;
+and in doing so, raises the spur-like branch, which itself also
+curves upwards; so that by these combined movements it rises
+above the projecting end of the shoot, and can now move freely
+without touching the shoot; and now it first becomes
+sensitive.</p>
+
+<p>The tips of both branches, when they come into contact with a
+stick, grasp it like any ordinary tendril. But in the
+course of a few days, the lower 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 discs formed by the extremities of the tendrils
+of some species of <i>Bignonia</i> and of <i>Ampelopsis</i>; but
+in the <i>Hanburya</i> the layer is developed along the terminal
+inner surface, sometimes for a length of 1&frac34; inches, and
+not at the extreme tip. The layer is white, whilst the
+tendril is green, and near the tip it is sometimes thicker than
+the tendril itself; it generally spreads a little beyond the
+sides of the tendril, and 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 an immersion of 24 hrs.
+in alcohol or water, but was quite loosened by a similar
+immersion in ether or turpentine. After a tendril has once
+firmly coiled itself round a stick, it is difficult to imagine of
+what use the adhesive cellular layer can be. Owing to the
+spiral contraction which soon ensues, the tendrils were never
+able to remain, excepting in one instance, in contact with a
+thick post or a nearly flat surface; if they had quickly become
+attached by means of the adhesive layer, this would evidently
+have been of service to the plant.</p>
+
+<p>The tendrils of <i>Bryonia dioica</i>, <i>Cucurbita
+ovifera</i>, and <i>Cucumis sativa</i> are sensitive and
+revolve. Whether the internodes likewise revolve I did not
+observe. In <i>Anguria Warscewiczii</i>, the internodes,
+though thick and stiff, revolve: in this plant the lower surface
+of the tendril, some time after clasping a stick, produces a
+coarsely cellular layer or cushion, which adapts itself closely
+to the wood, like that formed by the tendril of the
+<i>Hanburya</i>; but it is not in the least adhesive. In
+<i>Zanonia Indica</i>, which belongs to a different tribe of the
+family, the forked tendrils and the internodes revolve in periods
+between 2 hrs. 8 m. and 3 hrs. 35 m., moving against the sun.</p>
+
+<p><span class="smcap">Vitaceæ</span>.&mdash;In this family
+and in the two following, namely, the Sapindacæ and
+Passifloraceæ, the tendrils are modified flower-peduncles;
+and are therefore axial in their nature. In this respect
+they differ from all those previously described, with the
+exception, perhaps, of the Cucurbitaceæ. The
+homological nature, however, of a tendril seems to make no
+difference in its action.</p>
+<p style="text-align: center">
+<a href="images/p137b.jpg">
+<img alt=
+"Fig. 9.  Tendril of the Vine.  A.  Peduncle of tendril.  B.
+Longer Branch, with a scale at its base.  C.  Shorter branch.  D.
+ Petiole of the opposite leaf"
+title=
+"Fig. 9.  Tendril of the Vine.  A.  Peduncle of tendril.  B.
+Longer Branch, with a scale at its base.  C.  Shorter branch.  D.
+ Petiole of the opposite leaf"
+ src="images/p137s.jpg" />
+</a></p>
+
+<p><i>Vitis vinifera</i>.&mdash;The tendril is thick and of great
+length; one from a vine growing out of doors and not vigorously,
+was 16 inches long. It consists of a peduncle (A), bearing
+two branches which diverge equally from it. One of the
+branches (B) has a scale at its base; it is always, as far as I
+have seen, longer than the other and often bifurcates. The
+branches when rubbed become curved, and subsequently straighten
+themselves. After a tendril has clasped any object with its
+extremity, it contracts spirally; but this does not occur (Palm,
+p. 56) when no object has been seized. The tendrils move
+spontaneously from side to side; and on a very hot day, one made
+two elliptical revolutions, at an average rate of 2 hrs. 15
+m. During these movements a coloured line, painted along
+the convex surface, appeared after a time on one side, then on
+the concave side, then on the opposite side, and lastly again on
+the convex side. The two branches of the same tendril have
+independent movements. After a tendril has spontaneously
+revolved for a time, it bends from the light towards the dark: I
+do not state this on my own authority, but on that of Mohl and
+Dutrochet. Mohl (p. 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.</p>
+
+<p>The young internodes revolve spontaneously; but the movement
+is unusually slight. A shoot faced a window, and I traced
+its course on the glass during two perfectly calm and hot
+days. On one of these days it described, in the course of
+ten hours, a spire, representing two and a half ellipses. I
+also placed a bell-glass over a young Muscat grape in the
+hot-house, and it made each day three or four very small oval
+revolutions; the shoot moving less than half an inch from side to
+side. Had it not made at least three revolutions whilst the
+sky was uniformly overcast, I should have attributed this slight
+degree of movement to the varying action of the light. The
+extremity of the stem is more or less bent downwards, but it
+never reverses its curvature, as so generally occurs with twining
+plants.</p>
+<p style="text-align: center">
+<a href="images/p139b.jpg">
+<img alt=
+"Fig. 10.  Flower-stalk of the Vine.  A.  Common Peduncle.  B.
+Flower-tendril.  C.  Sub-Peduncle, bearing the flower-buds.  D.
+Petiole of the opposite leaf"
+title=
+"Fig. 10.  Flower-stalk of the Vine.  A.  Common Peduncle.  B.
+Flower-tendril.  C.  Sub-Peduncle, bearing the flower-buds.  D.
+Petiole of the opposite leaf"
+ src="images/p139s.jpg" />
+</a></p>
+
+<p>Various authors (Palm, p. 55; Mohl, p. 45; Lindley, &amp;c.)
+believe that the tendrils of the vine are modified
+flower-peduncles. I here give a drawing (fig. 10) of the
+ordinary state of a young flower-stalk: it consists of the
+&ldquo;common peduncle&rdquo; (A); of the
+&ldquo;flower-tendril&rdquo; (B), which is represented as having
+caught a twig; and of the &ldquo;sub-peduncle&rdquo; (C) bearing
+the flower-buds. The whole moves spontaneously, like a true
+tendril, but in a less degree; the movement, however, is greater
+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 of a true tendril. The
+flower-tendril (B) is always longer than the sub-peduncle (C) and
+has a scale at its base; it sometimes 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. When rubbed, it curves and subsequently
+straightens itself; and it can, as is shown in the drawing,
+securely clasp a support. I have seen an object as soft as
+a young vine-leaf caught by one.</p>
+
+<p>The lower and naked part of the sub-peduncle (C) is likewise
+slightly sensitive to a rub, and I have seen it 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
+corresponding branch of an ordinary tendril, is well shown when
+it bears only a few flowers; for in this case it becomes less
+branched, increases in length, and gains both in sensitiveness
+and in the power of spontaneous movement. I have twice seen
+sub-peduncles which bore from thirty to forty flower-buds, and
+which had become considerably elongated and were completely wound
+round sticks, exactly like true tendrils. The whole length
+of another sub-peduncle, bearing only eleven flower-buds, quickly
+became curved when slightly rubbed; but even this scanty number
+of flowers rendered the stalk less sensitive than the other
+branch, that is, the flower-tendril; for the latter after a
+lighter rub became curved more quickly and in a greater
+degree. I have seen a sub-peduncle thickly covered with
+flower-buds, with one of its 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 adjoining
+twig; in fact, it formed a little sub-tendril. The
+increasing length of the sub-peduncle (C) with the decreasing
+number of the flower-buds is a good instance of the law of
+compensation. In accordance with this same principle, the
+true tendril as a whole is always longer than the flower-stalk;
+for instance, on the same plant, the longest flower-stalk
+(measured from the base of the common peduncle to the tip of the
+flower-tendril) was 8&frac12; inches in length, whilst the
+longest tendril was nearly double this length, namely 16
+inches.</p>
+
+<p>The gradations from the ordinary state of a flower-stalk, as
+represented in the drawing (fig. 10), to that of a true tendril
+(fig. 9) are complete. We have seen that the sub-peduncle
+(C), whilst still bearing from thirty to forty flower-buds,
+sometimes becomes a little elongated and partially assumes all
+the characters of the corresponding branch of a true
+tendril. From this state we can trace every stage till we
+come to a full-sized perfect 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.</p>
+
+<p>Another kind of gradation well deserves notice.
+Flower-tendrils (B, fig. 10) sometimes produce a few
+flower-buds. For instance, on a vine growing against my
+house, there were thirteen and twenty-two flower-buds
+respectively on two flower-tendrils, which still retained their
+characteristic qualities of sensitiveness and spontaneous
+movement, but in a somewhat lessened degree. On vines in
+hothouses, so many flowers are occasionally produced on the
+flower-tendrils that a double bunch of grapes is the result; and
+this is technically called by gardeners a
+&ldquo;cluster.&rdquo; 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-stalks closely resemble in structure
+those borne by <i>Cissus</i>. This genus, belonging to the
+same family of the Vitaceæ, produces well-developed
+tendrils and ordinary bunches of flowers; but there are no
+gradations between the two states. If the genus
+<i>Vitis</i> had been unknown, the boldest believer in the
+modification of species would never 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
+such a case; and it seems to me as striking and curious an
+instance of transition as can well be conceived.</p>
+
+<p><i>Cissus discolor</i>.&mdash;The young shoots show no more
+movement than can be accounted for by daily variations in the
+action of the light. The tendrils, however, revolve with
+much regularity, following the sun; and, in the plants observed
+by me, swept circles of about 5 inches in diameter. Five
+circles were completed in the following times:&mdash;4 hrs. 45
+m., 4 hrs. 50 m., 4 hrs. 45 m., 4 hrs. 30 m., and 5 hrs. The same
+tendril continues to revolve during three or four days. The
+tendrils are from 3&frac12; to 5 inches in length. They are
+formed of a long foot-stalk, bearing two short branches, which in
+old plants again bifurcate. The two branches are not of
+quite equal length; and as with the vine, the longer one has a
+scale at its base. The tendril stands vertically upwards;
+the extremity of the shoot being bent abruptly downwards, and
+this position is probably of service to the plant by allowing the
+tendril to revolve freely and vertically.</p>
+
+<p>Both branches of the tendril, whilst young, are highly
+sensitive. A touch with a pencil, so gentle as only just to
+move a tendril borne at the end of a long flexible shoot,
+sufficed to cause it to become perceptibly curved in four or five
+minutes. It became straight again in rather above one
+hour. A loop of soft thread weighing one-seventh of a grain
+(9.25 mg.) was thrice tried, and each time caused the tendril to
+become curved in 30 or 40 m. Half this weight produced no
+effect. The long foot-stalk is much less sensitive, for a
+slight rubbing produced no effect, although prolonged contact
+with a stick caused it to bend. The two branches are
+sensitive on all sides, so that they converge if touched on their
+inner sides, and diverge if touched on their outer sides.
+If a branch be touched at the same time with equal force on
+opposite sides, both sides are equally stimulated and there is no
+movement. Before examining this plant, I had observed only
+tendrils which are sensitive on one side alone, and these when
+lightly pressed between the finger and thumb become curved; but
+on thus pinching many times the tendrils of the <i>Cissus</i> no
+curvature ensued, and I falsely inferred at first that they were
+not at all sensitive.</p>
+
+<p><i>Cissus antarcticus</i>.&mdash;The tendrils on a young plant
+were thick and straight, with the tips a little curved.
+When their concave surfaces were rubbed, and it was necessary to
+do this with some force, they very slowly became curved, and
+subsequently straight again. They are therefore much less
+sensitive than those of the last species; but they made two
+revolutions, following the sun, rather more rapidly, viz., in 3
+hrs. 30 m. and 4 hrs. The internodes do not revolve.</p>
+
+<p><i>Ampelopsis hederacea</i> (<i>Virginian
+Creeper</i>).&mdash;The internodes apparently do not move more
+than can be accounted for by the varying action of the
+light. The tendrils are from 4 to 5 inches in length, with
+the main stem sending off several lateral branches, which have
+their tips curved, as may be seen in the upper figure (fig.
+11). They exhibit no true spontaneous revolving movement,
+but turn, as was long ago observed by Andrew Knight, <a
+name="citation145"></a><a href="#footnote145"
+class="citation">[145]</a> from the light to the dark. I
+have seen several tendrils move in less than 24 hours, through an
+angle of 180&deg; to the dark side of a case in which a plant was
+placed, but the movement is sometimes much slower. The
+several lateral branches often move independently of one another,
+and sometimes irregularly, without any apparent cause.
+These tendrils are less sensitive to a touch than any others
+observed by me. By gentle but repeated rubbing with a twig,
+the lateral branches, but not the main stem, became in the course
+of three or four hours slightly curved; but they seemed to have
+hardly any power of again straightening themselves. The
+tendrils of a plant which had crawled over a large box-tree
+clasped several of the branches; but I have repeatedly seen that
+they will withdraw themselves after seizing a stick. When
+they meet with a flat surface of wood or a wall (and this is
+evidently what they are adapted for), they turn all their
+branches towards it, and, spreading them widely apart, bring
+their hooked tips laterally into contact with it. In
+effecting this, the several branches, after touching the surface,
+often rise up, place themselves in a new position, and again come
+down into contact with it.</p>
+
+<p>In the course of about two days after a tendril has arranged
+its branches so as to press on any surface, the curved tips
+swell, become bright red, and form on their under-sides the
+well-known little discs or cushions with which they adhere
+firmly. In one case the tips were slightly swollen in 38
+hrs. after coming into contact with a brick; in another case they
+were considerably swollen in 48 hrs., and in an additional 24
+hrs. were firmly attached to a smooth board; and lastly, the tips
+of a younger tendril not only swelled but became attached to a
+stuccoed wall in 42 hrs. These adhesive discs resemble,
+except in colour and in being larger, those of <i>Bignonia
+capreolata</i>. When they were developed in contact with a
+ball of tow, the fibres were separately enveloped, but not in so
+effective a manner as by <i>B. capreolata</i>. Discs are
+never developed, as far as I have seen, without the stimulus of
+at least temporary contact with some object. <a
+name="citation146"></a><a href="#footnote146"
+class="citation">[146]</a> They are generally first formed
+on one side of the curved tip, the whole of which often becomes
+so much changed in appearance, that a line of the original green
+tissue can be traced only along the concave surface. When,
+however, a tendril has clasped a cylindrical stick, an irregular
+rim or disc is sometimes formed along the inner surface at some
+little distance from the curved tip; this was also observed (p.
+71) by Mohl. The discs consist of enlarged cells, with
+smooth projecting hemispherical surfaces, coloured red; they are
+at first gorged with fluid (see section given by Mohl, p. 70),
+but ultimately become woody.</p>
+
+<p>As the discs soon adhere firmly to such smooth surfaces as
+planed or painted wood, or to the polished leaf of the ivy, this
+alone renders it probable that some cement is secreted, as has
+been asserted to be the case (quoted by Mohl, p. 71) by
+Malpighi. I removed a number of discs formed during the
+previous year from a stuccoed wall, and left them during many
+hours, in warm water, diluted acetic acid and alcohol; but the
+attached grains of silex were not loosened. Immersion in
+sulphuric ether for 24 hrs. loosened them much, but warmed
+essential oils (I tried oil of thyme and peppermint) completely
+released every particle of stone in the course of a few
+hours. This seems to prove that some resinous cement is
+secreted. The quantity, however, must be small; for when a
+plant ascended a thinly whitewashed wall, the discs adhered
+firmly to the whitewash; but as the cement never penetrated the
+thin layer, they were easily withdrawn, together with little
+scales of the whitewash. It must not be supposed that the
+attachment is effected exclusively by the cement; for the
+cellular outgrowth completely envelopes every minute and
+irregular projection, and insinuates itself into every
+crevice.</p>
+<p style="text-align: center">
+<a href="images/p148b.jpg">
+<img alt=
+"Fig. 11.  Ampelopsis hederacea.  A.  Tendril fully developed,
+with a young leaf on the opposite side of the stem.  B.  Older
+tendril, several weeks after its attachment to a wall, with the
+branches thickened and spirally contracted, and with the
+extremities developed into discs.  The unattached branches of
+this tendril have withered and dropped off"
+title=
+"Fig. 11.  Ampelopsis hederacea.  A.  Tendril fully developed,
+with a young leaf on the opposite side of the stem.  B.  Older
+tendril, several weeks after its attachment to a wall, with the
+branches thickened and spirally contracted, and with the
+extremities developed into discs.  The unattached branches of
+this tendril have withered and dropped off"
+ src="images/p148s.jpg" />
+</a></p>
+
+<p>A tendril which has not become attached to any body, does not
+contract spirally; and in course of a week or two shrinks into
+the finest thread, withers and drops off. An attached
+tendril, on the other hand, contracts spirally, and thus becomes
+highly elastic, so that when the main foot-stalk is pulled the
+strain is distributed equally between all the attached
+discs. For a few days after the attachment of the discs,
+the tendril remains weak and brittle, but it rapidly increases in
+thickness and acquires great strength. During the following
+winter it ceases to live, but adheres firmly in a dead state both
+to its own stem and to the surface of attachment. In the
+accompanying diagram (fig. 11.) we see the difference between a
+tendril (B) some weeks after its attachment to a wall, with one
+(A) from the same plant fully grown but unattached. That
+the change in the nature of the tissues, as well as the spiral
+contraction, are consequent on the formation of the discs, is
+well shown by any lateral branches which have not become
+attached; for these in a week or two wither and drop off, in the
+same manner as does the whole tendril if unattached. The
+gain in strength and durability in a tendril after its attachment
+is something wonderful. There are tendrils now adhering to
+my house which are still strong, and have been exposed to the
+weather in a dead state for fourteen or fifteen years. One
+single lateral branchlet of a tendril, estimated to be at least
+ten years old, was still elastic and supported a weight of
+exactly two pounds. The whole tendril had five disc-bearing
+branches of equal thickness and apparently of equal strength; so
+that after having been exposed during ten years to the weather,
+it would probably have resisted a strain of ten pounds!</p>
+
+<p><span
+class="smcap">Sapindaceæ</span>.&mdash;<i>Cardiospermum
+halicacabum</i>.&mdash;In this family, as in the last, the
+tendrils are modified flower-peduncles. In the present
+plant the two lateral branches of the main flower-peduncle have
+been converted into a pair of tendrils, corresponding with the
+single &ldquo;flower-tendril&rdquo; of the common vine. The
+main peduncle is thin, stiff, and from 3 to 4&frac12; inches in
+length. Near the summit, above two little bracts, it
+divides into three branches. The middle one divides and
+re-divides, and bears the flowers; ultimately it grows half as
+long again as the two other modified branches. These latter
+are the tendrils; they are at first thicker and longer than the
+middle branch, but never become more than an inch in
+length. They taper to a point and are flattened, with the
+lower clasping surface destitute of hairs. At first they
+project straight up; but soon diverging, spontaneously curl
+downwards so as to become symmetrically and elegantly hooked, as
+represented in the diagram. They are now, whilst the
+flower-buds are still small, ready for action.</p>
+<p style="text-align: center">
+<a href="images/p150b.jpg">
+<img alt=
+"Fig. 12.  Cardiospermum halicacabum.  Upper part of the
+flower-peduncle with its two tendrils"
+title=
+"Fig. 12.  Cardiospermum halicacabum.  Upper part of the
+flower-peduncle with its two tendrils"
+ src="images/p150s.jpg" />
+</a></p>
+
+<p>The two or three upper internodes, whilst young, steadily
+revolve; those on one plant made two circles, against the course
+of the sun, in 3 hrs. 12 m.; in a second plant the same course
+was followed, and the two circles were completed in 3 hrs. 41 m.;
+in a third plant, the internodes followed the sun and made two
+circles in 3 hrs. 47 m. The average rate of these six
+revolutions was 1 hr. 46 m. The stem shows no tendency to
+twine spirally round a support; but the allied tendril-bearing
+genus <i>Paullinia</i> is said (Mohl, p. 4) to be a twiner.
+The flower-peduncles, which stand up above the end of the shoot,
+are carried round and round by the revolving movement of the
+internodes; and when the stem is securely tied, the long and thin
+flower-peduncles themselves are seen to be in continued and
+sometimes rapid movement from side to side. They sweep a
+wide space, but only occasionally revolve in a regular elliptical
+course. By the combined movements of the internodes and
+peduncles, one of the two short hooked tendrils, sooner or later,
+catches hold of some twig or branch, and then it curls round and
+securely grasps it. These tendrils are, however, but
+slightly sensitive; for by rubbing their under surface only a
+slight movement is slowly produced. I hooked a tendril on
+to a twig; and in 1 hr. 45 m. it was curved considerably inwards;
+in 2 hrs. 30 m. it formed a ring; and in from 5 to 6 hours from
+being first hooked, it closely grasped the stick. A second
+tendril acted at nearly the same rate; but I observed one that
+took 24 hours before it curled twice round a thin twig.
+Tendrils which have caught nothing, spontaneously curl up to a
+close helix after the interval of several days. Those which
+have curled round some object, soon become a little thicker and
+tougher. The long and thin main peduncle, though
+spontaneously moving, is not sensitive and never clasps a
+support. Nor does it ever contract spirally, <a
+name="citation152"></a><a href="#footnote152"
+class="citation">[152]</a> although a contraction of this kind
+apparently would have been of service to the plant in
+climbing. Nevertheless it climbs pretty well without this
+aid. The seed-capsules though light, are of enormous size
+(hence its English name of balloon-vine), and as two or three are
+carried on the same peduncle, the tendrils rising close to them
+may be of service in preventing their being dashed to pieces by
+the wind. In the hothouse the tendrils served simply for
+climbing.</p>
+
+<p>The position of the tendrils alone suffices to show their
+homological nature. In two instances one of two tendrils
+produced a flower at its tip; this, however, did not prevent its
+acting properly and curling round a twig. In a third case
+both lateral branches which ought to have been modified into
+tendrils, produced flowers like the central branch, and had quite
+lost their tendril-structure.</p>
+
+<p>I have seen, but was not enabled carefully to observe, only
+one other climbing Sapindaceous plant, namely,
+<i>Paullinia</i>. It was not in flower, yet bore long
+forked tendrils. So that, <i>Paullinia</i>, with respect to
+its tendrils, appears to bear the same relation to
+<i>Cardiospermum</i> that <i>Cissus</i> does to <i>Vitis</i>.</p>
+
+<p><span class="smcap">Passifloraceæ</span>.&mdash;After
+reading the discussion and facts given by Mohl (p. 47) on the
+nature of the tendrils in this family, no one can doubt that they
+are modified flower-peduncles. The tendrils and the
+flower-peduncles rise close side by side; and my son, William E.
+Darwin, made sketches for me of their earliest state of
+development in the hybrid <i>P. floribunda</i>. The two
+organs appear at first as a single papilla which gradually
+divides; so that the tendril appears to be a modified branch of
+the flower-peduncle. My son found one very young tendril
+surmounted by traces of floral organs, exactly like those on the
+summit of the true flower-peduncle at the same early age.</p>
+
+<p><i>Passiflora gracilis</i>.&mdash;This well-named, elegant,
+annual species differs from the other members of the group
+observed by me, in the young internodes having the power of
+revolving. It exceeds all the other climbing plants which I
+have examined, in the rapidity of its movements, and all
+tendril-bearers in the sensitiveness of the tendrils. The
+internode which carries the upper active tendril and which
+likewise carries one or two younger immature internodes, made
+three revolutions, following the sun, at an average rate of 1 hr.
+4 m.; it then made, the day becoming very hot, three other
+revolutions at an average rate of between 57 and 58 m.; so that
+the average of all six revolutions was 1 hr. 1 m. The apex
+of the tendril describes elongated ellipses, sometimes narrow and
+sometimes broad, with their longer axes inclined in slightly
+different directions. The plant can ascend a thin upright
+stick by the aid of its tendrils; but the stem is too stiff for
+it to twine spirally round it, even when not interfered with by
+the tendrils, these having been successively pinched off at an
+early age.</p>
+
+<p>When the stem is secured, the tendrils are seen to revolve in
+nearly the same manner and at the same rate as the internodes. <a
+name="citation154"></a><a href="#footnote154"
+class="citation">[154]</a> The tendrils are very thin,
+delicate, and straight, with the exception of the tips, which are
+a little curved; they are from 7 to 9 inches in length. A
+half-grown tendril is not sensitive; but when nearly full-grown
+they are extremely sensitive. A single delicate touch on
+the concave surface of the tip soon caused one to curve; and in 2
+minutes it formed an open helix. A loop of soft thread
+weighing one thirty-second of a grain (2.02 mg.) placed most
+gently on the tip, thrice caused distinct curvature. A bent
+bit of thin platina wire weighing only fiftieth of a grain (1.23
+mg.) twice produced the same effect; but this latter weight, when
+left suspended, did not suffice to cause a permanent
+curvature. These trials were made under a bell-glass, so
+that the loops of thread and wire were not agitated by the
+wind. The movement after a touch is very rapid: I took hold
+of the lower part of several tendrils, and then touched their
+concave tips with a thin twig and watched them carefully through
+a lens; the tips evidently began to bend after the following
+intervals&mdash;31, 25, 32, 31, 28, 39, 31, and 30 seconds; so
+that the movement was generally perceptible in half a minute
+after a touch; but on one occasion it was distinctly visible in
+25 seconds. One of the tendrils which thus became bent in
+31 seconds, had been touched two hours previously and had coiled
+into a helix; so that in this interval it had straightened itself
+and had perfectly recovered its irritability.</p>
+
+<p>To ascertain how often the same tendril would become curved
+when touched, I kept a plant in my study, which from being cooler
+than the hot-house was not very favourable for the
+experiment. The extremity was gently rubbed four or five
+times with a thin stick, and this was done as often as it was
+observed to have become nearly straight again after having been
+in action; and in the course of 54 hrs. it answered to the
+stimulus 21 times, becoming each time hooked or spiral. On
+the last occasion, however, the movement was very slight, and
+soon afterwards permanent spiral contraction commenced. No
+trials were made during the night, so that the tendril would
+perhaps have answered a greater number of times to the stimulus;
+though, on the other hand, from having no rest it might have
+become exhausted from so many quickly repeated efforts.</p>
+
+<p>I repeated the experiment made on the <i>Echinocystis</i>, and
+placed several plants of this <i>Passiflora</i> so close
+together, that their tendrils were repeatedly dragged over each
+other; but no curvature ensued. I likewise repeatedly
+flirted small drops of water from a brush on many tendrils, and
+syringed others so violently that the whole tendril was dashed
+about, but they never became curved. The impact from the
+drops of water was felt far more distinctly on my hand than that
+from the loops of thread (weighing one thirty-second of a grain)
+when allowed to fall on it from a height, and these loops, which
+caused the tendrils to become curved, had been placed most gently
+on them. Hence it is clear, that the tendrils either have
+become habituated to the touch of other tendrils and drops of
+rain, or that they were from the first rendered sensitive only to
+prolonged though excessively slight pressure of solid objects,
+with the exclusion of that from other tendrils. To show the
+difference in the kind of sensitiveness in different plants and
+likewise to show the force of the syringe used, I may add that
+the lightest jet from it instantly caused the leaves of a
+<i>Mimosa</i> to close; whereas the loop of thread weighing one
+thirty-second of a grain, when rolled into a ball and placed
+gently on the glands at the bases of the leaflets of the
+<i>Mimosa</i>, caused no action.</p>
+
+<p><i>Passiflora punctata</i>.&mdash;The internodes do not move,
+but the tendrils revolve regularly. A half-grown and very
+sensitive tendril made three revolutions, opposed to the course
+of the sun, in 3 hrs. 5 m., 2 hrs. 40 m. and 2 hrs. 50 m.;
+perhaps it might have travelled more quickly when nearly
+full-grown. A plant was placed in front of a window, and,
+as with twining stems, the light accelerated the movement of the
+tendril in one direction and retarded it in the other; the
+semicircle towards the light being performed in one instance in
+15 m. less time and in a second instance in 20 m. less time than
+that required by the semicircle towards the dark end of the
+room. Considering the extreme tenuity of these tendrils,
+the action of the light on them is remarkable. The tendrils
+are long, and, as just stated, very thin, with the tip slightly
+curved or hooked. The concave side is extremely sensitive
+to a touch&mdash;even a single touch causing it to curl inwards;
+it subsequently straightened itself, and was again ready to
+act. A loop of soft thread weighing one fourteenth of a
+grain (4.625 mg.) caused the extreme tip to bend; another time I
+tried to hang the same little loop on an inclined tendril, but
+three times it slid off; yet this extraordinarily slight degree
+of friction sufficed to make the tip curl. The tendril,
+though so sensitive, does not move very quickly after a touch, no
+conspicuous movement being observable until 5 or 10 m. had
+elapsed. The convex side of the tip is not sensitive to a
+touch or to a suspended loop of thread. On one occasion I
+observed a tendril revolving with the convex side of the tip
+forwards, and in consequence it was not able to clasp a stick,
+against which it scraped; whereas tendrils revolving with the
+concave side forward, promptly seize any object in their
+path.</p>
+
+<p><i>Passiflora quadrangularis</i>.&mdash;This is a very
+distinct species. The tendrils are thick, long, and stiff;
+they are sensitive to a touch only on the concave surface towards
+the extremity. When a stick was placed so that the middle
+of the tendril came into contact with it, no curvature
+ensued. In the hothouse a tendril made two revolutions,
+each in 2 hrs. 22 m.; in a cool room one was completed in 3 hrs.,
+and a second in 4 hrs. The internodes do not revolve; nor
+do those of the hybrid <i>P. floribunda</i>.</p>
+
+<p><i>Tacsonia manicata</i>.&mdash;Here again the internodes do
+not revolve. The tendrils are moderately thin and long; one
+made a narrow ellipse in 5 hrs. 20 m., and the next day a broad
+ellipse in 5 hrs. 7 m. The extremity being lightly rubbed
+on the concave surface, became just perceptibly curved in 7 m.,
+distinctly in 10 m., and hooked in 20 m.</p>
+
+<p>We have seen that the tendrils in the last three families,
+namely, the Vitaceæ, Sapindaceæ and
+Passifloraceæ, are modified flower-peduncles. This is
+likewise the case, according to De Candolle (as quoted by Mohl),
+with the tendrils of <i>Brunnichia</i>, one of the
+Polygonaceæ. In two or three species of
+<i>Modecca</i>, one of the Papayaceæ, the tendrils, as I
+hear from Prof. Oliver, occasionally bear flowers and fruit; so
+that they are axial in their nature.</p>
+<h4><i>The Spiral Contraction of Tendrils</i>.</h4>
+<p>This movement, which shortens the tendrils and renders them
+elastic, commences in half a day, or in a day or two after their
+extremities have caught some object. There is no such
+movement in any leaf-climber, with the exception of an occasional
+trace of it in the petioles of <i>Tropæolum
+tricolorum</i>. On the other hand, the tendrils of all
+tendril-bearing plants, contract spirally after they have caught
+an object with the following exceptions. Firstly,
+<i>Corydalis claviculata</i>, but then this plant might be called
+a leaf-climber. Secondly and thirdly, <i>Bignonia
+unguis</i> with its close allies, and <i>Cardiospermum</i>; but
+their tendrils are so short that their contraction could hardly
+occur, and would be quite superfluous. Fourthly,
+<i>Smilaæ aspera</i> offers a more marked exception, as its
+tendrils are moderately long. The tendrils of
+<i>Dicentra</i>, whilst the plant is young, are short and after
+attachment only become slightly flexuous; in older plants they
+are longer and then they contract spirally. I have seen no
+other exceptions to the rule that tendrils, after clasping with
+their extremities a support, undergo spiral contraction.
+When, however, the tendril of a plant of which the stem is
+immovably fixed, catches some fixed object, it does not contract,
+simply because it cannot; this, however, rarely occurs. In
+the common Pea the lateral branches alone contract, and not the
+central stem; and with most plants, such as the Vine, Passiflora,
+Bryony, the basal portion never forms a spire.</p>
+
+<p>I have said that in <i>Corydalis claviculata</i> the end of
+the leaf or tendril (for this part may be indifferently so
+called) does not contract into a spire. The branchlets,
+however, after they have wound round thin twigs, become deeply
+sinuous or zigzag. Moreover the whole end of the petiole or
+tendril, if it seizes nothing, bends after a time abruptly
+downwards and inwards, showing that its outer surface has gone on
+growing after the inner surface has ceased to grow. That
+growth is the chief cause of the spiral contraction of tendrils
+may be safely admitted, as shown by the recent researches of H.
+de Vries. I will, however, add one little fact in support
+of this conclusion.</p>
+
+<p>If the short, nearly straight portion of an attached tendril
+of <i>Passiflora gracilis</i>, (and, as I believe, of other
+tendrils,) between the opposed spires, be examined, it will be
+found to be transversely wrinkled in a conspicuous manner on the
+outside; and this would naturally follow if the outer side had
+grown more than the inner side, this part being at the same time
+forcibly prevented from becoming curved. So again the whole
+outer surface of a spirally wound tendril becomes wrinkled if it
+be pulled straight. Nevertheless, as the contraction
+travels from the extremity of a tendril, after it has been
+stimulated by contact with a support, down to the base, I cannot
+avoid doubting, from reasons presently to be given, whether the
+whole effect ought to be attributed to growth. An
+unattached tendril rolls itself up into a flat helix, as in the
+case of Cardiospermum, if the contraction commences at the
+extremity and is quite regular; but if the continued growth of
+the outer surface is a little lateral, or if the process begins
+near the base, the terminal portion cannot be rolled up within
+the basal portion, and the tendril then forms a more or less open
+spire. A similar result follows if the extremity has caught
+some object, and is thus held fast.</p>
+
+<p>The tendrils of many kinds of plants, if they catch nothing,
+contract after an interval of several days or weeks into a spire;
+but in these cases the movement takes place after the tendril has
+lost its revolving power and hangs down; it has also then partly
+or wholly lost its sensibility; so that this movement can be of
+no use. The spiral contraction of unattached tendrils is a
+much slower process than that of attached ones. Young
+tendrils which have caught a support and are spirally contracted,
+may constantly be seen on the same stem with the much older
+unattached and uncontracted tendrils. In the
+<i>Echinocystis</i> I have seen a tendril with the two lateral
+branches encircling twigs and contracted into beautiful spires,
+whilst the main branch which had caught nothing remained for many
+days straight. In this plant I once observed a main branch
+after it had caught a stick become spirally flexuous in 7 hrs.,
+and spirally contracted in 18 hrs. Generally the tendrils
+of the <i>Echinocystis</i> begin to contract in from 12 hrs. to
+24 hrs. after catching some object; whilst unattached tendrils do
+not begin to contract until two or three or even more days after
+all revolving movement has ceased. A full-grown tendril of
+<i>Passiflora quadrangularis</i> which had caught a stick began
+in 8 hrs. to contract, and in 24 hrs. formed several spires; a
+younger tendril, only two-thirds grown, showed the first trace of
+contraction in two days after clasping a stick, and in two more
+days formed several spires. It appears, therefore, that the
+contraction does not begin until the tendril 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 formed one complete
+spire. This first spire was formed towards the basal end,
+and the contraction steadily but slowly progressed towards the
+apex; but the whole was not closely wound up into a spire until
+21 days had elapsed from the first observation, that is, until 17
+days after the tendril had grown to its full length.</p>
+
+<p>The spiral contraction of tendrils is quite independent of
+their power of spontaneously revolving, for it occurs in
+tendrils, such as those of <i>Lathyrus grandiflorus</i> and
+<i>Ampelopsis hederacea</i>, which do not revolve. It is
+not necessarily related to the curling of the tips round a
+support, as we see with the Ampelopsis and <i>Bignonia
+capreolata</i>, in which the development of adherent discs
+suffices to cause spiral contraction. Yet in some cases
+this contraction seems connected with the curling or clasping
+movement, due to contact with a support; for not only does it
+soon follow this act, but the contraction generally begins close
+to the curled extremity, and travels downwards to the base.
+If, however, a tendril be very slack, the whole length almost
+simultaneously becomes at first flexuous and then spiral.
+Again, the tendrils of some few plants never contract spirally
+unless they have first seized hold of some object; if they catch
+nothing they hang down, remaining straight, until they wither and
+drop off: this is the case with the tendrils of Bignonia, which
+consist of modified leaves, and with those of three genera of the
+Vitaceæ, which are modified flower-peduncles. But in
+the great majority of cases, tendrils which have never come in
+contact with any object, after a time contract spirally.
+All these facts taken together, show that the act of clasping a
+support and the spiral contraction of the whole length of the
+tendril, are phenomena not necessarily connected.</p>
+
+<p>The spiral contraction which ensues after a tendril has caught
+a support is of high service to the plant; hence its almost
+universal occurrence with species belonging to 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 stem, after the
+tendrils have seized some object above, would leave it slack,
+were it not for the spiral contraction which draws up the stem as
+it increases in length. Thus there is no waste of growth,
+and the stretched stem ascends by the shortest course. When
+a terminal branchlet of the tendril of Cobæa catches a
+stick, we have seen how well the spiral contraction successively
+brings the other branchlets, one after the other, into contact
+with the stick, until the whole tendril grasps it in an
+inextricable 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 <i>Passiflora
+quadrangularis</i>; but this action is of little importance.</p>
+
+<p>A far more important service rendered by the spiral
+contraction of the tendrils is that they are thus made highly
+elastic. As before remarked under Ampelopsis, the strain is
+thus distributed equally between the several attached branches;
+and this renders the whole far stronger than it otherwise would
+be, as the branches cannot break separately. It is this
+elasticity which protects both branched and simple tendrils from
+being torn away from their supports 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 thick and thin branches were
+tossed to and fro by the wind, the 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.</p>
+
+<p>When an unattached 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, although the same side is concave from end to end,
+invariably becomes twisted in one part in one direction, and in
+another part in the opposite direction; the oppositely turned
+spires being separated by a short straight portion. This
+curious and symmetrical structure has been noticed by several
+botanists, but has not been sufficiently explained. <a
+name="citation165"></a><a href="#footnote165"
+class="citation">[165]</a> It occurs without exception with
+all tendrils which after catching an 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 occurred, it will be found that the tendril had originally
+seized some object and had afterwards been torn free.
+Commonly, all the spires at one end of an attached 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 pieces between
+them; and M. Léon has seen seven or eight such
+alternations. Whether the spires turn once or more than
+once in opposite directions, there are as many turns in the one
+direction as in the other. For instance, I gathered ten
+attached tendrils of the Bryony, the longest with 33, and the
+shortest with only 8 spiral turns; and the number of turns in the
+one direction was in every case the same (within one) as in the
+opposite direction.</p>
+<p style="text-align: center">
+<a href="images/p165b.jpg">
+<img alt=
+"Fig. 13.  A caught tendril of Bryonia dioica, spirally
+contracted in reserved directions"
+title=
+"Fig. 13.  A caught tendril of Bryonia dioica, spirally
+contracted in reserved directions"
+ src="images/p165s.jpg" />
+</a></p>
+
+<p>The explanation of this curious little fact is not
+difficult. I will not attempt any geometrical reasoning,
+but will give only a practical illustration. 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, thus imitating the revolving
+movement of a twining plant, and the strings do not become
+twisted. But if we hold at the same time a stick in our
+left hand, in such a position that the strings become 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 wound round. I painted a red
+line on the straight internodes of a <i>Humulus</i>,
+<i>Mikania</i>, <i>Ceropegia</i>, <i>Convolvulus</i>, and
+<i>Phaseolus</i>, 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.</p>
+
+<p>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.
+When, therefore, a free tendril coils itself into a spire, it
+must either become twisted along its whole length (and this never
+occurs), or the free extremity must turn round as many times as
+there are spires formed. It was hardly necessary to observe
+this fact; but I did so by affixing little paper vanes to the
+extreme points of the tendrils of <i>Echinocystis</i> and
+<i>Passiflora quadrangularis</i>; and as the tendril contracted
+itself into successive spires, the vane slowly revolved.</p>
+
+<p>We can now understand the meaning of the spires being
+invariably turned in opposite directions, in tendrils which from
+having caught some object are fixed at both ends. Let us
+suppose a caught tendril to make thirty spiral turns all in the
+same direction; the inevitable result would be that it would
+become twisted thirty times on its own axis. This twisting
+would not only require considerable force, but, as I know by
+trial, would burst the tendril before the thirty turns were
+completed. Such cases never really occur; for, as already
+stated, when a tendril has caught a support and is spirally
+contracted, there are always as many turns in one direction as in
+the other; so that the twisting of the axis in the one direction
+is exactly compensated by the twisting in the opposite
+direction. We can further see how the tendency is given to
+make the later formed coils opposite 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 perpendicular pencil, and this will
+twist the lower part of the string; and after it has been
+sufficiently twisted, it will be seen to curve itself into an
+open spire, with the curves running in an opposite direction to
+those round the pencil, and consequently with a straight piece of
+string between the opposed 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 cannot resist giving one other illustration, though
+superfluous: when a haberdasher winds up ribbon for a customer,
+he does not wind it into a single coil; for, if he did, the
+ribbon would twist itself as many times as there were coils; but
+he winds it into a figure of eight on his thumb and little
+finger, so that he alternately takes turns in opposite
+directions, and thus the ribbon is not twisted. So it is
+with tendrils, with this sole difference, that they take several
+consecutive turns in one direction and then the same number in an
+opposite direction; but in both cases the self-twisting is
+avoided.</p>
+<h4><i>Summary on the Nature and Action of Tendrils</i>.</h4>
+<p>With the majority of tendril-bearing plants the young
+internodes revolve in more or less broad ellipses, like those
+made by twining plants; but the figures described, when carefully
+traced, generally form irregular ellipsoidal spires. The
+rate of revolution varies from one to five hours in different
+species, and consequently is in some cases 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 direction is variable even in the same
+individual plant. In <i>Passiflora</i>, the internodes of
+only one species have the power of revolving. The Vine is
+the weakest revolver observed by me, apparently exhibiting only a
+trace of a former power. In the <i>Eccremocarpus</i> the
+movement is interrupted by many long pauses. Very few
+tendril-bearing plants can spirally twine up an upright
+stick. Although the power of twining has generally been
+lost, either from the stiffness or shortness of the internodes,
+from the size of the leaves, or from some other unknown cause,
+the revolving movement of the stem serves to bring the tendrils
+into contact with surrounding objects.</p>
+
+<p>The tendrils themselves also spontaneously revolve. The
+movement begins whilst the tendril is young, and is at first
+slow. The mature tendrils of <i>Bignonia littoralis</i>
+move much slower than the internodes. Generally, the
+internodes and tendrils revolve together at the same rate; in
+Cissus, Cobæa, and most Passifloræ, the tendrils
+alone revolve; in other cases, as with <i>Lathyrus aphaca</i>,
+only the internodes move, carrying with them the motionless
+tendrils; and, lastly (and this is the fourth possible case),
+neither internodes nor tendrils spontaneously revolve, as with
+<i>Lathyrus grandiflorus</i> and <i>Ampelopsis</i>. In most
+Bignonias, Eccremocarpus Mutisia, and the Fumariaceæ, the
+internodes, petioles and tendrils all move harmoniously
+together. In every case the conditions of life must be
+favourable in order that the different parts should act in a
+perfect manner.</p>
+
+<p>Tendrils revolve by the curvature of their whole length,
+excepting the sensitive extremity and the base, which parts do
+not move, or move but little. The movement is of the same
+nature as that of the revolving internodes, and, from the
+observations of Sachs and H. de Vries, no doubt is due to the
+same cause, namely, the rapid growth of a longitudinal band,
+which travels round the tendril and successively bows each part
+to the opposite side. Hence, if a line be painted along
+that surface which happens at the time to be convex, the line
+becomes first lateral, then concave, then lateral, and ultimately
+again convex. This experiment can be tried only on the
+thicker tendrils, which are not affected by a thin crust of dried
+paint. The extremities are often slightly curved or hooked,
+and the curvature of this part is never reversed; in this respect
+they differ from the extremities of twining shoots, which not
+only reverse their curvature, or at least become periodically
+straight, but curve themselves in a greater degree than the lower
+part. In most other respects a tendril acts as if it were
+one of several revolving internodes, which all move together by
+successively bending to each point 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. With most tendril-bearers the summit of the
+stem or shoot projects above the point from which the tendril
+arises; and it is generally bent to 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, as we have seen with the Echinocystis, as soon as the
+tendril comes in its revolving course to this point, it stiffens
+and straightens itself, and thus rising vertically up passes over
+the obstacle in an admirable manner.</p>
+
+<p>All tendrils are sensitive, but in various degrees, to contact
+with an object, and curve towards the touched side. With
+several plants a single touch, so slight as only just to move the
+highly flexible tendril, is enough to induce curvature.
+<i>Passiflora gracilis</i> possesses the most sensitive tendrils
+which I have observed: a bit of platina wire 0.02 of a grain
+(1.23 mg.) in weight, gently placed on the concave point, caused
+a tendril to become hooked, as did a loop of soft, thin cotton
+thread weighing one thirty-second of a grain (2.02 mg.)
+With the tendrils of several other plants, loops weighing one
+sixteenth of a grain (4.05 mg.) sufficed. The point of a
+tendril of <i>Passiflora gracilis</i> began to move distinctly in
+25 seconds after a touch, and in many cases after 30
+seconds. Asa Gray also saw movement in the tendrils of the
+Cucurbitaceous genus, <i>Sicyos</i>, in 30 seconds. The
+tendrils of some other plants, when lightly rubbed, moved in a
+few minutes; with Dicentra in half-an-hour; with Smilax in an
+hour and a quarter or half; and with Ampelopsis still more
+slowly. The curling movement consequent on a single touch
+continues to increase for a considerable time, then ceases; after
+a few hours the tendril uncurls itself, and is again ready to
+act. When the tendrils of several kinds of plants were
+caused to bend by extremely light weights suspended on them, they
+seemed to grow accustomed to so slight a stimulus, and
+straightened themselves, as if the loops had been removed.
+It makes no difference what sort of object a tendril touches,
+with the remarkable exception of other tendrils and drops of
+water, as was observed with the extremely sensitive-tendrils of
+<i>Passiflora gracilis</i> and of the <i>Echinocystis</i>.
+I have, however, seen tendrils of the Bryony which had
+temporarily caught other tendrils, and often in the case of the
+vine.</p>
+
+<p>Tendrils of which the extremities are permanently and slightly
+curved, are sensitive only on the concave surface; other
+tendrils, such as those of the Cobæa (though furnished with
+horny hooks directed to one side) and those of <i>Cissus
+discolor</i>, are sensitive on all sides. Hence the
+tendrils of this latter plant, when stimulated by a touch of
+equal force on opposite sides, did not bend. The inferior
+and lateral surfaces of the tendrils of <i>Mutisia</i> are
+sensitive, but not the upper surface. With branched
+tendrils, the several branches act alike; but in the
+<i>Hanburya</i> the lateral spur-like branch does not acquire
+(for excellent reasons which have been explained) its
+sensitiveness nearly so soon as the main branch. With most
+tendrils the lower or basal part is either not at all sensitive,
+or sensitive only to prolonged contact. We thus see that
+the sensitiveness of tendrils is a special and localized
+capacity. It is quite independent of the power of
+spontaneously revolving; for the curling of the terminal portion
+from touch does not in the least interrupt the former
+movement. In <i>Bignonia unguis</i> and its close allies,
+the petioles of the leaves, as well as the tendrils, are
+sensitive to a touch.</p>
+
+<p>Twining plants when they come into contact with a stick, curl
+round it invariably in the direction of their revolving movement;
+but tendrils curl indifferently to either side, in accordance
+with the position of the stick and the side which is first
+touched. The clasping movement of the extremity is
+apparently not steady, but undulatory or vermicular in its
+nature, as may be inferred from the curious manner in which the
+tendrils of the Echinocystis slowly crawled round a smooth
+stick.</p>
+
+<p>As with a few exceptions tendrils spontaneously revolve, it
+may be asked,&mdash;why have they been endowed with
+sensitiveness?&mdash;why, when they come into contact with a
+stick, do they not, like twining plants, spirally wind round
+it? One reason may be that they are in most cases so
+flexible and thin, that when brought into contact with any
+object, they would almost certainly yield and be dragged onwards
+by the revolving movement. Moreover, the sensitive
+extremities have no revolving power as far as I have observed,
+and could not by this means curl round a support. With
+twining plants, on the other hand, the extremity spontaneously
+bends more than any other part; and this is of high importance
+for the ascent of the plant, as may be seen on a windy day.
+It is, however, possible that the slow movement of the basal and
+stiffer parts of certain tendrils, which wind round sticks placed
+in their path, may be analogous to that of twining plants.
+But I hardly attended sufficiently to this point, and it would
+have been difficult to distinguish between a movement due to
+extremely dull irritability, from the arrestment of the lower
+part, whilst the upper part continued to move onwards.</p>
+
+<p>Tendrils which are only three-fourths grown, and perhaps even
+at an earlier age, but not whilst extremely young, have the power
+of revolving and of grasping any object which they touch.
+These two capacities are generally acquired at about the same
+period, and both fail when the tendril is full grown. But
+in <i>Cobæa</i> and <i>Passiflora punctata</i> the tendrils
+begin to revolve in a useless manner, before they have become
+sensitive. In the Echinocystis they retain their
+sensitiveness for some time after they have ceased to revolve and
+after they have sunk downwards; in this position, even if they
+were able to seize an object, such power would be of no service
+in supporting the stem. It is a rare circumstance thus to
+detect any superfluity or imperfection in the action of
+tendrils&mdash;organs which are so excellently adapted for the
+functions which they have to perform; but we see that they are
+not always perfect, and it would be rash to assume that any
+existing tendril has reached the utmost limit of perfection.</p>
+
+<p>Some tendrils have their revolving motion accelerated or
+retarded, in moving to or from the light; others, as with the
+Pea, seem indifferent to its action; others move steadily from
+the light to the dark, and this aids them in an important manner
+in finding a support. For instance, the tendrils of
+<i>Bignonia capreolata</i> bend from the light to the dark as
+truly as a wind-vane from the wind. In the Eccremocarpus
+the extremities alone twist and turn about so as to bring their
+finer branches and hooks into close contact with any dark
+surface, or into crevices and holes.</p>
+
+<p>A short time after a tendril has caught a support, it
+contracts with some rare exceptions into a spire; but the manner
+of contraction and the several important advantages thus gained
+have been discussed so lately, that nothing need here be repeated
+on the subject. Tendrils soon after catching a support grow
+much stronger and thicker, and sometimes more durable to a
+wonderful degree; and this shows how much their internal tissues
+must be changed. Occasionally it is the part which is wound
+round a support which chiefly becomes thicker and stronger; I
+have seen, for instance, this part of a tendril of <i>Bignonia
+æquinoctialis</i> twice as thick and rigid as the free
+basal part. Tendrils which have caught nothing soon shrink
+and wither; but in some species of Bignonia they disarticulate
+and fall off like leaves in autumn.</p>
+
+<div class="gapspace">&nbsp;</div>
+<p>Any one who had not closely observed tendrils of many kinds
+would probably infer that their action was uniform. This is
+the case with the simpler kinds, which simply curl round an
+object of moderate thickness, whatever its nature may be. <a
+name="citation176"></a><a href="#footnote176"
+class="citation">[176]</a> But the genus Bignonia shows us
+what diversity of action there may be between the tendrils of
+closely allied species. In all the nine species observed by
+me, the young internodes revolve vigorously; the tendrils also
+revolve, but in some of the species in a very feeble manner; and
+lastly the petioles of nearly all revolve, though with unequal
+power. The petioles of three of the species, and the
+tendrils of all are sensitive to contact. In the
+first-described species, the tendrils resemble in shape a
+bird&rsquo;s foot, and they are of no service to the stem in
+spirally ascending a thin upright stick, but they can seize firm
+hold of a twig or branch. When the stem twines round a
+somewhat thick stick, a slight degree of sensitiveness possessed
+by the petioles is brought into play, and the whole leaf together
+with the tendril winds round it. In <i>B. unguis</i> the
+petioles are more sensitive, and have greater power of movement
+than those of the last species; they are able, together with the
+tendrils, to wind inextricably round a thin upright stick; but
+the stem does not twine so well. <i>B. Tweedyana</i> has
+similar powers, but in addition, emits aërial roots which
+adhere to the wood. In <i>B. venusta</i> the tendrils are
+converted into elongated three-pronged grapnels, which move
+spontaneously in a conspicuous manner; the petioles, however,
+have lost their sensitiveness. The stem of this species can
+twine round an upright stick, and is aided in its ascent by the
+tendrils seizing the stick alternately some way above and then
+contracting spirally. In <i>B. littoralis</i> the tendrils,
+petioles, and internodes, all revolve spontaneously. The
+stem, however, cannot twine, but ascends an upright stick by
+seizing it above with both tendrils together, which then contract
+into a spire. The tips of these tendrils become developed
+into adhesive discs. <i>B. speciosa</i> possesses similar
+powers of movement as the last species, but it cannot twine round
+a stick, though it can ascend by clasping the stick horizontally
+with one or both of its unbranched tendrils. These tendrils
+continually insert their pointed ends into minute crevices or
+holes, but as they are always withdrawn by the subsequent spiral
+contraction, the habit seems to us in our ignorance
+useless. Lastly, the stem of <i>B. capreolata</i> twines
+imperfectly; the much-branched tendrils revolve in a capricious
+manner, and bend from the light to the dark; their hooked
+extremities, even whilst immature, crawl into crevices, and, when
+mature, seize any thin projecting point; in either case they
+develop adhesive discs, and these have the power of enveloping
+the finest fibres.</p>
+
+<p>In the allied Eccremocarpus the internodes, petioles, and
+much-branched tendrils all spontaneously revolve together.
+The tendrils do not as a whole turn from the light; but their
+bluntly-hooked extremities arrange themselves neatly on any
+surface with which they come into contact, apparently so as to
+avoid the light. They act best when each branch seizes a
+few thin stems, like the culms of a grass, which they afterwards
+draw together into a solid bundle by the spiral contraction of
+all the branches. In Cobæa the finely-branched
+tendrils alone revolve; the branches terminate in sharp, hard,
+double, little hooks, with both points directed to the same side;
+and these turn by well-adapted movements to any object with which
+they come into contact. The tips of the branches also crawl
+into dark crevices or holes. The tendrils and internodes of
+Ampelopsis have little or no power of revolving; the tendrils are
+but little sensitive to contact; their hooked extremities cannot
+seize thin objects; they will not even clasp a stick, unless in
+extreme need of a support; but they turn from the light to the
+dark, and, spreading out their branches in contact with any
+nearly flat surface, develop discs. These adhere by the
+secretion of some cement to a wall, or even to a polished
+surface; and this is more than the discs of the <i>Bignonia
+capreolata</i> can effect.</p>
+
+<p>The rapid development of these adherent discs is one of the
+most remarkable peculiarities possessed by any tendrils. We
+have seen that such discs are formed by two species of Bignonia,
+by Ampelopsis, and, according to Naudin, <a
+name="citation179"></a><a href="#footnote179"
+class="citation">[179]</a> by the Cucurbitaceous genus
+<i>Peponopsis adhærens</i>. In Anguria 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; whilst in Hanburya a similar layer is adherent.
+The growth of these cellular out-growths depends, (except in the
+case of the <i>Haplolophium</i> and of one species of
+Ampelopsis,) on the stimulus from contact. It is a singular
+fact that three families, so widely distinct as the
+Bignoniaceæ, Vitaceæ, and Cucurbitaceæ, should
+possess species with tendrils having this remarkable power.</p>
+
+<div class="gapspace">&nbsp;</div>
+<p>Sachs attributes all the movements of tendrils to rapid growth
+on the side opposite to that which becomes concave. These
+movements consist of revolving nutation, the bending to and from
+the light, and in opposition to gravity, those caused by a touch,
+and spiral contraction. It is rash to differ from so great
+an authority, but I cannot believe that one at least of these
+movements&mdash;curvature from a touch&mdash;is thus caused. <a
+name="citation180"></a><a href="#footnote180"
+class="citation">[180]</a> In the first place it may be
+remarked that the movement of nutation differs from that due to a
+touch, in so far that in some cases the two powers are acquired
+by the same tendril at different periods of growth; and the
+sensitive part of the tendril does not seem capable of
+nutation. One of my chief reasons for doubting whether the
+curvature from a touch is the result of growth, is the
+extraordinary rapidity of the movement. I have seen the
+extremity of a tendril of <i>Passiflora gracilis</i>, after being
+touched, distinctly bent in 25 seconds, and often in 30 seconds;
+and so it is with the thicker tendril of Sicyos. It appears
+hardly credible that their outer surfaces could have actually
+grown in length, which implies a permanent modification of
+structure, in so short a time. The growth, moreover, on
+this view must be considerable, for if the touch has been at all
+rough the extremity is coiled in two or three minutes into a
+spire of several turns.</p>
+
+<p>When the extreme tip of the tendril of Echinocystis caught
+hold of a smooth stick, it coiled itself in a few hours (as
+described at p. 132) twice or thrice round the stick, apparently
+by an undulatory movement. At first I attributed this
+movement to the growth of the outside; black marks were therefore
+made, and the interspaces measured, but I could not thus detect
+any increase in length. Hence it seems probable in this
+case and in others, that the curvature of the tendril from a
+touch depends on the contraction of the cells along the concave
+side. Sachs himself admits <a name="citation181"></a><a
+href="#footnote181" class="citation">[181]</a> that &ldquo;if the
+growth which takes place in the entire tendril at the time of
+contact with a support is small, a considerable acceleration
+occurs on the convex surface, but in general there is no
+elongation on the concave surface, or there may even be a
+<i>contraction</i>; in the case of a tendril of Cucurbita this
+contraction amounted to nearly one-third of the original
+length.&rdquo; In a subsequent passage Sachs seems to feel
+some difficulty in accounting for this kind of contraction.
+It must not however be supposed from the foregoing remarks that I
+entertain any doubt, after reading De Vries&rsquo; observations,
+about the outer and stretched surfaces of attached tendrils
+afterwards increasing in length by growth. Such increase
+seems to me quite compatible with the first movement being
+independent of growth. Why a delicate touch should cause
+one side of a tendril to contract we know as little as why, on
+the view held by Sachs, it should lead to extraordinarily rapid
+growth of the opposite side. The chief or sole reason for
+the belief that the curvature of a tendril when touched is due to
+rapid growth, seems to be that tendrils lose their sensitiveness
+and power of movement after they have grown to their full length;
+but this fact is intelligible, if we bear in mind that all the
+functions of a tendril are adapted to drag up the terminal
+growing shoot towards the light. Of what use would it be,
+if an old and full-grown tendril, arising from the lower part of
+a shoot, were to retain its power of clasping a support?
+This would be of no use; and we have seen with tendrils so many
+instances of close adaptation and of the economy of means, that
+we may feel assured that they would acquire irritability and the
+power of clasping a support at the proper age&mdash;namely,
+youth&mdash;and would not uselessly retain such power beyond the
+proper age.</p>
+
+<h3>CHAPTER V.<br />
+<span class="smcap">Hook and Root-Climbers.&mdash;Concluding
+Remarks</span>.</h3>
+
+<p class="gutsumm">Plants climbing by the aid of hooks, or merely
+scrambling over other plants&mdash;Root-climbers, adhesive matter
+secreted by the rootlets&mdash;General conclusions with respect
+to climbing plants, and the stages of their development.</p>
+
+<p><i>Hook-Climbers</i>.&mdash;In my introductory remarks, I
+stated that, besides the two first great classes of climbing
+plants, namely, those which twine round a support, and those
+endowed with irritability enabling them to seize hold of objects
+by means of their petioles or tendrils, there are two other
+classes, hook-climbers and root-climbers. Many plants,
+moreover, as Fritz Müller has remarked, <a
+name="citation183"></a><a href="#footnote183"
+class="citation">[183]</a> climb or scramble up thickets in a
+still more simple fashion, without any special aid, excepting
+that their leading shoots are generally long and flexible.
+It may, however, be suspected from what follows, that these
+shoots in some cases tend to avoid the light. The few
+hook-climbers which I have observed, namely, <i>Galium
+aparine</i>, <i>Rubus australis</i>, and some climbing Roses,
+exhibit no spontaneous revolving movement. If they had
+possessed this power, and had been capable of twining, they would
+have been placed in the class of Twiners; for some twiners are
+furnished with spines or hooks, which aid them in their
+ascent. For instance, the Hop, which is a twiner, has
+reflexed hooks as large as those of the <i>Galium</i>; some other
+twiners have stiff reflexed hairs; and <i>Dipladenia</i> has a
+circle of blunt spines at the bases of its leaves. I have
+seen only one tendril-bearing plant, namely, <i>Smilax
+aspera</i>, which is furnished with reflexed spines; but this is
+the case with several branch-climbers in South Brazil and Ceylon;
+and their branches graduate into true tendrils. Some few
+plants apparently depend solely on their hooks for climbing, and
+yet do so efficiently, as certain palms in the New and Old
+Worlds. Even some climbing Roses will ascend the walls of a
+tall house, if covered with a trellis. How this is effected
+I know not; for the young shoots of one such Rose, when placed in
+a pot in a window, bent irregularly towards the light during the
+day and from the light during the night, like the shoots of any
+common plant; so that it is not easy to understand how they could
+have got under a trellis close to the wall. <a
+name="citation184"></a><a href="#footnote184"
+class="citation">[184]</a></p>
+
+<p><i>Root-climbers</i>.&mdash;A good many plants come under this
+class, and are excellent climbers. One of the most
+remarkable is the <i>Marcgravia umbellata</i>, the stem of 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 it puts 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
+produces free branches with rounded stems, clad with
+sharp-pointed leaves, wonderfully different in appearance from
+those borne by the stem as long as it remains adherent.
+This surprising difference in the leaves, I have also observed in
+a plant of <i>Marcgravia dubia</i> in my hothouse.
+Root-climbers, as far as I have seen, namely, the Ivy (<i>Hedera
+heliæ</i>), <i>Ficus repens</i>, and <i>F. barbatus</i>,
+have no power of movement, not even from the light to the
+dark. As previously stated, the <i>Hoya carnosa</i>
+(Asclepiadaceæ) is a spiral twiner, and likewise adheres by
+rootlets even to a flat wall. The tendril-bearing
+<i>Bignonia Tweedyana</i> emits roots, which curve half round and
+adhere to thin sticks. The <i>Tecoma radicans</i>
+(Bignoniaceæ), which is closely allied to many
+spontaneously revolving species, climbs by rootlets;
+nevertheless, its young shoots apparently move about more than
+can be accounted for by the varying action of the light.</p>
+
+<p>I have not closely observed many root-climbers, but can give
+one curious fact. <i>Ficus repens</i> climbs up a wall just
+like Ivy; and when the young rootlets are made to press lightly
+on slips of glass, they emit after about a week&rsquo;s interval,
+as I observed several times, minute drops of clear fluid, not in
+the least milky like that exuded from a wound. This fluid
+is slightly viscid, but cannot be drawn out into threads.
+It has the remarkable property of not soon drying; a drop, about
+the size of half a pin&rsquo;s head, was slightly spread out on
+glass, and I scattered on it some minute grains of sand.
+The glass was left exposed in a drawer during hot and dry
+weather, and if the fluid had been water, it would certainly have
+dried in a few minutes; but it remained fluid, closely
+surrounding each grain of sand, during 128 days: how much longer
+it would have remained I cannot say. Some other rootlets
+were left in contact with the glass for about ten days or a
+fortnight, and the drops of secreted fluid were now rather
+larger, and so viscid that they could be drawn out into
+threads. Some other rootlets were left in contact during
+twenty-three days, and these were firmly cemented to the
+glass. Hence we may conclude that the rootlets first
+secrete a slightly viscid fluid, subsequently absorb the watery
+parts, (for we have seen that the fluid will not dry by itself,)
+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 very much less volatile by
+what it had dissolved.</p>
+
+<p>As the bisulphide of carbon has a strong power of softening
+indurated caoutchouc, I soaked in it during a short time several
+rootlets of a plant which had grown up a plaistered wall; and I
+then found many extremely thin threads of transparent, not
+viscid, excessively elastic matter, precisely like caoutchouc,
+attached to two sets of rootlets on the same branch. These
+threads proceeded from the bark of the rootlet at one end, and at
+the other end were firmly attached to particles of silex or
+mortar from the wall. There could be no mistake in this
+observation, as I played with the threads for a long time under
+the microscope, drawing them out with my dissecting-needles and
+letting them spring back again. Yet I looked repeatedly at
+other rootlets similarly treated, and could never again discover
+these elastic threads. I therefore infer that the branch in
+question must have been slightly moved from the wall at some
+critical period, whilst the secretion was in the act of drying,
+through the absorption of its watery parts. The genus
+<i>Ficus</i> abounds with caoutchouc, and we may conclude from
+the facts just given that this substance, at first in solution
+and ultimately modified into an unelastic cement, <a
+name="citation187"></a><a href="#footnote187"
+class="citation">[187]</a> is used by the <i>Ficus repens</i> to
+cement its rootlets to any surface which it ascends.
+Whether 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 the <i>Marcgravia
+dubia</i> can adhere firmly to smooth painted wood.</p>
+
+<p><i>Vanilla aromatica</i> emits aërial roots a foot in
+length, which point straight down to the ground. According
+to Mohl (p. 49), these crawl into crevices, and when they meet
+with a thin support, wind round it, as do 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 a
+little to that side, in the course of about a day, and adhered by
+their rootlets to the wood; but they did not bend quite round the
+sticks, and afterwards they re-pursued their downward
+course. It is probable that these slight movements of the
+roots are due to the quicker growth of the side exposed to the
+light, in comparison with the other side, and not because the
+roots are sensitive to contact in the same manner as true
+tendrils. According to Mohl, the rootlets of certain
+species of <i>Lycopodium</i> act as tendrils. <a
+name="citation188"></a><a href="#footnote188"
+class="citation">[188]</a></p>
+<h4><i>Concluding Remarks on Climbing Plants</i>.</h4>
+<p>Plants become climbers, in order, as it may be presumed, to
+reach the light, and to expose a large surface of their leaves to
+its action and to that of the free air. This is effected by
+climbers with 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 so many climbing plants in all quarters of the
+world, belonging to so many different orders. These plants
+have been arranged under four classes, disregarding those which
+merely scramble over bushes without any special aid.
+Hook-climbers are the least efficient of all, at least in our
+temperate countries, and can climb only in the midst of an
+entangled mass of vegetation. Root-climbers are excellently
+adapted to ascend naked faces of rock or trunks of trees; when,
+however, they climb trunks 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 require long-continued
+and close contact with a steady surface in order to adhere.
+The two great classes of twiners and of plants with sensitive
+organs, namely, leaf-climbers and tendril-bearers taken together,
+far exceed in number and in the perfection of their mechanism the
+climbers of the two first classes. Those which have the
+power of spontaneously revolving and of grasping objects with
+which they come in contact, easily pass from branch to branch,
+and securely ramble over a wide, sun-lit surface.</p>
+
+<p>The divisions containing twining plants, leaf-climbers, and
+tendril-bearers graduate to a certain extent into one another,
+and nearly all have the same remarkable power of spontaneously
+revolving. Does this gradation, it may be asked, indicate
+that plants belonging to one subdivision have actually passed
+during the lapse of ages, or can pass, from one state to the
+other? Has, for instance, any tendril-bearing plant assumed
+its present structure without having previously existed as 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 exception,
+revolve in exactly the same manner as twiners; some few can still
+twine well, and many others in an imperfect manner. Several
+leaf-climbing genera are closely allied to other genera which are
+simple twiners. It should also be observed, that the
+possession of leaves with sensitive petioles, and with the
+consequent power of clasping an object, would be of comparatively
+little use to a plant, unless associated with revolving
+internodes, by which the leaves are brought into contact with a
+support; although no doubt a scrambling plant would be apt, as
+Professor Jaeger has remarked, to rest on other plants by its
+leaves. On the other hand, revolving internodes, without
+any other aid, suffice to give the power of climbing; so that it
+seems probable that leaf-climbers were in most cases at first
+twiners, and subsequently became capable of grasping a support;
+and this, as we shall presently see, is a great additional
+advantage.</p>
+
+<p>From analogous reasons, it is probable that all
+tendril-bearers were primordially twiners, that is, are the
+descendants of plants having this power and habit. For the
+internodes of the majority revolve; and, in a few species, the
+flexible stem still retains the capacity of spirally twining
+round an upright stick. Tendril-bearers have undergone much
+more modification than leaf-climbers; hence it is not surprising
+that their supposed primordial habits of revolving and twining
+have been more frequently lost or modified than in the case of
+leaf-climbers. The three great tendril-bearing families in
+which this loss has occurred in the most marked manner, are the
+Cucurbitaceæ, Passifloraceæ, and Vitaceæ.
+In the first, the internodes revolve; but I have heard of no
+twining form, with the exception (according to Palm, p. 29. 52)
+of <i>Momordica balsamina</i>, and this is only an imperfect
+twiner. In the two other families I can hear of no twiners;
+and the internodes rarely have the power of revolving, this power
+being confined to the tendrils. The internodes, however, of
+<i>Passiflora gracilis</i> have the 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 has been retained
+by some members of all the larger tendril-bearing groups.</p>
+
+<p>On the view here given, it may be asked, Why have the species
+which were aboriginally twiners been converted in so many groups
+into leaf-climbers or tendril-bearers? Of what advantage
+has this 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 tendrils or sensitive
+petioles, as some species of Bignonia, Clematis, and
+Tropæolum, it can readily be observed how incomparably
+better they grasp an upright stick than do simple twiners.
+Tendrils, from possessing this power of grasping an object, can
+be made long and thin; so that little organic matter is expended
+in their development, and yet they sweep a wide circle in search
+of a support. Tendril-bearers can, from their first growth,
+ascend along the outer branches of any neighbouring bush, and
+they are thus always fully exposed to the light; twiners, on the
+contrary, are best fitted to ascend bare stems, and generally
+have to start in the shade. Within tall and dense tropical
+forests, twining plants would probably 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 thick trunks, whereas this can be
+affected by tendril-bearers if the trunks are branched or bear
+twigs, and by some species if the bark is rugged.</p>
+
+<p>The advantage gained by climbing is to reach the light and
+free air with as little expenditure of organic matter as
+possible; now, with twining 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, on the other
+hand, which had ascended to the same height by the aid of its
+tendrils, was but little longer than the height reached.
+That this saving of the stem is really an advantage to climbing
+plants, I infer from the species that still twine but are aided
+by clasping petioles or tendrils, generally making more open
+spires than those made by simple twiners. Moreover, the
+plants thus aided, after taking one or two turns in one
+direction, generally 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 have been possible; and they do this
+with safety, as they secure themselves at intervals by their
+clasping petioles or tendrils.</p>
+
+<p>We have seen that tendrils consist of various organs in a
+modified state, namely, leaves, flower-peduncles, branches, and
+perhaps stipules. With respect to leaves, the evidence of
+their modification is ample. In young plants of Bignonia
+the lower leaves often remain quite unchanged, whilst the upper
+ones have their terminal leaflets converted into perfect
+tendrils; in <i>Eccremocarpus</i> I have seen a single lateral
+branch of a tendril replaced by a perfect leaflet; in <i>Vicia
+sativa</i>, 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 kinds of tendrils; he will wish to learn, as far as is
+possible, by what actual steps leaves, flower-peduncles, &amp;c.,
+have had their functions wholly changed, and have come to serve
+merely as prehensile organs.</p>
+
+<p>In the whole group of leaf-climbers abundant evidence has been
+given that an organ, still subserving the functions of a leaf,
+may become sensitive to a touch, and thus grasp an adjoining
+object. With several leaf-climbers the true leaves
+spontaneously revolve; and their petioles, after clasping a
+support grow thicker and stronger. We thus see that leaves
+may acquire all the leading and characteristic qualities of
+tendrils, namely, sensitiveness, spontaneous movement, and
+subsequently increased strength. If their blades or
+laminæ were to abort, they would form true tendrils.
+And of this process of abortion we can follow every step, until
+no trace of the original nature of the tendril is left. In
+<i>Mutisia clematis</i>, the tendril, in shape and colour,
+closely resembles the petiole of one of the ordinary leaves,
+together with the midribs of the leaflets, but vestiges of the
+laminæ are still occasionally retained. In four
+genera of the Fumariaceæ we can follow the whole process of
+transformation. The terminal leaflets of the leaf-climbing
+<i>Fumaria officinalis</i> are not smaller than the other
+leaflets; those of the leaf-climbing <i>Adlumia cirrhosa</i> are
+greatly reduced; those of <i>Corydalis claviculata</i> (a plant
+which may indifferently be called a leaf-climber or a
+tendril-bearer) are either reduced to microscopical dimensions or
+have their blades wholly aborted, so that this plant is actually
+in a state of transition; and, finally, in the <i>Dicentra</i>
+the tendrils are perfectly characterized. If, therefore, we
+could behold at the same time all the progenitors of
+<i>Dicentra</i>, we should almost certainly see a series like
+that now exhibited by the above-named three genera. In
+<i>Tropæolum tricolorum</i> we have another kind of
+passage; for the leaves which are first formed on the young stems
+are entirely destitute of laminæ, and must be called
+tendrils, whilst the later formed leaves have well-developed
+laminæ. In all cases the acquirement of sensitiveness
+by the mid-ribs of the leaves appears to stand in some close
+relation with the abortion of their laminæ or blades.</p>
+
+<p>On the view here given, leaf-climbers were primordially
+twiners, and tendril-bearers (when formed of modified leaves)
+were primordially leaf-climbers. The latter, therefore, are
+intermediate in nature between twiners and tendril-bearers, and
+ought to be related to both. This is the case: thus the
+several leaf-climbing species of the Antirrhineæ, of
+Solanum, Cocculus, and Gloriosa, have within the same family and
+even within the same genus, relatives which are twiners. In
+the genus Mikania, there are leaf-climbing and twining
+species. The leaf-climbing species of Clematis are very
+closely allied to the tendril-bearing Naravelia. The
+Fumariaceæ include closely allied genera which are
+leaf-climbers and tendril-bearers. Lastly, a species of
+Bignonia is at the same time both a leaf-climber and a
+tendril-bearer; and other closely allied species are twiners.</p>
+
+<p>Tendrils of another kind consist of modified
+flower-peduncles. In this case we likewise have many
+interesting transitional states. The common Vine (not to
+mention the <i>Cardiospermum</i>) gives us every possible
+gradation between a perfectly developed tendril and a
+flower-peduncle covered with flowers, yet furnished with a
+branch, forming the flower-tendril. When the latter itself
+bears a few flowers, as we know sometimes is the case, and still
+retains the power of clasping a support, we see an early
+condition of all those tendrils which have been formed by the
+modification of flower-peduncles.</p>
+
+<p>According to Mohl and others, some tendrils consist of
+modified branches: I have not observed any such cases, and know
+nothing of their transitional states, but these have been fully
+described by Fritz Müller. The genus Lophospermum also
+shows us how such a transition is possible; for its branches
+spontaneously revolve and are sensitive to contact. Hence,
+if the leaves on some of the branches of the Lophospermum were to
+abort, these branches would be converted into true
+tendrils. Nor is there anything improbable in certain
+branches alone being thus modified, whilst others remained
+unaltered; for we have seen with certain varieties of
+<i>Phaseolus</i>, that some of the branches are thin, flexible,
+and twine, whilst other branches on the same plant are stiff and
+have no such power.</p>
+
+<p>If we inquire how a petiole, a branch or flower-peduncle first
+became sensitive to a touch, and acquired the power of bending
+towards the touched side, we get no certain answer.
+Nevertheless an observation by Hofmeister <a
+name="citation197"></a><a href="#footnote197"
+class="citation">[197]</a> well deserves attention, namely, that
+the shoots and leaves of all plants, whilst young, move after
+being shaken. Kerner also finds, as we have seen, that the
+flower-peduncles of a large number of plants, if shaken or gently
+rubbed bend to this side. And it is young petioles and
+tendrils, whatever their homological nature may be, which move on
+being touched. It thus appears that climbing plants have
+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 further inquire how the stems,
+petioles, tendrils, and flower-peduncles of climbing plants first
+acquired their power of spontaneously 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 moving, both spontaneously and from various
+stimulants, is far more common with plants, than is generally
+supposed to be the case by those who have not attended to the
+subject. I have given one remarkable instance, namely that
+of the <i>Maurandia semperflorens</i>, the young flower-peduncles
+of which spontaneously revolve in very small circles, and bend
+when gently rubbed to the touched side; yet this plant certainly
+does not profit by these two feebly developed powers. A
+rigorous examination of other young plants would probably show
+slight spontaneous movements in their stems, petioles or
+peduncles, as well as sensitiveness to a touch. <a
+name="citation198"></a><a href="#footnote198"
+class="citation">[198]</a> We see at least that the
+<i>Maurandia</i> might, by a little augmentation of the powers
+which it already possesses, come first to grasp a support by its
+flower-peduncles, and then, by the abortion of some of its
+flowers (as with <i>Vitis</i> or <i>Cardiospermum</i>), acquire
+perfect tendrils.</p>
+
+<p>There is one other interesting point which deserves
+notice. We have seen that some tendrils owe their origin to
+modified leaves, and others to modified flower-peduncles; so that
+some are foliar and others axial in their nature. It might
+therefore have been expected that they would have presented some
+difference in function. This is not the case. On the
+contrary, they present the most complete identity in their
+several characteristic powers. 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. Both are either attracted or repelled by the
+light. The latter property is seen in the foliar tendrils
+of <i>Bignonia capreolata</i> and in the axial tendrils of
+<i>Ampelopsis</i>. The tips of the tendrils in these two
+plants become, after contact, enlarged into discs, 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 that the
+petiole of <i>Solanum jasminoides</i>, after it has clasped a
+support, assumes one of the most characteristic features of the
+axis, namely, a closed ring of woody vessels, we can hardly avoid
+asking, whether the difference between foliar and axial organs
+can be of so fundamental a nature as is generally supposed? <a
+name="citation199"></a><a href="#footnote199"
+class="citation">[199]</a></p>
+
+<p>We have attempted to trace some of the stages in the genesis
+of climbing plants. But, during the endless fluctuations of
+the conditions of life to which all organic beings have been
+exposed, it might be 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 their native country never twine, but reassume this
+habit when cultivated in England, we have a case in point.
+In the leaf-climbing <i>Clematis flammula</i>, and in the
+tendril-bearing Vine, we see no loss in the power of climbing,
+but only a remnant of the revolving power which is indispensable
+to all twiners, and is so common as well as so advantageous to
+most climbers. In <i>Tecoma radicans</i>, one of the
+Bignoniaceæ, we see a last and doubtful trace of the power
+of revolving.</p>
+
+<p>With respect to the abortion of tendrils, certain cultivated
+varieties of <i>Cucurbita pepo</i> have, according to Naudin, <a
+name="citation200"></a><a href="#footnote200"
+class="citation">[200]</a> either quite lost these organs or bear
+semi-monstrous representatives of them. In my limited
+experience, I have met with only one apparent instance of their
+natural suppression, namely, in the common bean. All the
+other species of <i>Vicia</i>, 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, according to analogy,
+a tendril ought to have existed, a small pointed filament
+projects, about a third of an inch in length, and which is
+probably the rudiment of a tendril. This may be the more
+safely inferred, as in young and unhealthy specimens of other
+tendril-bearing plants similar rudiments may occasionally be
+observed. In the bean these filaments are variable in
+shape, as is so frequently the case with rudimentary organs; they
+are either cylindrical, or foliaceous, or are deeply furrowed on
+the upper surface. They have not retained any vestige of
+the power of revolving. It is a curious fact, that many of
+these filaments, when foliaceous, have on their lower surfaces,
+dark-coloured glands like those on the stipules, which excrete a
+sweet fluid; so that these rudiments have been feebly
+utilized.</p>
+
+<p>One other analogous case, though hypothetical, is worth
+giving. Nearly all the species of <i>Lathyrus</i> possesses
+tendrils; but <i>L. nissolia</i> is destitute of them. This
+plant has leaves, which must have struck everyone with surprise
+who has noticed them, for they are quite unlike those of all
+common papilionaceous plants, and resemble those of a
+grass. In another species, <i>L. aphaca</i>, the tendril,
+which is not highly developed (for it is unbranched, and has no
+spontaneous revolving-power), replaces the leaves, the latter
+being replaced in function by large stipules. Now if we
+suppose the tendrils of <i>L. aphaca</i> to become flattened and
+foliaceous, like the little rudimentary tendrils of the bean, and
+the large stipules to become at the same time reduced in size,
+from not being any longer wanted, we should have the exact
+counterpart of <i>L. nissolia</i>, and its curious leaves are at
+once rendered intelligible to us.</p>
+
+<p>It may be added, as serving to sum up the foregoing views on
+the origin of tendril-bearing plants, that <i>L. nissolia</i> is
+probably descended from a plant which was primordially a twiner;
+this then became a leaf-climber, the leaves being afterwards
+converted by degrees into tendrils, with the stipules greatly
+increased in size through the law of compensation. <a
+name="citation202"></a><a href="#footnote202"
+class="citation">[202]</a> After a time the tendrils lost
+their branches and became simple; they then lost their
+revolving-power (in which state they would have resembled the
+tendrils of the existing <i>L. aphaca</i>), and afterwards losing
+their prehensile power and becoming foliaceous would no longer be
+thus designated. In this last stage (that of the existing
+<i>L. nissolia</i>) the former tendrils would reassume their
+original function of leaves, and the stipules which were recently
+much developed being no longer wanted, would decrease in
+size. If species become modified in the course of ages, as
+almost all naturalists now admit, we may conclude that <i>L.
+nissolia</i> has passed through a series of changes, in some
+degree like those here indicated.</p>
+
+<p>The most interesting point in the natural history of climbing
+plants is the various kinds of movement which they display in
+manifest relation to their wants. The most different
+organs&mdash;stems, branches, flower-peduncles, petioles,
+mid-ribs of the leaf and leaflets, and apparently aërial
+roots&mdash;all possess this power.</p>
+
+<p>The first action of a tendril is to place itself in a proper
+position. For instance, the tendril of Cobæa first
+rises vertically up, with its branches divergent and with the
+terminal hooks turned outwards; the young shoot at the extremity
+of the stem is at the same time bent to one side, so as to be out
+of the way. The young leaves of Clematis, on the other
+hand, prepare for action by temporarily curving themselves
+downwards, so as to serve as grapnels.</p>
+
+<p>Secondly, if a twining plant or a tendril gets by any accident
+into an inclined position, it soon bends upwards, though secluded
+from the light. The guiding stimulus no doubt is the
+attraction of gravity, as Andrew Knight showed to be the case
+with germinating plants. If a shoot of any ordinary 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 downward-bent
+shoot reverses its curvature; but if the stolen of a strawberry,
+which has no tendency to grow upwards, be thus treated, it will
+curve downwards in the direction of, instead of in opposition to,
+the force of gravity. As with the strawberry, so it is
+generally with the twining shoots of the <i>Hibbertia
+dentata</i>, which climbs laterally from bush to bush; for these
+shoots, if placed in a position inclined downwards, show little
+and sometimes no tendency to curve upwards.</p>
+
+<p>Thirdly, climbing plants, like other plants, bend towards the
+light by a movement closely analogous to the incurvation which
+causes them to revolve, so that their revolving movement is often
+accelerated or retarded in travelling to or from the light.
+On the other hand, in a few instances tendrils bend towards the
+dark.</p>
+
+<p>Fourthly, we have the spontaneous revolving movement which is
+independent of any outward stimulus, but is contingent on the
+youth of the part, and on vigorous health; and this again of
+course depends on a proper temperature and other favourable
+conditions of life.</p>
+
+<p>Fifthly, tendrils, whatever their homological nature may be,
+and the petioles or tips of the leaves of leaf-climbers, and
+apparently certain roots, all have the power of movement when
+touched, and bend quickly towards the touched side.
+Extremely slight pressure often suffices. If the pressure
+be not permanent, the part in question straightens itself and is
+again ready to bend on being touched.</p>
+
+<p>Sixthly, and lastly, tendrils, soon after clasping a support,
+but not after a mere temporary curvature, contract
+spirally. If they have not come into contact with any
+object, they ultimately contract spirally, after ceasing to
+revolve; but in this case the movement is useless, and occurs
+only after a considerable lapse of time.</p>
+
+<p>With respect to the means by which these various movements are
+effected, there can be little doubt from the researches of Sachs
+and H. de Vries, that they are due to unequal growth; but from
+the reasons already assigned, I cannot believe that this
+explanation applies to the rapid movements from a delicate
+touch.</p>
+
+<p>Finally, climbing plants are sufficiently numerous to form a
+conspicuous feature in the vegetable kingdom, more especially in
+tropical forests. America, which so abounds with arboreal
+animals, as Mr. Bates remarks, likewise abounds according to Mohl
+and Palm with climbing plants; and of the tendril-bearing plants
+examined by me, the highest developed kinds are natives of this
+grand continent, namely, the several species of <i>Bignonia</i>,
+<i>Eccremocarpus</i>, <i>Cobæa</i>, and
+<i>Ampelopsis</i>. But even in the thickets of our
+temperate regions the number of climbing species and individuals
+is considerable, as will be found by counting them. They
+belong to many and widely different orders. To gain some
+rude 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 have added many
+more), all those families in Lindley&rsquo;s &lsquo;Vegetable
+Kingdom&rsquo; which include twiners, leaf-climbers, or
+tendril-bearers. Lindley divides Phanerogamic plants into
+fifty-nine Alliances; of these, no less than thirty-five include
+climbing plants of the above kinds, hook and root-climbers being
+excluded. To these a few Cryptogamic plants must be
+added. When we reflect on the wide separation of these
+plants in the series, and when we know that in some of the
+largest, well-defined orders, such as the Compositæ,
+Rubiaceæ, Scrophulariaceæ, Liliaceæ, &amp;c.,
+species in only two or three genera have the power of climbing,
+the conclusion is forced on our minds that the capacity of
+revolving, on which most climbers depend, is inherent, though
+undeveloped, in almost every plant in the vegetable kingdom.</p>
+
+<p>It has often been vaguely asserted that plants are
+distinguished from animals by not having the power of
+movement. It should rather be said that plants acquire and
+display this power only when it is of some advantage to them;
+this being of comparatively rare occurrence, as they are affixed
+to the ground, and food is brought to them by the air 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
+it self. 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 tendrils or
+internodes, or both, spontaneously revolve with a steady
+motion. The tendril strikes some object, and quickly curls
+round and firmly grasps it. In the course of some hours it
+contracts into a spire, dragging up the stem, and forming an
+excellent spring. All movements now cease. By growth
+the tissues soon become wonderfully strong and durable. The
+tendril has done its work, and has done it in an admirable
+manner.</p>
+<h3>FOOTNOTES.</h3>
+
+<p><a name="footnoteiv"></a><a href="#citationiv"
+class="footnote">[iv]</a> An English translation of the
+&lsquo;Lehrbuch der Botanik&rsquo; by Professor Sachs, has
+recently (1875), appeared under the title of &lsquo;Text-Book of
+Botany,&rsquo; and this is a great boon to all lovers of natural
+science in England.</p>
+
+<p><a name="footnote1a"></a><a href="#citation1a"
+class="footnote">[1a]</a> &lsquo;Proc. Amer. Acad. of Arts
+and Sciences,&rsquo; vol. iv. Aug. 12, 1858, p. 98.</p>
+
+<p><a name="footnote1b"></a><a href="#citation1b"
+class="footnote">[1b]</a> Ludwig H. Palm, &lsquo;Ueber das
+Winden der Pflanzen;&rsquo; Hugo von Mohl, &lsquo;Ueber den Bau
+und des Winden der Ranken und Schlingpflanzen,&rsquo; 1827.
+Palm&rsquo;s Treatise was published only a few weeks before
+Mohl&rsquo;s. See also &lsquo;The Vegetable Cell&rsquo;
+(translated by Henfrey), by H. von Mohl, p. 147 to end.</p>
+
+<p><a name="footnote1c"></a><a href="#citation1c"
+class="footnote">[1c]</a> &ldquo;Des Mouvements
+révolutife Respontanés,&rdquo; &amp;c.,
+&lsquo;Comptes Rendus,&rsquo; tom. xvii. (1843) p. 989;
+&ldquo;Recherches sur la Volubilité des Tiges,&rdquo;
+&amp;c., tom. xix. (1844) p. 295.</p>
+
+<p><a name="footnote8"></a><a href="#citation8"
+class="footnote">[8]</a> &lsquo;Bull. Bot Soc. de
+France,&rsquo; tom. v. 1858, p. 356.</p>
+
+<p><a name="footnote9a"></a><a href="#citation9a"
+class="footnote">[9a]</a> This whole subject has been ably
+discussed and explained by H. de Vries, &lsquo;Arbeiten des Bot.
+Instituts in Würzburg,&rsquo; Heft iii. pp. 331, 336.
+See also Sachs (&lsquo;Text-Book of Botany,&rsquo; English
+translation, 1875, p. 770), who concludes &ldquo;that torsion is
+the result of growth continuing in the outer layers after it has
+ceased or begun to cease in the inner layers.&rdquo;</p>
+
+<p><a name="footnote9b"></a><a href="#citation9b"
+class="footnote">[9b]</a> Professor Asa Gray has remarked
+to me, in a letter, that in <i>Thuja occidentalis</i> the
+twisting of the bark is very conspicuous. The twist is
+generally to the right of the observer; but, in noticing about a
+hundred trunks, four or five were observed to be twisted in an
+opposite direction. The Spanish chestnut is often much
+twisted: there is an interesting article on this subject in the
+&lsquo;Scottish Farmer,&rsquo; 1865, p. 833.</p>
+
+<p><a name="footnote10"></a><a href="#citation10"
+class="footnote">[10]</a> It is well known that the stems
+of many plants occasionally become spirally twisted in a
+monstrous manner; and after my paper was read before the Linnean
+Society, Dr. Maxwell Masters remarked to me in a letter that
+&ldquo;some of these cases, if not all, are dependent upon some
+obstacle or resistance to their upward growth.&rdquo; This
+conclusion agrees with what I have said about the twisting of
+stems, which have twined round rugged supports; but does not
+preclude the twisting being of service to the plant by giving
+greater rigidity to the stem.</p>
+
+<p><a name="footnote12"></a><a href="#citation12"
+class="footnote">[12]</a> The view that the revolving
+movement or nutation of the stems of twining plants is due to
+growth is that advanced by Sachs and H. de Vries; and the truth
+of this view is proved by their excellent observations.</p>
+
+<p><a name="footnote14"></a><a href="#citation14"
+class="footnote">[14]</a> The mechanism by which the end of the
+shoot remains hooked appears to be a difficult and complex
+problem, discussed by Dr. H. de Vries (ibid. p. 337): he
+concludes that &ldquo;it depends on the relation between the
+rapidity of torsion and the rapidity of nutation.&rdquo;</p>
+
+<p><a name="footnote16"></a><a href="#citation16"
+class="footnote">[16]</a> Dr. H. de Vries also has shown
+(ibid. p. 321 and 325) by a better method than that employed by
+me, that the stems of twining plants are not irritable, and that
+the cause of their winding up a support is exactly what I have
+described.</p>
+
+<p><a name="footnote17"></a><a href="#citation17"
+class="footnote">[17]</a> Dr. H. de Vries states (ibid. p.
+322) that the stem of Cuscuta is irritable like a tendril.</p>
+
+<p><a name="footnote18"></a><a href="#citation18"
+class="footnote">[18]</a> See Dr. H. de Vries (ibid.
+p. 324) on this subject.</p>
+
+<p><a name="footnote19"></a><a href="#citation19"
+class="footnote">[19]</a> Comptes Rendus, 1844, tom. xix.
+p. 295, and Annales des Sc. Nat 3rd series, Bot., tom. ii. p.
+163.</p>
+
+<p><a name="footnote24"></a><a href="#citation24"
+class="footnote">[24]</a> I am much indebted to Dr. Hooker
+for having sent me many plants from Kew; and to Mr. Veitch, of
+the Royal Exotic Nursery, for having generously given me a
+collection of fine specimens of climbing plants. Professor
+Asa Gray, Prof. Oliver, and Dr. Hooker have afforded me, as on
+many previous occasions, much information and many
+references.</p>
+
+<p><a name="footnote33"></a><a href="#citation33"
+class="footnote">[33]</a> Journal of the Linn. Soc. (Bot.)
+vol. ix. p. 344. I shall have occasion often to quote this
+interesting paper, in which he corrects or confirms various
+statements made by me.</p>
+
+<p><a name="footnote34"></a><a href="#citation34"
+class="footnote">[34]</a> I raised nine plants of the
+hybrid <i>Loasa Herbertii</i>, and six of these also reversed
+their spire in ascending a support.</p>
+
+<p><a name="footnote36"></a><a href="#citation36"
+class="footnote">[36]</a> In another genus, namely Davilla,
+belonging to the same family with Hibbertia, Fritz Müller
+says (ibid. p. 349) that &ldquo;the stem twines indifferently
+from left to right, or from right to left; and I once saw a shoot
+which ascended a tree about five inches in diameter, reverse its
+course in the same manner as so frequently occurs with
+Loasa.&rdquo;</p>
+
+<p><a name="footnote37"></a><a href="#citation37"
+class="footnote">[37]</a> Fritz Müller states (ibid.
+p. 349) that he saw on one occasion in the forests of South
+Brazil a trunk about five feet in circumference spirally ascended
+by a plant, apparently belonging to the
+Menispermaceæ. He adds in his letter to me that most
+of the climbing plants which there ascend thick trees, are
+root-climbers; some being tendril-bearers.</p>
+
+<p><a name="footnote44"></a><a href="#citation44"
+class="footnote">[44]</a> Fritz Müller has published
+some interesting facts and views on the structure of the wood of
+climbing plants in &lsquo;Bot. Zeitung,&rsquo; 1866, pp. 57,
+66.</p>
+
+<p><a name="footnote68"></a><a href="#citation68"
+class="footnote">[68]</a> It appears from A. Kerner&rsquo;s
+interesting observations, that the flower-peduncles of a large
+number of plants are irritable, and bend when they are rubbed or
+shaken: Die Schutzmittel des Pollens, 1873, p. 34.</p>
+
+<p><a name="footnote71"></a><a href="#citation71"
+class="footnote">[71]</a> I have already referred to the
+case of the twining stem of Cuscuta, which, according to H. de
+Vries (ibid. p. 322) is sensitive to a touch like a tendril.</p>
+
+<p><a name="footnote75"></a><a href="#citation75"
+class="footnote">[75]</a> Dr. Maxwell Masters informs me
+that in almost all petioles which are cylindrical, such as those
+bearing peltate leaves, the woody vessels form a closed ring;
+semilunar bands of vessels being confined to petioles which are
+channelled along their upper surfaces. In accordance with
+this statement, it may be observed that the enlarged and clasped
+petiole of the <i>Solanum</i>, with its closed ring of woody
+vessels, has become more cylindrical than it was in its original
+unclasped condition.</p>
+
+<p><a name="footnote84"></a><a href="#citation84"
+class="footnote">[84]</a> Never having had the opportunity
+of examining tendrils produced by the modification of branches, I
+spoke doubtfully about them in this essay when originally
+published. But since then Fritz Müller has described
+(Journal of Linn. Soc. vol. ix. p. 344) many striking cases in
+South Brazil. In speaking of plants which climb by the aid
+of their branches, more or less modified, he states that the
+following stages of development can be traced: (1.) Plants
+supporting themselves simply by their branches stretched out at
+right angles&mdash;for example, <i>Chiococca</i>. (2.)
+Plants clasping a support with their unmodified branches, as with
+<i>Securidaca</i>. (3.) Plants climbing by the extremities
+of their branches which appear like tendrils, as is the case
+according to Endlicher with <i>Helinus</i>. (4.) Plants
+with their branches much modified and temporarily converted into
+tendrils, but which may be again transformed into branches, as
+with certain Papilionaceous plants. (5.) Plants with their
+branches forming true tendrils, and used exclusively for
+climbing&mdash;as with <i>Strychnos</i> and
+<i>Caulotretus</i>. Even the unmodified branches become
+much thickened when they wind round a support. I may add
+that Mr. Thwaites sent me from Ceylon a specimen of an Acacia
+which had climbed up the trunk of a rather large tree, by the aid
+of tendril-like, curved or convoluted branchlets, arrested in
+their growth and furnished with sharp recurved hooks.</p>
+
+<p><a name="footnote85"></a><a href="#citation85"
+class="footnote">[85]</a> As far as I can make out, the
+history of our knowledge of tendrils is as follows:&mdash;We have
+seen that Palm and von Mohl observed about the same time the
+singular phenomenon of the spontaneous revolving movement of
+twining-plants. Palm (p. 58), I presume, observed likewise
+the revolving movement 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 common
+pea. Mohl first discovered that tendrils are 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 their
+movement. Professor Asa Gray, in a paper already quoted,
+first noticed the extreme sensitiveness and rapidity of the
+movements of the tendrils of certain Cucurbitaceous plants.</p>
+
+<p><a name="footnote102"></a><a href="#citation102"
+class="footnote">[102]</a> Fritz Müller states (ibid.
+p. 348) that in South Brazil the trifid tendrils of Haplolophium,
+(one of the Bignoniaceæ) without having come into contact
+with any object, terminate in smooth shining discs. These,
+however, after adhering to any object, sometimes become
+considerably enlarged.</p>
+
+<p><a name="footnote111"></a><a href="#citation111"
+class="footnote">[111]</a> Comptes Rendus, tom. xvii. 1843,
+p. 989.</p>
+
+<p><a name="footnote113"></a><a href="#citation113"
+class="footnote">[113]</a> Diagram showing the movement of
+the upper internode of the common Pea, traced on a hemispherical
+glass, and transferred to paper; reduced one-half in size (Aug.
+1st)</p>
+<table>
+<tr>
+<td><p>No.</p>
+</td>
+<td><p style="text-align: center"><span
+class="GutSmall">H.</span></p>
+</td>
+<td><p style="text-align: center"><span
+class="GutSmall">M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">46 <span
+class="GutSmall">A.M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">11</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">11</p>
+</td>
+<td><p style="text-align: right">37</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">12</p>
+</td>
+<td><p style="text-align: right">7 <span
+class="GutSmall">P.M.</span></p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">12</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">9</p>
+</td>
+<td><p style="text-align: right">1</p>
+</td>
+<td><p style="text-align: right">44</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">10</p>
+</td>
+<td><p style="text-align: right">2</p>
+</td>
+<td><p style="text-align: right">25</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">11</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">12</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">13</p>
+</td>
+<td><p style="text-align: right">3</p>
+</td>
+<td><p style="text-align: right">48</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">14</p>
+</td>
+<td><p style="text-align: right">4</p>
+</td>
+<td><p style="text-align: right">40</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">15</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">16</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">25</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">17</p>
+</td>
+<td><p style="text-align: right">5</p>
+</td>
+<td><p style="text-align: right">50</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">18</p>
+</td>
+<td><p style="text-align: right">6</p>
+</td>
+<td><p style="text-align: right">25</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">19</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">0</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">20</p>
+</td>
+<td><p style="text-align: right">7</p>
+</td>
+<td><p style="text-align: right">45</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">21</p>
+</td>
+<td><p style="text-align: right">8</p>
+</td>
+<td><p style="text-align: right">30</p>
+</td>
+</tr>
+<tr>
+<td><p style="text-align: right">22</p>
+</td>
+<td><p style="text-align: right">9</p>
+</td>
+<td><p style="text-align: right">15</p>
+</td>
+</tr>
+</table>
+<p><a name="footnote118"></a><a href="#citation118"
+class="footnote">[118]</a> &lsquo;Leçons de
+Botanique,&rsquo; &amp;c., 1841, p. 170.</p>
+
+<p><a name="footnote127a"></a><a href="#citation127a"
+class="footnote">[127a]</a> I am indebted to Prof. Oliver
+for information on this head. In the Bulletin de la
+Société Botanique de France, 1857, there are
+numerous discussions on the nature of the tendrils in this
+family.</p>
+
+<p><a name="footnote127b"></a><a href="#citation127b"
+class="footnote">[127b]</a> &lsquo;Gardeners&rsquo;
+Chronicle,&rsquo; 1864, p. 721. From the affinity of the
+Cucurbitaceæ to the Passifloraceæ, it might be argued
+that the tendrils of the former are modified flower-peduncles, as
+is certainly the case with those of Passion flowers. Mr. R.
+Holland (Hardwicke&rsquo;s &lsquo;Science-Gossip,&rsquo; 1865, p.
+105) states that &ldquo;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.&rdquo;</p>
+
+<p><a name="footnote145"></a><a href="#citation145"
+class="footnote">[145]</a> Trans. Phil. Soc. 1812, p.
+314.</p>
+
+<p><a name="footnote146"></a><a href="#citation146"
+class="footnote">[146]</a> Dr. M&rsquo;Nab remarks (Trans.
+Bot. Soc. Edinburgh, vol xi. p. 292) that the tendrils of <i>Amp.
+Veitchii</i> bear small globular discs before they have came into
+contact with any object; and I have since observed the same
+fact. These discs, however, increase greatly in size, if
+they press against and adhere to any surface. The tendrils,
+therefore, of one species of <i>Ampelopsis</i> require the
+stimulus of contact for the first development of their discs,
+whilst those of another species do not need any such
+stimulus. We have seen an exactly parallel case with two
+species of <i>Bignoniaceæ</i>.</p>
+
+<p><a name="footnote152"></a><a href="#citation152"
+class="footnote">[152]</a> Fritz Müller remarks (ibid.
+p. 348) that a related genus, Serjania, differs from
+Cardiospermum in bearing only a single tendril; and that the
+common peduncle contracts spirally, when, as frequently happens,
+the tendril has clasped the plant&rsquo;s own stem.</p>
+
+<p><a name="footnote154"></a><a href="#citation154"
+class="footnote">[154]</a> Prof. Asa Gray informs me that
+the tendrils of <i>P. sicyoides</i> revolve even at a quicker
+rate than those of <i>P. gracilis</i>; four revolutions were
+completed (the temperature varying from 88 degrees-92 degrees
+Fahr.) in the following times, 40 m., 45 m., 38&frac12; m., and
+46 m. One half-revolution was performed in 15 m.</p>
+
+<p><a name="footnote165"></a><a href="#citation165"
+class="footnote">[165]</a> See M. Isid. Léon in
+Bull. Soc. Bot. de France, tom. v. 1858, p. 650. Dr. H. de
+Vries points out (p. 306) that I have overlooked, in the first
+edition of this essay, the following sentence by Mohl:
+&ldquo;After a tendril has caught a support, it begins in some
+days to wind into a spire, which, since the tendril is made fast
+at both extremities, must of necessity be in some places to the
+right, in others to the left.&rdquo; But I am not surprised
+that this brief sentence, without any further explanation did not
+attract my attention.</p>
+
+<p><a name="footnote176"></a><a href="#citation176"
+class="footnote">[176]</a> Sachs, however (&lsquo;Text-Book
+of Botany,&rsquo; Eng. Translation, 1875, p. 280), has shown that
+which I overlooked, namely, that the tendrils of different
+species are adapted to clasp supports of different
+thicknesses. He further shows that after a tendril has
+clasped a support it subsequently tightens its hold.</p>
+
+<p><a name="footnote179"></a><a href="#citation179"
+class="footnote">[179]</a> Annales des Sc. Nat. Bot. 4th
+series, tom. xii. p. 89.</p>
+
+<p><a name="footnote180"></a><a href="#citation180"
+class="footnote">[180]</a> It occurred to me that the
+movement of notation and that from a touch might be differently
+affected by anæsthetics, in the same manner as Paul Bert
+has shown to be the case with the sleep-movements of Mimosa and
+those from a touch. I tried the common pea and
+<i>Passiflora gracilis</i>, but I succeeded only in observing
+that both movements were unaffected by exposure for 1&frac12;
+hrs. to a rather large dose of sulphuric ether. In this
+respect they present a wonderful contrast with Drosera, owing no
+doubt to the presence of absorbent glands in the latter
+plant.</p>
+
+<p><a name="footnote181"></a><a href="#citation181"
+class="footnote">[181]</a> Text-Book of Botany, 1875, p.
+779.</p>
+
+<p><a name="footnote183"></a><a href="#citation183"
+class="footnote">[183]</a> Journal of Linn. Soc. vol. ix. p.
+348. Professor G. Jaeger has well remarked (&lsquo;In
+Sachen Darwin&rsquo;s, insbesondere contra Wigand,&rsquo; 1874,
+p. 106) that it is highly characteristic of climbing plants to
+produce thin, elongated, and flexible stems. He further
+remarks that plants growing beneath other and taller species or
+trees, are naturally those which would be developed into
+climbers; anti such plants, from stretching towards the light,
+and from not being much agitated by the wind, tend to produce
+long, thin and flexible shoots.</p>
+
+<p><a name="footnote184"></a><a href="#citation184"
+class="footnote">[184]</a> Professor Asa Gray has
+explained, as it would appear, this difficulty in his review
+(American Journal of Science, vol. xl. Sept. 1865, p. 282) of the
+present work. He has observed that the strong summer shoots
+of the Michigan rose (<i>Rosa setigera</i>) are strongly disposed
+to push into dark crevices and away from the light, so that they
+would be almost sure to place themselves under a trellis.
+He adds that the lateral shoots, made on the following spring
+emerged from the trellis as they sought the light.</p>
+
+<p><a name="footnote187"></a><a href="#citation187"
+class="footnote">[187]</a> Mr. Spiller has recently shown
+(Chemical Society, Feb. 16, 1865), in a paper on the oxidation of
+india-rubber or caoutchouc, that this substance, when exposed in
+a fine state of division to the air, gradually becomes converted
+into brittle, resinous matter, very similar to shell-lac.</p>
+
+<p><a name="footnote188"></a><a href="#citation188"
+class="footnote">[188]</a> Fritz Müller informs me
+that he saw in the forests of South Brazil numerous black
+strings, from some lines to nearly an inch in diameter, winding
+spirally round the trunks of gigantic trees. At first sight
+he thought that they were the stems of twining plants which were
+thus ascending the trees: but he afterwards found that they were
+the aërial roots of a Philodendron which grew on the
+branches above. These roots therefore seem to be true
+twiners, though they use their powers to descend, instead of to
+ascend like twining plants. The aërial roots of some
+other species of Philodendron hang vertically downwards,
+sometimes for a length of more than fifty feet.</p>
+
+<p><a name="footnote197"></a><a href="#citation197"
+class="footnote">[197]</a> Quoted by Cohn, in his
+remarkable memoir, &ldquo;Contractile Gewebe im
+Pflanzenreiche,&rdquo; &lsquo;Abhandl. der Schlesischen
+Gesell. 1861, Heft i. s. 35.</p>
+
+<p><a name="footnote198"></a><a href="#citation198"
+class="footnote">[198]</a> Such slight spontaneous
+movements, I now find, have been for some time known to occur,
+for instance with the flower-stems of <i>Brassica napus</i> and
+with the leaves of many plants: Sachs&rsquo; &lsquo;Text-Book of
+Botany&rsquo; 1875, pp. 766, 785. Fritz Müller also
+has shown in relation to our present subject (&lsquo;Jenaischen
+Zeitschrift,&rsquo; Bd. V. Heft 2, p. 133) that the stems, whilst
+young, of an Alisma and of a Linum are continually performing
+slight movements to all points of the compass, like those of
+climbing plants.</p>
+
+<p><a name="footnote199"></a><a href="#citation199"
+class="footnote">[199]</a> Mr. Herbert Spencer has recently
+argued (&lsquo;Principles of Biology,&rsquo; 1865, p. 37 et seq.)
+with much force that there is no fundamental distinction between
+the foliar and axial organs of plants.</p>
+
+<p><a name="footnote200"></a><a href="#citation200"
+class="footnote">[200]</a> Annales des Sc. Nat. 4th series,
+Bot. tom. vi. 1856, p. 31.</p>
+
+<p><a name="footnote202"></a><a href="#citation202"
+class="footnote">[202]</a> Moquin-Tandon (Eléments
+de Tératologie. 1841, p. 156) gives the case of a
+monstrous bean, in which a case of compensation of this nature
+was suddenly effected; for the leaves completely disappeared and
+the stipules grew to an enormous size.</p>
+
+<div style='display:block; margin-top:4em'>*** END OF THE PROJECT GUTENBERG EBOOK THE MOVEMENT AND HABITS OF CLIMBING PLANTS ***</div>
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+The Project Gutenberg Etext of Climbing Plants by Charles Darwin
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+The Movements and Habits of Climbing Plants
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+by Charles Darwin
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+January, 2001 [Etext #2485]
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+from the 1906 John Murray edition.
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+
+THE MOVEMENTS AND HABITS OF CLIMBING PLANTS
+
+
+
+
+PREFACE
+
+
+
+This Essay first appeared in the ninth volume of the 'Journal of the
+Linnean Society,' published in 1865.  It is here reproduced in a
+corrected and, I hope, clearer form, with some additional facts.  The
+illustrations were drawn by my son, George Darwin.  Fritz Muller,
+after the publication of my paper, sent to the Linnean Society
+(Journal, vol. ix., p. 344) some interesting observations on the
+climbing plants of South Brazil, to which I shall frequently refer.
+Recently two important memoirs, chiefly on the difference in growth
+between the upper and lower sides of tendrils, and on the mechanism
+of the movements of twining-plants, by Dr. Hugo de Vries, have
+appeared in the 'Arbeiten des Botanischen Instituts in Wurzburg,'
+Heft. iii., 1873.  These memoirs ought to be carefully studied by
+every one interested in the subject, as I can here give only
+references to the more important points.  This excellent observer, as
+well as Professor Sachs, {1} attributes all the movements of tendrils
+to rapid growth along one side; but, from reasons assigned towards
+the close of my fourth chapter, I cannot persuade myself that this
+holds good with respect to those due to a touch.  In order that the
+reader may know what points have interested me most, I may call his
+attention to certain tendril-bearing plants; for instance, Bignonia
+capreolata, Cobaea, Echinocystis, and Hanburya, which display as
+beautiful adaptations as can be found in any part of the kingdom of
+nature.  It is, also, an interesting fact that intermediate states
+between organs fitted for widely different functions, may be observed
+on the same individual plant of Corydalis claviculata and the common
+vine; and these cases illustrate in a striking manner the principle
+of the gradual evolution of species.
+
+
+
+APPENDIX TO PREFACE (1882).
+
+
+
+Since the publication of this Edition two papers by eminent botanists
+have appeared; Schwendener, 'Das Winden der Pflanzen' (Monatsberichte
+der Berliner Akademie, Dec. 1881), and J. Sachs, 'Notiz uber
+Schlingpflanzen' (Arbeiten des botanischen Instituts in Wurzburg, Bd.
+ii. p. 719, 1882).  The view "that the capacity of revolving, on
+which most climbers depend, is inherent, though undeveloped, in
+almost every plant in the vegetable kingdom" ('Climbing Plants,' p.
+205), has been confirmed by the observations on circumnutation since
+given in 'The Power of Movement in Plants.'
+
+
+
+ERRATA.
+
+
+
+On pp. 28, 32, 40, 53, statements are made with reference to the
+supposed acceleration of the revolving movement towards the light.
+It appears from the observations given in 'The Power of Movement in
+Plants,' p. 451, that these conclusions were drawn from insufficient
+observations, and are erroneous.
+
+
+
+
+THE MOVEMENTS AND HABITS OF CLIMBING PLANTS.
+
+
+
+
+CHAPTER I.--TWINING PLANTS.
+
+
+
+Introductory remarks--Description of the twining of the Hop--Torsion
+of the stems--Nature of the revolving movement, and manner of ascent-
+-Stems not irritable--Rate of revolution in various plants--Thickness
+of the support round which plants can twine--Species which revolve in
+an anomalous manner.
+
+I was led to this subject by an interesting, but short paper by
+Professor Asa Gray on the movements of the tendrils of some
+Cucurbitaceous plants. {2}  My observations were more than half
+completed before I learnt that the surprising phenomenon of the
+spontaneous revolutions of the stems and tendrils of climbing plants
+had been long ago observed by Palm and by Hugo von Mohl, {3} and had
+subsequently been the subject of two memoirs by Dutrochet. {4}
+Nevertheless, I believe that my observations, founded on the
+examination of above a hundred widely distinct living species,
+contain sufficient novelty to justify me in publishing them.
+
+Climbing plants may be divided into four classes.  First, those which
+twine spirally round a support, and are not aided by any other
+movement.  Secondly, those endowed with irritable organs, which when
+they touch any object clasp it; such organs consisting of modified
+leaves, branches, or flower-peduncles.  But these two classes
+sometimes graduate to a certain extent into one another.  Plants of
+the third class ascend merely by the aid of hooks; and those of the
+fourth by rootlets; but as in neither class do the plants exhibit any
+special movements, they present little interest, and generally when I
+speak of climbing plants I refer to the two first great classes.
+
+
+TWINING PLANTS.
+
+
+This is the largest subdivision, and is apparently the primordial and
+simplest condition of the class.  My observations will be best given
+by taking a few special cases.  When the shoot of a Hop (Humulus
+lupulus) rises from the ground, the two or three first-formed joints
+or internodes are straight and remain stationary; but the next-
+formed, whilst very young, may be seen to bend to one side and to
+travel slowly round towards all points of the compass, moving, like
+the hands of a watch, with the sun.  The movement very soon acquires
+its full ordinary velocity.  From seven observations made during
+August on shoots proceeding from a plant which had been cut down, and
+on another plant during April, the average rate during hot weather
+and during the day is 2 hrs. 8 m. for each revolution; and none of
+the revolutions varied much from this rate.  The revolving movement
+continues as long as the plant continues to grow; but each separate
+internode, as it becomes old, ceases to move.
+
+To ascertain more precisely what amount of movement each internode
+underwent, I kept a potted plant, during the night and day, in a
+well-warmed room to which I was confined by illness.  A long shoot
+projected beyond the upper end of the supporting stick, and was
+steadily revolving.  I then took a longer stick and tied up the
+shoot, so that only a very young internode, 1.75 of an inch in
+length, was left free.  This was so nearly upright that its
+revolution could not be easily observed; but it certainly moved, and
+the side of the internode which was at one time convex became
+concave, which, as we shall hereafter see, is a sure sign of the
+revolving movement.  I will assume that it made at least one
+revolution during the first twenty-four hours.  Early the next
+morning its position was marked, and it made a second revolution in 9
+hrs.; during the latter part of this revolution it moved much
+quicker, and the third circle was performed in the evening in a
+little over 3 hrs.  As on the succeeding morning I found that the
+shoot revolved in 2 hrs. 45 m., it must have made during the night
+four revolutions, each at the average rate of a little over 3 hrs.  I
+should add that the temperature of the room varied only a little.
+The shoot had now grown 3.5 inches in length, and carried at its
+extremity a young internode 1 inch in length, which showed slight
+changes in its curvature.  The next or ninth revolution was effected
+in 2 hrs. 30 m.  From this time forward, the revolutions were easily
+observed.  The thirty-sixth revolution was performed at the usual
+rate; so was the last or thirty-seventh, but it was not completed;
+for the internode suddenly became upright, and after moving to the
+centre, remained motionless.  I tied a weight to its upper end, so as
+to bow it slightly and thus detect any movement; but there was none.
+Some time before the last revolution was half performed, the lower
+part of the internode ceased to move.
+
+A few more remarks will complete all that need be said about this
+internode.  It moved during five days; but the more rapid movements,
+after the performance of the third revolution, lasted during three
+days and twenty hours.  The regular revolutions, from the ninth to
+thirty-sixth inclusive, were effected at the average rate of 2 hrs.
+31 m.; but the weather was cold, and this affected the temperature of
+the room, especially during the night, and consequently retarded the
+rate of movement a little.  There was only one irregular movement,
+which consisted in the stem rapidly making, after an unusually slow
+revolution, only the segment of a circle.  After the seventeenth
+revolution the internode had grown from 1.75 to 6 inches in length,
+and carried an internode 1.875 inch long, which was just perceptibly
+moving; and this carried a very minute ultimate internode.  After the
+twenty-first revolution, the penultimate internode was 2.5 inches
+long, and probably revolved in a period of about three hours.  At the
+twenty-seventh revolution the lower and still moving internode was
+8.375, the penultimate 3.5, and the ultimate 2.5 inches in length;
+and the inclination of the whole shoot was such, that a circle 19
+inches in diameter was swept by it.  When the movement ceased, the
+lower internode was 9 inches, and the penultimate 6 inches in length;
+so that, from the twenty-seventh to thirty-seventh revolutions
+inclusive, three internodes were at the same time revolving.
+
+The lower internode, when it ceased revolving, became upright and
+rigid; but as the whole shoot was left to grow unsupported, it became
+after a time bent into a nearly horizontal position, the uppermost
+and growing internodes still revolving at the extremity, but of
+course no longer round the old central point of the supporting stick.
+From the changed position of the centre of gravity of the extremity,
+as it revolved, a slight and slow swaying movement was given to the
+long horizontally projecting shoot; and this movement I at first
+thought was a spontaneous one.  As the shoot grew, it hung down more
+and more, whilst the growing and revolving extremity turned itself up
+more and more.
+
+With the Hop we have seen that three internodes were at the same time
+revolving; and this was the case with most of the plants observed by
+me.  With all, if in full health, two internodes revolved; so that by
+the time the lower one ceased to revolve, the one above was in full
+action, with a terminal internode just commencing to move.  With Hoya
+carnosa, on the other hand, a depending shoot, without any developed
+leaves, 32 inches in length, and consisting of seven internodes (a
+minute terminal one, an inch in length, being counted), continually,
+but slowly, swayed from side to side in a semicircular course, with
+the extreme internodes making complete revolutions.  This swaying
+movement was certainly due to the movement of the lower internodes,
+which, however, had not force sufficient to swing the whole shoot
+round the central supporting stick.  The case of another
+Asclepiadaceous plant, viz., Ceropegia Gardnerii, is worth briefly
+giving.  I allowed the top to grow out almost horizontally to the
+length of 31 inches; this now consisted of three long internodes,
+terminated by two short ones.  The whole revolved in a course opposed
+to the sun (the reverse of that of the Hop), at rates between 5 hrs.
+15 m. and 6 hrs. 45 m. for each revolution.  The extreme tip thus
+made a circle of above 5 feet (or 62 inches) in diameter and 16 feet
+in circumference, travelling at the rate of 32 or 33 inches per hour.
+The weather being hot, the plant was allowed to stand on my study-
+table; and it was an interesting spectacle to watch the long shoot
+sweeping this grand circle, night and day, in search of some object
+round which to twine.
+
+If we take hold of a growing sapling, we can of course bend it to all
+sides in succession, so as to make the tip describe a circle, like
+that performed by the summit of a spontaneously revolving plant.  By
+this movement the sapling is not in the least twisted round its own
+axis.  I mention this because if a black point be painted on the
+bark, on the side which is uppermost when the sapling is bent towards
+the holder's body, as the circle is described, the black point
+gradually turns round and sinks to the lower side, and comes up again
+when the circle is completed; and this gives the false appearance of
+twisting, which, in the case of spontaneously revolving plants,
+deceived me for a time.  The appearance is the more deceitful because
+the axes of nearly all twining-plants are really twisted; and they
+are twisted in the same direction with the spontaneous revolving
+movement.  To give an instance, the internode of the Hop of which the
+history has been recorded, was at first, as could be seen by the
+ridges on its surface, not in the least twisted; but when, after the
+37th revolution, it had grown 9 inches long, and its revolving
+movement had ceased, it had become twisted three times round its own
+axis, in the line of the course of the sun; on the other hand, the
+common Convolvulus, which revolves in an opposite course to the Hop,
+becomes twisted in an opposite direction.
+
+Hence it is not surprising that Hugo von Mohl (p. 105, 108, &c.)
+thought that the twisting of the axis caused the revolving movement;
+but it is not possible that the twisting of the axis of the Hop three
+times should have caused thirty-seven revolutions.  Moreover, the
+revolving movement commenced in the young internode before any
+twisting of its axis could be detected.  The internodes of a young
+Siphomeris and Lecontea revolved during several days, but became
+twisted only once round their own axes.  The best evidence, however,
+that the twisting does not cause the revolving movement is afforded
+by many leaf-climbing and tendril-bearing plants (as Pisum sativum,
+Echinocystis lobata, Bignonia capreolata, Eccremocarpus scaber, and
+with the leaf-climbers, Solanum jasminoides and various species of
+Clematis), of which the internodes are not twisted, but which, as we
+shall hereafter see, regularly perform revolving movements like those
+of true twining-plants.  Moreover, according to Palm (pp. 30, 95) and
+Mohl (p. 149), and Leon, {5} internodes may occasionally, and even
+not very rarely, be found which are twisted in an opposite direction
+to the other internodes on the same plant, and to the course of their
+revolutions; and this, according to Leon (p. 356), is the case with
+all the internodes of a certain variety of Phaseolus multiflorus.
+Internodes which have become twisted round their own axes, if they
+have not ceased to revolve, are still capable of twining round a
+support, as I have several times observed.
+
+Mohl has remarked (p. 111) that when a stem twines round a smooth
+cylindrical stick, it does not become twisted. {6}  Accordingly I
+allowed kidney-beans to run up stretched string, and up smooth rods
+of iron and glass, one-third of an inch in diameter, and they became
+twisted only in that degree which follows as a mechanical necessity
+from the spiral winding.  The stems, on the other hand, which had
+ascended ordinary rough sticks were all more or less and generally
+much twisted.  The influence of the roughness of the support in
+causing axial twisting was well seen in the stems which had twined up
+the glass rods; for these rods were fixed into split sticks below,
+and were secured above to cross sticks, and the stems in passing
+these places became much twisted.  As soon as the stems which had
+ascended the iron rods reached the summit and became free, they also
+became twisted; and this apparently occurred more quickly during
+windy than during calm weather.  Several other facts could be given,
+showing that the axial twisting stands in some relation to
+inequalities in the support, and likewise to the shoot revolving
+freely without any support.  Many plants, which are not twiners,
+become in some degree twisted round their own axes; {7} but this
+occurs so much more generally and strongly with twining-plants than
+with other plants, that there must be some connexion between the
+capacity for twining and axial twisting.  The stem probably gains
+rigidity by being twisted (on the same principle that a much twisted
+rope is stiffer than a slackly twisted one), and is thus indirectly
+benefited so as to be enabled to pass over inequalities in its spiral
+ascent, and to carry its own weight when allowed to revolve freely.
+{8}
+
+I have alluded to the twisting which necessarily follows on
+mechanical principles from the spiral ascent of a stem, namely, one
+twist for each spire completed.  This was well shown by painting
+straight lines on living stems, and then allowing them to twine; but,
+as I shall have to recur to this subject under Tendrils, it may be
+here passed over.
+
+The revolving movement of a twining plant has been compared with that
+of the tip of a sapling, moved round and round by the hand held some
+way down the stem; but there is one important difference.  The upper
+part of the sapling when thus moved remains straight; but with
+twining plants every part of the revolving shoot has its own separate
+and independent movement.  This is easily proved; for when the lower
+half or two-thirds of a long revolving shoot is tied to a stick, the
+upper free part continues steadily revolving.  Even if the whole
+shoot, except an inch or two of the extremity, be tied up, this part,
+as I have seen in the case of the Hop, Ceropegia, Convolvulus, &c.,
+goes on revolving, but much more slowly; for the internodes, until
+they have grown to some little length, always move slowly.  If we
+look to the one, two, or several internodes of a revolving shoot,
+they will be all seen to be more or less bowed, either during the
+whole or during a large part of each revolution.  Now if a coloured
+streak be painted (this was done with a large number of twining
+plants) along, we will say, the convex surface, the streak will after
+a time (depending on the rate of revolution) be found to be running
+laterally along one side of the bow, then along the concave side,
+then laterally on the opposite side, and, lastly, again on the
+originally convex surface.  This clearly proves that during the
+revolving movement the internodes become bowed in every direction.
+The movement is, in fact, a continuous self-bowing of the whole
+shoot, successively directed to all points of the compass; and has
+been well designated by Sachs as a revolving nutation.
+
+As this movement is rather difficult to understand, it will be well
+to give an illustration.  Take a sapling and bend it to the south,
+and paint a black line on the convex surface; let the sapling spring
+up and bend it to the east, and the black line will be seen to run
+along the lateral face fronting the north; bend it to the north, the
+black line will be on the concave surface; bend it to the west, the
+line will again be on the lateral face; and when again bent to the
+south, the line will be on the original convex surface.  Now, instead
+of bending the sapling, let us suppose that the cells along its
+northern surface from the base to the tip were to grow much more
+rapidly than on the three other sides, the whole shoot would then
+necessarily be bowed to the south; and let the longitudinal growing
+surface creep round the shoot, deserting by slow degrees the northern
+side and encroaching on the western side, and so round by the south,
+by the east, again to the north.  In this case the shoot would remain
+always bowed with the painted line appearing on the several above
+specified surfaces, and with the point of the shoot successively
+directed to each point of the compass.  In fact, we should have the
+exact kind of movement performed by the revolving shoots of twining
+plants. {9}
+
+It must not be supposed that the revolving movement is as regular as
+that given in the above illustration; in very many cases the tip
+describes an ellipse, even a very narrow ellipse.  To recur once
+again to our illustration, if we suppose only the northern and
+southern surfaces of the sapling alternately to grow rapidly, the
+summit would describe a simple arc; if the growth first travelled a
+very little to the western face, and during the return a very little
+to the eastern face, a narrow ellipse would be described; and the
+sapling would be straight as it passed to and fro through the
+intermediate space; and a complete straightening of the shoot may
+often be observed in revolving plants.  The movement is frequently
+such that three of the sides of the shoot seem to be growing in due
+order more rapidly than the remaining side; so that a semi-circle
+instead of a circle is described, the shoot becoming straight and
+upright during half of its course.
+
+When a revolving shoot consists of several internodes, the lower ones
+bend together at the same rate, but one or two of the terminal ones
+bend at a slower rate; hence, though at times all the internodes are
+in the same direction, at other times the shoot is rendered slightly
+serpentine.  The rate of revolution of the whole shoot, if judged by
+the movement of the extreme tip, is thus at times accelerated or
+retarded.  One other point must be noticed.  Authors have observed
+that the end of the shoot in many twining plants is completely
+hooked; this is very general, for instance, with the Asclepiadaceae.
+The hooked tip, in all the cases observed by me, viz, in Ceropegia,
+Sphaerostemma, Clerodendron, Wistaria, Stephania, Akebia, and
+Siphomeris, has exactly the same kind of movement as the other
+internodes; for a line painted on the convex surface first becomes
+lateral and then concave; but, owing to the youth of these terminal
+internodes, the reversal of the hook is a slower process than that of
+the revolving movement. {10}  This strongly marked tendency in the
+young, terminal and flexible internodes, to bend in a greater degree
+or more abruptly than the other internodes, is of service to the
+plant; for not only does the hook thus formed sometimes serve to
+catch a support, but (and this seems to be much more important) it
+causes the extremity of the shoot to embrace the support much more
+closely than it could otherwise have done, and thus aids in
+preventing the stem from being blown away during windy weather, as I
+have many times observed.  In Lonicera brachypoda the hook only
+straightens itself periodically, and never becomes reversed.  I will
+not assert that the tips of all twining plants when hooked, either
+reverse themselves or become periodically straight, in the manner
+just described; for the hooked form may in some cases be permanent,
+and be due to the manner of growth of the species, as with the tips
+of the shoots of the common vine, and more plainly with those of
+Cissus discolor--plants which are not spiral twiners.
+
+The first purpose of the spontaneous revolving movement, or, more
+strictly speaking, of the continuous bowing movement directed
+successively to all points of the compass, is, as Mohl has remarked,
+to favour the shoot finding a support.  This is admirably effected by
+the revolutions carried on night and day, a wider and wider circle
+being swept as the shoot increases in length.  This movement likewise
+explains how the plants twine; for when a revolving shoot meets with
+a support, its motion is necessarily arrested at the point of
+contact, but the free projecting part goes on revolving.  As this
+continues, higher and higher points are brought into contact with the
+support and are arrested; and so onwards to the extremity; and thus
+the shoot winds round its support.  When the shoot follows the sun in
+its revolving course, it winds round the support from right to left,
+the support being supposed to stand in front of the beholder; when
+the shoot revolves in an opposite direction, the line of winding is
+reversed.  As each internode loses from age its power of revolving,
+it likewise loses its power of spirally twining.  If a man swings a
+rope round his head, and the end hits a stick, it will coil round the
+stick according to the direction of the swinging movement; so it is
+with a twining plant, a line of growth travelling round the free part
+of the shoot causing it to bend towards the opposite side, and this
+replaces the momentum of the free end of the rope.
+
+All the authors, except Palm and Mohl, who have discussed the spiral
+twining of plants, maintain that such plants have a natural tendency
+to grow spirally.  Mohl believes (p. 112) that twining stems have a
+dull kind of irritability, so that they bend towards any object which
+they touch; but this is denied by Palm.  Even before reading Mohl's
+interesting treatise, this view seemed to me so probable that I
+tested it in every way that I could, but always with a negative
+result.  I rubbed many shoots much harder than is necessary to excite
+movement in any tendril or in the foot-stalk of any leaf climber, but
+without any effect.  I then tied a light forked twig to a shoot of a
+Hop, a Ceropegia, Sphaerostemma, and Adhatoda, so that the fork
+pressed on one side alone of the shoot and revolved with it; I
+purposely selected some very slow revolvers, as it seemed most likely
+that these would profit most from possessing irritability; but in no
+case was any effect produced. {11}  Moreover, when a shoot winds
+round a support, the winding movement is always slower, as we shall
+immediately see, than whilst it revolves freely and touches nothing.
+Hence I conclude that twining stems are not irritable; and indeed it
+is not probable that they should be so, as nature always economizes
+her means, and irritability would have been superfluous.
+Nevertheless I do not wish to assert that they are never irritable;
+for the growing axis of the leaf-climbing, but not spirally twining,
+Lophospermum scandens is, certainly irritable; but this case gives me
+confidence that ordinary twiners do not possess any such quality, for
+directly after putting a stick to the Lophopermum, I saw that it
+behaved differently from a true twiner or any other leaf-climber.
+{12}
+
+The belief that twiners have a natural tendency to grow spirally,
+probably arose from their assuming a spiral form when wound round a
+support, and from the extremity, even whilst remaining free,
+sometimes assuming this form.  The free internodes of vigorously
+growing plants, when they cease to revolve, become straight, and show
+no tendency to be spiral; but when a shoot has nearly ceased to grow,
+or when the plant is unhealthy, the extremity does occasionally
+become spiral.  I have seen this in a remarkable manner with the ends
+of the shoots of the Stauntonia and of the allied Akebia, which
+became wound up into a close spire, just like a tendril; and this was
+apt to occur after some small, ill-formed leaves had perished.  The
+explanation, I believe, is, that in such cases the lower parts of the
+terminal internodes very gradually and successively lose their power
+of movement, whilst the portions just above move onwards and in their
+turn become motionless; and this ends in forming an irregular spire.
+
+When a revolving shoot strikes a stick, it winds round it rather more
+slowly than it revolves.  For instance, a shoot of the Ceropegia,
+revolved in 6 hrs., but took 9 hrs. 30 m. to make one complete spire
+round a stick; Aristolochia gigas revolved in about 5 hrs., but took
+9 hrs. 15 m. to complete its spire.  This, I presume, is due to the
+continued disturbance of the impelling force by the arrestment of the
+movement at successive points; and we shall hereafter see that even
+shaking a plant retards the revolving movement.  The terminal
+internodes of a long, much-inclined, revolving shoot of the
+Ceropegia, after they had wound round a stick, always slipped up it,
+so as to render the spire more open than it was at first; and this
+was probably in part due to the force which caused the revolutions,
+being now almost freed from the constraint of gravity and allowed to
+act freely.  With the Wistaria, on the other hand, a long horizontal
+shoot wound itself at first into a very close spire, which remained
+unchanged; but subsequently, as the shoot twined spirally up its
+support, it made a much more open spire.  With all the many plants
+which were allowed freely to ascend a support, the terminal
+internodes made at first a close spire; and this, during windy
+weather, served to keep the shoots in close contact with their
+support; but as the penultimate internodes grew in length, they
+pushed themselves up for a considerable space (ascertained by
+coloured marks on the shoot and on the support) round the stick, and
+the spire became more open. {13}
+
+It follows from this latter fact that the position occupied by each
+leaf with respect to the support depends on the growth of the
+internodes after they have become spirally wound round it.  I mention
+this on account of an observation by Palm (p. 34), who states that
+the opposite leaves of the Hop always stand in a row, exactly over
+one another, on the same side of the supporting stick, whatever its
+thickness may be.  My sons visited a hop-field for me, and reported
+that though they generally found the points of insertion of the
+leaves standing over each other for a space of two or three feet in
+height, yet this never occurred up the whole length of the pole; the
+points of insertion forming, as might have been expected, an
+irregular spire.  Any irregularity in the pole entirely destroyed the
+regularity of position of the leaves.  From casual inspection, it
+appeared to me that the opposite leaves of Thunbergia alata were
+arranged in lines up the sticks round which they had twined;
+accordingly, I raised a dozen plants, and gave them sticks of various
+thicknesses, as well as string, to twine round; and in this case one
+alone out of the dozen had its leaves arranged in a perpendicular
+line:  I conclude, therefore, Palm's statement is not quite accurate.
+
+The leaves of different twining-plants are arranged on the stem
+(before it has twined) alternately, or oppositely, or in a spire.  In
+the latter case the line of insertion of the leaves and the course of
+the revolutions coincide.  This fact has been well shown by
+Dutrochet, {14} who found different individuals of Solanum dulcamara
+twining in opposite directions, and these had their leaves in each
+case spirally arranged in the same direction.  A dense whorl of many
+leaves would apparently be incommodious for a twining plant, and some
+authors assert that none have their leaves thus arranged; but a
+twining Siphomeris has whorls of three leaves.
+
+If a stick which has arrested a revolving shoot, but has not as yet
+been encircled, be suddenly taken away, the shoot generally springs
+forward, showing that it was pressing with some force against the
+stick.  After a shoot has wound round a stick, if this be withdrawn,
+it retains for a time its spiral form; it then straightens itself,
+and again commences to revolve.  The long, much-inclined shoot of the
+Ceropegia previously alluded to offered some curious peculiarities.
+The lower and older internodes, which continued to revolve, were
+incapable, on repeated trials, of twining round a thin stick; showing
+that, although the power of movement was retained, this was not
+sufficient to enable the plant to twine.  I then moved the stick to a
+greater distance, so that it was struck by a point 2.5 inches from
+the extremity of the penultimate internode; and it was then neatly
+encircled by this part of the penultimate and by the ultimate
+internode.  After leaving the spirally wound shoot for eleven hours,
+I quietly withdrew the stick, and in the course of the day the curled
+portion straightened itself and recommenced revolving; but the lower
+and not curled portion of the penultimate internode did not move, a
+sort of hinge separating the moving and the motionless part of the
+same internode.  After a few days, however, I found that this lower
+part had likewise recovered its revolving power.  These several facts
+show that the power of movement is not immediately lost in the
+arrested portion of a revolving shoot; and that after being
+temporarily lost it can be recovered.  When a shoot has remained for
+a considerable time round a support, it permanently retains its
+spiral form even when the support is removed.
+
+When a tall stick was placed so as to arrest the lower and rigid
+internodes of the Ceropegia, at the distance at first of 15 and then
+of 21 inches from the centre of revolution, the straight shoot slowly
+and gradually slid up the stick, so as to become more and more highly
+inclined, but did not pass over the summit.  Then, after an interval
+sufficient to have allowed of a semi-revolution, the shoot suddenly
+bounded from the stick and fell over to the opposite side or point of
+the compass, and reassumed its previous slight inclination.  It now
+recommenced revolving in its usual course, so that after a semi-
+revolution it again came into contact with the stick, again slid up
+it, and again bounded from it and fell over to the opposite side.
+This movement of the shoot had a very odd appearance, as if it were
+disgusted with its failure but was resolved to try again.  We shall,
+I think, understand this movement by considering the former
+illustration of the sapling, in which the growing surface was
+supposed to creep round from the northern by the western to the
+southern face; and thence back again by the eastern to the northern
+face, successively bowing the sapling in all directions.  Now with
+the Ceropegia, the stick being placed to the south of the shoot and
+in contact with it, as soon as the circulatory growth reached the
+western surface, no effect would be produced, except that the shoot
+would be pressed firmly against the stick.  But as soon as growth on
+the southern surface began, the shoot would be slowly dragged with a
+sliding movement up the stick; and then, as soon as the eastern
+growth commenced, the shoot would be drawn from the stick, and its
+weight coinciding with the effects of the changed surface of growth,
+would cause it suddenly to fall to the opposite side, reassuming its
+previous slight inclination; and the ordinary revolving movement
+would then go on as before.  I have described this curious case with
+some care, because it first led me to understand the order in which,
+as I then thought, the surfaces contracted; but in which, as we now
+know from Sachs and II. de Vries, they grow for a time rapidly, thus
+causing the shoot to bow towards the opposite side.
+
+The view just given further explains, as I believe, a fact observed
+by Mohl (p. 135), namely, that a revolving shoot, though it will
+twine round an object as thin as a thread, cannot do so round a thick
+support.  I placed some long revolving shoots of a Wistaria close to
+a post between 5 and 6 inches in diameter, but, though aided by me in
+many ways, they could not wind round it.  This apparently was due to
+the flexure of the shoot, whilst winding round an object so gently
+curved as this post, not being sufficient to hold the shoot to its
+place when the growing surface crept round to the opposite surface of
+the shoot; so that it was withdrawn at each revolution from its
+support.
+
+When a free shoot has grown far beyond its support, it sinks
+downwards from its weight, as already explained in the case of the
+Hop, with the revolving extremity turned upwards.  If the support be
+not lofty, the shoot falls to the ground, and resting there, the
+extremity rises up.  Sometimes several shoots, when flexible, twine
+together into a cable, and thus support one another.  Single thin
+depending shoots, such as those of the Sollya Drummondii, will turn
+abruptly backwards and wind up on themselves.  The greater number of
+the depending shoots, however, of one twining plant, the Hibbertia
+dentata, showed but little tendency to turn upwards.  In other cases,
+as with the Cryptostegia grandiflora, several internodes which were
+at first flexible and revolved, if they did not succeed in twining
+round a support, become quite rigid, and supporting themselves
+upright, carried on their summits the younger revolving internodes.
+
+Here will be a convenient place to give a Table showing the direction
+and rate of movement of several twining plants, with a few appended
+remarks.  These plants are arranged according to Lindley's 'Vegetable
+Kingdom' of 1853; and they have been selected from all parts of the
+series so as to show that all kinds behave in a nearly uniform
+manner. {15}
+
+
+The Rate of Revolution of various Twining Plants.
+
+(ACOTYLEDONS.)
+
+Lygodium scandens (Polypodiaceae) moves against the sun.
+
+                                      H.  M.
+June 18, 1st circle was made in       6   0
+     18, 2nd                          6  15 (late in evening)
+     19, 3rd                          5  32 (very hot day)
+     19, 4th                          5   0 (very hot day)
+     20, 5th                          6   0
+
+Lygodium articulatum moves against the sun.
+
+                                      H.  M.
+July 19, 1st circle was made in      16  30 (shoot very young)
+     20, 2nd                         15   0
+     21, 3rd                          8   0
+     22, 4th                         10  30
+
+(MONOCOTYLEDONS.)
+
+Ruscus androgynus (Liliaceae), placed in the hot-house, moves against
+the sun.
+
+                                      H.  M.
+May 24, 1st circle was made in        6   14 (shoot very young)
+    25, 2nd                           2   21
+    25, 3rd                           3   37
+    25, 4th                           3   22
+    26, 5th                           2   50
+    27, 6th                           3   52
+    27, 7th                           4   11
+
+Asparagus (unnamed species from Kew) (Liliaceae) moves against the
+sun, placed in hothouse.
+
+                                      H.  M.
+Dec. 26, 1st circle was made in       5    0
+     27, 2nd                          5   40
+
+Tamus communis (Dioscoreaceae).  A young shoot from a tuber in a pot
+placed in the greenhouse:  follows the sun.
+
+                                      H.  M.
+July, 7, 1st circle was made in       3   10
+      7, 2nd                          2   38
+      8, 3rd                          3    5
+      8, 4th                          2   56
+      8, 5th                          2   30
+      8, 6th                          2   30
+
+Lapagerea rosea (Philesiaceae), in greenhouse, follows the sun.
+
+                                      H.  M.
+March 9, 1st circle was made in      26   15 (shoot young)
+     10, semicircle                   8   15
+     11, 2nd circle                  11    0
+     12, 3rd                         15   30
+     13, 4th                         14   15
+     16, 5th                          8   40 when placed in the
+hothouse; but the next day the shoot remained stationary.
+
+Roxburghia viridiflora (Roxburghiaceae) moves against the sun; it
+completed a circle in about 24 hours.
+
+(DICOTYLEDONS.)
+
+Humulus Lupulus (Urticaceae) follows the sun.  The plant was kept in
+a room during warm weather.
+
+                                      H.  M.
+April 9, 2 circles were made in       4   16
+Aug. 13, 3rd circle was               2    0
+     14, 4th                          2   20
+     14, 5th                          2   16
+     14, 6th                          2    2
+     14, 7th                          2    0
+     14, 8th                          2    4
+
+With the Hop a semicircle was performed, in travelling from the
+light, in 1 hr. 33 m.; in travelling to the light, in 1 hr. 13 m.;
+difference of rate, 20 m.
+
+Akebia quinata (Lardizabalaceae), placed in hothouse, moves against
+the sun.
+
+                                      H.  M.
+March 17, 1st circle was made in      4    0 (shoot young)
+      18, 2nd                         1   40
+      18, 3rd                         1   30
+      19, 4th                         1   45
+
+Stauntonia latifolia (Lardizabalaceae), placed in hothouse, moves
+against the sun.
+
+                                      H.   M.
+March 28, 1st circle was made in      3   30
+      29, 2nd                         3   45
+
+Sphaerostemma marmoratum (Schizandraceae) follows the sun.
+
+                                           H.  M.
+August 5th, 1st circle was made in about   24   0
+       5th, 2nd circle was made in         18  30
+
+Stephania rotunda (Menispermaceae) moves against the sun
+
+                                           H.  M.
+May 27, 1st circle was made in             5    5
+     30, 2nd                               7    6
+June 2, 3rd                                5   15
+     3, 4th                                6   28
+
+Thryallis brachystachys (Malpighiaceae) moves against the sun:  one
+shoot made a circle in 12 hrs., and another in 10 hrs. 30 m.; but the
+next day, which was much colder, the first shoot took 10 hrs. to
+perform only a semicircle.
+
+Hibbertia dentata (Dilleniaceae), placed in the hothouse, followed
+the sun, and made (May 18th) a circle in 7 hrs. 20 m.; on the 19th,
+reversed its course, and moved against the sun, and made a circle in
+7 hrs.; on the 20th, moved against the sun one-third of a circle, and
+then stood still; on the 26th, followed the sun for two-thirds of a
+circle, and then returned to its starting-point, taking for this
+double course 11 hrs. 46 m.
+
+Sollya Drummondii (Pittosporaceae) moves against the sun kept in
+greenhouse.
+
+                                  H.  M.
+April 4, 1st circle was made in   4   25
+      5, 2nd                      8    0 (very cold day)
+      6, 3rd                      6   25
+      7, 4th                      7    5
+
+Polygonum dumetorum (Polygonaceae).  This case is taken from
+Dutrochet (p.  299), as I observed, no allied plant:  follows the
+sun.  Three shoots, cut off a plant, and placed in water made circles
+in 3 hrs. 10 m., 5 hrs. 20 m., and 7 hrs. 15 m.
+
+Wistaria Chinensis (Leguminosae), in greenhouse, moves against the
+sun.
+
+                                  H.  M.
+May 13, 1st circle was made in     3   5
+    13, 2nd                        3  20
+    16, 3rd                        2   5
+    24, 4th                        3  21
+    25, 5th                        2  37
+    25, 6th                        2  35
+
+Phaseolus vulgaris (Leguminosae), in greenhouse, moves against the
+sun.
+
+                                   H.  M.
+May, 1st circle was made in         2   0
+     2nd                            1  55
+     3rd                            1  55
+
+Dipladenia urophylla (Apocynaceae) moves against the sun.
+
+                                   H.   M.
+April 18, 1st circle was made in    8    0
+      19, 2nd                       9   15
+      30, 3rd                       9   40
+
+Dipladenia crassinoda moves against the sun.
+
+                                    H.  M.
+May  16, 1st circle was made in      9   5
+July 20, 2nd                         8   0
+     21, 3rd                         8   5
+
+Ceropegia Gardnerii (Asclepiadaceae) moves against the sun.
+
+                                                         H.  M.
+Shoot very young, 2 inches }
+      in length            } 1st circle was performed in 7   55
+Shoot still young            2nd                         7    0
+Long shoot                   3rd                         6   33
+Long shoot                   4th                         5   15
+Long shoot                   5th                         6   45
+
+Stephanotis floribunda (Asclepiadaceae) moves against the sun and
+made a circle in 6 hrs. 40 m., a second circle in about 9 hrs.
+
+Hoya carnosa (Asclepiadaceae) made several circles in from 16 hrs. to
+22 hrs. or 24 hrs.
+
+Ipomaea purpurea (Convolvulaceae) moves against the sun.  Plant
+placed in room with lateral light.
+
+                                    {Semicircle, from the light in
+1st circle was made in 2 hrs. 42 m. { 1 hr. 14 m., to the light
+                                    { 1 hr. 28 m.:  difference 14 m.
+
+                                    {Semicircle, from the light in
+2nd circle was made in 2 hrs. 47 m. { 1 hr. 17 m., to the light 1 hr.
+                                    { 30 m.:  difference 13 m.
+
+Ipomaea jucunda (Convolvulaceae) moves against the sun, placed in my
+study, with windows facing the north-east.  Weather hot.
+
+                                    {Semicircle, from the light in
+1st circle was made in 5 hrs. 30 m. { 4 hrs. 30 m., to the light 1
+hr.
+                                    { 0 m.:  difference 3 hrs. 30 m.
+
+2nd circle was made in 5 hrs.       {Semicircle, from the light in
+  20 m.  (Late in afternoon:         { 3 hrs. 50 m., to the light 1
+hr.
+  circle completed at 6 hrs. 40 m.  { 30 m.:  difference 2 hrs. 20 m.
+  P.M.)
+
+We have here a remarkable instance of the power of light in retarding
+and hastening the revolving movement.  (See ERRATA.)
+
+Convolvulus sepium (large-flowered cultivated var.) moves against the
+sun.  Two circles, were made each in 1 hr. 42 m.:  difference in
+semicircle from and to the light 14 m.
+
+Rivea tiliaefolia (Convolvulaceae) moves against the sun, made four
+revolutions in 9 hrs.; so that, on an average, each was performed in
+2 hrs. 15 m.
+
+Plumbago rosea (Plumbaginaceae) follows the sun.  The shoot did not
+begin to revolve until nearly a yard in height; it then made a fine
+circle in 10 hrs. 45 m.  During the next few days it continued to
+move, but irregularly.  On August 15th the shoot followed, during a
+period of 10 hrs. 40 m., a long and deeply zigzag course and then
+made a broad ellipse.  The figure apparently represented three
+ellipses, each of which averaged 3 hrs. 38 m. for its completion.
+
+Jasminum pauciflorum, Bentham (Jasminaceae), moves against the sun.
+A circle was made in 7 hrs. 15 m., and a second rather more quickly.
+
+Clerodendrum Thomsonii (Verbenaceae) follows the sun.
+
+                                        H.   M.
+April 12, 1st circle was made in         5   45 (shoot very young)
+      14, 2nd                            3   30
+                                                {(directly after the
+       18, a semicircle                  5    0 { plant was shaken
+                                                { on being moved)
+       19, 3rd circle                    3    0
+       20, 4th                           4   20
+
+Tecoma jasminoides (Bignoniaceae) moves against the sun.
+
+                                         H.  M.
+March 17, 1st circle was made in         6   30
+      19, 2nd                            7    0
+      22, 3rd                            8   30 (very cold day)
+      24, 4th                            6   45
+
+Thunbergia alata (Acanthaceae) moves against sun.
+
+                                          H.  M.
+April 14, 1st circle was made in          3   20
+      18, 2nd                             2   50
+      18, 3rd                             2   55
+      18, 4th                             3   55 (late in afternoon)
+
+Adhadota cydonaefolia (Acanthaceae) follows the sun.  A young shoot
+made a semicircle in 24 hrs.; subsequently it made a circle in
+between 40 hrs. and 48 hrs.  Another shoot, however, made a circle in
+26 hrs. 30 m.
+
+Mikania scandens (Compositae) moves against the sun.
+
+                                          H.  M.
+March 14, 1st circle was made in           3  10
+      15, 2nd                              3   0
+      16, 3rd                              3   0
+      17, 4th                              3  33
+April  7, 5th                              2  50
+       7, 6th                              2  40 {This circle was
+made
+                                                 { after a copious
+water-
+                                                 { ing with cold
+water at
+                                                 { 47 degrees Fahr.
+
+Combretum argenteum (Combretaceae) moves against the sun.  Kept in
+hothouse.
+
+                                          H.  M.
+                                                 {Early in morning,
+when
+Jan. 24, 1st circle was made in           2   55 { the temperature of
+the
+                                                 { house had fallen a
+                                                 { little.
+
+     24, 2 circles each at an }
+           average of         }           2   20
+     25, 4th circle was made in           2   25
+
+Combretum purpureum revolves not quite so quickly as C. argenteum.
+
+Loasa aurantiaca (Loasaceae).  Revolutions variable in their course:
+a plant which moved against the sun.
+
+                                       H.   M.
+June 20, 1st circle was made in         2   37
+     20, 2nd                            2   13
+     20, 3rd                            4    0
+     21, 4th                            2   35
+     22, 5th                            3   26
+     23, 6th                            3    5
+
+Another plant which followed the sun in its revolutions.
+
+                                       H.   M.
+July 11, 1st circle was made in         1   51 }
+     11, 2nd                            1   46 } Very hot day.
+     11, 3rd                            1   41 }
+     11, 4th                            1   48 }
+     12, 5th                            2   35 }
+
+Scyphanthus elegans (Loasaceae) follows the sun.
+
+                                       H.   M.
+June 13, 1st circle was made in         1   45
+     13, 2nd                            1   17
+     14, 3rd                            1   36
+     14, 4th                            1   59
+     14, 5th                            2    3
+
+Siphomeris or Lecontea (unnamed sp.) (Cinchonaceae) follows the sun.
+
+                                       H.  M.
+                                              {(shoot extremely
+May 25, semicircle was made in         10  27 { young)
+    26, 1st circle                     10  15 (shoot still young)
+    30, 2nd                             8  55
+June 2, 3rd                             8  11
+     6, 4th                             6   8
+                                              { Taken from the
+     8, 5th                             7  20 { hothouse, and
+     9, 6th                             8  36 { placed in a room
+                                              { in my house.
+
+Manettia bicolor (Cinchonaceae), young plant, follows the sun.
+
+                                        H.  M.
+July 7, 1st circle was made in          6   18
+     8, 2nd                             6   53
+     9, 3rd                             6   30
+
+Lonicera brachypoda (Caprifoliaceae) follows the sun, kept in a warm
+room in the house.
+
+                                       H.   M.
+April, 1st circle was made in           9   10 (about)
+                                               {(a distinct shoot,
+very
+April, 2nd circle was made in          12   20 { young, on same
+plant)
+       3rd                              7   30
+                                               {In this latter
+circle,
+                                               { the semicircle from
+                                               { the light took 5
+hrs.
+       4th                              8    0 { 23 m., and to the
+                                               { light 2 hrs. 37
+min.:
+                                               { difference 2 hrs
+46m.
+
+Aristolochia gigas (Aristolochiaceae) moves against the sun.
+
+                                       H.   M.
+ July 22, 1st circle was made in        8    0 (rather young shoot)
+     23, 2nd                            7   15
+     24, 3rd                            5    0 (about)
+
+In the foregoing Table, which includes twining plants belonging to
+widely different orders, we see that the rate at which growth travels
+or circulates round the axis (on which the revolving movement
+depends), differs much.  As long as a plant remains under the same
+conditions, the rate is often remarkably uniform, as with the Hop,
+Mikania, Phaseolus, &c.  The Scyphanthus made one revolution in 1 hr.
+17 m., and this is the quickest rate observed by me; but we shall
+hereafter see a tendril-bearing Passiflora revolving more rapidly.  A
+shoot of the Akebia quinata made a revolution in 1 hr. 30 m., and
+three revolutions at the average rate of 1 hr. 38 m.; a Convolvulus
+made two revolutions at the average of 1 hr. 42 m., and Phaseolus
+vulgaris three at the average of 1 hr. 57 m.  On the other hand, some
+plants take 24 hrs. for a single revolution, and the Adhadota
+sometimes required 48 hrs.; yet this latter plant is an efficient
+twiner.  Species of the same genus move at different rates.  The rate
+does not seem governed by the thickness of the shoots:  those of the
+Sollya are as thin and flexible as string, but move more slowly than
+the thick and fleshy shoots of the Ruscus, which seem little fitted
+for movement of any kind.  The shoots of the Wistaria, which become
+woody, move faster than those of the herbaceous Ipomoea or
+Thunbergia.
+
+We know that the internodes, whilst still very young, do not acquire
+their proper rate of movement; hence the several shoots on the same
+plant may sometimes be seen revolving at different rates.  The two or
+three, or even more, internodes which are first formed above the
+cotyledons, or above the root-stock of a perennial plant, do not
+move; they can support themselves, and nothing superfluous is
+granted.
+
+A greater number of twiners revolve in a course opposed to that of
+the sun, or to the hands of a watch, than in the reversed course,
+and, consequently, the majority, as is well known, ascend their
+supports from left to right.  Occasionally, though rarely, plants of
+the same order twine in opposite directions, of which Mohl (p. 125)
+gives a case in the Leguminosae, and we have in the table another in
+the Acanthaceae.  I have seen no instance of two species of the same
+genus twining in opposite directions, and such cases must be rare;
+but Fritz Muller {16} states that although Mikania scandens twines,
+as I have described, from left to right, another species in South
+Brazil twines in an opposite direction.  It would have been an
+anomalous circumstance if no such cases had occurred, for different
+individuals of the same species, namely, of Solanum dulcamara
+(Dutrochet, tom. xix. p. 299), revolve and twine in two directions:
+this plant, however; is a most feeble twiner.  Loasa aurantiaca
+(Leon, p. 351) offers a much more curious case:  I raised seventeen
+plants:  of these eight revolved in opposition to the sun and
+ascended from left to right; five followed the sun and ascended from
+right to left; and four revolved and twined first in one direction,
+and then reversed their course, {17} the petioles of the opposite
+leaves affording a point d'appui for the reversal of the spire.  One
+of these four plants made seven spiral turns from right to left, and
+five turns from left to right.  Another plant in the same family, the
+Scyphanthus elegans, habitually twines in this same manner.  I raised
+many plants of it, and the stems of all took one turn, or
+occasionally two or even three turns in one direction, and then,
+ascending for a short space straight, reversed their course and took
+one or two turns in an opposite direction.  The reversal of the
+curvature occurred at any point in the stem, even in the middle of an
+internode.  Had I not seen this case, I should have thought its
+occurrence most improbable.  It would be hardly possible with any
+plant which ascended above a few feet in height, or which lived in an
+exposed situation; for the stem could be pulled away easily from its
+support, with but little unwinding; nor could it have adhered at all,
+had not the internodes soon become moderately rigid.  With leaf-
+climbers, as we shall soon see, analogous cases frequently occur; but
+these present no difficulty, as the stem is secured by the clasping
+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 Ipomoea jucunda; but frequently with Hibbertia dentata.
+This plant at first perplexed me much, for I continually observed its
+long and flexible shoots, evidently well fitted for twining, make a
+whole, or half, or quarter circle in one direction and then in an
+opposite direction; consequently, when I placed the shoots near thin
+or thick sticks, or perpendicularly stretched string, they seemed as
+if constantly trying to ascend, but always failed.  I then surrounded
+the plant with a mass of branched twigs; the shoots ascended, and
+passed through them, but several came out laterally, and their
+depending extremities seldom turned upwards as is usual with twining
+plants.  Finally, I surrounded a second plant with many thin upright
+sticks, and placed it near the first one with twigs; and now both had
+got what they liked, for they twined up the parallel sticks,
+sometimes winding round one and sometimes round several; and the
+shoots travelled laterally from one to the other pot; but as the
+plants grew older, some of the shoots twined regularly up thin
+upright sticks.  Though the revolving movement was sometimes in one
+direction and sometimes in the other, the twining was invariably from
+left to right; {18} so that the more potent or persistent movement of
+revolution must have been in opposition to the course of the sun.  It
+would appear that this Hibbertia is adapted both to ascend by
+twining, and to ramble laterally through the thick Australian scrub.
+
+I have described the above case in some detail, because, as far as I
+have seen, it is rare to find any special adaptations with twining
+plants, in which respect they differ much from the more highly
+organized tendril-bearers.  The Solanum dulcamara, as we shall
+presently see, can twine only round stems which are both thin and
+flexible.  Most twining plants are adapted to ascend supports of
+moderate though of different thicknesses.  Our English twiners, as
+far as I have seen, never twine round trees, excepting the
+honeysuckle (Lonicera periclymenum), which I have observed twining up
+a young beech-tree nearly 4.5 inches in diameter.  Mohl (p. 134)
+found that the Phaseolus multiflorus and Ipomoea purpurea could not,
+when placed in a room with the light entering on one side, twine
+round sticks between 3 and 4 inches in diameter; for this interfered,
+in a manner presently to be explained, with the revolving movement.
+In the open air, however, the Phaseolus twined round a support of the
+above thickness, but failed in twining round one 9 inches in
+diameter.  Nevertheless, some twiners of the warmer temperate regions
+can manage this latter degree of thickness; for I hear from Dr.
+Hooker that at Kew the Ruscus androgynus has ascended a column 9
+inches in diameter; and although a Wistaria grown by me in a small
+pot tried in vain for weeks to get round a post between 5 and 6
+inches in thickness, yet at Kew a plant ascended a trunk above 6
+inches in diameter.  The tropical twiners, on the other hand, can
+ascend thicker trees; I hear from Drs. Thomson and Hooker that this
+is the case with the Butea parviflora, one of the Menispermaceae, and
+with some Dalbergias and other Leguminosae. {19}  This power would be
+necessary for any species which had to ascend by twining the large
+trees of a tropical forest; otherwise they would hardly ever be able
+to reach the light.  In our temperate countries it would be injurious
+to the twining plants which die down every year if they were enabled
+to twine round trunks of trees, for they could not grow tall enough
+in a single season to reach the summit and gain the light.
+
+By what means certain twining plants are adapted to ascend only thin
+stems, whilst others can twine round thicker ones, I do not know.  It
+appeared to me probable that twining plants with very long revolving
+shoots would be able to ascend thick supports; accordingly I placed
+Ceropegia Gardnerii near a post 6 inches in diameter, but the shoots
+entirely failed to wind round it; their great length and power of
+movement merely aid them in finding a distant stem round which to
+twine.  The Sphaerostemma marmoratum is a vigorous tropical twiner;
+and as it is a very slow revolver, I thought that this latter
+circumstance might help it in ascending a thick support; but though
+it was able to wind round a 6-inch post, it could do this only on the
+same level or plane, and did not form a spire and thus ascend.
+
+As ferns differ so much in structure from phanerogamic plants, it may
+be worth while here to show that twining ferns do not differ in their
+habits from other twining plants.  In Lygodium articulatum the two
+internodes of the stem (properly the rachis) which are first formed
+above the root-stock do not move; the third from the ground revolves,
+but at first very slowly.  This species is a slow revolver:  but L.
+scandens made five revolutions, each at the average rate of 5 hrs. 45
+m.; and this represents fairly well the usual rate, taking quick and
+slow movers, amongst phanerogamic plants.  The rate was accelerated
+by increased temperature.  At each stage of growth only the two upper
+internodes revolved.  A line painted along the convex surface of a
+revolving internode becomes first lateral, then concave, then lateral
+and ultimately again convex.  Neither the internodes nor the petioles
+are irritable when rubbed.  The movement is in the usual direction,
+namely, in opposition to the course of the sun; and when the stem
+twines round a thin stick, it becomes twisted on its own axis in the
+same direction.  After the young internodes have twined round a
+stick, their continued growth causes them to slip a little upwards.
+If the stick be soon removed, they straighten themselves, and
+recommence revolving.  The extremities of the depending shoots turn
+upwards, and twine on themselves.  In all these respects we have
+complete identity with twining phanerogamic plants; and the above
+enumeration may serve as a summary of the leading characteristics of
+all twining plants.
+
+The power of revolving depends on the general health and vigour of
+the plant, as has been laboriously shown by Palm.  But the movement
+of each separate internode is so independent of the others, that
+cutting off an upper one does not affect the revolutions of a lower
+one.  When, however, Dutrochet cut off two whole shoots of the Hop,
+and placed them in water, the movement was greatly retarded; for one
+revolved in 20 hrs. and the other in 23 hrs., whereas they ought to
+have revolved in between 2 hrs. and 2 hrs. 30 m.  Shoots of the
+Kidney-bean, cut off and placed in water, were similarly retarded,
+but in a less degree.  I have repeatedly observed that carrying a
+plant from the greenhouse to my room, or from one part to another of
+the greenhouse, always stopped the movement for a time; hence I
+conclude that plants in a state of nature and growing in exposed
+situations, would not make their revolutions during very stormy
+weather.  A decrease in temperature always caused a considerable
+retardation in the rate of revolution; but Dutrochet (tom. xvii. pp.
+994, 996) has given such precise observations on this head with
+respect to the common pea that I need say nothing more.  When twining
+plants are placed near a window in a room, the light in some cases
+has a remarkable power (as was likewise observed by Dutrochet, p.
+998, with the pea) on the revolving movement, but this differs in
+degree with different plants; thus Ipomoea jucunda made a complete
+circle in 5 hrs. 30 m.; the semicircle from the light taking 4 hrs.
+80 m., and that towards the light only 1 hr.  Lonicera brachypoda
+revolved, in a reversed direction to the Ipomoea, in 8 hrs.; the
+semicircle from the light taking 5 hrs. 23 m., and that to the light
+only 2 hrs. 37 m.  From the rate of revolution in all the plants
+observed by me, being nearly the same during the night and the day, I
+infer that the action of the light is confined to retarding one
+semicircle and accelerating the other, so as not to modify greatly
+the rate of the whole revolution.  This action of the light is
+remarkable, when we reflect how little the leaves are developed on
+the young and thin revolving internodes.  It is all the more
+remarkable, as botanists believe (Mohl, p. 119) that twining plants
+are but little sensitive to the action of light.
+
+I will conclude my account of twining plants by giving a few
+miscellaneous and curious cases.  With most twining plants all the
+branches, however many there may be, go on revolving together; but,
+according to Mohl (p. 4), only the lateral branches of Tamus
+elephantipes twine, and not the main stem.  On the other hand, with a
+climbing species of Asparagus, the leading shoot alone, and not the
+branches, revolved and twined; but it should be stated that the plant
+was not growing vigorously.  My plants of Combretum argenteum and C.
+purpureum made numerous short healthy shoots; but they showed no
+signs of revolving, and I could not conceive how these plants could
+be climbers; but at last C. argenteum put forth from the lower part
+of one of its main branches a thin shoot, 5 or 6 feet in length,
+differing greatly in appearance from the previous shoots, owing to
+its leaves being little developed, and this shoot revolved vigorously
+and twined.  So that this plant produces shoots of two kinds.  With
+Periploca Graeca (Palm, p. 43) the uppermost shoots alone twine.
+Polygonum convolvulus twines only during the middle of the summer
+(Palm, p. 43, 94); and plants growing vigorously in the autumn show
+no inclination to climb.  The majority of Asclepiadaceae are twiners;
+but Asclepias nigra only "in fertiliori solo incipit scandere
+subvolubili caule" (Willdenow, quoted and confirmed by Palm, p. 41).
+Asclepias vincetoxicum does not regularly twine, but occasionally
+does so (Palm, p. 42; Mohl, p. 112) when growing under certain
+conditions.  So it is with two species of Ceropegia, as I hear from
+Prof.  Harvey, for these plants in their native dry South African
+home generally grow erect, from 6 inches to 2 feet in height,--a very
+few taller specimens showing some inclination to curve; but when
+cultivated near Dublin, they regularly twined up sticks 5 or 6 feet
+in height.  Most Convolvulaceae are excellent twiners; but in South
+Africa Ipomoea argyraeoides almost always grows erect and compact,
+from about 12 to 18 inches in height, one specimen alone in Prof.
+Harvey's collection showing an evident disposition to twine.  On the
+other hand, seedlings raised near Dublin twined up sticks above 8
+feet in height.  These facts are remarkable; for there can hardly be
+a doubt that in the dryer provinces of South Africa these plants have
+propagated themselves for thousands of generations in an erect
+condition; and yet they have retained during this whole period the
+innate power of spontaneously revolving and twining, whenever their
+shoots become elongated under proper conditions of life.  Most of the
+species of Phaseolus are twiners; but certain varieties of the P.
+multiflorus produce (Leon, p. 681) two kinds of shoots, some upright
+and thick, and others thin and twining.  I have seen striking
+instances of this curious case of variability in "Fulmer's dwarf
+forcing-bean," which occasionally produced a single long twining
+shoot.
+
+Solanum dulcamara is one of the feeblest and poorest of twiners:  it
+may often be seen growing as an upright bush, and when growing in the
+midst of a thicket merely scrambles up between the branches without
+twining; but when, according to Dutrochet (tom. xix. p. 299), it
+grows near a thin and flexible support, such as the stem of a nettle,
+it twines round it.  I placed sticks round several plants, and
+vertically stretched strings close to others, and the strings alone
+were ascended by twining.  The stem twines indifferently to the right
+or left.  Some others species of Solanum, and of another genus, viz.
+Habrothamnus, belonging to the same family, are described in
+horticultural works as twining plants, but they seem to possess this
+faculty in a very feeble degree.  We may suspect that the species of
+these two genera have as yet only partially acquired the habit of
+twining.  On the other hand with Tecoma radicans, a member of a
+family abounding with twiners and tendril-bearers, but which climbs,
+like the ivy, by the aid of rootlets, we may suspect that a former
+habit of twining has been lost, for the stem exhibited slight
+irregular movements which could hardly be accounted for by changes in
+the action of the light.  There is no difficulty in understanding how
+a spirally twining plant could graduate into a simple root-climber;
+for the young internodes of Bignonia Tweedyana and of Hoya carnosa
+revolve and twine, but likewise emit rootlets which adhere to any
+fitting surface, so that the loss of twining would be no great
+disadvantage and in some respects an advantage to these species, as
+they would then ascend their supports in a more direct line. {20}
+
+
+
+CHAPTER II.--LEAF-CLIMBERS.
+
+
+
+Plants which climb by the aid of spontaneously revolving and
+sensitive petioles--Clematis--Tropaeolum--Maurandia, flower-peduncles
+moving spontaneously and sensitive to a touch--Rhodochiton--
+Lophospermum--internodes sensitive--Solanum, thickening of the
+clasped petioles--Fumaria--Adlumia--Plants which climb by the aid of
+their produced midribs--Gloriosa--Flagellaria--Nepenthes--Summary on
+leaf-climbers.
+
+We now come to our second class of climbing plants, namely, those
+which ascend by the aid of irritable or sensitive organs.  For
+convenience' sake the plants in this class have been grouped under
+two sub-divisions, namely, leaf-climbers, or those which retain their
+leaves in a functional condition, and tendril-bearers.  But these
+sub-divisions graduate into each other, as we shall see under
+Corydalis and the Gloriosa lily.
+
+It has long been observed that several plants climb by the aid of
+their leaves, either by their petioles (foot-stalks) or by their
+produced midribs; but beyond this simple fact they have not been
+described.  Palm and Mohl class these plants with those which bear
+tendrils; but as a leaf is generally a defined object, the present
+classification, though artificial, has at least some advantages.
+Leaf-climbers are, moreover, intermediate in many respects between
+twiners and tendril-bearers.  Eight species of Clematis and seven of
+Tropaeolum were observed, in order to see what amount of difference
+in the manner of climbing existed within the same genus; and the
+differences are considerable.
+
+CLEMATIS.--C. glandulosa.--The thin upper internodes revolve, moving
+against the course of the sun, precisely like those of a true twiner,
+at an average rate, judging from three revolutions, of 3 hrs. 48 m.
+The leading shoot immediately twined round a stick placed near it;
+but, after making an open spire of only one turn and a half, it
+ascended for a short space straight, and then reversed its course and
+wound two turns in an opposite direction.  This was rendered possible
+by the straight piece between the opposed spires having become rigid.
+The simple, broad, ovate leaves of this tropical species, with their
+short thick petioles, seem but ill-fitted for any movement; and
+whilst twining up a vertical stick, no use is made of them.
+Nevertheless, if the footstalk of a young leaf be rubbed with a thin
+twig a few times on any side, it will in the course of a few hours
+bend to that side; afterwards becoming straight again.  The under
+side seemed to be the most sensitive; but the sensitiveness or
+irritability is slight compared to that which we shall meet with in
+some of the following species; thus, a loop of string, weighing 1.64
+grain (106.2 mg.) and hanging for some days on a young footstalk,
+produced a scarcely perceptible effect.  A sketch is here given of
+two young leaves which had naturally caught hold of two thin
+branches.  A forked twig placed so as to press lightly on the under
+side of a young footstalk caused it, in 12 hrs., to bend greatly, and
+ultimately to such an extent that the leaf passed to the opposite
+side of the stem; the forked stick having been removed, the leaf
+slowly recovered its former position.
+
+The young leaves spontaneously and gradually change their position:
+when first developed the petioles are upturned and parallel to the
+stem; they then slowly bend downwards, remaining for a short time at
+right angles to the stem, and then become so much arched downwards
+that the blade of the leaf points to the ground with its tip curled
+inwards, so that the whole petiole and leaf together form a hook.
+They are thus enabled to catch hold of any twig with which they may
+be brought into contact by the revolving movement of the internodes.
+If this does not happen, they retain their hooked shape for a
+considerable time, and then bending upwards reassume their original
+upturned position, which is preserved ever afterwards.  The petioles
+which have clasped any object soon become much thickened and
+strengthened, as may be seen in the drawing.
+
+Clematis montana.--The long, thin petioles of the leaves, whilst
+young, are sensitive, and when lightly rubbed bend to the rubbed
+side, subsequently becoming straight.  They are far more sensitive
+than the petioles of C. glandulosa; for a loop of thread weighing a
+quarter of a grain (16.2 mg.) caused them to bend; a loop weighing
+only one-eighth of a grain (8.1 mg.) sometimes acted and sometimes
+did not act.  The sensitiveness extends from the blade of the leaf to
+the stem.  I may here state that I ascertained in all cases the
+weights of the string and thread used by carefully weighing 50 inches
+in a chemical balance, and then cutting off measured lengths.  The
+main petiole carries three leaflets; but their short, sub-petioles
+are not sensitive.  A young, inclined shoot (the plant being in the
+greenhouse) made a large circle opposed to the course of the sun in 4
+hrs. 20 m., but the next day, being very cold, the time was 5 hrs. 10
+m.  A stick placed near a revolving stem was soon struck by the
+petioles which stand out at right angles, and the revolving movement
+was thus arrested.  The petioles then began, being excited by the
+contact, to slowly wind round the stick.  When the stick was thin, a
+petiole sometimes wound twice round it.  The opposite leaf was in no
+way affected.  The attitude assumed by the stem after the petiole had
+clasped the stick, was that of a man standing by a column, who throws
+his arm horizontally round it.  With respect to the stem's power of
+twining, some remarks will be made under C. calycina.
+
+Clematis Sieboldi.--A shoot made three revolutions against the sun at
+an average rate of 3 hrs. 11 m.  The power of twining is like that of
+the last species.  Its leaves are nearly similar in structure and in
+function, excepting that the sub-petioles of the lateral and terminal
+leaflets are sensitive.  A loop of thread, weighing one-eighth of a
+grain, acted on the main petiole, but not until two or three days had
+elapsed.  The leaves have the remarkable habit of spontaneously
+revolving, generally in vertical ellipses, in the same manner, but in
+a less degree, as will be described under C. microphylla.
+
+Clematis calycina.--The young shoots are thin and flexible:  one
+revolved, describing a broad oval, in 5 hrs. 30 m., and another in 6
+hrs. 12 m.  They followed the course of the sun; but the course, if
+observed long enough, would probably be found to vary in this
+species, as well as in all the others of the genus.  It is a rather
+better twiner than the two last species:  the stem sometimes made two
+spiral turns round a thin stick, if free from twigs; it then ran
+straight up for a space, and reversing its course took one or two
+turns in an opposite direction.  This reversal of the spire occurred
+in all the foregoing species.  The leaves are so small compared with
+those of most of the other species, that the petioles at first seem
+ill-adapted for clasping.  Nevertheless, the main service of the
+revolving movement is to bring them into contact with surrounding
+objects, which are slowly but securely seized.  The young petioles,
+which alone are sensitive, have their ends bowed a little downwards,
+so as to be in a slight degree hooked; ultimately the whole leaf, if
+it catches nothing, becomes level.  I gently rubbed with a thin twig
+the lower surfaces of two young petioles; and in 2 hrs. 30 m. they
+were slightly curved downwards; in 5 hrs., after being rubbed, the
+end of one was bent completely back, parallel to the basal portion;
+in 4 hrs. subsequently it became nearly straight again.  To show how
+sensitive the young petioles are, I may mention that I just touched
+the under sides of two with a little water-colour, which when dry
+formed an excessively thin and minute crust; but this sufficed in 24
+hrs. to cause both to bend downwards.  Whilst the plant is young,
+each leaf consists of three divided leaflets, which barely have
+distinct petioles, and these are not sensitive; but when the plant is
+well grown, the petioles of the two lateral and terminal leaflets are
+of considerable length, and become sensitive so as to be capable of
+clasping an object in any direction.
+
+When a petiole has clasped a twig, it undergoes some remarkable
+changes, which may be observed with the other species, but in a less
+strongly marked manner, and will here be described once for all.  The
+clasped petiole in the course of two or three days swells greatly,
+and ultimately becomes nearly twice as thick as the opposite one
+which has clasped nothing.  When thin transverse slices of the two
+are placed under the microscope their difference is conspicuous:  the
+side of the petiole which has been in contact with the support, is
+formed of a layer of colourless cells with their longer axes directed
+from the centre, and these are very much larger than the
+corresponding cells in the opposite or unchanged petiole; the central
+cells, also, are in some degree enlarged, and the whole is much
+indurated.  The exterior surface generally becomes bright red.  But a
+far greater change takes place in the nature of the tissues than that
+which is visible:  the petiole of the unclasped leaf is flexible and
+can be snapped easily, whereas the clasped one acquires an
+extraordinary degree of toughness and rigidity, so that considerable
+force is required to pull it into pieces.  With this change, great
+durability is probably acquired; at least this is the case with the
+clasped petioles of Clematis vitalba.  The meaning of these changes
+is obvious, namely, that the petioles may firmly and durably support
+the stem.
+
+Clematis microphylla, var. leptophylla.--The long and thin internodes
+of this Australian species revolve sometimes in one direction and
+sometimes in an opposite one, describing long, narrow, irregular
+ellipses or large circles.  Four revolutions were completed within
+five minutes of the same average rate of 1 hr. 51 m.; so that this
+species moves more quickly than the others of the genus.  The shoots,
+when placed near a vertical stick, either twine round it, or clasp it
+with the basal portions of their petioles.  The leaves whilst young
+are nearly of the same shape as those of C. viticella, and act in the
+same manner like a hook, as will be described under that species.
+But the leaflets are more divided, and each segment whilst young
+terminates in a hardish point, which is much curved downwards and
+inwards; so that the whole leaf readily catches hold of any
+neighbouring object.  The petioles of the young terminal leaflets are
+acted on by loops of thread weighing 0.125th and even 0.0625th of a
+grain.  The basal portion of the main petiole is much less sensitive,
+but will clasp a stick against which it presses.
+
+The leaves, whilst young, are continually and spontaneously moving
+slowly.  A bell-glass was placed over a shoot secured to a stick, and
+the movements of the leaves were traced on it during several days.  A
+very irregular line was generally formed; but one day, in the course
+of eight hours and three quarters, the figure clearly represented
+three and a half irregular ellipses, the most perfect one of which
+was completed in 2 hrs. 35 m.  The two opposite leaves moved
+independently of each other.  This movement of the leaves would aid
+that of the internodes in bringing the petioles into contact with
+surrounding objects.  I discovered this movement too late to be
+enabled to observe it in the other species; but from analogy I can
+hardly doubt that the leaves of at least C. viticella, C. flammula,
+and C. vitalba move spontaneously; and, judging from C Sieboldi, this
+probably is the case with C. montana and C. calycina.  I ascertained
+that the simple leaves of C. glandulosa exhibited no spontaneous
+revolving movement.
+
+Clematis viticella, var. venosa.--In this and the two following
+species the power of spirally twining is completely lost, and this
+seems due to the lessened flexibility of the internodes and to the
+interference caused by the large size of the leaves.  But the
+revolving movement, though restricted, is not lost.  In our present
+species a young internode, placed in front of a window, made three
+narrow ellipses, transversely to the direction of the light, at an
+average rate of 2 hrs. 40 m.  When placed so that the movements were
+to and from the light, the rate was greatly accelerated in one half
+of the course, and retarded in the other, as with twining plants.
+The ellipses were small; the longer diameter, described by the apex
+of a shoot bearing a pair of not expanded leaves, was only 4.625
+inches, and that by the apex of the penultimate internode only 1.125
+inch.  At the most favourable period of growth each leaf would hardly
+be carried to and fro by the movement of the internodes more than two
+or three inches, but, as above stated, it is probable that the leaves
+themselves move spontaneously.  The movement of the whole shoot by
+the wind and by its rapid growth, would probably be almost equally
+efficient as these spontaneous movements, in bringing the petioles
+into contact with surrounding objects.
+
+The leaves are of large size.  Each bears three pairs of lateral
+leaflets and a terminal one, all supported on rather long sub-
+petioles.  The main petiole bends a little angularly downwards at
+each point where a pair of leaflets arises (see fig. 2), and the
+petiole of the terminal leaflet is bent downwards at right angles;
+hence the whole petiole, with its rectangularly bent extremity, acts
+as a hook.  This hook, the lateral petioles being directed a little
+upwards; forms an excellent grappling apparatus, by which the leaves
+readily become entangled with surrounding objects.  If they catch
+nothing, the whole petiole ultimately grows straight.  The main
+petiole, the sub-petioles, and the three branches into which each
+basi-lateral sub-petiole is generally subdivided, are all sensitive.
+The basal portion of the main petiole, between the stem and the first
+pair of leaflets, is less sensitive than the remainder; it will,
+however, clasp a stick with which it is left in contact.  The
+inferior surface of the rectangularly bent terminal portion (carrying
+the terminal leaflet), which forms the inner side of the end of the
+hook, is the most sensitive part; and this portion is manifestly best
+adapted to catch a distant support.  To show the difference in
+sensibility, I gently placed loops of string of the same weight (in
+one instance weighing only 0.82 of a grain or 53.14 mg.) on the
+several lateral sub-petioles and on the terminal one; in a few hours
+the latter was bent, but after 24 hrs. no effect was produced on the
+other sub-petioles.  Again, a terminal sub-petiole placed in contact
+with a thin stick became sensibly curved in 45 m., and in 1 hr. 10m.
+moved through ninety degrees; whilst a lateral sub-petiole did not
+become sensibly curved until 3 hrs. 30 m. had elapsed.  In all cases,
+if the sticks are taken away, the petioles continue to move during
+many hours afterwards; so they do after a slight rubbing; but they
+become straight again, after about a day's interval, that is if the
+flexure has not been very great or long continued.
+
+The graduated difference in the extension of the sensitiveness in the
+petioles of the above-described species deserves notice.  In C.
+montana it is confined to the main petiole, and has not spread to the
+sub-petioles of the three leaflets; so it is with young plants of C.
+calycina, but in older plants it spreads to the three sub-petioles.
+In C. viticella the sensitiveness has spread to the petioles of the
+seven leaflets, and to the subdivisions of the basi-lateral sub-
+petioles.  But in this latter species it has diminished in the basal
+part of the main petiole, in which alone it resided in C. montana;
+whilst it has increased in the abruptly bent terminal portion.
+
+Clematis flammula.--The rather thick, straight, and stiff shoots,
+whilst growing vigorously in the spring, make small oval revolutions,
+following the sun in their course.  Four were made at an average rate
+of 3 hrs. 45 m.  The longer axis of the oval, described by the
+extreme tip, was directed at right angles to the line joining the
+opposite leaves; its length was in one case only 1.375, and in
+another case 1.75 inch; so that the young leaves were moved a very
+short distance.  The shoots of the same plant observed in midsummer,
+when growing not so quickly, did not revolve at all.  I cut down
+another plant in the early summer, so that by August 1st it had
+formed new and moderately vigorous shoots; these, when observed under
+a bell-glass, were on some days quite stationary, and on other days
+moved to and fro only about the eighth of an inch.  Consequently the
+revolving power is much enfeebled in this species, and under
+unfavourable circumstances is completely lost.  The shoot must depend
+for coming into contact with surrounding objects on the probable,
+though not ascertained spontaneous movement of the leaves, on rapid
+growth, and on movement from the wind.  Hence, perhaps, it is that
+the petioles have acquired a high degree of sensitiveness as a
+compensation for the little power of movement in the shoots.
+
+The petioles are bowed downwards, and have the same general hook-like
+form as in C. viticella.  The medial petiole and the lateral sub-
+petioles are sensitive, especially the much bent terminal portion.
+As the sensitiveness is here greater than in any other species of the
+genus observed by me, and is in itself remarkable, I will give fuller
+details.  The petioles, when so young that they have not separated
+from one another, are not sensitive; when the lamina of a leaflet has
+grown to a quarter of an inch in length (that is, about one-sixth of
+its full size), the sensitiveness is highest; but at this period the
+petioles are relatively much more fully developed than are the blades
+of the leaves.  Full-grown petioles are not in the least sensitive.
+A thin stick placed so as to press lightly against a petiole, having
+a leaflet a quarter of an inch in length, caused the petiole to bend
+in 3 hrs. 15 m.  In another case a petiole curled completely round a
+stick in 12 hrs. These petioles were left curled for 24 hrs., and the
+sticks were then removed; but they never straightened themselves.  I
+took a twig, thinner than the petiole itself, and with it lightly
+rubbed several petioles four times up and down; these in 1 hr. 45 m.
+became slightly curled; the curvature increased during some hours and
+then began to decrease, but after 25 hrs. from the time of rubbing a
+vestige of the curvature remained.  Some other petioles similarly
+rubbed twice, that is, once up and once down, became perceptibly
+curved in about 2 hrs. 30 m., the terminal sub-petiole moving more
+than the lateral sub-petioles; they all became straight again in
+between 12 hrs. and 14 hrs.  Lastly, a length of about one-eighth of
+an inch of a sub-petiole, was lightly rubbed with the same twig only
+once; it became slightly curved in 3 hrs., remaining so during 11
+hrs., but by the next morning was quite straight.
+
+The following observations are more precise.  After trying heavier
+pieces of string and thread, I placed a loop of fine string, weighing
+1.04 gr. (67.4 mg.) on a terminal sub-petiole:  in 6 hrs. 40 m. a
+curvature could be seen; in 24 hrs. the petiole formed an open ring
+round the string; in 48 hrs. the ring had almost closed on the
+string, and in 72 hrs. seized it so firmly, that some force was
+necessary for its withdrawal.  A loop weighing 0.52 of a grain (33.7
+mg.) caused in 14 hrs. a lateral sub-petiole just perceptibly to
+curve, and in 24 hrs. it moved through ninety degrees.  These
+observations were made during the summer:  the following were made in
+the spring, when the petioles apparently are more sensitive:- A loop
+of thread, weighing one-eighth of a grain (8.1 mg.), produced no
+effect on the lateral sub-petioles, but placed on a terminal one,
+caused it, after 24 hrs., to curve moderately; the curvature, though
+the loop remained suspended, was after 48 hrs. diminished, but never
+disappeared; showing that the petiole had become partially accustomed
+to the insufficient stimulus.  This experiment was twice repeated
+with nearly the same result.  Lastly, a loop of thread, weighing only
+one-sixteenth of a grain (4.05 mg.) was twice gently placed by a
+forceps on a terminal sub-petiole (the plant being, of course, in a
+still and closed room), and this weight certainly caused a flexure,
+which very slowly increased until the petiole moved through nearly
+ninety degrees:  beyond this it did not move; nor did the petiole,
+the loop remaining suspended, ever become perfectly straight again.
+
+When we consider, on the one hand, the thickness and stiffness of the
+petioles, and, on the other hand, the thinness and softness of fine
+cotton thread, and what an extremely small weight one-sixteenth of a
+grain (4.05 mg.) is, these facts are remarkable.  But I have reason
+to believe that even a less weight excites curvature when pressing
+over a broader surface than that acted on by a thread.  Having
+noticed that the end of a suspended string which accidentally touched
+a petiole, caused it to bend, I took two pieces of thin twine, 10
+inches in length (weighing 1.64 gr.), and, tying them to a stick, let
+them hang as nearly perpendicularly downwards as their thinness and
+flexuous form, after being stretched, would permit; I then quietly
+placed their ends so as just to rest on two petioles, and these
+certainly became curved in 36 hrs. One of the ends touched the angle
+between a terminal and lateral sub-petiole, and it was in 48 hours
+caught between them as by a forceps.  In these cases the pressure,
+though spread over a wider surface than that touched by the cotton
+thread, must have been excessively slight.
+
+Clematis vitalba.--The plants were in pots and not healthy, so that I
+dare not trust my observations, which indicate much similarity in
+habits with C. flammula.  I mention this species only because I have
+seen many proofs that the petioles in a state of nature are excited
+to movement by very slight pressure.  For instance, I have found them
+embracing thin withered blades of grass, the soft young leaves of a
+maple, and the flower-peduncles of the quaking-grass or Briza.  The
+latter are about as thick as the hair of a man's beard, but they were
+completely surrounded and clasped.  The petioles of a leaf, so young
+that none of the leaflets were expanded, had partially seized a twig.
+Those of almost all the old leaves, even when unattached to any
+object, are much convoluted; but this is owing to their having come,
+whilst young, into contact during several hours with some object
+subsequently removed.  With none of the above-described species,
+cultivated in pots and carefully observed, was there any permanent
+bending of the petioles without the stimulus of contact.  In winter,
+the blades of the leaves of C. vitalba drop off; but the petioles (as
+was observed by Mohl) remain attached to the branches, sometimes
+during two seasons; and, being convoluted, they curiously resemble
+true tendrils, such as those possessed by the allied genus Naravelia.
+The petioles which have clasped some object become much more stiff,
+hard, and polished than those which have failed in this their proper
+function.
+
+TROPAEOLUM.--I observed T. tricolorum, T. azureum, T. pentaphyllum,
+T. peregrinum, T. elegans, T. tuberosum, and a dwarf variety of, as I
+believe, T. minus.
+
+Tropaeolum tricolorum, var. grandiflorum.--The flexible shoots, which
+first rise from the tubers, are as thin as fine twine.  One such
+shoot revolved in a course opposed to the sun, at an average rate,
+judging from three revolutions, of 1 hr. 23 m.; but no doubt the
+direction of the revolving movement is variable.  When the plants
+have grown tall and are branched, all the many lateral shoots
+revolve.  The stem, whilst young, twines regularly round a thin
+vertical stick, and in one case I counted eight spiral turns in the
+same direction; but when grown older, the stem often runs straight up
+for a space, and, being arrested by the clasping petioles, makes one
+or two spires in a reversed direction.  Until the plant grows to a
+height of two or three feet, requiring about a month from the time
+when the first shoot appears above ground, no true leaves are
+produced, but, in their place, filaments coloured like the stem.  The
+extremities of these filaments are pointed, a little flattened, and
+furrowed on the upper surface.  They never become developed into
+leaves.  As the plant grows in height new filaments are produced with
+slightly enlarged tips; then others, bearing on each side of the
+enlarged medial tip a rudimentary segment of a leaf; soon other
+segments appear, and at last a perfect leaf is formed, with seven
+deep segments.  So that on the same plant we may see every step, from
+tendril-like clasping filaments to perfect leaves with clasping
+petioles.  After the plant has grown to a considerable height, and is
+secured to its support by the petioles of the true leaves, the
+clasping filaments on the lower part of the stem wither and drop off;
+so that they perform only a temporary service.
+
+These filaments or rudimentary leaves, as well as the petioles of the
+perfect leaves, whilst young, are highly sensitive on all sides to a
+touch.  The slightest rub caused them to curve towards the rubbed
+side in about three minutes, and one bent itself into a ring in six
+minutes; they subsequently became straight.  When, however, they have
+once completely clasped a stick, if this is removed, they do not
+straighten themselves.  The most remarkable fact, and one which I
+have observed in no other species of the genus, is that the filaments
+and the petioles of the young leaves, if they catch no object, after
+standing for some days in their original position, spontaneously and
+slowly oscillate a little from side to side, and then move towards
+the stem and clasp it.  They likewise often become, after a time, in
+some degree spirally contracted.  They therefore fully deserve to be
+called tendrils, as they are used for climbing, are sensitive to a
+touch, move spontaneously, and ultimately contract into a spire,
+though an imperfect one.  The present species would have been classed
+amongst the tendril-bearers, had not these characters been confined
+to early youth.  During maturity it is a true leaf-climber.
+
+Tropaeolum azureum.--An upper internode made four revolutions,
+following the sun, at an average rate of 1 hr. 47 m.  The stem twined
+spirally round a support in the same irregular manner as that of the
+last species.  Rudimentary leaves or filaments do not exist.  The
+petioles of the young leaves are very sensitive:  a single light rub
+with a twig caused one to move perceptibly in 5 m., and another in 6
+m.  The former became bent at right angles in 15 min., and became
+straight again in between 5 hrs. and 6 hrs.  A loop of thread
+weighing 0.125th of a grain caused another petiole to curve.
+
+Tropaeolum pentaphyllum.--This species has not the power of spirally
+twining, which seems due, not so much to a want of flexibility in the
+stem, as to continual interference from the clasping petioles.  An
+upper internode made three revolutions, following the sun, at an
+average rate of 1 hr. 46 m.  The main purpose of the revolving
+movement in all the species of Tropaeolum manifestly is to bring the
+petioles into contact with some supporting object.  The petiole of a
+young leaf, after a slight rub, became curved in 6 m.; another, on a
+cold day, in 20 m., and others in from 8 m. to 10 m.  Their curvature
+usually increased greatly in from 15 m. to 20 m., and they became
+straight again in between 5 hrs. and 6 hrs., but on one occasion in 3
+hrs.  When a petiole has fairly clasped a stick, it is not able, on
+the removal of the stick, to straighten itself.  The free upper part
+of one, the base of which had already clasped a stick, still retained
+the power of movement.  A loop of thread weighing 0.125th of a grain
+caused a petiole to curve; but the stimulus was not sufficient, the
+loop remaining suspended, to cause a permanent flexure.  If a much
+heavier loop be placed in the angle between the petiole and the stem,
+it produces no effect; whereas we have seen with Clematis montana
+that the angle between the stem and petiole is sensitive.
+
+Tropaeolum peregrinum.--The first-formed internodes of a young plant
+did not revolve, resembling in this respect those of a twining plant.
+In an older plant the four upper internodes made three irregular
+revolutions, in a course opposed to the sun, at an average rate of 1
+hr. 48 min.  It is remarkable that the average rate of revolution
+(taken, however, but from few observations) is very nearly the same
+in this and the two last species, namely, 1 hr. 47 m., 1 hr. 46 m.,
+and 1 hr. 48 m.  The present species cannot twine spirally, which
+seems mainly due to the rigidity of the stem.  In a very young plant,
+which did not revolve, the petioles were not sensitive.  In older
+plants the petioles of quite young leaves, and of leaves as much as
+an inch and a quarter in diameter, are sensitive.  A moderate rub
+caused one to curve in 10 m., and others in 20 m.  They became
+straight again in between 5 hrs. 45m. and 8 hrs.  Petioles which have
+naturally come into contact with a stick, sometimes take two turns
+round it.  After they have clasped a support, they become rigid and
+hard.  They are less sensitive to a weight than in the previous
+species; for loops of string weighing 0.82 of a grain (53.14 mg.),
+did not cause any curvature, but a loop of double this weight (1.64
+gr.) acted.
+
+Tropaeolum elegans.--I did not make many observations on this
+species.  The short and stiff internodes revolve irregularly,
+describing small oval figures.  One oval was completed in 3 hrs. A
+young petiole, when rubbed, became slightly curved in 17 m.; and
+afterwards much more so.  It was nearly straight again in 8 hrs.
+
+Tropaeolum tuberosum.--On a plant nine inches in height, the
+internodes did not move at all; but on an older plant they moved
+irregularly and made small imperfect ovals.  These movements could be
+detected only by being traced on a bell-glass placed over the plant.
+Sometimes the shoots stood still for hours; during some days they
+moved only in one direction in a crooked line; on other days they
+made small irregular spires or circles, one being completed in about
+4 hrs.  The extreme points reached by the apex of the shoot were only
+about one or one and a half inches asunder; yet this slight movement
+brought the petioles into contact with some closely surrounding
+twigs, which were then clasped.  With the lessened power of
+spontaneously revolving, compared with that of the previous species,
+the sensitiveness of the petioles is also diminished.  These, when
+rubbed a few times, did not become curved until half an hour had
+elapsed; the curvature increased during the next two hours, and then
+very slowly decreased; so that they sometimes required 24 hrs. to
+become straight again.  Extremely young leaves have active petioles;
+one with the lamina only 0.15 of an inch in diameter, that is, about
+a twentieth of the full size, firmly clasped a thin twig.  But leaves
+grown to a quarter of their full size can likewise act.
+
+Tropaeolum minus (?).--The internodes of a variety named "dwarf
+crimson Nasturtium" did not revolve, but moved in a rather irregular
+course during the day to the light, and from the light at night.  The
+petioles, when well rubbed, showed no power of curving; nor could I
+see that they ever clasped any neighbouring object.  We have seen in
+this genus a gradation from species such as T. tricolorum, which have
+extremely sensitive petioles, and internodes which rapidly revolve
+and spirally twine up a support, to other species such as T. elegans
+and T. tuberosum, the petioles of which are much less sensitive, and
+the internodes of which have very feeble revolving powers and cannot
+spirally twine round a support, to this last species, which has
+entirely lost or never acquired these faculties.  From the general
+character of the genus, the loss of power seems the more probable
+alternative.
+
+In the present species, in T. elegans, and probably in others, the
+flower-peduncle, as soon as the seed-capsule begins to swell,
+spontaneously bends abruptly downwards and becomes somewhat
+convoluted.  If a stick stands in the way, it is to a certain extent
+clasped; but, as far as I have been able to observe, this clasping
+movement is independent of the stimulus from contact.
+
+ANTIRRHINEAE.--In this tribe (Lindley) of the Scrophulariaceae, at
+least four of the seven included genera have leaf-climbing species.
+
+Maurandia Barclayana.--A thin, slightly bowed shoot made two
+revolutions, following the sun, each in 3 hrs. 17 min.; on the
+previous day this same shoot revolved in an opposite direction.  The
+shoots do not twine spirally, but climb excellently by the aid of
+their young and sensitive petioles.  These petioles, when lightly
+rubbed, move after a considerable interval of time, and subsequently
+become straight again.  A loop of thread weighing 0.125th of a grain
+caused them to bend.
+
+Maurandia semperflorens.--This freely growing species climbs exactly
+like the last, by the aid of its sensitive petioles.  A young
+internode made two circles, each in 1 hr. 46 mm.; so that it moved
+almost twice as rapidly as the last species.  The internodes are not
+in the least sensitive to a touch or pressure.  I mention this
+because they are sensitive in a closely allied genus, namely,
+Lophospermum.  The present species is unique in one respect.  Mohl
+asserts (p. 45) that "the flower-peduncles, as well as the petioles,
+wind like tendrils;" but he classes as tendrils such objects as the
+spiral flower-stalks of the Vallisneria.  This remark, and the fact
+of the flower-peduncles being decidedly flexuous, led me carefully to
+examine them.  They never act as true tendrils; I repeatedly placed
+thin sticks in contact with young and old peduncles, and I allowed
+nine vigorous plants to grow through an entangled mass of branches;
+but in no one instance did they bend round any object.  It is indeed
+in the highest degree improbable that this should occur, for they are
+generally developed on branches which have already securely clasped a
+support by the petioles of their leaves; and when borne on a free
+depending branch, they are not produced by the terminal portion of
+the internode which alone has the power of revolving; so that they
+could be brought only by accident into contact with any neighbouring
+object.  Nevertheless (and this is the remarkable fact) the flower-
+peduncles, whilst young, exhibit feeble revolving powers, and are
+slightly sensitive to a touch.  Having selected some stems which had
+firmly clasped a stick by their petioles, and having placed a bell-
+glass over them, I traced the movements of the young flower-
+peduncles.  The tracing generally formed a short and extremely
+irregular line, with little loops in its course.  A young peduncle
+1.5 inch in length was carefully observed during a whole day, and it
+made four and a half narrow, vertical, irregular, and short ellipses-
+-each at an average rate of about 2 hrs. 25 m.  An adjoining peduncle
+described during the same time similar, though fewer, ellipses.  As
+the plant had occupied for some time exactly the same position, these
+movements could not be attributed to any change in the action of the
+light.  Peduncles, old enough for the coloured petals to be just
+visible, do not move.  With respect to irritability, {21} I rubbed
+two young peduncles (1.5 inch in length) a few times very lightly
+with a thin twig; one was rubbed on the upper, and the other on the
+lower side, and they became in between 4 hrs. and 5 hrs. distinctly
+bowed towards these sides; in 24 hrs. subsequently, they straightened
+themselves.  Next day they were rubbed on the opposite sides, and
+they became perceptibly curved towards these sides.  Two other and
+younger peduncles (three-fourths of an inch in length) were lightly
+rubbed on their adjoining sides, and they became so much curved
+towards one another, that the arcs of the bows stood at nearly right
+angles to their previous direction; and this was the greatest
+movement seen by me.  Subsequently they straightened themselves.
+Other peduncles, so young as to be only three-tenths of an inch in
+length, became curved when rubbed.  On the other hand, peduncles
+above 1.5 inch in length required to be rubbed two or three times,
+and then became only just perceptibly bowed.  Loops of thread
+suspended on the peduncles produced no effect; loops of string,
+however, weighing 0.82 and 1.64 of a grain sometimes caused a slight
+curvature; but they were never closely clasped, as were the far
+lighter loops of thread by the petioles.
+
+In the nine vigorous plants observed by me, it is certain that
+neither the slight spontaneous movements nor the slight sensitiveness
+of the flower-peduncles aided the plants in climbing.  If any member
+of the Scrophulariaceae had possessed tendrils produced by the
+modification of flower-peduncles, I should have thought that this
+species of Maurandia had perhaps retained a useless or rudimentary
+vestige of a former habit; but this view cannot be maintained.  We
+may suspect that, owing to the principle of correlation, the power of
+movement has been transferred to the flower-peduncles from the young
+internodes, and sensitiveness from the young petioles.  But to
+whatever cause these capacities are due, the case is interesting;
+for, by a little increase in power through natural selection, they
+might easily have been rendered as useful to the plant in climbing,
+as are the flower-peduncles (hereafter to be described) of Vitis or
+Cardiospermum.
+
+Rhodochiton volubile.--A long flexible shoot swept a large circle,
+following the sun, in 5 hrs. 30 m.; and, as the day became warmer, a
+second circle was completed in 4 hrs. 10 m.  The shoots sometimes
+make a whole or a half spire round a vertical stick, they then run
+straight up for a space, and afterwards turn spirally in an opposite
+direction.  The petioles of very young leaves about one-tenth of
+their full size, are highly sensitive, and bend towards the side
+which is touched; but they do not move quickly.  One was perceptibly
+curved in 1 hr. 10 m., after being lightly rubbed, and became
+considerably curved in 5 hrs. 40 m.; some others were scarcely curved
+in 5 hrs. 30 m., but distinctly so in 6 hrs. 30 m.  A curvature was
+perceptible in one petiole in between 4 hrs. 30 m. and 5 hrs., after
+the suspension of a little loop of string.  A loop of fine cotton
+thread, weighing one sixteenth of a grain (4.05 mg.), not only caused
+a petiole slowly to bend, but was ultimately so firmly clasped that
+it could be withdrawn only by some little force.  The petioles, when
+coming into contact with a stick, take either a complete or half a
+turn round it, and ultimately increase much in thickness.  They do
+not possess the power of spontaneously revolving.
+
+Lophospermum scandens, var. purpureum.--Some long, moderately thin
+internodes made four revolutions at an average rate of 3 hrs. 15 m.
+The course pursued was very irregular, namely, an extremely narrow
+ellipse, a large circle, an irregular spire or a zigzag line, and
+sometimes the apex stood still.  The young petioles, when brought by
+the revolving movement into contact with sticks, clasped them, and
+soon increased considerably in thickness.  But they are not quite so
+sensitive to a weight as those of the Rhodochiton, for loops of
+thread weighing one-eighth of a grain did not always cause them to
+bend.
+
+This plant presents a case not observed by me in any other leaf-
+climber or twiner, {22} namely, that the young internodes of the stem
+are sensitive to a touch.  When a petiole of this species clasps a
+stick, it draws the base of the internode against it; and then the
+internode itself bends towards the stick, which is caught between the
+stem and the petiole as by a pair of pincers.  The internode
+afterwards straightens itself, excepting the part in actual contact
+with the stick.  Young internodes alone are sensitive, and these are
+sensitive on all sides along their whole length.  I made fifteen
+trials by twice or thrice lightly rubbing with a thin twig several
+internodes; and in about 2 hrs., but in one case in 3 hrs., all were
+bent:  they became straight again in about 4 hrs. afterwards.  An
+internode, which was rubbed as often as six or seven times, became
+just perceptibly curved in 1 hr. 15 m., and in 3 hrs. the curvature
+increased much; it became straight again in the course of the
+succeeding night.  I rubbed some internodes one day on one side, and
+the next day either on the opposite side or at right angles to the
+first side; and the curvature was always towards the rubbed side.
+
+According to Palm (p. 63), the petioles of Linaria cirrhosa and, to a
+limited degree, those of L. elatine have the power of clasping a
+support.
+
+SOLANACEAE.--Solanum jasminoides.--Some of the species in this large
+genus are twiners; but the present species is a true leaf-climber.  A
+long, nearly upright shoot made four revolutions, moving against the
+sun, very regularly at an average rate of 3 hrs. 26 m.  The shoots,
+however, sometimes stood still.  It is considered a greenhouse plant;
+but when kept there, the petioles took several days to clasp a stick:
+in the hothouse a stick was clasped in 7 hrs.  In the greenhouse a
+petiole was not affected by a loop of string, suspended during
+several days and weighing 2.5 grains (163 mg.); but in the hothouse
+one was made to curve by a loop weighing 1.64 gr. (106.27 mg.); and,
+on the removal of the string, it became straight again.  Another
+petiole was not at all acted on by a loop weighing only 0.82 of a
+grain (53.14 mg.) We have seen that the petioles of some other leaf-
+climbing plants are affected by one-thirteenth of this latter weight.
+In this species, and in no other leaf-climber seen by me, a full-
+grown leaf is capable of clasping a stick; but in the greenhouse the
+movement was so extraordinarily slow that the act required several
+weeks; on each succeeding week it was clear that the petiole had
+become more and more curved, until at last it firmly clasped the
+stick.
+
+The flexible petiole of a half or a quarter grown leaf which has
+clasped an object for three or four days increases much in thickness,
+and after several weeks becomes so wonderfully hard and rigid that it
+can hardly be removed from its support.  On comparing a thin
+transverse slice of such a petiole with one from an older leaf
+growing close beneath, which had not clasped anything, its diameter
+was found to be fully doubled, and its structure greatly changed.  In
+two other petioles similarly compared, and here represented, the
+increase in diameter was not quite so great.  In the section of the
+petiole in its ordinary state (A), we see a semilunar band of
+cellular tissue (not well shown in the woodcut) differing slightly in
+appearance from that outside it, and including three closely
+approximate groups of dark vessels.  Near the upper surface of the
+petiole, beneath two exterior ridges, there are two other small
+circular groups of vessels.  In the section of the petiole (B) which
+had clasped during several weeks a stick, the two exterior ridges
+have become much less prominent, and the two groups of woody vessels
+beneath them much increased in diameter.  The semilunar band has been
+converted into a complete ring of very hard, white, woody tissue,
+with lines radiating from the centre.  The three groups of vessels,
+which, though near together, were before distinct, are now completely
+blended.  The upper part of this ring of woody vessels, formed by the
+prolongation of the horns of the original semilunar band, is narrower
+than the lower part, and slightly less compact.  This petiole after
+clasping the stick had actually become thicker than the stem from
+which it arose; and this was chiefly due to the increased thickness
+of the ring of wood.  This ring presented, both in a transverse and
+longitudinal section, a closely similar structure to that of the
+stem.  It is a singular morphological fact that the petiole should
+thus acquire a structure almost identically the same with that of the
+axis; and it is a still more singular physiological fact that so
+great a change should have been induced by the mere act of clasping a
+support. {23}
+
+FUMARIACEAE.--Fumaria officinalis.--It could not have been
+anticipated that so lowly a plant as this Fumaria should have been a
+climber.  It climbs by the aid of the main and lateral petioles of
+its compound leaves; and 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 become rather thicker and more cylindrical.  On
+lightly rubbing several petioles with a twig, they became perceptibly
+curved in 1 hr. 15 m., and subsequently straightened themselves.  A
+stick gently placed in the angle between two sub-petioles excited
+them to move, and was almost clasped in 9 hrs.  A loop of thread,
+weighing one-eighth of a grain, caused, after 12 hrs. and before 20
+hrs, had elapsed, a considerable curvature; but it was never fairly
+clasped by the petiole.  The young internodes are in continual
+movement, which is considerable in extent, but very irregular; a
+zigzag line, or a spire crossing itself; or a figure of 8 being
+formed.  The course during 12 hrs., when traced on a bell-glass,
+apparently represented about four ellipses.  The leaves themselves
+likewise move spontaneously, the main petioles curving themselves in
+accordance with the movements of the internodes; so that when the
+latter moved to one side, the petioles moved to the same side, then,
+becoming straight, reversed their curvature.  The petioles, however,
+do not move over a wide space, as could be seen when a shoot was
+securely tied to a stick.  The leaf in this case followed an
+irregular course, like that made by the internodes.
+
+Adlumia cirrhosa.--I raised some plants late in the summer; they
+formed very fine leaves, but threw up no central stem.  The first-
+formed leaves were not sensitive; some of the later ones were so, but
+only towards their extremities, which were thus enabled 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 have been, had it grown tall enough to climb.  The tip of
+one of these basal leaves, whilst young, described in 1 hr. 36 m. a
+narrow ellipse, open at one end, and exactly three inches in length;
+a second ellipse was broader, more irregular, and shorter, viz., only
+2.5 inches in length, and was completed in 2 hrs. 2 m.  From the
+analogy of Fumaria and Corydalis, I have no doubt that the internodes
+of Adlumia have the power of revolving.
+
+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 has been classed amongst
+tendril-bearers.
+
+Besides the plants already described, Bignonia unguis and its close
+allies, though aided by tendrils, have clasping petioles.  According
+to Mohl (p. 40), Cocculus Japonicus (one of the Menispermaceae) and a
+fern, the Ophioglossum Japonicum (p. 39), climb by their leaf-stalks.
+
+
+We now come to a small section of plants which climb by means of the
+produced midribs or tips of their leaves.
+
+LILIACEAE.--Gloriosa Plantii.--The stem of a half-grown plant
+continually moved, generally describing an irregular spire, but
+sometimes oval figures with the longer axes directed in different
+lines.  It either followed the sun, or moved in an opposite course,
+and sometimes stood still before reversing its direction.  One oval
+was completed in 3 hrs. 40 m.; of two horseshoe-shaped figures, one
+was completed in 4 hrs. 35 m. and the other in 3 hrs.  The shoots, in
+their 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 gets into an inclined position, the end bends
+downwards into a well-formed hook.  This hook is now strong and rigid
+enough to catch any object, and, when caught, to anchor the plant and
+stop the revolving movement.  Its inner surface is sensitive, but not
+in nearly so high a degree as that of the many before-described
+petioles; for a loop of string, weighing 1.64 grain, produced no
+effect.  When the hook has caught a thin twig or even a rigid fibre,
+the point may be perceived in from 1 hr. to 3 hrs. to have curled a
+little inwards; and, under favourable circumstances, it curls round
+and permanently seizes an object in from 8 hrs. to 10 hrs.  The hook
+when first formed, before the leaf has bent downwards, is but little
+sensitive.  If it catches hold of nothing, it remains open and
+sensitive for a long time; ultimately the extremity spontaneously and
+slowly curls inwards, and makes a button-like, flat, spiral coil at
+the end of the leaf.  One leaf was watched, and the hook remained
+open for thirty-three days; but during the last week the tip had
+curled so much inwards that only a very thin twig could have been
+inserted within it.  As soon as the tip has curled so much inwards
+that the hook is converted into a ring, its sensibility is lost; but
+as long as it remains open some sensibility is retained.
+
+Whilst the plant was only about six inches in height, the leaves,
+four or five in number, were broader than those subsequently
+produced; their soft and but little-attenuated tips were not
+sensitive, and did not form hooks; nor did the stem then revolve.  At
+this early period of growth, the plant can support itself; its
+climbing powers are not required, and consequently are not developed.
+So again, the leaves on the summit of a full-grown flowering plant,
+which would not require to climb any higher, were not sensitive and
+could not clasp a stick.  We thus see how perfect is the economy of
+nature.
+
+COMMELYNACEAE.--Flagellaria Indica.--From dried specimens it is
+manifest that this plant climbs exactly like the Gloriosa.  A young
+plant 12 inches in height, and bearing fifteen leaves, had not a
+single leaf as yet produced into a hook or tendril-like filament; nor
+did the stem revolve.  Hence this plant acquires its climbing powers
+later in life than does the Gloriosa lily.  According to Mohl (p.
+41), Uvularia (Melanthaceae) also climbs like Gloriosa.
+
+These three last-named genera are Monocotyledons; but there is one
+Dicotyledon, namely Nepenthes, which is ranked by Mohl (p. 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 coiling round any support.  The
+twisted part becomes thicker; but I observed in Mr. Veitch's hothouse
+that the stalk often takes a turn when not in contact with any
+object, and that this twisted part is likewise thickened.  Two
+vigorous young plants of N. laevis and N. distillatoria, in my
+hothouse, whilst less than a foot in height, showed no sensitiveness
+in their leaves, and had no power of climbing.  But when N. laevis
+had grown to a height of 16 inches, there were signs of these powers.
+The young leaves when first formed stand upright, but soon become
+inclined; at this period they terminate in a stalk or filament, with
+the pitcher at the extremity hardly at all developed.  The leaves now
+exhibited slight spontaneous movements; and when the terminal
+filaments came into contact with a stick, they slowly bent round and
+firmly seized it.  But owing to the subsequent growth of the leaf,
+this filament became after a time quite slack, though still remaining
+firmly coiled round the stick.  Hence it would appear that the chief
+use of the coiling, at least whilst the plant is young, is to support
+the pitcher with its load of secreted fluid.
+
+
+Summary on Leaf-climbers.--Plants belonging to eight families are
+known to have clasping petioles, and plants belonging to four
+families climb by the tips of their leaves.  In all the species
+observed by me, with one exception, the young internodes revolve more
+or less regularly, in some cases as regularly as those of a twining
+plant.  They revolve at various rates, in most cases rather rapidly.
+Some few can ascend by spirally twining round a support.  Differently
+from most twiners, there is a strong tendency in the same shoot to
+revolve first in one and then in an opposite direction.  The object
+gained by the revolving movement is to bring the petioles or the tips
+of the leaves into contact with surrounding objects; and without this
+aid the plant would be much less successful in climbing.  With rare
+exceptions, the petioles are sensitive only whilst young.  They are
+sensitive on all sides, but in different degrees in different plants;
+and in some species of Clematis the several parts of the same petiole
+differ much in sensitiveness.  The hooked tips of the leaves of the
+Gloriosa are sensitive only on their inner or inferior surfaces.  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 (4.05 mg.); and there is reason to believe that
+the rather thick and stiff petioles of Clematis flammula are
+sensitive to even much less weight if spread over a wide surface.
+The petioles always bend towards the side which is pressed or
+touched, at different rates in different species, 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 accustomed to the
+stimulus, and either bends no more or becomes straight again, the
+weight still remaining suspended.  Petioles which have clasped an
+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 throughout their whole diameter or
+on one side alone; they subsequently become stronger and more woody,
+sometimes to a wonderful degree; and in some cases they acquire an
+internal structure like that of the stem or axis.
+
+The young internodes of the Lophospermum as well as the petioles are
+sensitive to a touch, and by their combined movement seize an object.
+The flower-peduncles of the Maurandia semperflorens revolve
+spontaneously and are sensitive to a touch, yet are not used for
+climbing.  The leaves of at least two, and probably of most, of the
+species of Clematis, of Fumaria and Adlumia, spontaneously curve from
+side to side, like the internodes, and are thus better adapted to
+seize distant objects.  The petioles of the perfect leaves of
+Tropaeolum tricolorum, as well as the tendril-like filaments of the
+plants whilst young, ultimately move towards the stem or the
+supporting stick, which they then clasp.  These petioles and
+filaments also show some tendency to contract spirally.  The tips of
+the uncaught leaves of the Gloriosa, as they grow old, contract into
+a flat spire or helix.  These several facts are interesting in
+relation to true tendrils.
+
+With leaf climbers, as with twining plants, the first internodes
+which rise from the ground do not, at least in the cases observed by
+me, spontaneously revolve; nor are the petioles or tips of the first-
+formed leaves sensitive.  In certain species of Clematis, the large
+size of the leaves, together with their habit of revolving, and the
+extreme sensitiveness of their petioles, appear to render the
+revolving movement of the internodes superfluous; and this latter
+power has consequently become much enfeebled.  In certain species of
+Tropaeolum, both the spontaneous movements of the internodes and the
+sensitiveness of the petioles have become much enfeebled, and in one
+species have been completely lost.
+
+
+
+CHAPTER III.--TENDRIL-BEARERS.
+
+
+
+Nature of tendrils--BIGNONIACEAE, various species of, and their
+different modes of climbing--Tendrils which avoid the light and creep
+into crevices--Development of adhesive discs--Excellent adaptations
+for seizing different kinds of supports.--POLEMONIACEAE--Cobaea
+scandens much branched and hooked tendrils, their manner of action--
+LEGUMINOSAE--COMPOSITAE--SMILACEAE--Smilax aspera, its inefficient
+tendrils--FUMARIACEAE--Corydalis claviculata, its state intermediate
+between that of a leaf-climber and a tendril-bearer.
+
+By tendrils I mean filamentary organs, sensitive to contact and used
+exclusively for climbing.  By this definition, spines, 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, branches, {24} and perhaps stipules.
+Mohl, who includes under the name of tendrils various organs having a
+similar external appearance, classes them according to their
+homological nature, as being modified leaves, flower-peduncles, &c.
+This would be an excellent scheme; but I observe that botanists are
+by no means unanimous on the homological nature of certain tendrils.
+Consequently I will describe tendril-bearing plants by natural
+families, following Lindley's classification; and this will in most
+cases keep those of the same nature together.  The species to be
+described belong to ten families, and will be given in the following
+order: --Bignoniaceae, Polemoniaceae, Leguminosae, Compositae,
+Smilaceae, Fumariaceae, Cucurbitaceae, Vitaceae, Sapindaceae,
+Passifloraceae. {25}
+
+BIGNONIACEAE.--This family contains many tendril-bearers, some
+twiners, and some root-climbers.  The tendrils always consist of
+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 within the same genus, and to show what
+remarkable powers some tendrils possess.  The species, taken
+together, afford connecting links between twiners, leaf-climbers,
+tendril-bearers, and root-climbers.
+
+Bignonia (an unnamed species from Kew, closely allied to B. unguis,
+but with smaller and rather broader leaves).--A young shoot from a
+cut-down plant made three revolutions against the sun, at an average
+rate of 2 hrs. 6m.  The stem is thin and flexible; it twined round a
+slender vertical stick, ascending from left to right, as perfectly
+and as regularly as any true twining-plant.  When thus ascending, it
+makes no use of its tendrils or petioles; but when it twined round a
+rather thick stick, and its petioles were brought into contact with
+it, these curved round the stick, showing that they have some degree
+of irritability.  The petioles also exhibit a slight degree of
+spontaneous movement; for in one case they certainly described
+minute, irregular, vertical ellipses.  The tendrils apparently curve
+themselves spontaneously to the same side with the petioles; but from
+various causes, it was difficult to observe the movement of either
+the tendrils or petioles, in this and the two following species.  The
+tendrils are so closely similar in all respects to those of B.
+unguis, that one description will suffice.
+
+Bignonia unguis.--The young shoots revolve, but less regularly and
+less quickly than those of the last species.  The stem twines
+imperfectly round a vertical stick, sometimes reversing its
+direction, in the same manner as described in so many leaf-climbers;
+and this plant though possessing tendrils, climbs to a certain extent
+like a leaf-climber.  Each leaf consists of a petiole bearing a pair
+of leaflets, and terminates in a tendril, which is formed by the
+modification of three leaflets, and closely resembles that above
+figured (fig. 5).  But it is a little larger, and in a young plant
+was about half an inch in length.  It is curiously like 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 are of equal length, and
+diverging, lie in the same plane.  The toes terminate in sharp, hard
+claws, much curved downwards, like those on a bird's foot.  The
+petiole of the leaf is sensitive to contact; even a small loop of
+thread suspended for two days caused it to bend upwards; but the sub-
+petioles of the two lateral leaflets are not sensitive.  The whole
+tendril, namely, the tarsus and the three toes, are likewise
+sensitive to contact, especially on their under surfaces.  When a
+shoot grows in the midst of thin branches, the tendrils are soon
+brought by the revolving movement of the internodes into contact with
+them; and then one toe of the tendril or more, commonly all three,
+bend, and after several hours seize fast hold of the twigs, like a
+bird when perched.  If the tarsus of the tendril comes into contact
+with a twig, it goes on slowly bending, until the whole foot is
+carried quite round, and the toes pass on each side of the tarsus and
+seize it.  In like manner, if the petiole comes into contact with a
+twig, it bends round, carrying the tendril, which then seizes its own
+petiole or that of the opposite leaf.  The petioles move
+spontaneously, and thus, when a shoot attempts to twine round an
+upright stick, those on both sides after a time come into contact
+with it, and are excited to bend.  Ultimately the two petioles clasp
+the stick in opposite directions, and the foot-like tendrils, seizing
+on each other or on their own petioles, fasten the stem to the
+support with surprising security.  The tendrils are thus brought into
+action, if the stem twines round a thin vertical stick; and in this
+respect the present species differs from the last.  Both species use
+their tendrils in the same manner when passing through a thicket.
+This plant is one of the most efficient climbers which I have
+observed; 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 moderately well, though not vigorously, I
+concluded that the tendrils acted only like the hooks on a bramble,
+and that it was the most feeble and inefficient of all climbers!
+
+Bignonia Tweedyana.--This species is closely allied to the last, and
+behaves in the same manner; but perhaps twines rather better round a
+vertical stick.  On the same plant, one branch twined in one
+direction and another in an opposite direction.  The internodes in
+one case made two circles, each in 2 hrs. 33 m.  I was enabled to
+observe the spontaneous movements of the petioles better in this than
+in the two preceding species:  one petiole described three small
+vertical ellipses in the course of 11 hrs., whilst another moved in
+an irregular spire.  Some little time after a stem has twined round
+an upright stick, and is securely fastened to it by the clasping
+petioles and tendrils, it emits aerial roots from the bases of its
+leaves; and these roots curve partly round and adhere to the stick.
+This species of Bignonia, therefore, combines four different methods
+of climbing generally characteristic of distinct plants, namely,
+twining, leaf-climbing, tendril-climbing, and root-climbing.
+
+In the three foregoing species, when the foot-like tendril has caught
+an object, it continues to grow and thicken, and ultimately becomes
+wonderfully strong, in the same manner as 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, and drops off
+like a leaf in autumn.  I have seen this process of disarticulation
+in no other tendrils, for these, when they fail to catch an object,
+merely wither away.
+
+Bignonia venusta.--The tendrils differ considerably from those of the
+previous species.  The lower part, or tarsus, is four times as long
+as the three toes; these are of equal length and diverge equally, but
+do not lie in the same plane; their tips are bluntly hooked, and the
+whole tendril makes an excellent grapnel.  The tarsus is sensitive on
+all sides; but the three toes are sensitive only on their outer
+surfaces.  The sensitiveness is not much developed; for a slight
+rubbing with a twig did not cause the tarsus or the toes to become
+curved until an hour had elapsed, and then only in a slight degree.
+Subsequently they straightened themselves.  Both the tarsus and toes
+can seize well hold of sticks.  If the stem is secured, the tendrils
+are seen spontaneously to sweep large ellipses; the two opposite
+tendrils moving independently of one another.  I have no doubt, from
+the analogy of the two following allied species, that the petioles
+also move spontaneously; but they are not irritable like those of B.
+unguis and B. Tweedyana.  The young internodes sweep large circles,
+one being completed in 2 hrs. 15 m., and a second in 2 hrs. 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 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 completed circle.
+
+The tendrils contract spirally a short time after catching any
+object; those which catch nothing merely bend slowly downwards.  But
+the whole subject of the spiral contraction of tendrils will be
+discussed after all the tendril-bearing species have been described.
+
+Bignonia littoralis.--The young internodes revolve in large ellipses.
+An internode bearing immature tendrils made two revolutions, each in
+3 hrs. 50 m.; but when grown older with the tendrils mature, it made
+two ellipses, each at the rate of 2 hrs. 44 m.  This species, unlike
+the preceding, is incapable of twining round a stick:  this does not
+appear to be due to any want of flexibility in the internodes or to
+the action of the tendrils, and certainly not to any want of the
+revolving power; nor can I account for the fact.  Nevertheless the
+plant readily ascends a thin upright stick by seizing a point above
+with its two opposite tendrils, which then contract spirally.  If the
+tendrils seize nothing, they do not become spiral.
+
+The species last described, ascended a vertical stick by twining
+spirally and by seizing it alternately with its opposite tendrils,
+like a sailor pulling himself up a rope, hand over hand; the present
+species pulls itself up, like a sailor seizing with both hands
+together a rope above his head.
+
+The tendrils are similar in structure to those of the last species.
+They continue growing for some time, even after they have clasped an
+object.  When fully grown, though borne by a young plant, they are 9
+inches in length.  The three divergent toes are shorter relatively to
+the tarsus than in the former species; they are blunt at their tips
+and but slightly hooked; they are not quite equal in length, the
+middle one being rather longer than the others.  Their outer surfaces
+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
+hrs. they became straight again and were ready to re-act.  The
+tarsus, for the space of one inch close to the toes, is sensitive,
+but in a rather less degree than the toes; for the latter after a
+slight rubbing, became curved in about half the time.  Even the
+middle part of the tarsus is sensitive to prolonged contact, as soon
+as the tendril has arrived at maturity.  After it has grown old, the
+sensitiveness is confined to the toes, and these are only able to
+curl very slowly round a stick.  A tendril is perfectly ready to act,
+as soon as the three toes have diverged, and at this period their
+outer surfaces first become irritable.  The irritability spreads but
+little from one part when excited to another:  thus, when a stick was
+caught by the part immediately beneath the three toes, these seldom
+clasped it, but remained sticking straight out.
+
+The tendrils revolve spontaneously.  The movement begins before the
+tendril is converted into a three-pronged grapnel by the divergence
+of the toes, and before any part has become sensitive; so that the
+revolving movement is useless at this early period.  The movement is,
+also, now slow, two ellipses being completed conjointly in 24 hrs. 18
+m.  A mature tendril made an ellipse in 6 hrs.; so that it moved much
+more slowly than the internodes.  The ellipses which were swept, both
+in a vertical and horizontal plane, were of large size.  The petioles
+are not in the least sensitive, but revolve like the tendrils.  We
+thus see that the young internodes, the petioles, and the tendrils
+all continue revolving together, but at different rates.  The
+movements of the tendrils which rise opposite one another are quite
+independent.  Hence, when the whole shoot is allowed freely to
+revolve, nothing can be more intricate than the course followed by
+the extremity of each tendril.  A wide space is thus irregularly
+searched for some object to be grasped.
+
+One other curious point remains to be mentioned.  In the course of a
+few days after the toes have closely clasped a stick, their blunt
+extremities become developed, though not invariably, into irregular
+disc-like balls which have the power of adhering firmly to the wood.
+As similar cellular outgrowths will be fully described under B.
+capreolata, I will here say nothing more about them.
+
+Bignonia aequinoctialis, var. Chamberlaynii.--The internodes, the
+elongated non-sensitive petioles, and the tendrils all revolve.  The
+stem does not twine, but ascends a vertical stick in the same manner
+as the last species.  The tendrils also resemble those of the last
+species, but are shorter; the three toes are more unequal in length,
+the two outer ones being about one-third shorter and rather thinner
+than the middle toe; but they vary in this respect.  They terminate
+in small hard points; and what is important, cellular adhesive discs
+are not developed.  The reduced size of two of the toes as well as
+their lessened sensitiveness, seem to indicate a tendency to
+abortion; and on one of my plants the first-formed tendrils were
+sometimes simple, that is, were not divided into three toes.  We are
+thus naturally led to the three following species with undivided
+tendrils
+
+Bignonia speciosa.--The young shoots revolve irregularly, making
+narrow ellipses, spires or circles, at rates varying from 3 hrs. 30
+m. to 4 hrs. 40 m.; but they show no tendency to twine.  Whilst the
+plant is young and does not require a support, tendrils are not
+developed.  Those borne by a moderately young plant were five inches
+in length.  They revolve spontaneously, as do the short and non-
+sensitive petioles.  When rubbed, they slowly bend to the rubbed side
+and subsequently straighten themselves; but they are not highly
+sensitive.  There is something strange in their behaviour:  I
+repeatedly placed close to them, thick and thin, rough and smooth
+sticks and posts, as well as string suspended vertically, but none of
+these objects were well seized.  After clasping an upright stick,
+they repeatedly loosed it again, and often would not seize it at all,
+or their extremities did not coil closely round.  I have observed
+hundreds of tendrils belonging to various Cucurbitaceous,
+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.  They now seized a
+thin, upright stick horizontally, that is, at a point on their own
+level, and not some way up the stick as in the case of all the
+previous species.  Nevertheless, the non-twining stem was enabled by
+this means to ascend the stick.
+
+The extremity of the tendril is almost straight and sharp.  The whole
+terminal portion exhibits a singular habit, which in an animal would
+be called an instinct; for it continually searches for any little
+crevice or hole into which to insert itself.  I had two young plants;
+and, after having observed this habit, I placed near them posts,
+which had been bored by beetles, or had become fissured by 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; in order to effect this the
+extremity for a length of half or quarter of an inch, would often
+bend 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
+hole.  I have also seen a tendril keep its point, in one case for 20
+hrs. and in another for 36 hrs., in a minute hole, and then withdraw
+it.  Whilst the point is thus temporarily inserted, the opposite
+tendril goes on revolving.
+
+The whole length of a tendril often fits itself closely to any
+surface of wood with which it has come into contact; and I have
+observed one bent at right angles, from having entered a wide and
+deep fissure, with its apex abruptly re-bent and inserted into a
+minute lateral hole.  After a tendril has clasped a stick, it
+contracts spirally; if it remains unattached it hangs straight
+downwards.  If it has merely adapted itself to the inequalities of a
+thick post, though it has clasped nothing, or if it has inserted its
+apex into some little fissure, this stimulus suffices to induce
+spiral contraction; but the contraction always draws the tendril away
+from the post.  So that in every case these movements, which seem so
+nicely adapted for some purpose, were useless.  On one occasion,
+however, the tip became permanently jammed into a narrow fissure.  I
+fully expected, from the analogy of B. capreolata and B. littoralis,
+that the tips would have been developed into adhesive discs; but I
+could never detect even a trace of this process.  There is therefore
+at present something unintelligible about the habits of this plant.
+
+Bignonia picta.--This species closely resembles the last in the
+structure and movements of its tendrils.  I also casually examined a
+fine growing plant of the allied B. Lindleyi, and this apparently
+behaved in all respects in the same manner.
+
+Bignonia capreolata.--We now come to a species having tendrils 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
+hrs. 23 m.  The stem is thin and flexible, and I have seen one make
+four regular spiral turns round a thin upright stick, ascending of
+course from right to left, and therefore in a reversed direction
+compared with the before described species.  Afterwards, from the
+interference of the tendrils, it ascended either straight up the
+stick or in an irregular spire.  The tendrils are in some respects
+highly remarkable.  In a young plant they were about 2.5 inches in
+length and much branched, the five chief branches apparently
+representing two pairs of leaflets and a terminal one.  Each branch
+is, however, bifid or more commonly trifid towards the extremity,
+with the points blunt yet distinctly hooked.  A tendril bends to any
+side which is lightly rubbed, and subsequently becomes straight
+again; but a loop of thread weighing 0.25th of a grain produced no
+effect.  On two occasions the terminal branches became slightly
+curved in 10 m. after they had touched a stick; and in 30 m. the tips
+were curled quite round it.  The basal part is less sensitive.  The
+tendrils revolved in an apparently capricious manner, sometimes very
+slightly or not at all; at other times they described large regular
+ellipses.  I could detect no spontaneous movement in the petioles of
+the leaves.
+
+Whilst the tendrils are revolving more or less regularly, another
+remarkable movement takes place, namely, a slow inclination from the
+light towards the darkest side of the house.  I repeatedly changed
+the position of my plants, and some little time after the revolving
+movement had ceased, the successively formed tendrils always ended by
+pointing to the darkest side.  When I placed a thick post near a
+tendril, between it and the light, the tendril pointed in that
+direction.  In two instances a pair of leaves stood so that one of
+the two tendrils was directed towards the light and the other to the
+darkest side of the house; the latter did not move, but the opposite
+one bent itself first upwards and then right over its fellow, so that
+the two became parallel, one above the other, both pointing to the
+dark:  I then turned the plant half round; and the tendril which had
+turned over recovered its original position, and the opposite one
+which had not before moved, now turned over to the dark side.
+Lastly, on another plant, three pairs of tendrils were produced at
+the same time by three shoots, and all happened to be differently
+directed:  I placed the pot in a box open only on one side, and
+obliquely facing the light; in two days all six tendrils pointed with
+unerring truth to the darkest corner of the box, though to do this
+each had to bend in a different manner.  Six wind-vanes could not
+have more truly shown the direction of the wind, than did these
+branched tendrils the course of the stream of light which entered the
+box.  I left these tendrils undisturbed for above 24 hrs., and then
+turned the pot half round; but they had now lost their power of
+movement, and could not any longer avoid the light.
+
+When a tendril has not succeeded in clasping a support, either
+through its own revolving movement or that of the shoot, or by
+turning towards any object which intercepts the light, 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 seizes an object, all the branches contract
+spirally.
+
+I have stated that after a tendril has come into contact with a
+stick, it bends round it in about half an hour; but I repeatedly
+observed, as in the case of B. speciosa and its allies, that it often
+again loosed the stick; sometimes seizing and loosing the same stick
+three or four times.  Knowing that the tendrils avoided the light, I
+gave them a glass tube blackened within, and a well-blackened zinc
+plate:  the branches curled round the tube and abruptly bent
+themselves round the edges of the zinc plate; but they soon recoiled
+from these objects with what I can only call disgust, and
+straightened themselves.  I then placed a post with extremely rugged
+bark close to a pair of tendrils; twice they touched it for an hour
+or two, and twice they withdrew; at last one of the hooked
+extremities curled round and firmly seized an excessively minute
+projecting point of bark, and then the other branches spread
+themselves out, following with accuracy every inequality of the
+surface.  I afterwards placed near the plant a post without bark but
+much fissured, and the points of the tendrils crawled into all the
+crevices in a beautiful manner.  To my surprise, I observed that the
+tips of the immature 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 minute points,
+the final process, now to be described, commenced.
+
+This process I discovered by having accidentally left a piece of wool
+near a tendril; and this led me to bind a quantity of flax, moss, and
+wool loosely round sticks, and to place them near tendrils.  The wool
+must not be dyed, for these tendrils are excessively sensitive to
+some poisons.  The hooked points soon caught hold of the fibres, even
+loosely floating fibres, and now there was no recoiling; on the
+contrary, the excitement caused the hooks to penetrate the fibrous
+mass and to curl inwards, so that each hook caught firmly 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 were
+visibly enlarged.  After a few more days the hooks were converted
+into whitish, irregular balls, rather above the 0.05th of an inch
+(1.27 mm.) in diameter, 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 cellular 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, adhered
+firmly together.  As the whole surface of the ball continues to grow,
+fresh fibres adhere and are afterwards enveloped; so that I have seen
+a little ball with between fifty and sixty fibres of flax crossing it
+at various angles and all embedded more or less deeply.  Every
+gradation in the process could be followed--some fibres merely
+sticking to the surface, others lying in more or less deep furrows,
+or deeply embedded, or passing through the very centre of the
+cellular ball.  The embedded fibres are so closely clasped that they
+cannot be withdrawn.  The outgrowing tissue has so strong a tendency
+to unite, that two balls produced by distinct tendrils sometimes
+unite and grow into a single one.
+
+On one occasion, when a tendril had curled round a stick, half an
+inch in diameter, an adhesive disc was formed; but this does not
+generally occur in the case of smooth sticks or posts.  If, however,
+the tip catches a minute projecting point, the other branches form
+discs, especially if they find crevices to crawl into.  The tendrils
+failed to attach themselves to a brick wall.
+
+I infer from the adherence of the fibres to the discs or balls, that
+these secrete some resinous adhesive matter; and more especially from
+such fibres becoming loose if immersed in sulphuric ether.  This
+fluid likewise removes small, brown, glistening points which can
+generally be seen on the surfaces of the older discs.  If the hooked
+extremities of the tendrils do not touch anything, discs, as far as I
+have seen, are never formed; {26} but temporary contact during a
+moderate time suffices to cause their development.  I have seen eight
+discs formed on the same tendril.  After their development the
+tendrils contract spirally, and 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 discs were attached yielded.
+
+From the facts now given, we may 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 other such productions;
+and I hear from Professor Asa Gray that the Polypodium incanum
+abounds on the forest-trees in the districts of North America where
+this species of Bignonia grows.  Finally, I may remark how singular a
+fact it is that a leaf should be 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 afterwards forming cellular outgrowths
+which secrete an adhesive cement, and then envelop by their continued
+growth the finest fibres.
+
+Eccremocarpus scaber (Bignoniaceae).--Plants, though growing pretty
+well in my green-house, showed no spontaneous movements in their
+shoots or tendrils; but when removed to the hot-house, the young
+internodes revolved at rates varying from 3 hrs. 15 m. to 1 hr. 13 m.
+One large circle was swept at this latter unusually quick rate; but
+generally the circles or ellipses were small, and sometimes the
+course pursued was quite irregular.  An internode, after making
+several revolutions, sometimes stood still for 12 hrs. or 18 hrs.,
+and then recommenced revolving.  Such strongly marked interruptions
+in the movements of the internodes I have observed in hardly any
+other plant.
+
+The leaves bear four leaflets, themselves subdivided, and terminate
+in much-branched tendrils.  The main petiole of the leaf, whilst
+young, moves spontaneously, and follows nearly the same irregular
+course and at about the same rate as the internodes.  The movement to
+and from the stem is the most conspicuous, and I have seen the chord
+of a curved petiole which formed an angle of 59 degrees with the
+stem, in an hour afterwards making an angle of 106 degrees.  The two
+opposite petioles do not move together, and one is sometimes so much
+raised as to stand close to the stem, whilst the other is not far
+from horizontal.  The basal part of the petiole moves less than the
+distal part.  The tendrils, besides being carried by the moving
+petioles and internodes, themselves move spontaneously; and the
+opposite tendrils occasionally move in opposite directions.  By these
+combined movements of the young internodes, petioles, and tendrils, a
+considerable space is swept in search of a support.
+
+In young plants the tendrils are about three inches in length:  they
+bear two lateral and two terminal branches; and each branch
+bifurcates twice, with the tips terminating in blunt double hooks,
+having both points directed to the same side.  All the branches are
+sensitive on all sides; and after being lightly rubbed, or after
+coming into contact with a stick, bend in about 10 m.  One which had
+become curved in 10 m. after a light rub, continued bending for
+between 3 hrs. and 4 hrs., and became straight again in 8 hrs. or 9
+hrs.  Tendrils, which have caught nothing, ultimately contract into
+an irregular spire, as they likewise do, only much more quickly,
+after clasping a support.  In both cases the main petiole bearing the
+leaflets, which is at first straight and inclined a little upwards,
+moves downwards, with the middle part bent abruptly into a right
+angle; but this is seen in E. miniatus more plainly than in E.
+scaber.  The tendrils in this genus act in some respects like those
+of Bignonia capreolata; but the whole does not move from the light,
+nor do the hooked tips become enlarged into cellular discs.  After
+the tendrils have come into contact with a moderately thick
+cylindrical stick or with rugged bark, the several branches may be
+seen slowly to lift themselves up, change their positions, and again
+come into contact with the supporting surface.  The object of these
+movements is to bring the double-hooks at the extremities of the
+branches, which naturally face in all directions, into contact with
+the wood.  I have watched a tendril, half of which had bent itself at
+right angles round the sharp corner of a square post, neatly bring
+every single hook into contact with both rectangular surfaces.  The
+appearance suggested the belief, that though the whole tendril is not
+sensitive to light, yet that the tips are so, and that they turn and
+twist themselves towards any dark surface.  Ultimately the branches
+arrange themselves very neatly to all the irregularities 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
+wound round a rather thick stick, the subsequent spiral contraction
+generally draws it away and spoils the neat arrangement.  So it is,
+but not in quite so marked a manner, when a tendril has spread itself
+over a large, nearly flat surface of rugged bark.  We may therefore
+conclude that these tendrils are not perfectly adapted to seize
+moderately thick sticks or rugged bark.  If a thin stick or twig is
+placed near a tendril, the terminal branches wind quite round it, and
+then seize their own lower branches or the main stem.  The stick is
+thus firmly, but not neatly, grasped.  What the tendrils are really
+adapted for, appears to be such objects as the thin culms of certain
+grasses, or the long flexible bristles of a brush, or thin rigid
+leaves such as those of the Asparagus, all of which they seize in an
+admirable manner.  This is due to the extremities of the branches
+close to the little hooks being extremely sensitive to a touch from
+the thinnest object, which they consequently curl round and clasp.
+When a small brush, for instance, was placed near a tendril, the tips
+of each sub-branch seized one, two, or three of the bristles; 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, which afforded an excellent support.
+
+POLEMONIACEAE.--Cobaea scandens.--This is an excellently constructed
+climber.  The tendrils on a fine plant were eleven inches long, with
+the petiole bearing two pairs of leaflets, only two and a half inches
+in length.  They revolve more rapidly and vigorously than those of
+any other tendril-bearer observed by me, with the exception of one
+kind of Passiflora.  Three large, nearly circular sweeps, directed
+against the sun were completed, each in 1 hr. 15 m.; and two other
+circles in 1 hr. 20 m. and 1 hr. 23 m.  Sometimes a tendril travels
+in a much inclined position, and sometimes nearly upright.  The lower
+part moves but little and the petiole not at all; nor do the
+internodes revolve; so that here we have the tendril alone moving.
+On the other hand, with most of the species of Bignonia and the
+Eccremocarpus, the internodes, tendrils, and petioles all revolved.
+The long, straight, tapering main stem of the tendril of the Cobaea
+bears alternate branches; and each branch is several times divided,
+with the finer branches as thin as very thin bristles and extremely
+flexible, so that they are blown about by a breath of air; yet they
+are strong and highly elastic.  The extremity of each branch is a
+little flattened, and terminates in a minute double (though sometimes
+single) hook, formed of a hard, translucent, woody substance, and as
+sharp as the finest needle.  On a tendril which was eleven inches
+long I counted ninety-four of these beautifully constructed little
+hooks.  They readily catch soft wood, or gloves, or the skin of the
+naked hand.  With the exception of these hardened hooks, and of the
+basal part of the central stem, every part of every branchlet is
+highly sensitive on all sides to a slight touch, and bends in a few
+minutes towards the touched side.  By lightly rubbing several sub-
+branches on opposite sides, the whole tendril rapidly assumed an
+extraordinarily crooked shape.  These movements from contact do not
+interfere with the ordinary revolving 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, spiral contraction likewise begins after an unusually
+short interval of time, namely, in about twelve hours.
+
+Before the tendril is mature, the terminal branchlets cohere, and the
+hooks are curled closely inwards.  At this period no part is
+sensitive to a touch; but as soon as the branches diverge and the
+hooks stand out, full sensitiveness is acquired.  It is a singular
+circumstance that immature tendrils revolve at their full velocity
+before they become sensitive, but in a useless manner, as in this
+state they can catch nothing.  This want of perfect co-adaptation,
+though only for a short time, between the structure and the functions
+of a climbing-plant is a rare event.  A tendril, as soon as it is
+ready to act, stands, together with the supporting petiole,
+vertically upwards.  The leaflets borne by the petiole are at this
+time quite small, and the extremity of the growing stem is bent to
+one side so as to be out of the way of the revolving tendril, which
+sweeps large circles directly over head.  The tendrils thus revolve
+in a position well adapted for catching objects standing above; and
+by this means the ascent of the plant is favoured.  If no object is
+caught, the leaf with its tendril bends downwards and ultimately
+assumes a horizontal position.  An open space is thus left for the
+next succeeding and younger tendril to stand vertically upwards and
+to revolve freely.  As soon as an old tendril bends downwards, it
+loses all power of movement, and contracts spirally into an entangled
+mass.  Although the tendrils revolve with unusual rapidity, the
+movement lasts for only a short time.  In a plant placed in the hot-
+house and growing vigorously, a tendril revolved for not longer than
+36 hours, counting from the period when it first became sensitive;
+but during this period it probably made at least 27 revolutions.
+
+When a revolving tendril strikes against a stick, the branches
+quickly bend round and clasp it.  The little hooks here play an
+important part, as they prevent the branches from being dragged away
+by the rapid revolving movement, before they have had time to clasp
+the stick securely.  This is especially the case when only the
+extremity of a branch has caught hold of a support.  As soon as a
+tendril has bent a smooth stick or a thick rugged post, or has come
+into contact with planed wood (for it can adhere temporarily even to
+so smooth a surface as this), the same peculiar movements may be
+observed as those described under Bignonia capreolata and
+Eccremocarpus.  The branches repeatedly lift themselves up and down;
+those which have their hooks already directed downwards remaining in
+this position and securing the tendril, whilst the others twist about
+until they succeed in arranging themselves in conformity with every
+irregularity of the surface, and in bringing their hooks into contact
+with the wood.  The use of the hooks was well shown by giving the
+tendrils tubes and slips of glass to catch; for these, though
+temporarily seized, were invariably lost, either during the re-
+arrangement of the branches or ultimately when spiral contraction
+ensued.
+
+The perfect manner in which the branches arranged themselves,
+creeping like rootlets over every inequality of the surface and into
+any deep crevice, is a pretty sight; for it is perhaps more
+effectually performed by this than by any other species.  The action
+is certainly more conspicuous, as the upper surfaces of the main
+stem, as well as of every branch to the extreme hooks, are angular
+and green, whilst the lower surfaces are rounded and purple.  I was
+led to infer, as in former cases, that a less amount of light guided
+these movements of the branches of the tendrils.  I made many trials
+with black and white cards and glass tubes to prove it, but failed
+from various causes; yet these trials countenanced the belief.  As a
+tendril consists of a leaf split into numerous segments, there is
+nothing surprising in all the segments turning their upper surfaces
+towards the light, as soon as the tendril is caught and the revolving
+movement is arrested.  But this will not account for the whole
+movement, for the segments actually bend or curve to the dark side
+besides turning round on their axes so that their upper surfaces may
+face the light.
+
+When the Cobaea grows in the open air, the wind must aid the
+extremely flexible tendrils in seizing a support, for I found that a
+mere breath sufficed to cause the extreme branches to catch hold by
+their hooks of twigs, which they could not have reached by the
+revolving movement.  It might have been thought that a tendril, thus
+hooked by the extremity of a single branch, could not have fairly
+grasped its support.  But several times I watched cases like the
+following:  tendril caught a thin stick by the hooks of one of its
+two extreme branches; though thus held by the tip, it still tried to
+revolve, bowing itself to all sides, and by this movement the other
+extreme branch soon caught the stick.  The first branch then loosed
+itself, and, arranging its hooks, again caught hold.  After a time,
+from the continued movement of the tendril, the hooks of a third
+branch caught hold.  No other branches, as the tendril then stood,
+could possibly have touched the stick.  But before long the upper
+part of the main stem began to contract into an open spire.  It thus
+dragged the shoot which bore the tendril towards the stick; and as
+the tendril continually tried to revolve, a fourth branch was brought
+into contact.  And lastly, from the spiral contraction travelling
+down both the main stem and the branches, all of them, one after
+another, were ultimately brought into contact with the stick.  They
+then wound themselves round it and round one another, until the whole
+tendril was tied together in an inextricable knot.  The tendrils,
+though at first quite flexible, after having clasped a support for a
+time, become more rigid and stronger than they were at first.  Thus
+the plant is secured to its support in a perfect manner.
+
+LEGUMINOSAE.--Pisum sativum.--The common pea was the subject of a
+valuable memoir by Dutrochet, {27} who discovered that the internodes
+and tendrils revolve 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 wider space.  Owing to this
+change of direction, and likewise to the movement of the stem towards
+the light, the successive irregular ellipses generally form an
+irregular spire.  I have thought it worth while to annex a tracing of
+the course pursued by the upper internode (the movement of the
+tendril being neglected) of a young plant from 8.40 A.M. to 9.15 P.M.
+The course was traced on a hemispherical glass placed over the plant,
+and the dots with figures give the hours of observation; each dot
+being joined by a straight line.  No doubt all the lines would have
+been curvilinear if the course had been observed at much shorter
+intervals.  The extremity of the petiole, from which the young
+tendril arose, was two inches from the glass, so that if a pencil two
+inches in length could have been 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 reduced by one-half.
+Neglecting the first great sweep towards the light from the figure 1
+to 2, the end of the petiole swept a space 4 inches across in one
+direction, and 3 inches in another.  As a full-grown tendril is
+considerably above two inches in length, and as the tendril itself
+bends and revolves in harmony with the internode, a considerably
+wider space is swept than is here represented on a reduced scale.
+Dutrochet observed the completion of an ellipse in 1 hr. 20 m.; and I
+saw one completed in 1 hr. 30 m.  The direction followed is variable,
+either with or against the sun.
+
+Dutrochet asserts that the petioles of the leaves spontaneously
+revolve, as well as the young internodes and tendrils; but he does
+not say that he secured the internodes; when this was done, I could
+never detect any movement in the petiole, except to and from the
+light.
+
+The tendrils, on the other hand, when the internodes and petioles are
+secured, describe irregular spires or regular ellipses, exactly like
+those made by the internodes.  A young tendril, only 1.125 of an 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 sensitive tendrils, and tied the
+petiole so that the tendril alone could move; it completed a perfect
+ellipse in 1 hr. 30 m.; I then turned the plant partly round, but
+this made no change in the direction of the succeeding ellipse.  The
+next day I watched a plant similarly secured until the tendril (which
+was highly sensitive) made an ellipse in a line exactly to and from
+the light; the movement was so great that the tendril at the two ends
+of its elliptical course bent itself 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
+no longer curved in harmony together, owing to inequality of age.
+
+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 concave surface near the
+tip caused them to bend quickly, as did occasionally a loop of thread
+weighing one-seventh of a grain (9.25 mg.).  The upper or convex
+surface is barely or not at all sensitive.  Tendrils, after bending
+from a touch, straighten themselves in about two hours, and are then
+ready to act again.  As soon as they begin to grow old, the
+extremities of their two or three pairs of branches become hooked,
+and they then appear to form an excellent grappling instrument; but
+this is not the case.  For at this period they have generally quite
+lost their sensitiveness; and when hooked on to twigs, some were not
+at all affected, and others required from 18 hrs. to 24 hrs. before
+clasping such twigs; nevertheless, they were able to utilise the last
+vestige of irritability owing to their extremities being hooked.
+Ultimately the lateral branches contract spirally, but not the middle
+or main stem.
+
+Lathyrus aphaca.--This plant is destitute of leaves, except during a
+very early age, these being replaced by tendrils, and the leaves
+themselves by large stipules.  It might therefore have been expected
+that the tendrils would have been highly organized, but this is not
+so.  They are moderately long, thin, and unbranched, with their tips
+slightly curved.  Whilst young they are sensitive on all sides, but
+chiefly on the concave side of the extremity.  They have no
+spontaneous revolving power, but are at first inclined upwards at an
+angle of about 45 degrees, then move into a horizontal position, and
+ultimately bend downwards.  The young internodes, on the other hand,
+revolve in ellipses, and carry with them the tendrils.  Two ellipses
+were completed, each in nearly 5 hrs.; their longer axes were
+directed at about an angle of 45 degrees to the axis of the
+previously made ellipse.
+
+Lathyrus grandiflorus.--The plants observed were young and not
+growing vigorously, yet sufficiently so, I think, for my observations
+to be trusted.  If so, we have the rare case of neither internodes
+nor tendrils revolving.  The tendrils of vigorous plants are above 4
+inches in length, and are often twice divided into three branches;
+the tips are curved and are sensitive on their concave sides; the
+lower part of the central stem is hardly at all sensitive.  Hence
+this plant appears to climb simply by its tendrils being brought,
+through the growth of the stem, or more efficiently by the wind, into
+contact with surrounding objects, which they then clasp.  I may add
+that the tendrils, or the internodes, or both, of Vicia sativa
+revolve.
+
+COMPOSITAE.--Mutisia clematis.--The immense family of the Compositae
+is well known to include very few climbing plants.  We have seen in
+the Table in the first chapter that Mikania scandens is a regular
+twiner, and F. Muller informs me that in S. Brazil there is another
+species which is a leaf-climber.  Mutisia is the only genus in the
+family, as far as I can learn, which bears tendrils:  it is therefore
+interesting to find that these, though rather less metamorphosed from
+their primordial foliar condition than are most other tendrils, yet
+display all the ordinary characteristic movements, both those that
+are spontaneous and those which are excited by contact.
+
+The long leaf bears seven or eight alternate leaflets, and terminates
+in a tendril which, in a plant of considerable size, was 5 inches in
+length.  It consists generally of three branches; and these, although
+much elongated, evidently represent the petioles and midribs of three
+leaflets; for they closely resemble the same parts in an ordinary
+leaf, in being rectangular on the upper surface, furrowed, and edged
+with green.  Moreover, the green edging of the tendrils of young
+plants sometimes expands into a narrow lamina or blade.  Each branch
+is curved a little downwards, and is slightly hooked at the
+extremity.
+
+A young upper internode revolved, judging from three revolutions, at
+an average rate of 1 hr. 38 m.; it swept ellipses with the longer
+axes directed at right angles to one another; but the plant,
+apparently, cannot twine.  The petioles and the tendrils are both in
+constant movement.  But their movement is slower and much less
+regularly elliptical than that of the internodes.  They appear to be
+much affected by the light, for the whole leaf usually sinks down
+during the night and rises during the day, moving, also, during the
+day in a crooked course to the west.  The tip of the tendril is
+highly sensitive on the lower surface; and one which was just touched
+with a twig became perceptibly curved in 3 m., and another in 5 m.;
+the upper surface is not at all sensitive; the sides are moderately
+sensitive, so that two branches which were rubbed on their inner
+sides converged and crossed each other.  The petiole of the leaf and
+the lower parts of the tendril, halfway between the upper leaflet and
+the lowest branch, are not sensitive.  A tendril after curling from a
+touch became straight again in about 6 hrs., and was ready to re-act;
+but one that had been so roughly rubbed as to have coiled into a
+helix did not become perfectly straight until after 13 hrs.  The
+tendrils retain their sensibility to an unusually late age; for one
+borne by a leaf with five or six fully developed leaves above, was
+still active.  If a tendril catches nothing, after a considerable
+interval of time the tips of the branches curl a little inwards; but
+if it clasps some object, the whole contracts spirally.
+
+SMILACEAE.--Smilax aspera, var. maculata.--Aug. St.-Hilaire {28}
+considers that the tendrils, which rise in pairs from the petiole,
+are modified lateral leaflets; but Mohl (p. 41) ranks them as
+modified stipules.  These tendrils are from 1.5 to 1.75 inches in
+length, are thin, and have slightly curved, pointed extremities.
+They diverge a little from each other, and 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 when placed in contact with a stick became just
+perceptibly curved in 1 hr. 20 m., but did not completely surround it
+until 48 hrs. had elapsed; the concave side of another became
+considerably curved in 2 hrs. and clasped a stick in 5 hrs.  As the
+pairs of tendrils grow old, one tendril diverges more and more from
+the other, and both slowly bend backwards and downwards, so that
+after a time they project on the opposite side of the stem to that
+from which they arise.  They then still retain their sensitiveness,
+and can clasp a support placed BEHIND the stem.  Owing to this power,
+the plant is able to ascend a thin upright stick.  Ultimately the two
+tendrils belonging to the same petiole, if they do not come into
+contact with any object, loosely cross each other behind the stem, as
+at B, in fig. 7.  This movement of the tendrils towards and round the
+stem is, to a certain extent, guided by their avoidance of the light;
+for when a plant stood so that one of the two tendrils was compelled
+in thus slowly moving to travel towards the light, and the other from
+the light, the latter always moved, as I repeatedly observed, more
+quickly than its fellow.  The tendrils do not contract 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, as we have just seen, is guided, to a certain
+extent, by the avoidance of the light; 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 is a
+less perfect climber than any other tendril-bearing species observed
+by me.  The plant whilst young and only a few inches in height, does
+not produce any tendrils; and considering that it grows to only about
+8 feet in height, 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 these are.
+The plant might have been left, one would have thought, to climb by
+the aid of its spines alone, like our brambles.  As, however, it
+belongs to a genus, some of the species of which are furnished with
+much longer tendrils, we may suspect that it possesses these organs
+solely from being descended from progenitors more highly organized in
+this respect.
+
+FUMARIACEAE.--Corydalis claviculata.--According to Mohl (p. 43), the
+extremities of the branched stem, as well as the leaves, 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 a widely different homological
+nature.  Nevertheless, from this statement by Mohl, I have ranked
+this species amongst the tendril-bearers; if classed exclusively by
+its foliar tendrils, it would be doubtful whether it ought not to
+have been placed amongst the leaf-climbers, with its allies, Fumaria
+and Adlumia.  A large majority of its so-called tendrils still bear
+leaflets, though excessively reduced in size; but some few of them
+may properly be designated as tendrils, for they are completely
+destitute of laminae 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 rather young, only the outer leaves, but
+when full-grown all the leaves, have their extremities converted into
+more or less perfect 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
+structure represented in the following drawing.  This leaf bore nine
+leaflets; the lower ones being much subdivided.  The terminal portion
+of the petiole, about 1.5 inch in length (above the leaflet f), is
+thinner and more elongated than the lower part, and may 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 (2.116 mm. and 0.339 mm.), so
+that it was almost microscopically minute.  All the reduced leaflets
+have branching nerves, and terminate in little spines, like those of
+the fully developed leaflets.  Every gradation could 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 condition, and we then have a
+true tendril.
+
+The several terminal branches of the petiole bearing the much reduced
+leaflets (a, b, c, d) are highly sensitive, for a loop of thread
+weighing only the one-sixteenth of a grain (4.05 mg.) caused them to
+become greatly curved in under 4 hrs.  When the loop was removed, the
+petioles straightened themselves in about the same time.  The petiole
+(e) was rather less sensitive; and in another specimen, in which the
+corresponding petiole bore rather larger leaflets, a loop of thread
+weighing one-eighth of a grain did not cause curvature until 18 hrs.
+had elapsed.  Loops of thread weighing one-fourth of a grain, left
+suspended on the lower petioles (f to l) during several days,
+produced no effect.  Yet the three petioles f, g, and h were not
+quite insensible, for when left in contact with a stick for a day or
+two they slowly curled round it.  Thus the sensibility of the petiole
+gradually diminishes from the tendril-like extremity to the base.
+The internodes of the stem are not at all sensitive, which makes
+Mohl's statement that they are sometimes converted into tendrils the
+more surprising, not to say improbable.
+
+The whole leaf, whilst young and sensitive, stands almost vertically
+upwards, as we have seen to be the case with many tendrils.  It is in
+continual movement, and one that I observed swept at an average rate
+of about 2 hrs. for each revolution, large, though irregular,
+ellipses, which were sometimes narrow, sometimes broad, with their
+longer axes directed to different points of the compass.  The young
+internodes, likewise revolved irregularly in ellipses or spires; so
+that by these combined movements a considerable space was swept for a
+support.  If the terminal and attenuated portion of a petiole fails
+to seize any object, it ultimately bends downwards and inwards, and
+soon loses all irritability and power of movement.  This bending down
+differs much in nature from that which occurs with the extremities of
+the young leaves in many species of Clematis; for these, when thus
+bent downwards or hooked, first acquire their full degree of
+sensitiveness.
+
+Dicentra thalictrifolia.--In this allied plant the metamorphosis of
+the terminal leaflets is complete, and they are converted into
+perfect tendrils.  Whilst the plant is young, the tendrils appear
+like modified branches, and a distinguished botanist thought that
+they were of this nature; but in a full-grown plant there can be no
+doubt, as I am assured by Dr. Hooker, that they are modified leaves.
+When of full size, they are above 5 inches in length; they bifurcate
+twice, thrice, or even four times; their extremities are hooked and
+blunt.  All the branches of the tendrils are sensitive on all sides,
+but the basal portion of the main stem is only slightly so.  The
+terminal branches when lightly rubbed with a twig became curved in
+the course of from 30 m. to 42 m., and straightened themselves in
+between 10 hrs. and 20 hrs.  A loop of thread weighing one-eighth of
+a grain plainly caused the thinner branches to bend, as did
+occasionally a loop weighing one-sixteenth of a grain; but this
+latter weight, though left suspended, was not sufficient to cause a
+permanent flexure.  The whole leaf with its tendril, as well as the
+young upper internodes, revolves vigorously and quickly, though
+irregularly, and thus sweeps 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, and this was completed in 1 hr. 53 m.  During a
+period of 6 hrs. 17 m. another shoot made a complex figure,
+apparently representing 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 done in so perfect a
+manner by some Bignoniaceae and Cobaea.  The tendrils of young
+plants, two or three feet in height, are only half the length of
+those borne by the same plant when grown taller, and they do not
+contract spirally after clasping a support, but only become slightly
+flexuous.  Full-sized tendrils, on the other hand, contract spirally,
+with the exception of 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 is angularly and abruptly bent
+downwards like that of Eccremocarpus.
+
+
+
+CHAPTER IV.--TENDRIL-BEARERS--(continued).
+
+
+
+CUCURBITACEAE.--Homologous nature of the tendrils--Echinocystis
+lobata, remarkable movements of the tendrils to avoid seizing the
+terminal shoot--Tendrils not excited by contact with another tendril
+or by drops of water--Undulatory movement of the extremity of the
+tendril--Hanburya, adherent discs--VITACAE--Gradation between the
+flower-peduncles and tendrils of the vine--Tendrils of the Virginian
+Creeper turn from the light, and, after contact, develop adhesive
+discs--SAPINDACEAE--PASSIFLORACEAE--Passiflora gracilis--Rapid
+revolving movement and sensitiveness of the tendrils--Not sensitive
+to the contact of other tendrils or of drops of water--Spiral
+contraction of tendrils--Summary on the nature and action of
+tendrils.
+
+CUCURBITACEAE.--The tendrils in this family have been ranked by
+competent judges as modified leaves, stipules, or branches; or as
+partly a leaf and partly a branch.  De Candolle believes that the
+tendrils differ in their homological nature in two of the tribes.
+{29}  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;" but much may be said in favour of the
+belief that it is a modified flower-peduncle. {30}
+
+Echinocystis lobata.--Numerous observations were made on this plant
+(raised from seed sent me by Prof. Asa Gray), for the spontaneous
+revolving movements of the internodes and tendrils were first
+observed by me in this case, and greatly perplexed me.  My
+observations may now be much condensed.  I observed thirty-five
+revolutions of the internodes and tendrils; the slowest rate was 2
+hrs. and the average rate, with no great fluctuations, 1 hr. 40 m.
+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 an opposite direction.  Sometimes the movement during a short time
+would either stop or be reversed; and this apparently was due to
+interference from the light, as, for instance, when I placed a plant
+close to a window.  In one instance, an old tendril, which had nearly
+ceased revolving, moved in one direction, whilst a young tendril
+above moved in an opposite course.  The two uppermost internodes
+alone revolve; and as soon as the lower one grows old, only its upper
+part continues to move.  The ellipses or circles swept by the summits
+of the internodes are about three inches in diameter; whilst those
+swept by the tips of the tendrils, are from 15 to 16 inches in
+diameter.  During the revolving movement, the internodes become
+successively curved to all points of the compass; in one part of
+their course they are often inclined, together with the tendrils, at
+about 45 degrees to the horizon, and in another part stand vertically
+up.  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 cutting off the latter with sharp
+scissors, the top of the shoot rose only a little, and went on
+revolving.  This false appearance is apparently due to the internodes
+and tendrils all curving and moving harmoniously together.
+
+A revolving tendril, though inclined during the greater part of its
+course at an angle of about 45 degrees (in one case of only 37
+degrees) above the horizon, stiffened and straightened itself from
+tip to base in a certain part of its course, thus becoming nearly or
+quite vertical.  I witnessed this repeatedly; and it occurred both
+when the supporting internodes were free and when they were tied up;
+but was perhaps most conspicuous in the latter case, or when the
+whole shoot happened to be much inclined.  The tendril forms a very
+acute angle with the projecting extremity of the stem or shoot; and
+the stiffening always occurred as the tendril approached, and had to
+pass over the shoot in its circular course.  If it had not possessed
+and exercised this curious power, it would infallibly have struck
+against the extremity of the shoot and been arrested.  As soon as the
+tendril with its three branches begins to stiffen itself in this
+manner and to rise from an inclined into a vertical position, the
+revolving motion becomes more rapid; and as soon as the tendril has
+succeeded in passing over the extremity of the shoot or point of
+difficulty, its motion, coinciding with that from its weight, often
+causes it to fall into its previously inclined position so quickly,
+that the apex could be 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 and 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 to be the case
+with other species of the family by Mohl (p. 65).  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 the tendrils which had been rubbed on the
+concave side had straightened themselves, I reversed the process of
+rubbing, and always with the same result.  After touching the concave
+side, the tip becomes sensibly curved in one or two minutes; and
+subsequently, if the touch has been at all rough, it coils itself
+into a helix.  But the helix will, after a time, straighten itself,
+and be again ready to act.  A loop of thin thread only one-sixteenth
+of a grain in weight caused a temporary flexure.  The lower part was
+repeatedly rubbed rather roughly, but no curvature ensued; yet this
+part is sensitive to prolonged pressure, for when it came into
+contact with a stick, it would slowly wind round it.
+
+One of my plants bore two shoots near together, and the tendrils were
+repeatedly drawn across one another, but it is a singular fact that
+they did not once catch each other.  It would appear as if they had
+become habituated to contact of this kind, for the pressure thus
+caused must have been much greater than that caused by a loop of soft
+thread weighing only the one-sixteenth of a grain.  I have, however,
+seen several tendrils of Bryonia dioica interlocked, but they
+subsequently released one another.  The tendrils of the Echinocystis
+are also habituated to drops of water or to rain; for artificial rain
+made by violently flirting a wet brush over them produced not the
+least effect.
+
+The revolving movement of a tendril is not stopped by the curving of
+its extremity after it has been touched.  When one of the lateral
+branches has firmly clasped an object, the middle branch continues to
+revolve.  When a stem is bent down and secured, so that the tendril
+depends but is left free to move, its previous revolving movement is
+nearly or quite stopped; but it soon begins to bend upwards, and as
+soon as it has become horizontal the revolving movement recommences.
+I tried this four times; the tendril generally rose to a horizontal
+position in an hour or an hour and a half; but in one case, in which
+a tendril depended at an angle of 45 degrees beneath the horizon, the
+uprising took two hours; in half an hour afterwards it rose to 23
+degrees above the horizon and then recommenced revolving.  This
+upward movement is independent of the action of light, for it
+occurred twice in the dark, and on another occasion the light came 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
+germinating seeds.
+
+A tendril does not long retain its revolving power; and as soon as
+this is lost, it bends downwards and contracts spirally.  After the
+revolving movement has ceased, the tip still retains for a short time
+its sensitiveness to contact, but this can be of little or no use 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 that the tip
+managed in the course of a few hours to curl twice or even thrice
+round the stick.  I at first thought that this was due to rapid
+growth on the outside; but by coloured points and measurements I
+proved that there had been no sensible increase of length within the
+time.  When a stick, flat on one side, was similarly placed, the tip
+of the tendril could not curl beyond the flat surface, but coiled
+itself into a helix, which, turning to one side, lay flat on the
+little flat surface of wood.  In one instance a portion of tendril
+three-quarters of an inch in length was thus dragged on to the flat
+surface by the coiling in of the helix.  But the tendril thus
+acquires a very insecure hold, and generally after a time slips off.
+In one case alone the helix subsequently uncoiled itself, and the tip
+then passed round and clasped the stick.  The formation of the helix
+on the flat side of the 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 observed several times through a lens that the
+whole surface was not in close contact with the stick; and I can
+understand the onward progress only by supposing that the movement is
+slightly undulatory or vermicular, and that the tip alternately
+straightens itself a little and then again curls inwards.  It thus
+drags 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
+with its extreme point, can work itself onwards until it has passed
+twice or even thrice round the stick, and has permanently grasped it.
+
+Hanburya Mexicana.--The young internodes and tendrils of this
+anomalous member of the family, revolve in the same manner and at
+about the same rate as those of 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 it had become
+rapidly coiled into a ring owing to a single touch, it straightened
+itself in 50 m.  The tendril, when in full action, stands vertically
+up, with the projecting extremity of the young stem thrown a little
+on one side, so as to be out of the way; but the tendril bears on the
+inner side, near its base, a short rigid branch, which projects out
+at right angles like a spur, with the terminal half bowed a little
+downwards.  Hence, as the main vertical branch revolves, the spur,
+from its position and rigidity, cannot pass over the extremity of the
+shoot, in the same curious manner as do the three branches of the
+tendril of the Echinocystis, namely, by stiffening themselves at the
+proper point.  The spur is therefore pressed laterally against the
+young stem in one part of the revolving course, and thus the sweep of
+the lower part of the main branch is much restricted.  A nice case of
+co-adaptation here comes into play:  in all the other tendrils
+observed by me, the several branches become sensitive at the same
+period:  had this been the case with the Hanburya, the inwardly
+directed, spur-like branch, from being pressed, during the revolving
+movement, against the projecting end of the shoot, would infallibly
+have seized it in a useless or injurious manner.  But the main branch
+of the tendril, after revolving for a time in a vertical position,
+spontaneously bends downwards; and in doing so, raises the spur-like
+branch, which itself also curves upwards; so that by these combined
+movements it rises above the projecting end of the shoot, and can now
+move freely without touching the shoot; and now it first becomes
+sensitive.
+
+The tips of both branches, when they come into contact with a stick,
+grasp it like any ordinary tendril.  But in the course of a few days,
+the lower 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 discs formed by the
+extremities of the tendrils of some species of Bignonia and of
+Ampelopsis; but in the Hanburya the layer is developed along the
+terminal inner surface, sometimes for a length of 1.75 inches, and
+not at the extreme tip.  The layer is white, whilst the tendril is
+green, and near the tip it is sometimes thicker than the tendril
+itself; it generally spreads a little beyond the sides of the
+tendril, and 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 an immersion of 24 hrs. in alcohol or water,
+but was quite loosened by a similar immersion in ether or turpentine.
+After a tendril has once firmly coiled itself round a stick, it is
+difficult to imagine of what use the adhesive cellular layer can be.
+Owing to the spiral contraction which soon ensues, the tendrils were
+never able to remain, excepting in one instance, in contact with a
+thick post or a nearly flat surface; if they had quickly become
+attached by means of the adhesive layer, this would evidently have
+been of service to the plant.
+
+The tendrils of Bryonia dioica, Cucurbita ovifera, and Cucumis sativa
+are sensitive and revolve.  Whether the internodes likewise revolve I
+did not observe.  In Anguria Warscewiczii, the internodes, though
+thick and stiff, revolve:  in this plant the lower surface of the
+tendril, some time after clasping a stick, produces a coarsely
+cellular layer or cushion, which adapts itself closely to the wood,
+like that formed by the tendril of the Hanburya; but it is not in the
+least adhesive.  In Zanonia Indica, which belongs to a different
+tribe of the family, the forked tendrils and the internodes revolve
+in periods between 2 hrs. 8 m. and 3 hrs. 35 m., moving against the
+sun.
+
+VITACEAE.--In this family and in the two following, namely, the
+Sapindaceae and Passifloraceae, the tendrils are modified flower-
+peduncles; and are therefore axial in their nature.  In this respect
+they differ from all those previously described, with the exception,
+perhaps, of the Cucurbitaceae.  The homological nature, however, of a
+tendril seems to make no difference in its action.
+
+Vitis vinifera.--The tendril is thick and of great length; one from a
+vine growing out of doors and not vigorously, was 16 inches long.  It
+consists of a peduncle (A), bearing two branches which diverge
+equally from it.  One of the branches (B) has a scale at its base; it
+is always, as far as I have seen, longer than the other and often
+bifurcates.  The branches when rubbed become curved, and subsequently
+straighten themselves.  After a tendril has clasped any object with
+its extremity, it contracts spirally; but this does not occur (Palm,
+p. 56) when no object has been seized.  The tendrils move
+spontaneously from side to side; and on a very hot day, one made two
+elliptical revolutions, at an average rate of 2 hrs. 15 m.  During
+these movements a coloured line, painted along the convex surface,
+appeared after a time on one side, then on the concave side, then on
+the opposite side, and lastly again on the convex side.  The two
+branches of the same tendril have independent movements.  After a
+tendril has spontaneously revolved for a time, it bends from the
+light towards the dark:  I do not state this on my own authority, but
+on that of Mohl and Dutrochet.  Mohl (p. 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 revolve spontaneously; but the movement is
+unusually slight.  A shoot faced a window, and I traced its course on
+the glass during two perfectly calm and hot days.  On one of these
+days it described, in the course of ten hours, a spire, representing
+two and a half ellipses.  I also placed a bell-glass over a young
+Muscat grape in the hot-house, and it made each day three or four
+very small oval revolutions; the shoot moving less than half an inch
+from side to side.  Had it not made at least three revolutions whilst
+the sky was uniformly overcast, I should have attributed this slight
+degree of movement to the varying action of the light.  The extremity
+of the stem is more or less bent downwards, but it never reverses its
+curvature, as so generally occurs with twining plants.
+
+Various authors (Palm, p. 55; Mohl, p. 45; Lindley, &c.) believe that
+the tendrils of the vine are modified flower-peduncles.  I here give
+a drawing (fig. 10) of the ordinary state of a young flower-stalk:
+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 moves
+spontaneously, like a true tendril, but in a less degree; the
+movement, however, is greater 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 of a true tendril.
+The flower-tendril (B) is always longer than the sub-peduncle (C) and
+has a scale at its base; it sometimes 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.  When
+rubbed, it curves and subsequently straightens itself; and it can, as
+is 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 slightly
+sensitive to a rub, and I have seen it 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 corresponding branch of an
+ordinary tendril, is well shown when it bears only a few flowers; for
+in this case it becomes less branched, increases in length, and gains
+both in sensitiveness and in the power of spontaneous movement.  I
+have twice seen sub-peduncles which bore from thirty to forty flower-
+buds, and which had become considerably elongated and were completely
+wound round sticks, exactly like true tendrils.  The whole length of
+another sub-peduncle, bearing only eleven flower-buds, quickly became
+curved when slightly rubbed; but even this scanty number of flowers
+rendered the stalk less sensitive than the other branch, that is, the
+flower-tendril; for the latter after a lighter rub became curved more
+quickly and in a greater degree.  I have seen a sub-peduncle thickly
+covered with flower-buds, with one of its 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
+adjoining twig; in fact, it formed a little sub-tendril.  The
+increasing length of the sub-peduncle (C) with the decreasing number
+of the flower-buds is a good instance of the law of compensation.  In
+accordance with this same principle, the true tendril as a whole is
+always longer than the flower-stalk; for instance, on the same plant,
+the longest flower-stalk (measured from the base of the common
+peduncle to the tip of the flower-tendril) was 8.5 inches in length,
+whilst the longest tendril was nearly double this length, namely 16
+inches.
+
+The gradations from the ordinary state of a flower-stalk, as
+represented in the drawing (fig. 10), to that of a true tendril (fig.
+9) are complete.  We have seen that the sub-peduncle (C), whilst
+still bearing from thirty to forty flower-buds, sometimes becomes a
+little elongated and partially assumes all the characters of the
+corresponding branch of a true tendril.  From this state we can trace
+every stage till we come to a full-sized perfect 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.  Flower-tendrils (B,
+fig. 10) sometimes produce a few flower-buds.  For instance, on a
+vine growing against my house, there were thirteen and twenty-two
+flower-buds respectively on two flower-tendrils, which still retained
+their characteristic qualities of sensitiveness and spontaneous
+movement, but in a somewhat lessened degree.  On vines in hothouses,
+so many flowers are occasionally produced on 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-
+stalks closely resemble in structure those borne by Cissus.  This
+genus, belonging to the same family of the Vitaceae, produces well-
+developed tendrils and ordinary bunches of flowers; but there are no
+gradations between the two states.  If the genus Vitis had been
+unknown, the boldest believer in the modification of species would
+never 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 such a case; and it seems to me as striking and curious an
+instance of transition as can well be conceived.
+
+Cissus discolor.--The young shoots show no more movement than can be
+accounted for by daily variations in the action of the light.  The
+tendrils, however, revolve with much regularity, following the sun;
+and, in the plants observed by me, swept circles of about 5 inches in
+diameter.  Five circles were completed in the following times:- 4
+hrs. 45 m., 4 hrs. 50 m., 4 hrs. 45 m., 4 hrs. 30 m., and 5 hrs. The
+same tendril continues to revolve during three or four days.  The
+tendrils are from 3.5 to 5 inches in length.  They are formed of a
+long foot-stalk, bearing two short branches, which in old plants
+again bifurcate.  The two branches are not of quite equal length; and
+as with the vine, the longer one has a scale at its base.  The
+tendril stands vertically upwards; the extremity of the shoot being
+bent abruptly downwards, and this position is probably of service to
+the plant by allowing the tendril to revolve freely and vertically.
+
+Both branches of the tendril, whilst young, are highly sensitive.  A
+touch with a pencil, so gentle as only just to move a tendril borne
+at the end of a long flexible shoot, sufficed to cause it to become
+perceptibly curved in four or five minutes.  It became straight again
+in rather above one hour.  A loop of soft thread weighing one-seventh
+of a grain (9.25 mg.) was thrice tried, and each time caused the
+tendril to become curved in 30 or 40 m.  Half this weight produced no
+effect.  The long foot-stalk is much less sensitive, for a slight
+rubbing produced no effect, although prolonged contact with a stick
+caused it to bend.  The two branches are sensitive on all sides, so
+that they converge if touched on their inner sides, and diverge if
+touched on their outer sides.  If a branch be touched at the same
+time with equal force on opposite sides, both sides are equally
+stimulated and there is no movement.  Before examining this plant, I
+had observed only tendrils which are sensitive on one side alone, and
+these when lightly pressed between the finger and thumb become
+curved; but on thus pinching many times the tendrils of the Cissus no
+curvature ensued, and I falsely inferred at first that they were not
+at all sensitive.
+
+Cissus antarcticus.--The tendrils on a young plant were thick and
+straight, with the tips a little curved.  When their concave surfaces
+were rubbed, and it was necessary to do this with some force, they
+very slowly became curved, and subsequently straight again.  They are
+therefore much less sensitive than those of the last species; but
+they made two revolutions, following the sun, rather more rapidly,
+viz., in 3 hrs. 30 m. and 4 hrs. The internodes do not revolve.
+
+Ampelopsis hederacea (Virginian Creeper).--The internodes apparently
+do not move more than can be accounted for by the varying action of
+the light.  The tendrils are from 4 to 5 inches in length, with the
+main stem sending off several lateral branches, which have their tips
+curved, as may be seen in the upper figure (fig. 11).  They exhibit
+no true spontaneous revolving movement, but turn, as was long ago
+observed by Andrew Knight, {31} from the light to the dark.  I have
+seen several tendrils move in less than 24 hours, through an angle of
+180 degrees to the dark side of a case in which a plant was placed,
+but the movement is sometimes much slower.  The several lateral
+branches often move independently of one another, and sometimes
+irregularly, without any apparent cause.  These tendrils are less
+sensitive to a touch than any others observed by me.  By gentle but
+repeated rubbing with a twig, the lateral branches, but not the main
+stem, became in the course of three or four hours slightly curved;
+but they seemed to have hardly any power of again straightening
+themselves.  The tendrils of a plant which had crawled over a large
+box-tree clasped several of the branches; but I have repeatedly seen
+that they will withdraw themselves after seizing a stick.  When they
+meet with a flat surface of wood or a wall (and this is evidently
+what they are adapted for), they turn all their branches towards it,
+and, spreading them widely apart, bring their hooked tips laterally
+into contact with it.  In effecting this, the several branches, after
+touching the surface, often rise up, place themselves in a new
+position, and again come down into contact with it.
+
+In the course of about two days after a tendril has arranged its
+branches so as to press on any surface, the curved tips swell, become
+bright red, and form on their under-sides the well-known little discs
+or cushions with which they adhere firmly.  In one case the tips were
+slightly swollen in 38 hrs. after coming into contact with a brick;
+in another case they were considerably swollen in 48 hrs., and in an
+additional 24 hrs. were firmly attached to a smooth board; and
+lastly, the tips of a younger tendril not only swelled but became
+attached to a stuccoed wall in 42 hrs.  These adhesive discs
+resemble, except in colour and in being larger, those of Bignonia
+capreolata.  When they were developed in contact with a ball of tow,
+the fibres were separately enveloped, but not in so effective a
+manner as by B. capreolata.  Discs are never developed, as far as I
+have seen, without the stimulus of at least temporary contact with
+some object. {32}  They are generally first formed on one side of the
+curved tip, the whole of which often becomes so much changed in
+appearance, that a line of the original green tissue can be traced
+only along the concave surface.  When, however, a tendril has clasped
+a cylindrical stick, an irregular rim or disc is sometimes formed
+along the inner surface at some little distance from the curved tip;
+this was also observed (p. 71) by Mohl.  The discs consist of
+enlarged cells, with smooth projecting hemispherical surfaces,
+coloured red; they are at first gorged with fluid (see section given
+by Mohl, p. 70), but ultimately become woody.
+
+As the discs soon adhere firmly to such smooth surfaces as planed or
+painted wood, or to the polished leaf of the ivy, this alone renders
+it probable that some cement is secreted, as has been asserted to be
+the case (quoted by Mohl, p. 71) by Malpighi.  I removed a number of
+discs formed during the previous year from a stuccoed wall, and left
+them during many hours, in warm water, diluted acetic acid and
+alcohol; but the attached grains of silex were not loosened.
+Immersion in sulphuric ether for 24 hrs. loosened them much, but
+warmed essential oils (I tried oil of thyme and peppermint)
+completely released every particle of stone in the course of a few
+hours.  This seems to prove that some resinous cement is secreted.
+The quantity, however, must be small; for when a plant ascended a
+thinly whitewashed wall, the discs adhered firmly to the whitewash;
+but as the cement never penetrated the thin layer, they were easily
+withdrawn, together with little scales of the whitewash.  It must not
+be supposed that the attachment is effected exclusively by the
+cement; for the cellular outgrowth completely envelopes every minute
+and irregular projection, and insinuates itself into every crevice.
+
+A tendril which has not become attached to any body, does not
+contract spirally; and in course of a week or two shrinks into the
+finest thread, withers and drops off.  An attached tendril, on the
+other hand, contracts spirally, and thus becomes highly elastic, so
+that when the main foot-stalk is pulled the strain is distributed
+equally between all the attached discs.  For a few days after the
+attachment of the discs, the tendril remains weak and brittle, but it
+rapidly increases in thickness and acquires great strength.  During
+the following winter it ceases to live, but adheres firmly in a dead
+state both to its own stem and to the surface of attachment.  In the
+accompanying diagram (fig. 11.) we see the difference between a
+tendril (B) some weeks after its attachment to a wall, with one (A)
+from the same plant fully grown but unattached.  That the change in
+the nature of the tissues, as well as the spiral contraction, are
+consequent on the formation of the discs, is well shown by any
+lateral branches which have not become attached; for these in a week
+or two wither and drop off, in the same manner as does the whole
+tendril if unattached.  The gain in strength and durability in a
+tendril after its attachment is something wonderful.  There are
+tendrils now adhering to my house which are still strong, and have
+been exposed to the weather in a dead state for fourteen or fifteen
+years.  One single lateral branchlet of a tendril, estimated to be at
+least ten years old, was still elastic and supported a weight of
+exactly two pounds.  The whole tendril had five disc-bearing branches
+of equal thickness and apparently of equal strength; so that after
+having been exposed during ten years to the weather, it would
+probably have resisted a strain of ten pounds!
+
+SAPINDACEAE.--Cardiospermum halicacabum.--In this family, as in the
+last, the tendrils are modified flower-peduncles.  In the present
+plant the two lateral branches of the main flower-peduncle have been
+converted into a pair of tendrils, corresponding with the single
+"flower-tendril" of the common vine.  The main peduncle is thin,
+stiff, and from 3 to 4.5 inches in length.  Near the summit, above
+two little bracts, it divides into three branches.  The middle one
+divides and re-divides, and bears the flowers; ultimately it grows
+half as long again as the two other modified branches.  These latter
+are the tendrils; they are at first thicker and longer than the
+middle branch, but never become more than an inch in length.  They
+taper to a point and are flattened, with the lower clasping surface
+destitute of hairs.  At first they project straight up; but soon
+diverging, spontaneously curl downwards so as to become symmetrically
+and elegantly hooked, as represented in the diagram.  They are now,
+whilst the flower-buds are still small, ready for action.
+
+The two or three upper internodes, whilst young, steadily revolve;
+those on one plant made two circles, against the course of the sun,
+in 3 hrs. 12 m.; in a second plant the same course was followed, and
+the two circles were completed in 3 hrs. 41 m.; in a third plant, the
+internodes followed the sun and made two circles in 3 hrs. 47 m.  The
+average rate of these six revolutions was 1 hr. 46 m.  The stem shows
+no tendency to twine spirally round a support; but the allied
+tendril-bearing genus Paullinia is said (Mohl, p. 4) to be a twiner.
+The flower-peduncles, which stand up above the end of the shoot, are
+carried round and round by the revolving movement of the internodes;
+and when the stem is securely tied, the long and thin flower-
+peduncles themselves are seen to be in continued and sometimes rapid
+movement from side to side.  They sweep a wide space, but only
+occasionally revolve in a regular elliptical course.  By the combined
+movements of the internodes and peduncles, one of the two short
+hooked tendrils, sooner or later, catches hold of some twig or
+branch, and then it curls round and securely grasps it.  These
+tendrils are, however, but slightly sensitive; for by rubbing their
+under surface only a slight movement is slowly produced.  I hooked a
+tendril on to a twig; and in 1 hr. 45 m. it was curved considerably
+inwards; in 2 hrs. 30 m. it formed a ring; and in from 5 to 6 hours
+from being first hooked, it closely grasped the stick.  A second
+tendril acted at nearly the same rate; but I observed one that took
+24 hours before it curled twice round a thin twig.  Tendrils which
+have caught nothing, spontaneously curl up to a close helix after the
+interval of several days.  Those which have curled round some object,
+soon become a little thicker and tougher.  The long and thin main
+peduncle, though spontaneously moving, is not sensitive and never
+clasps a support.  Nor does it ever contract spirally, {33} although
+a contraction of this kind apparently would have been of service to
+the plant in climbing.  Nevertheless it climbs pretty well without
+this aid.  The seed-capsules though light, are of enormous size
+(hence its English name of balloon-vine), and as two or three are
+carried on the same peduncle, the tendrils rising close to them may
+be of service in preventing their being dashed to pieces by the wind.
+In the hothouse the tendrils served simply for climbing.
+
+The position of the tendrils alone suffices to show their homological
+nature.  In two instances one of two tendrils produced a flower at
+its tip; this, however, did not prevent its acting properly and
+curling round a twig.  In a third case both lateral branches which
+ought to have been modified into tendrils, produced flowers like the
+central branch, and had quite lost their tendril-structure.
+
+I have seen, but was not enabled carefully to observe, only one other
+climbing Sapindaceous plant, namely, Paullinia.  It was not in
+flower, yet bore long forked tendrils.  So that, Paullinia, with
+respect to its tendrils, appears to bear the same relation to
+Cardiospermum that Cissus does to Vitis.
+
+PASSIFLORACEAE.--After reading the discussion and facts given by Mohl
+(p. 47) on the nature of the tendrils in this family, no one can
+doubt that they are modified flower-peduncles.  The tendrils and the
+flower-peduncles rise close side by side; and my son, William E.
+Darwin, made sketches for me of their earliest state of development
+in the hybrid P. floribunda.  The two organs appear at first as a
+single papilla which gradually divides; so that the tendril appears
+to be a modified branch of the flower-peduncle.  My son found one
+very young tendril surmounted by traces of floral organs, exactly
+like those on the summit of the true flower-peduncle at the same
+early age.
+
+Passiflora gracilis.--This well-named, elegant, annual species
+differs from the other members of the group observed by me, in the
+young internodes having the power of revolving.  It exceeds all the
+other climbing plants which I have examined, in the rapidity of its
+movements, and all tendril-bearers in the sensitiveness of the
+tendrils.  The internode which carries the upper active tendril and
+which likewise carries one or two younger immature internodes, made
+three revolutions, following the sun, at an average rate of 1 hr. 4
+m.; it then made, the day becoming very hot, three other revolutions
+at an average rate of between 57 and 58 m.; so that the average of
+all six revolutions was 1 hr. 1 m.  The apex of the tendril describes
+elongated ellipses, sometimes narrow and sometimes broad, with their
+longer axes inclined in slightly different directions.  The plant can
+ascend a thin upright stick by the aid of its tendrils; but the stem
+is too stiff for it to twine spirally round it, even when not
+interfered with by the tendrils, these having been successively
+pinched off at an early age.
+
+When the stem is secured, the tendrils are seen to revolve in nearly
+the same manner and at the same rate as the internodes. {34}  The
+tendrils are very thin, delicate, and straight, with the exception of
+the tips, which are a little curved; they are from 7 to 9 inches in
+length.  A half-grown tendril is not sensitive; but when nearly full-
+grown they are extremely sensitive.  A single delicate touch on the
+concave surface of the tip soon caused one to curve; and in 2 minutes
+it formed an open helix.  A loop of soft thread weighing one thirty-
+second of a grain (2.02 mg.) placed most gently on the tip, thrice
+caused distinct curvature.  A bent bit of thin platina wire weighing
+only fiftieth of a grain (1.23 mg.) twice produced the same effect;
+but this latter weight, when left suspended, did not suffice to cause
+a permanent curvature.  These trials were made under a bell-glass, so
+that the loops of thread and wire were not agitated by the wind.  The
+movement after a touch is very rapid:  I took hold of the lower part
+of several tendrils, and then touched their concave tips with a thin
+twig and watched them carefully through a lens; the tips evidently
+began to bend after the following intervals--31, 25, 32, 31, 28, 39,
+31, and 30 seconds; so that the movement was generally perceptible in
+half a minute after a touch; but on one occasion it was distinctly
+visible in 25 seconds.  One of the tendrils which thus became bent in
+31 seconds, had been touched two hours previously and had coiled into
+a helix; so that in this interval it had straightened itself and had
+perfectly recovered its irritability.
+
+To ascertain how often the same tendril would become curved when
+touched, I kept a plant in my study, which from being cooler than the
+hot-house was not very favourable for the experiment.  The extremity
+was gently rubbed four or five times with a thin stick, and this was
+done as often as it was observed to have become nearly straight again
+after having been in action; and in the course of 54 hrs. it answered
+to the stimulus 21 times, becoming each time hooked or spiral.  On
+the last occasion, however, the movement was very slight, and soon
+afterwards permanent spiral contraction commenced.  No trials were
+made during the night, so that the tendril would perhaps have
+answered a greater number of times to the stimulus; though, on the
+other hand, from having no rest it might have become exhausted from
+so many quickly repeated efforts.
+
+I repeated the experiment made on the Echinocystis, and placed
+several plants of this Passiflora so close together, that their
+tendrils were repeatedly dragged over each other; but no curvature
+ensued.  I likewise repeatedly flirted small drops of water from a
+brush on many tendrils, and syringed others so violently that the
+whole tendril was dashed about, but they never became curved.  The
+impact from the drops of water was felt far more distinctly on my
+hand than that from the loops of thread (weighing one thirty-second
+of a grain) when allowed to fall on it from a height, and these
+loops, which caused the tendrils to become curved, had been placed
+most gently on them.  Hence it is clear, that the tendrils either
+have become habituated to the touch of other tendrils and drops of
+rain, or that they were from the first rendered sensitive only to
+prolonged though excessively slight pressure of solid objects, with
+the exclusion of that from other tendrils.  To show the difference in
+the kind of sensitiveness in different plants and likewise to show
+the force of the syringe used, I may add that the lightest jet from
+it instantly caused the leaves of a Mimosa to close; whereas the loop
+of thread weighing one thirty-second of a grain, when rolled into a
+ball and placed gently on the glands at the bases of the leaflets of
+the Mimosa, caused no action.
+
+Passiflora punctata.--The internodes do not move, but the tendrils
+revolve regularly.  A half-grown and very sensitive tendril made
+three revolutions, opposed to the course of the sun, in 3 hrs. 5 m.,
+2 hrs. 40 m. and 2 hrs. 50 m.; perhaps it might have travelled more
+quickly when nearly full-grown.  A plant was placed in front of a
+window, and, as with twining stems, the light accelerated the
+movement of the tendril in one direction and retarded it in the
+other; the semicircle towards the light being performed in one
+instance in 15 m. less time and in a second instance in 20 m. less
+time than that required by the semicircle towards the dark end of the
+room.  Considering the extreme tenuity of these tendrils, the action
+of the light on them is remarkable.  The tendrils are long, and, as
+just stated, very thin, with the tip slightly curved or hooked.  The
+concave side is extremely sensitive to a touch--even a single touch
+causing it to curl inwards; it subsequently straightened itself, and
+was again ready to act.  A loop of soft thread weighing one
+fourteenth of a grain (4.625 mg.) caused the extreme tip to bend;
+another time I tried to hang the same little loop on an inclined
+tendril, but three times it slid off; yet this extraordinarily slight
+degree of friction sufficed to make the tip curl.  The tendril,
+though so sensitive, does not move very quickly after a touch, no
+conspicuous movement being observable until 5 or 10 m. had elapsed.
+The convex side of the tip is not sensitive to a touch or to a
+suspended loop of thread.  On one occasion I observed a tendril
+revolving with the convex side of the tip forwards, and in
+consequence it was not able to clasp a stick, against which it
+scraped; whereas tendrils revolving with the concave side forward,
+promptly seize any object in their path.
+
+Passiflora quadrangularis.--This is a very distinct species.  The
+tendrils are thick, long, and stiff; they are sensitive to a touch
+only on the concave surface towards the extremity.  When a stick was
+placed so that the middle of the tendril came into contact with it,
+no curvature ensued.  In the hothouse a tendril made two revolutions,
+each in 2 hrs. 22 m.; in a cool room one was completed in 3 hrs., and
+a second in 4 hrs.  The internodes do not revolve; nor do those of
+the hybrid P. floribunda.
+
+Tacsonia manicata.--Here again the internodes do not revolve.  The
+tendrils are moderately thin and long; one made a narrow ellipse in 5
+hrs. 20 m., and the next day a broad ellipse in 5 hrs. 7 m.  The
+extremity being lightly rubbed on the concave surface, became just
+perceptibly curved in 7 m., distinctly in 10 m., and hooked in 20 m.
+
+We have seen that the tendrils in the last three families, namely,
+the Vitaceae, Sapindaceae and Passifloraceae, are modified flower-
+peduncles.  This is likewise the case, according to De Candolle (as
+quoted by Mohl), with the tendrils of Brunnichia, one of the
+Polygonaceae.  In two or three species of Modecca, one of the
+Papayaceae, the tendrils, as I hear from Prof. Oliver, occasionally
+bear flowers and fruit; so that they are axial in their nature.
+
+
+The Spiral Contraction of Tendrils.
+
+
+This movement, which shortens the tendrils and renders them elastic,
+commences in half a day, or in a day or two after their extremities
+have caught some object.  There is no such movement in any leaf-
+climber, with the exception of an occasional trace of it in the
+petioles of Tropaeolum tricolorum.  On the other hand, the tendrils
+of all tendril-bearing plants, contract spirally after they have
+caught an object with the following exceptions.  Firstly, Corydalis
+claviculata, but then this plant might be called a leaf-climber.
+Secondly and thirdly, Bignonia unguis with its close allies, and
+Cardiospermum; but their tendrils are so short that their contraction
+could hardly occur, and would be quite superfluous.  Fourthly, Smilax
+aspera offers a more marked exception, as its tendrils are moderately
+long.  The tendrils of Dicentra, whilst the plant is young, are short
+and after attachment only become slightly flexuous; in older plants
+they are longer and then they contract spirally.  I have seen no
+other exceptions to the rule that tendrils, after clasping with their
+extremities a support, undergo spiral contraction.  When, however,
+the tendril of a plant of which the stem is immovably fixed, catches
+some fixed object, it does not contract, simply because it cannot;
+this, however, rarely occurs.  In the common Pea the lateral branches
+alone contract, and not the central stem; and with most plants, such
+as the Vine, Passiflora, Bryony, the basal portion never forms a
+spire.
+
+I have said that in Corydalis claviculata the end of the leaf or
+tendril (for this part may be indifferently so called) does not
+contract into a spire.  The branchlets, however, after they have
+wound round thin twigs, become deeply sinuous or zigzag.  Moreover
+the whole end of the petiole or tendril, if it seizes nothing, bends
+after a time abruptly downwards and inwards, showing that its outer
+surface has gone on growing after the inner surface has ceased to
+grow.  That growth is the chief cause of the spiral contraction of
+tendrils may be safely admitted, as shown by the recent researches of
+H. de Vries.  I will, however, add one little fact in support of this
+conclusion.
+
+If the short, nearly straight portion of an attached tendril of
+Passiflora gracilis, (and, as I believe, of other tendrils,) between
+the opposed spires, be examined, it will be found to be transversely
+wrinkled in a conspicuous manner on the outside; and this would
+naturally follow if the outer side had grown more than the inner
+side, this part being at the same time forcibly prevented from
+becoming curved.  So again the whole outer surface of a spirally
+wound tendril becomes wrinkled if it be pulled straight.
+Nevertheless, as the contraction travels from the extremity of a
+tendril, after it has been stimulated by contact with a support, down
+to the base, I cannot avoid doubting, from reasons presently to be
+given, whether the whole effect ought to be attributed to growth.  An
+unattached tendril rolls itself up into a flat helix, as in the case
+of Cardiospermum, if the contraction commences at the extremity and
+is quite regular; but if the continued growth of the outer surface is
+a little lateral, or if the process begins near the base, the
+terminal portion cannot be rolled up within the basal portion, and
+the tendril then forms a more or less open spire.  A similar result
+follows if the extremity has caught some object, and is thus held
+fast.
+
+The tendrils of many kinds of plants, if they catch nothing, contract
+after an interval of several days or weeks into a spire; but in these
+cases the movement takes place after the tendril has lost its
+revolving power and hangs down; it has also then partly or wholly
+lost its sensibility; so that this movement can be of no use.  The
+spiral contraction of unattached tendrils is a much slower process
+than that of attached ones.  Young tendrils which have caught a
+support and are spirally contracted, may constantly be seen on the
+same stem with the much older unattached and uncontracted tendrils.
+In the Echinocystis I have seen a tendril with the two lateral
+branches encircling twigs and contracted into beautiful spires,
+whilst the main branch which had caught nothing remained for many
+days straight.  In this plant I once observed a main branch after it
+had caught a stick become spirally flexuous in 7 hrs., and spirally
+contracted in 18 hrs.  Generally the tendrils of the Echinocystis
+begin to contract in from 12 hrs. to 24 hrs. after catching some
+object; whilst unattached tendrils do not begin to contract until two
+or three or even more days after all revolving movement has ceased.
+A full-grown tendril of Passiflora quadrangularis which had caught a
+stick began in 8 hrs. to contract, and in 24 hrs. formed several
+spires; a younger tendril, only two-thirds grown, showed the first
+trace of contraction in two days after clasping a stick, and in two
+more days formed several spires.  It appears, therefore, that the
+contraction does not begin until the tendril 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 formed one complete spire.  This first spire was formed
+towards the basal end, and the contraction steadily but slowly
+progressed towards the apex; but the whole was not closely wound up
+into a spire until 21 days had elapsed from the first observation,
+that is, until 17 days after the tendril had grown to its full
+length.
+
+The spiral contraction of tendrils is quite independent of their
+power of spontaneously revolving, for it occurs in tendrils, such as
+those of Lathyrus grandiflorus and Ampelopsis hederacea, which do not
+revolve.  It is not necessarily related to the curling of the tips
+round a support, as we see with the Ampelopsis and Bignonia
+capreolata, in which the development of adherent discs suffices to
+cause spiral contraction.  Yet in some cases this contraction seems
+connected with the curling or clasping movement, due to contact with
+a support; for not only does it soon follow this act, but the
+contraction generally begins close to the curled extremity, and
+travels downwards to the base.  If, however, a tendril be very slack,
+the whole length almost simultaneously becomes at first flexuous and
+then spiral.  Again, the tendrils of some few plants never contract
+spirally unless they have first seized hold of some object; if they
+catch nothing they hang down, remaining straight, until they wither
+and drop off:  this is the case with the tendrils of Bignonia, which
+consist of modified leaves, and with those of three genera of the
+Vitaceae, which are modified flower-peduncles.  But in the great
+majority of cases, tendrils which have never come in contact with any
+object, after a time contract spirally.  All these facts taken
+together, show that the act of clasping a support and the spiral
+contraction of the whole length of the tendril, are phenomena not
+necessarily connected.
+
+The spiral contraction which ensues after a tendril has caught a
+support is of high service to the plant; hence its almost universal
+occurrence with species belonging to 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 stem, after the tendrils have seized some object
+above, would leave it slack, were it not for the spiral contraction
+which draws up the stem as it increases in length.  Thus there is no
+waste of growth, and the stretched stem ascends by the shortest
+course.  When a terminal branchlet of the tendril of Cobaea catches a
+stick, we have seen how well the spiral contraction successively
+brings the other branchlets, one after the other, into contact with
+the stick, until the whole tendril grasps it in an inextricable knot.
+When a tendril has caught a yielding object, this is sometimes
+enveloped and still further secured by the spiral folds, as I have
+seen with Passiflora quadrangularis; but this action is of little
+importance.
+
+A far more important service rendered by the spiral contraction of
+the tendrils is that they are thus made highly elastic.  As before
+remarked under Ampelopsis, the strain is thus distributed equally
+between the several attached branches; and this renders the whole far
+stronger than it otherwise would be, as the branches cannot break
+separately.  It is this elasticity which protects both branched and
+simple tendrils from being torn away from their supports 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 thick and thin
+branches were tossed to and fro by the wind, the 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.
+
+When an unattached 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, although the same
+side is concave from end to end, invariably becomes twisted in one
+part in one direction, and in another part in the opposite direction;
+the oppositely turned spires being separated by a short straight
+portion.  This curious and symmetrical structure has been noticed by
+several botanists, but has not been sufficiently explained. {35}  It
+occurs without exception with all tendrils which after catching an
+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 occurred, it will be found that the tendril had
+originally seized some object and had afterwards been torn free.
+Commonly, all the spires at one end of an attached 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 pieces between them; and M. Leon has seen
+seven or eight such alternations.  Whether the spires turn once or
+more than once in opposite directions, there are as many turns in the
+one direction as in the other.  For instance, I gathered ten attached
+tendrils of the Bryony, the longest with 33, and the shortest with
+only 8 spiral turns; and the number of turns in the one direction was
+in every case the same (within one) as in the opposite direction.
+
+The explanation of this curious little fact is not difficult.  I will
+not attempt any geometrical reasoning, but will give only a practical
+illustration.  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, thus imitating the revolving
+movement of a twining plant, and the strings do not become twisted.
+But if we hold at the same time a stick in our left hand, in such a
+position that the strings become 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 wound round.  I
+painted a red line on the straight internodes of a Humulus, Mikania,
+Ceropegia, Convolvulus, and Phaseolus, and saw it become twisted as
+the plant wound round a stick.  It is possible that the stems of some
+plants by spontaneously turning on their own axes, at the proper rate
+and in the proper direction, might avoid becoming twisted; but I have
+seen no such case.
+
+In the above illustration, the parallel strings were wound round a
+stick; but this is by no means necessary, for if wound into a hollow
+coil (as can be done with a narrow slip of elastic paper) there is
+the same inevitable twisting of the axis.  When, therefore, a free
+tendril coils itself into a spire, it must either become twisted
+along its whole length (and this never occurs), or the free extremity
+must turn round as many times as there are spires formed.  It was
+hardly necessary to observe this fact; but I did so by affixing
+little paper vanes to the extreme points of the tendrils of
+Echinocystis and Passiflora quadrangularis; and as the tendril
+contracted itself into successive spires, the vane slowly revolved.
+
+We can now understand the meaning of the spires being invariably
+turned in opposite directions, in tendrils which from having caught
+some object are fixed at both ends.  Let us suppose a caught tendril
+to make thirty spiral turns all in the same direction; the inevitable
+result would be that it would become twisted thirty times on its own
+axis.  This twisting would not only require considerable force, but,
+as I know by trial, would burst the tendril before the thirty turns
+were completed.  Such cases never really occur; for, as already
+stated, when a tendril has caught a support and is spirally
+contracted, there are always as many turns in one direction as in the
+other; so that the twisting of the axis in the one direction is
+exactly compensated by the twisting in the opposite direction.  We
+can further see how the tendency is given to make the later formed
+coils opposite 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 perpendicular
+pencil, and this will twist the lower part of the string; and after
+it has been sufficiently twisted, it will be seen to curve itself
+into an open spire, with the curves running in an opposite direction
+to those round the pencil, and consequently with a straight piece of
+string between the opposed 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 cannot resist giving one other
+illustration, though superfluous:  when a haberdasher winds up ribbon
+for a customer, he does not wind it into a single coil; for, if he
+did, the ribbon would twist itself as many times as there were coils;
+but he winds it into a figure of eight on his thumb and little
+finger, so that he alternately takes turns in opposite directions,
+and thus the ribbon is not twisted.  So it is with tendrils, with
+this sole difference, that they take several consecutive turns in one
+direction and then the same number in an opposite direction; but in
+both cases the self-twisting is avoided.
+
+
+Summary on the Nature and Action of Tendrils.
+
+
+With the majority of tendril-bearing plants the young internodes
+revolve in more or less broad ellipses, like those made by twining
+plants; but the figures described, when carefully traced, generally
+form irregular ellipsoidal spires.  The rate of revolution varies
+from one to five hours in different species, and consequently is in
+some cases 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 direction is variable even in the same
+individual plant.  In Passiflora, the internodes of only one species
+have the power of revolving.  The Vine is the weakest revolver
+observed by me, apparently exhibiting only a trace of a former power.
+In the Eccremocarpus the movement is interrupted by many long pauses.
+Very few tendril-bearing plants can spirally twine up an upright
+stick.  Although the power of twining has generally been lost, either
+from the stiffness or shortness of the internodes, from the size of
+the leaves, or from some other unknown cause, the revolving movement
+of the stem serves to bring the tendrils into contact with
+surrounding objects.
+
+The tendrils themselves also spontaneously revolve.  The movement
+begins whilst the tendril is young, and is at first slow.  The mature
+tendrils of Bignonia littoralis move much slower than the internodes.
+Generally, the internodes and tendrils revolve together at the same
+rate; in Cissus, Cobaea, and most Passiflorae, the tendrils alone
+revolve; in other cases, as with Lathyrus aphaca, only the internodes
+move, carrying with them the motionless tendrils; and, lastly (and
+this is the fourth possible case), neither internodes nor tendrils
+spontaneously revolve, as with Lathyrus grandiflorus and Ampelopsis.
+In most Bignonias, Eccremocarpus Mutisia, and the Fumariaceae, the
+internodes, petioles and tendrils all move harmoniously together.  In
+every case the conditions of life must be favourable in order that
+the different parts should act in a perfect manner.
+
+Tendrils revolve by the curvature of their whole length, excepting
+the sensitive extremity and the base, which parts do not move, or
+move but little.  The movement is of the same nature as that of the
+revolving internodes, and, from the observations of Sachs and H. de
+Vries, no doubt is due to the same cause, namely, the rapid growth of
+a longitudinal band, which travels round the tendril and successively
+bows each part to the opposite side.  Hence, if a line be painted
+along that surface which happens at the time to be convex, the line
+becomes first lateral, then concave, then lateral, and ultimately
+again convex.  This experiment can be tried only on the thicker
+tendrils, which are not affected by a thin crust of dried paint.  The
+extremities are often slightly curved or hooked, and the curvature of
+this part is never reversed; in this respect they differ from the
+extremities of twining shoots, which not only reverse their
+curvature, or at least become periodically straight, but curve
+themselves in a greater degree than the lower part.  In most other
+respects a tendril acts as if it were one of several revolving
+internodes, which all move together by successively bending to each
+point 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.  With most tendril-bearers
+the summit of the stem or shoot projects above the point from which
+the tendril arises; and it is generally bent to 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, as we have seen with the Echinocystis, as soon as the tendril
+comes in its revolving course to this point, it stiffens and
+straightens itself, and thus rising vertically up passes over the
+obstacle in an admirable manner.
+
+All tendrils are sensitive, but in various degrees, to contact with
+an object, and curve towards the touched side.  With several plants a
+single touch, so slight as only just to move the highly flexible
+tendril, is enough to induce curvature.  Passiflora gracilis
+possesses the most sensitive tendrils which I have observed:  a bit
+of platina wire 0.02 of a grain (1.23 mg.) in weight, gently placed
+on the concave point, caused a tendril to become hooked, as did a
+loop of soft, thin cotton thread weighing one thirty-second of a
+grain (2.02 mg.)  With the tendrils of several other plants, loops
+weighing one sixteenth of a grain (4.05 mg.) sufficed.  The point of
+a tendril of Passiflora gracilis began to move distinctly in 25
+seconds after a touch, and in many cases after 30 seconds.  Asa Gray
+also saw movement in the tendrils of the Cucurbitaceous genus,
+Sicyos, in 30 seconds.  The tendrils of some other plants, when
+lightly rubbed, moved in a few minutes; with Dicentra in half-an-
+hour; with Smilax in an hour and a quarter or half; and with
+Ampelopsis still more slowly.  The curling movement consequent on a
+single touch continues to increase for a considerable time, then
+ceases; after a few hours the tendril uncurls itself, and is again
+ready to act.  When the tendrils of several kinds of plants were
+caused to bend by extremely light weights suspended on them, they
+seemed to grow accustomed to so slight a stimulus, and straightened
+themselves, as if the loops had been removed.  It makes no difference
+what sort of object a tendril touches, with the remarkable exception
+of other tendrils and drops of water, as was observed with the
+extremely sensitive-tendrils of Passiflora gracilis and of the
+Echinocystis.  I have, however, seen tendrils of the Bryony which had
+temporarily caught other tendrils, and often in the case of the vine.
+
+Tendrils of which the extremities are permanently and slightly
+curved, are sensitive only on the concave surface; other tendrils,
+such as those of the Cobaea (though furnished with horny hooks
+directed to one side) and those of Cissus discolor, are sensitive on
+all sides.  Hence the tendrils of this latter plant, when stimulated
+by a touch of equal force on opposite sides, did not bend.  The
+inferior and lateral surfaces of the tendrils of Mutisia are
+sensitive, but not the upper surface.  With branched tendrils, the
+several branches act alike; but in the Hanburya the lateral spur-like
+branch does not acquire (for excellent reasons which have been
+explained) its sensitiveness nearly so soon as the main branch.  With
+most tendrils the lower or basal part is either not at all sensitive,
+or sensitive only to prolonged contact.  We thus see that the
+sensitiveness of tendrils is a special and localized capacity.  It is
+quite independent of the power of spontaneously revolving; for the
+curling of the terminal portion from touch does not in the least
+interrupt the former movement.  In Bignonia unguis and its close
+allies, the petioles of the leaves, as well as the tendrils, are
+sensitive to a touch.
+
+Twining plants when they come into contact with a stick, curl round
+it invariably in the direction of their revolving movement; but
+tendrils curl indifferently to either side, in accordance with the
+position of the stick and the side which is first touched.  The
+clasping movement of the extremity is apparently not steady, but
+undulatory or vermicular in its nature, as may be inferred from the
+curious manner in which the tendrils of the Echinocystis slowly
+crawled round a smooth stick.
+
+As with a few exceptions tendrils spontaneously revolve, it may be
+asked,--why have they been endowed with sensitiveness?--why, when
+they come into contact with a stick, do they not, like twining
+plants, spirally wind round it?  One reason may be that they are in
+most cases so flexible and thin, that when brought into contact with
+any object, they would almost certainly yield and be dragged onwards
+by the revolving movement.  Moreover, the sensitive extremities have
+no revolving power as far as I have observed, and could not by this
+means curl round a support.  With twining plants, on the other hand,
+the extremity spontaneously bends more than any other part; and this
+is of high importance for the ascent of the plant, as may be seen on
+a windy day.  It is, however, possible that the slow movement of the
+basal and stiffer parts of certain tendrils, which wind round sticks
+placed in their path, may be analogous to that of twining plants.
+But I hardly attended sufficiently to this point, and it would have
+been difficult to distinguish between a movement due to extremely
+dull irritability, from the arrestment of the lower part, whilst the
+upper part continued to move onwards.
+
+Tendrils which are only three-fourths grown, and perhaps even at an
+earlier age, but not whilst extremely young, have the power of
+revolving and of grasping any object which they touch.  These two
+capacities are generally acquired at about the same period, and both
+fail when the tendril is full grown.  But in Cobaea and Passiflora
+punctata the tendrils begin to revolve in a useless manner, before
+they have become sensitive.  In the Echinocystis they retain their
+sensitiveness for some time after they have ceased to revolve and
+after they have sunk downwards; in this position, even if they were
+able to seize an object, such power would be of no service in
+supporting the stem.  It is a rare circumstance thus to detect any
+superfluity or imperfection in the action of tendrils--organs which
+are so excellently adapted for the functions which they have to
+perform; but we see that they are not always 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 or retarded, in
+moving to or from the light; others, as with the Pea, seem
+indifferent to its action; others move steadily from the light to the
+dark, and this aids them in an important manner in finding a support.
+For instance, the tendrils of Bignonia capreolata bend from the light
+to the dark as truly as a wind-vane from the wind.  In the
+Eccremocarpus the extremities alone twist and turn about so as to
+bring their finer branches and hooks into close contact with any dark
+surface, or into crevices and holes.
+
+A short time after a tendril has caught a support, it contracts with
+some rare exceptions into a spire; but the manner of contraction and
+the several important advantages thus gained have been discussed so
+lately, that nothing need here be repeated on the subject.  Tendrils
+soon after catching a support grow much stronger and thicker, and
+sometimes more durable to a wonderful degree; and this shows how much
+their internal tissues must be changed.  Occasionally it is the part
+which is wound round a support which chiefly becomes thicker and
+stronger; I have seen, for instance, this part of a tendril of
+Bignonia aequinoctialis twice as thick and rigid as the free basal
+part.  Tendrils which have caught nothing soon shrink and wither; but
+in some species of Bignonia they disarticulate and fall off like
+leaves in autumn.
+
+
+Any one who had not closely observed tendrils of many kinds would
+probably infer that their action was uniform.  This is the case with
+the simpler kinds, which simply curl round an object of moderate
+thickness, whatever its nature may be. {36}  But the genus Bignonia
+shows us what diversity of action there may be between the tendrils
+of closely allied species.  In all the nine species observed by me,
+the young internodes revolve vigorously; the tendrils also revolve,
+but in some of the species in a very feeble manner; and lastly the
+petioles of nearly all revolve, though with unequal power.  The
+petioles of three of the species, and the tendrils of all are
+sensitive to contact.  In the first-described species, the tendrils
+resemble in shape a bird's foot, and they are of no service to the
+stem in spirally ascending a thin upright stick, but they can seize
+firm hold of a twig or branch.  When the stem twines round a somewhat
+thick stick, a slight degree of sensitiveness possessed by the
+petioles is brought into play, and the whole leaf together with the
+tendril winds round it.  In B. unguis the petioles are more
+sensitive, and have greater power of movement than those of the last
+species; they are able, together with the tendrils, to wind
+inextricably round a thin upright stick; but the stem does not twine
+so well.  B. Tweedyana has similar powers, but in addition, emits
+aerial roots which adhere to the wood.  In B. venusta the tendrils
+are converted into elongated three-pronged grapnels, which move
+spontaneously in a conspicuous manner; the petioles, however, have
+lost their sensitiveness.  The stem of this species can twine round
+an upright stick, and is aided in its ascent by the tendrils seizing
+the stick alternately some way above and then contracting spirally.
+In B. littoralis the tendrils, petioles, and internodes, all revolve
+spontaneously.  The stem, however, cannot twine, but ascends an
+upright stick by seizing it above with both tendrils together, which
+then contract into a spire.  The tips of these tendrils become
+developed into adhesive discs.  B. speciosa possesses similar powers
+of movement as the last species, but it cannot twine round a stick,
+though it can ascend by clasping the stick horizontally with one or
+both of its unbranched tendrils.  These tendrils continually insert
+their pointed ends into minute crevices or holes, but as they are
+always withdrawn by the subsequent spiral contraction, the habit
+seems to us in our ignorance useless.  Lastly, the stem of B.
+capreolata twines imperfectly; the much-branched tendrils revolve in
+a capricious manner, and bend from the light to the dark; their
+hooked extremities, even whilst immature, crawl into crevices, and,
+when mature, seize any thin projecting point; in either case they
+develop adhesive discs, and these have the power of enveloping the
+finest fibres.
+
+In the allied Eccremocarpus the internodes, petioles, and much-
+branched tendrils all spontaneously revolve together.  The tendrils
+do not as a whole turn from the light; but their bluntly-hooked
+extremities arrange themselves neatly on any surface with which they
+come into contact, apparently so as to avoid the light.  They act
+best when each branch seizes a few thin stems, like the culms of a
+grass, which they afterwards draw together into a solid bundle by the
+spiral contraction of all the branches.  In Cobaea the finely-
+branched tendrils alone revolve; the branches terminate in sharp,
+hard, double, little hooks, with both points directed to the same
+side; and these turn by well-adapted movements to any object with
+which they come into contact.  The tips of the branches also crawl
+into dark crevices or holes.  The tendrils and internodes of
+Ampelopsis have little or no power of revolving; the tendrils are but
+little sensitive to contact; their hooked extremities cannot seize
+thin objects; they will not even clasp a stick, unless in extreme
+need of a support; but they turn from the light to the dark, and,
+spreading out their branches in contact with any nearly flat surface,
+develop discs.  These adhere by the secretion of some cement to a
+wall, or even to a polished surface; and this is more than the discs
+of the Bignonia capreolata can effect.
+
+The rapid development of these adherent discs is one of the most
+remarkable peculiarities possessed by any tendrils.  We have seen
+that such discs are formed by two species of Bignonia, by Ampelopsis,
+and, according to Naudin, {37} by the Cucurbitaceous genus Peponopsis
+adhaerens.  In Anguria 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; whilst in Hanburya a similar
+layer is adherent.  The growth of these cellular out-growths depends,
+(except in the case of the Haplolophium and of one species of
+Ampelopsis,) on the stimulus from contact.  It is a singular fact
+that three families, so widely distinct as the Bignoniaceae,
+Vitaceae, and Cucurbitaceae, should possess species with tendrils
+having this remarkable power.
+
+
+Sachs attributes all the movements of tendrils to rapid growth on the
+side opposite to that which becomes concave.  These movements consist
+of revolving nutation, the bending to and from the light, and in
+opposition to gravity, those caused by a touch, and spiral
+contraction.  It is rash to differ from so great an authority, but I
+cannot believe that one at least of these movements--curvature from a
+touch--is thus caused. {38}  In the first place it may be remarked
+that the movement of nutation differs from that due to a touch, in so
+far that in some cases the two powers are acquired by the same
+tendril at different periods of growth; and the sensitive part of the
+tendril does not seem capable of nutation.  One of my chief reasons
+for doubting whether the curvature from a touch is the result of
+growth, is the extraordinary rapidity of the movement.  I have seen
+the extremity of a tendril of Passiflora gracilis, after being
+touched, distinctly bent in 25 seconds, and often in 30 seconds; and
+so it is with the thicker tendril of Sicyos.  It appears hardly
+credible that their outer surfaces could have actually grown in
+length, which implies a permanent modification of structure, in so
+short a time.  The growth, moreover, on this view must be
+considerable, for if the touch has been at all rough the extremity is
+coiled in two or three minutes into a spire of several turns.
+
+When the extreme tip of the tendril of Echinocystis caught hold of a
+smooth stick, it coiled itself in a few hours (as described at p.
+132) twice or thrice round the stick, apparently by an undulatory
+movement.  At first I attributed this movement to the growth of the
+outside; black marks were therefore made, and the interspaces
+measured, but I could not thus detect any increase in length.  Hence
+it seems probable in this case and in others, that the curvature of
+the tendril from a touch depends on the contraction of the cells
+along the concave side.  Sachs himself admits {39} that "if the
+growth which takes place in the entire tendril at the time of contact
+with a support is small, a considerable acceleration occurs on the
+convex surface, but in general there is no elongation on the concave
+surface, or there may even be a contraction; in the case of a tendril
+of Cucurbita this contraction amounted to nearly one-third of the
+original length."  In a subsequent passage Sachs seems to feel some
+difficulty in accounting for this kind of contraction.  It must not
+however be supposed from the foregoing remarks that I entertain any
+doubt, after reading De Vries' observations, about the outer and
+stretched surfaces of attached tendrils afterwards increasing in
+length by growth.  Such increase seems to me quite compatible with
+the first movement being independent of growth.  Why a delicate touch
+should cause one side of a tendril to contract we know as little as
+why, on the view held by Sachs, it should lead to extraordinarily
+rapid growth of the opposite side.  The chief or sole reason for the
+belief that the curvature of a tendril when touched is due to rapid
+growth, seems to be that tendrils lose their sensitiveness and power
+of movement after they have grown to their full length; but this fact
+is intelligible, if we bear in mind that all the functions of a
+tendril are adapted to drag up the terminal growing shoot towards the
+light.  Of what use would it be, if an old and full-grown tendril,
+arising from the lower part of a shoot, were to retain its power of
+clasping a support?  This would be of no use; and we have seen with
+tendrils so many instances of close adaptation and of the economy of
+means, that we may feel assured that they would acquire irritability
+and the power of clasping a support at the proper age--namely, youth-
+-and would not uselessly retain such power beyond the proper age.
+
+
+
+CHAPTER V.--HOOK AND ROOT-CLIMBERS.--CONCLUDING REMARKS.
+
+
+
+Plants climbing by the aid of hooks, or merely scrambling over other
+plants--Root-climbers, adhesive matter secreted by the rootlets--
+General conclusions with respect to climbing plants, and the stages
+of their development.
+
+Hook-Climbers.--In my introductory remarks, I stated that, besides
+the two first great classes of climbing plants, namely, those which
+twine round a support, and those endowed with irritability enabling
+them to seize hold of objects by means of their petioles or tendrils,
+there are two other classes, hook-climbers and root-climbers.  Many
+plants, moreover, as Fritz Muller has remarked, {40} climb or
+scramble up thickets in a still more simple fashion, without any
+special aid, excepting that their leading shoots are generally long
+and flexible.  It may, however, be suspected from what follows, that
+these shoots in some cases tend to avoid the light.  The few hook-
+climbers which I have observed, namely, Galium aparine, Rubus
+australis, and some climbing Roses, exhibit no spontaneous revolving
+movement.  If they had possessed this power, and had been capable of
+twining, they would have been placed in the class of Twiners; for
+some twiners are furnished with spines or hooks, which aid them in
+their ascent.  For instance, the Hop, which is a twiner, has reflexed
+hooks as large as those of the Galium; some other twiners have stiff
+reflexed hairs; and Dipladenia has a circle of blunt spines at the
+bases of its leaves.  I have seen only one tendril-bearing plant,
+namely, Smilax aspera, which is furnished with reflexed spines; but
+this is the case with several branch-climbers in South Brazil and
+Ceylon; and their branches graduate into true tendrils.  Some few
+plants apparently depend solely on their hooks for climbing, and yet
+do so efficiently, as certain palms in the New and Old Worlds.  Even
+some climbing Roses will ascend the walls of a tall house, if covered
+with a trellis.  How this is effected I know not; for the young
+shoots of one such Rose, when placed in a pot in a window, bent
+irregularly towards the light during the day and from the light
+during the night, like the shoots of any common plant; so that it is
+not easy to understand how they could have got under a trellis close
+to the wall. {41}
+
+Root-climbers.--A good many plants come under this class, and are
+excellent climbers.  One of the most remarkable is the Marcgravia
+umbellata, the stem of 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 it puts 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 produces free branches with rounded stems, clad with sharp-
+pointed leaves, wonderfully different in appearance from those borne
+by the stem as long as it remains adherent.  This surprising
+difference in the leaves, I have also observed in a plant of
+Marcgravia dubia in my hothouse.  Root-climbers, as far as I have
+seen, namely, the Ivy (Hedera helix), Ficus repens, and F. barbatus,
+have no power of movement, not even from the light to the dark.  As
+previously stated, the Hoya carnosa (Asclepiadaceae) is a spiral
+twiner, and likewise adheres by rootlets even to a flat wall.  The
+tendril-bearing Bignonia Tweedyana emits roots, which curve half
+round and adhere to thin sticks.  The Tecoma radicans (Bignoniaceae),
+which is closely allied to many spontaneously revolving species,
+climbs by rootlets; nevertheless, its young shoots apparently move
+about more than can be accounted for by the varying action of the
+light.
+
+I have not closely observed many root-climbers, but can give one
+curious fact.  Ficus repens climbs up a wall just like Ivy; and when
+the young rootlets are made to press lightly on slips of glass, they
+emit after about a week's interval, as I observed several times,
+minute drops of clear fluid, not in the least milky like that exuded
+from a wound.  This fluid is slightly viscid, but cannot be drawn out
+into threads.  It has the remarkable property of not soon drying; a
+drop, about the size of half a pin's head, was slightly spread out on
+glass, and I scattered on it some minute grains of sand.  The glass
+was left exposed in a drawer during hot and dry weather, and if the
+fluid had been water, it would certainly have dried in a few minutes;
+but it remained fluid, closely surrounding each grain of sand, during
+128 days:  how much longer it would have remained I cannot say.  Some
+other rootlets were left in contact with the glass for about ten days
+or a fortnight, and the drops of secreted fluid were now rather
+larger, and so viscid that they could be drawn out into threads.
+Some other rootlets were left in contact during twenty-three days,
+and these were firmly cemented to the glass.  Hence we may conclude
+that the rootlets first secrete a slightly viscid fluid, subsequently
+absorb the watery parts, (for we have seen that the fluid will not
+dry by itself,) 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 very much less volatile by
+what it had dissolved.
+
+As the bisulphide of carbon has a strong power of softening indurated
+caoutchouc, I soaked in it during a short time several rootlets of a
+plant which had grown up a plaistered wall; and I then found many
+extremely thin threads of transparent, not viscid, excessively
+elastic matter, precisely like caoutchouc, attached to two sets of
+rootlets on the same branch.  These threads proceeded from the bark
+of the rootlet at one end, and at the other end were firmly attached
+to particles of silex or mortar from the wall.  There could be no
+mistake in this observation, as I played with the threads for a long
+time under the microscope, drawing them out with my dissecting-
+needles and letting them spring back again.  Yet I looked repeatedly
+at other rootlets similarly treated, and could never again discover
+these elastic threads.  I therefore infer that the branch in question
+must have been slightly moved from the wall at some critical period,
+whilst the secretion was in the act of drying, through the absorption
+of its watery parts.  The genus Ficus abounds with caoutchouc, and we
+may conclude from the facts just given that this substance, at first
+in solution and ultimately modified into an unelastic cement, {42} is
+used by the Ficus repens to cement its rootlets to any surface which
+it ascends.  Whether 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 the Marcgravia 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 (p. 49), these crawl
+into crevices, and when they meet with a thin support, wind round it,
+as do 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 a little to that side, in the course of about a day,
+and adhered by their rootlets to the wood; but they did not bend
+quite round the sticks, and afterwards they re-pursued their downward
+course.  It is probable that these slight movements of the roots are
+due to the quicker growth of the side exposed to the light, in
+comparison with the other side, and not because the roots are
+sensitive to contact in the same manner as true tendrils.  According
+to Mohl, the rootlets of certain species of Lycopodium act as
+tendrils. {43}
+
+
+Concluding Remarks on Climbing Plants.
+
+
+Plants become climbers, in order, as it may be presumed, to reach the
+light, and to expose a large surface of their leaves to its action
+and to that of the free air.  This is effected by climbers with
+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 so many
+climbing plants in all quarters of the world, belonging to so many
+different orders.  These plants have been arranged under four
+classes, disregarding those which merely scramble over bushes without
+any special aid.  Hook-climbers are the least efficient of all, at
+least in our temperate countries, and can climb only in the midst of
+an entangled mass of vegetation.  Root-climbers are excellently
+adapted to ascend naked faces of rock or trunks of trees; when,
+however, they climb trunks 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 require long-continued and
+close contact with a steady surface in order to adhere.  The two
+great classes of twiners and of plants with sensitive organs, namely,
+leaf-climbers and tendril-bearers taken together, far exceed in
+number and in the perfection of their mechanism the climbers of the
+two first classes.  Those which have the power of spontaneously
+revolving and of grasping objects with which they come in contact,
+easily pass from branch to branch, and securely ramble over a wide,
+sun-lit surface.
+
+The divisions containing twining plants, leaf-climbers, and tendril-
+bearers graduate to a certain extent into one another, and nearly all
+have the same remarkable power of spontaneously revolving.  Does this
+gradation, it may be asked, indicate that plants belonging to one
+subdivision have actually passed during the lapse of ages, or can
+pass, from one state to the other?  Has, for instance, any tendril-
+bearing plant assumed its present structure without having previously
+existed as 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 exception, revolve in
+exactly the same manner as twiners; some few can still twine well,
+and many others in an imperfect manner.  Several leaf-climbing genera
+are closely allied to other genera which are simple twiners.  It
+should also be observed, that the possession of leaves with sensitive
+petioles, and with the consequent power of clasping an object, would
+be of comparatively little use to a plant, unless associated with
+revolving internodes, by which the leaves are brought into contact
+with a support; although no doubt a scrambling plant would be apt, as
+Professor Jaeger has remarked, to rest on other plants by its leaves.
+On the other hand, revolving internodes, without any other aid,
+suffice to give the power of climbing; so that it seems probable that
+leaf-climbers were in most cases at first twiners, and subsequently
+became capable of grasping a support; and this, as we shall presently
+see, is a great additional advantage.
+
+From analogous reasons, it is probable that all tendril-bearers were
+primordially twiners, that is, are the descendants of plants having
+this power and habit.  For the internodes of the majority revolve;
+and, in a few species, the flexible stem still retains the capacity
+of spirally twining round an upright stick.  Tendril-bearers have
+undergone much more modification than leaf-climbers; hence it is not
+surprising that their supposed primordial habits of revolving and
+twining have been more frequently lost or modified than in the case
+of leaf-climbers.  The three great tendril-bearing families in which
+this loss has occurred in the most marked manner, are the
+Cucurbitaceae, Passifloraceae, and Vitaceae.  In the first, the
+internodes revolve; but I have heard of no twining form, with the
+exception (according to Palm, p. 29. 52) of Momordica balsamina, and
+this is only an imperfect twiner.  In the two other families I can
+hear of no twiners; and the internodes rarely have the power of
+revolving, this power being confined to the tendrils.  The
+internodes, however, of Passiflora gracilis have the 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 has been
+retained by some members of all the larger tendril-bearing groups.
+
+On the view here given, it may be asked, Why have the species which
+were aboriginally twiners been converted in so many groups into leaf-
+climbers or tendril-bearers?  Of what advantage has this 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 tendrils or sensitive petioles, as some species of Bignonia,
+Clematis, and Tropaeolum, it can readily be observed how incomparably
+better they grasp an upright stick than do simple twiners.  Tendrils,
+from possessing this power of grasping an object, can be made long
+and thin; so that little organic matter is expended in their
+development, and yet they sweep a wide circle in search of a support.
+Tendril-bearers can, from their first growth, ascend along the outer
+branches of any neighbouring bush, and they are thus always fully
+exposed to the light; twiners, on the contrary, are best fitted to
+ascend bare stems, and generally have to start in the shade.  Within
+tall and dense tropical forests, twining plants would probably
+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 thick trunks, whereas this
+can be affected by tendril-bearers if the trunks are branched or bear
+twigs, and by some species if the bark is rugged.
+
+The advantage gained by climbing is to reach the light and free air
+with as little expenditure of organic matter as possible; now, with
+twining 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, on the other hand, which had ascended to the same
+height by the aid of its tendrils, was but little longer than the
+height reached.  That this saving of the stem is really an advantage
+to climbing plants, I infer from the species that still twine but are
+aided by clasping petioles or tendrils, generally making more open
+spires than those made by simple twiners.  Moreover, the plants thus
+aided, after taking one or two turns in one direction, generally
+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 have been
+possible; and they do this with safety, as they secure themselves at
+intervals by their clasping petioles or tendrils.
+
+We have seen that tendrils consist of various organs in a modified
+state, namely, leaves, flower-peduncles, branches, and perhaps
+stipules.  With respect to leaves, the evidence of their modification
+is ample.  In young plants of Bignonia the lower leaves often remain
+quite unchanged, whilst the upper ones have their terminal leaflets
+converted into perfect tendrils; in Eccremocarpus I have seen a
+single lateral branch of a tendril replaced by a perfect leaflet; 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 kinds of
+tendrils; he will wish to learn, as far as is possible, by what
+actual steps leaves, flower-peduncles, &c., have had their functions
+wholly changed, and have come to serve merely as prehensile organs.
+
+In the whole group of leaf-climbers abundant evidence has been given
+that an organ, still subserving the functions of a leaf, may become
+sensitive to a touch, and thus grasp an adjoining object.  With
+several leaf-climbers the true leaves spontaneously revolve; and
+their petioles, after clasping a support grow thicker and stronger.
+We thus see that leaves may acquire all the leading and
+characteristic qualities of tendrils, namely, sensitiveness,
+spontaneous movement, and subsequently increased strength.  If their
+blades or laminae were to abort, they would form true tendrils.  And
+of this process of abortion we can follow every step, until no trace
+of the original nature of the tendril is left.  In Mutisia clematis,
+the tendril, in shape and colour, closely resembles the petiole of
+one of the ordinary leaves, together with the midribs of the
+leaflets, but vestiges of the laminae are still occasionally
+retained.  In four genera of the Fumariaceae we can follow the whole
+process of transformation.  The terminal leaflets of the leaf-
+climbing Fumaria officinalis are not smaller than the other leaflets;
+those of the leaf-climbing Adlumia cirrhosa are greatly reduced;
+those of Corydalis claviculata (a plant which may indifferently be
+called a leaf-climber or a tendril-bearer) are either reduced to
+microscopical dimensions or have their blades wholly aborted, so that
+this plant is actually in a state of transition; and, finally, in the
+Dicentra the tendrils are perfectly characterized.  If, therefore, we
+could behold at the same time all the progenitors of Dicentra, we
+should almost certainly see a series like that now exhibited by the
+above-named three genera.  In Tropaeolum tricolorum we have another
+kind of passage; for the leaves which are first formed on the young
+stems are entirely destitute of laminae, and must be called tendrils,
+whilst the later formed leaves have well-developed laminae.  In all
+cases the acquirement of sensitiveness by the mid-ribs of the leaves
+appears to stand in some close relation with the abortion of their
+laminae or blades.
+
+On the view here given, leaf-climbers were primordially twiners, and
+tendril-bearers (when formed of modified leaves) were primordially
+leaf-climbers.  The latter, therefore, are intermediate in nature
+between twiners and tendril-bearers, and ought to be related to both.
+This is the case:  thus the several leaf-climbing species of the
+Antirrhineae, of Solanum, Cocculus, and Gloriosa, have within the
+same family and even within the same genus, relatives which are
+twiners.  In the genus Mikania, there are leaf-climbing and twining
+species.  The leaf-climbing species of Clematis are very closely
+allied to the tendril-bearing Naravelia.  The Fumariaceae include
+closely allied genera which are leaf-climbers and tendril-bearers.
+Lastly, a species of Bignonia is at the same time both a leaf-climber
+and a tendril-bearer; and other closely allied species are twiners.
+
+Tendrils of another kind consist of modified flower-peduncles.  In
+this case we likewise have many interesting transitional states.  The
+common Vine (not to mention the Cardiospermum) gives us every
+possible gradation between a perfectly developed tendril and a
+flower-peduncle covered with flowers, yet furnished with a branch,
+forming the flower-tendril.  When the latter itself bears a few
+flowers, as we know sometimes is the case, and still retains the
+power of clasping a support, we see an early condition of all those
+tendrils which have been formed by the modification of flower-
+peduncles.
+
+According to Mohl and others, some tendrils consist of modified
+branches:  I have not observed any such cases, and know nothing of
+their transitional states, but these have been fully described by
+Fritz Muller.  The genus Lophospermum also shows us how such a
+transition is possible; for its branches spontaneously revolve and
+are sensitive to contact.  Hence, if the leaves on some of the
+branches of the Lophospermum were to abort, these branches would be
+converted into true tendrils.  Nor is there anything improbable in
+certain branches alone being thus modified, whilst others remained
+unaltered; for we have seen with certain varieties of Phaseolus, that
+some of the branches are thin, flexible, and twine, whilst other
+branches on the same plant are stiff and have no such power.
+
+If we inquire how a petiole, a branch or flower-peduncle first became
+sensitive to a touch, and acquired the power of bending towards the
+touched side, we get no certain answer.  Nevertheless an observation
+by Hofmeister {44} well deserves attention, namely, that the shoots
+and leaves of all plants, whilst young, move after being shaken.
+Kerner also finds, as we have seen, that the flower-peduncles of a
+large number of plants, if shaken or gently rubbed bend to this side.
+And it is young petioles and tendrils, whatever their homological
+nature may be, which move on being touched.  It thus appears that
+climbing plants have 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 further inquire how the stems,
+petioles, tendrils, and flower-peduncles of climbing plants first
+acquired their power of spontaneously 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
+moving, both spontaneously and from various stimulants, is far more
+common with plants, than is generally supposed to be the case by
+those who have not attended to the subject.  I have given one
+remarkable instance, namely that of the Maurandia semperflorens, the
+young flower-peduncles of which spontaneously revolve in very small
+circles, and bend when gently rubbed to the touched side; yet this
+plant certainly does not profit by these two feebly developed powers.
+A rigorous examination of other young plants would probably show
+slight spontaneous movements in their stems, petioles or peduncles,
+as well as sensitiveness to a touch. {45}  We see at least that the
+Maurandia might, by a little augmentation of the powers which it
+already possesses, come first to grasp a support by its flower-
+peduncles, and then, by the abortion of some of its flowers (as with
+Vitis or Cardiospermum), acquire perfect tendrils.
+
+There is one other interesting point which deserves notice.  We have
+seen that some tendrils owe their origin to modified leaves, and
+others to modified flower-peduncles; so that some are foliar and
+others axial in their nature.  It might therefore have been expected
+that they would have presented some difference in function.  This is
+not the case.  On the contrary, they present the most complete
+identity in their several characteristic powers.  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.  Both
+are either attracted or repelled by the light.  The latter property
+is seen in the foliar tendrils of Bignonia capreolata and in the
+axial tendrils of Ampelopsis.  The tips of the tendrils in these two
+plants become, after contact, enlarged into discs, 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 that the petiole of Solanum jasminoides,
+after it has clasped a support, assumes one of the most
+characteristic features of the axis, namely, a closed ring of woody
+vessels, we can hardly avoid asking, whether the difference between
+foliar and axial organs can be of so fundamental a nature as is
+generally supposed? {46}
+
+We have attempted to trace some of the stages in the genesis of
+climbing plants.  But, during the endless fluctuations of the
+conditions of life to which all organic beings have been exposed, it
+might be 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 their native country
+never twine, but reassume this habit when cultivated in England, we
+have a case in point.  In the leaf-climbing Clematis flammula, and in
+the tendril-bearing Vine, we see no loss in the power of climbing,
+but only a remnant of the 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 Bignoniaceae, we see a last
+and doubtful trace of the power of revolving.
+
+With respect to the abortion of tendrils, certain cultivated
+varieties of Cucurbita pepo have, according to Naudin, {47} either
+quite lost these organs or bear semi-monstrous representatives of
+them.  In my limited experience, I have met with only one apparent
+instance 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, according to analogy, a tendril ought
+to have existed, a small pointed filament projects, about a third of
+an inch in length, and which is probably the rudiment of a tendril.
+This may be the more safely inferred, as in young and unhealthy
+specimens of other tendril-bearing plants similar rudiments may
+occasionally be observed.  In the bean these filaments are variable
+in shape, as is so frequently the case with rudimentary organs; they
+are either cylindrical, or foliaceous, or are deeply furrowed on the
+upper surface.  They have not retained any vestige of the power of
+revolving.  It is a curious fact, that many of these filaments, when
+foliaceous, have on their lower surfaces, dark-coloured glands like
+those on the stipules, which excrete a sweet fluid; so that these
+rudiments have been feebly utilized.
+
+One other analogous case, though hypothetical, is worth giving.
+Nearly all the species of Lathyrus possesses tendrils; but L.
+nissolia is destitute of them.  This plant has leaves, which must
+have struck everyone with surprise who has noticed them, for they are
+quite unlike those of all common papilionaceous plants, and resemble
+those of a grass.  In another species, L. aphaca, the tendril, which
+is not highly developed (for it is unbranched, and has no spontaneous
+revolving-power), replaces the leaves, the latter being replaced in
+function by large stipules.  Now if we suppose the tendrils of L.
+aphaca to become flattened and foliaceous, like the little
+rudimentary tendrils of the bean, and the large stipules to become at
+the same time reduced in size, from not being any longer wanted, 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 serving to sum up the foregoing views on the
+origin of tendril-bearing plants, that L. nissolia is probably
+descended from a plant which was primordially a twiner; this then
+became a leaf-climber, the leaves being afterwards converted by
+degrees into tendrils, with the stipules greatly increased in size
+through the law of compensation. {48}  After a time the tendrils lost
+their branches and became simple; they then lost their revolving-
+power (in which state they would have resembled the tendrils of the
+existing L. aphaca), and afterwards losing their prehensile power and
+becoming foliaceous would no longer be thus designated.  In this last
+stage (that of the existing L. nissolia) the former tendrils would
+reassume their original function of leaves, and the stipules which
+were recently much developed being no longer wanted, would decrease
+in size.  If species become modified in the course of ages, as almost
+all naturalists now admit, we may conclude that L. nissolia has
+passed through a series of changes, in some degree like those here
+indicated.
+
+The most interesting point in the natural history of climbing plants
+is the various kinds of movement which they display in manifest
+relation to their wants.  The most different organs--stems, branches,
+flower-peduncles, petioles, mid-ribs of the leaf and leaflets, and
+apparently aerial roots--all possess this power.
+
+The first action of a tendril is to place itself in a proper
+position.  For instance, the tendril of Cobaea first rises vertically
+up, with its branches divergent and with the terminal hooks turned
+outwards; the young shoot at the extremity of the stem is at the same
+time bent to one side, so as to be out of the way.  The young leaves
+of Clematis, on the other hand, prepare for action by temporarily
+curving themselves downwards, so as to serve as grapnels.
+
+Secondly, if a twining plant or a tendril gets by any accident into
+an inclined position, it soon bends upwards, though secluded from the
+light.  The guiding stimulus no doubt is the attraction of gravity,
+as Andrew Knight showed to be the case with germinating plants.  If a
+shoot of any ordinary 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
+downward-bent shoot reverses its curvature; but if the stolen of a
+strawberry, which has no tendency to grow upwards, be thus treated,
+it will curve downwards in the direction of, instead of in opposition
+to, the force of gravity.  As with the strawberry, so it is generally
+with the twining shoots of the Hibbertia dentata, which climbs
+laterally from bush to bush; for these shoots, if placed in a
+position inclined downwards, 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 the incurvation which causes them
+to revolve, so that their revolving movement is often accelerated or
+retarded in travelling to or from the light.  On the other hand, in a
+few instances tendrils bend towards the dark.
+
+Fourthly, we have the spontaneous revolving movement which is
+independent of any outward stimulus, but is contingent on the youth
+of the part, and on vigorous health; and this again of course depends
+on a proper temperature and other favourable conditions of life.
+
+Fifthly, tendrils, whatever their homological nature may be, and the
+petioles or tips of the leaves of leaf-climbers, and apparently
+certain roots, all have the power of movement when touched, and bend
+quickly towards the touched side.  Extremely slight pressure often
+suffices.  If the pressure be not permanent, the part in question
+straightens itself and is again ready to bend on being touched.
+
+Sixthly, and lastly, tendrils, soon after clasping a support, but not
+after a mere temporary curvature, contract spirally.  If they have
+not come into contact with any object, they ultimately contract
+spirally, after ceasing to revolve; but in this case the movement is
+useless, and occurs only after a considerable lapse of time.
+
+With respect to the means by which these various movements are
+effected, there can be little doubt from the researches of Sachs and
+H. de Vries, that they are due to unequal growth; but from the
+reasons already assigned, I cannot believe that this explanation
+applies to the rapid movements from a delicate touch.
+
+Finally, climbing plants are sufficiently numerous to form a
+conspicuous feature in the vegetable kingdom, more especially in
+tropical forests.  America, which so abounds with arboreal animals,
+as Mr. Bates remarks, likewise abounds according to Mohl and Palm
+with climbing plants; and of the tendril-bearing plants examined by
+me, the highest developed kinds are natives of this grand continent,
+namely, the several species of Bignonia, Eccremocarpus, Cobaea, and
+Ampelopsis.  But even in the thickets of our temperate regions the
+number of climbing species and individuals is considerable, as will
+be found by counting them.  They belong to many and widely different
+orders.  To gain some rude 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 have
+added many more), all those families in Lindley's 'Vegetable Kingdom'
+which include twiners, leaf-climbers, or tendril-bearers.  Lindley
+divides Phanerogamic plants into fifty-nine Alliances; of these, no
+less than thirty-five include climbing plants of the above kinds,
+hook and root-climbers being excluded.  To these a few Cryptogamic
+plants must be added.  When we reflect on the wide separation of
+these plants in the series, and when we know that in some of the
+largest, well-defined orders, such as the Compositae, Rubiaceae,
+Scrophulariaceae, Liliaceae, &c., species in only two or three genera
+have the power of climbing, the conclusion is forced on our minds
+that the capacity of revolving, 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 be
+said that plants acquire and display this power only when it is of
+some advantage to them; this being of comparatively rare occurrence,
+as they are affixed to the ground, and food is brought to them by the
+air 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 it self.  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 tendrils or internodes, or
+both, spontaneously revolve with a steady motion.  The tendril
+strikes some object, and quickly curls round and firmly grasps it.
+In the course of some hours it contracts into a spire, dragging up
+the stem, and forming an excellent spring.  All movements now cease.
+By growth the tissues soon become wonderfully strong and durable.
+The tendril has done its work, and has done it in an admirable
+manner.
+
+
+
+Footnotes:
+
+{1}  An English translation of the 'Lehrbuch der Botanik' by
+Professor Sachs, has recently (1875), appeared under the title of
+'Text-Book of Botany,' and this is a great boon to all lovers of
+natural science in England.
+
+{2}  'Proc. Amer. Acad. of Arts and Sciences,' vol. iv. Aug. 12,
+1858, p. 98.
+
+{3}  Ludwig H. Palm, 'Ueber das Winden der Pflanzen;' Hugo von Mohl,
+'Ueber den Bau und des Winden der Ranken und Schlingpflanzen,' 1827.
+Palm's Treatise was published only a few weeks before Mohl's.  See
+also 'The Vegetable Cell' (translated by Henfrey), by H. von Mohl, p.
+147 to end.
+
+{4}  "Des Mouvements revolutife Respontanes," &c., 'Comptes Rendus,'
+tom. xvii. (1843) p. 989; "Recherches sur la Volubilite des Tiges,"
+&c., tom. xix. (1844) p. 295.
+
+{5}  'Bull. Bot Soc. de France,' tom. v. 1858, p. 356.
+
+{6}  This whole subject has been ably discussed and explained by H.
+de Vries, 'Arbeiten des Bot. Instituts in Wurzburg,' Heft iii. pp.
+331, 336.  See also Sachs ('Text-Book of Botany,' English
+translation, 1875, p. 770), who concludes "that torsion is the result
+of growth continuing in the outer layers after it has ceased or begun
+to cease in the inner layers."
+
+{7}  Professor Asa Gray has remarked to me, in a letter, that in
+Thuja occidentalis the twisting of the bark is very conspicuous.  The
+twist is generally to the right of the observer; but, in noticing
+about a hundred trunks, four or five were observed to be twisted in
+an opposite direction.  The Spanish chestnut is often much twisted:
+there is an interesting article on this subject in the 'Scottish
+Farmer,' 1865, p. 833.
+
+{8}  It is well known that the stems of many plants occasionally
+become spirally twisted in a monstrous manner; and after my paper was
+read before the Linnean Society, Dr. Maxwell Masters 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 what I have said about the twisting of stems, which have
+twined round rugged supports; but does not preclude the twisting
+being of service to the plant by giving greater rigidity to the stem.
+
+{9}  The view that the revolving movement or nutation of the stems of
+twining plants is due to growth is that advanced by Sachs and H. de
+Vries; and the truth of this view is proved by their excellent
+observations.
+
+{10} The mechanism by which the end of the shoot remains hooked
+appears to be a difficult and complex problem, discussed by Dr. H. de
+Vries (ibid. p. 337):  he concludes that "it depends on the relation
+between the rapidity of torsion and the rapidity of nutation."
+
+{11}  Dr. H. de Vries also has shown (ibid. p. 321 and 325) by a
+better method than that employed by me, that the stems of twining
+plants are not irritable, and that the cause of their winding up a
+support is exactly what I have described.
+
+{12}  Dr. H. de Vries states (ibid. p. 322) that the stem of Cuscuta
+is irritable like a tendril.
+
+{13}  See Dr. H. de Vries (ibid.  p. 324) on this subject.
+
+{14}  Comptes Rendus, 1844, tom. xix. p. 295, and Annales des Sc. Nat
+3rd series, Bot., tom. ii.  p. 163.
+
+{15}  I am much indebted to Dr. Hooker for having sent me many plants
+from Kew; and to Mr. Veitch, of the Royal Exotic Nursery, for having
+generously given me a collection of fine specimens of climbing
+plants.  Professor Asa Gray, Prof. Oliver, and Dr. Hooker have
+afforded me, as on many previous occasions, much information and many
+references.
+
+{16}  Journal of the Linn. Soc. (Bot.) vol. ix. p. 344.  I shall have
+occasion often to quote this interesting paper, in which he corrects
+or confirms various statements made by me.
+
+{17}  I raised nine plants of the hybrid Loasa Herbertii, and six of
+these also reversed their spire in ascending a support.
+
+{18}  In another genus, namely Davilla, belonging to the same family
+with Hibbertia, Fritz Muller says (ibid. p. 349) that "the stem
+twines indifferently from left to right, or from right to left; and I
+once saw a shoot which ascended a tree about five inches in diameter,
+reverse its course in the same manner as so frequently occurs with
+Loasa."
+
+{19}  Fritz Muller states (ibid. p. 349) that he saw on one occasion
+in the forests of South Brazil a trunk about five feet in
+circumference spirally ascended by a plant, apparently belonging to
+the Menispermaceae.  He adds in his letter to me that most of the
+climbing plants which there ascend thick trees, are root-climbers;
+some being tendril-bearers.
+
+{20}  Fritz Muller has published some interesting facts and views on
+the structure of the wood of climbing plants in 'Bot. Zeitung,' 1866,
+pp. 57, 66.
+
+{21}  It appears from A. Kerner's interesting observations, that the
+flower-peduncles of a large number of plants are irritable, and bend
+when they are rubbed or shaken:  Die Schutzmittel des Pollens, 1873,
+p. 34.
+
+{22}  I have already referred to the case of the twining stem of
+Cuscuta, which, according to H. de Vries (ibid. p. 322) is sensitive
+to a touch like a tendril.
+
+{23}  Dr. Maxwell Masters informs me that in almost all petioles
+which are cylindrical, such as those bearing peltate leaves, the
+woody vessels form a closed ring; semilunar bands of vessels being
+confined to petioles which are channelled along their upper surfaces.
+In accordance with this statement, it may be observed that the
+enlarged and clasped petiole of the Solanum, with its closed ring of
+woody vessels, has become more cylindrical than it was in its
+original unclasped condition.
+
+{24}  Never having had the opportunity of examining tendrils produced
+by the modification of branches, I spoke doubtfully about them in
+this essay when originally published.  But since then Fritz Muller
+has described (Journal of Linn. Soc. vol. ix. p. 344) many striking
+cases in South Brazil.  In speaking of plants which climb by the aid
+of their branches, more or less modified, he states that the
+following stages of development can be traced:  (1.) Plants
+supporting themselves simply by their branches stretched out at right
+angles--for example, Chiococca.  (2.) Plants clasping a support with
+their unmodified branches, as with Securidaca.  (3.) Plants climbing
+by the extremities of their branches which appear like tendrils, as
+is the case according to Endlicher with Helinus.  (4.) Plants with
+their branches much modified and temporarily converted into tendrils,
+but which may be again transformed into branches, as with certain
+Papilionaceous plants.  (5.) Plants with their branches forming true
+tendrils, and used exclusively for climbing--as with Strychnos and
+Caulotretus.  Even the unmodified branches become much thickened when
+they wind round a support.  I may add that Mr. Thwaites sent me from
+Ceylon a specimen of an Acacia which had climbed up the trunk of a
+rather large tree, by the aid of tendril-like, curved or convoluted
+branchlets, arrested in their growth and furnished with sharp
+recurved hooks.
+
+{25}  As far as I can make out, the history of our knowledge of
+tendrils is as follows:- We have seen that Palm and von Mohl observed
+about the same time the singular phenomenon of the spontaneous
+revolving movement of twining-plants.  Palm (p. 58), I presume,
+observed likewise the revolving movement 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 common pea.  Mohl
+first discovered that tendrils are 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 their movement.  Professor Asa Gray, in a
+paper already quoted, first noticed the extreme sensitiveness and
+rapidity of the movements of the tendrils of certain Cucurbitaceous
+plants.
+
+{26}  Fritz Muller states (ibid. p. 348) that in South Brazil the
+trifid tendrils of Haplolophium, (one of the Bignoniaceae) without
+having come into contact with any object, terminate in smooth shining
+discs.  These, however, after adhering to any object, sometimes
+become considerably enlarged.
+
+{27}  Comptes Rendus, tom. xvii. 1843, p. 989.
+
+{28} 'Lecons de Botanique,' &c., 1841, p. 170.
+
+{29}  I am indebted to Prof. Oliver for information on this head.  In
+the Bulletin de la Societe Botanique de France, 1857, there are
+numerous discussions on the nature of the tendrils in this family.
+
+{30}  'Gardeners' Chronicle,' 1864, p. 721.  From the affinity of the
+Cucurbitaceae to the Passifloraceae, it might be argued that the
+tendrils of the former are modified flower-peduncles, as is certainly
+the case with those of Passion flowers.  Mr. R.  Holland (Hardwicke's
+'Science-Gossip,' 1865, p. 105) states that "a cucumber grew, a few
+years ago in my own garden, where one of the short prickles upon the
+fruit had grown out into a long, curled tendril."
+
+{31}  Trans. Phil. Soc. 1812, p. 314.
+
+{32}  Dr. M'Nab remarks (Trans. Bot. Soc. Edinburgh, vol xi. p. 292)
+that the tendrils of Amp. Veitchii bear small globular discs before
+they have came into contact with any object; and I have since
+observed the same fact.  These discs, however, increase greatly in
+size, if they press against and adhere to any surface.  The tendrils,
+therefore, of one species of Ampelopsis require the stimulus of
+contact for the first development of their discs, whilst those of
+another species do not need any such stimulus.  We have seen an
+exactly parallel case with two species of Bignoniaceae.
+
+{33}  Fritz Muller remarks (ibid. p. 348) that a related genus,
+Serjania, differs from Cardiospermum in bearing only a single
+tendril; and that the common peduncle contracts spirally, when, as
+frequently happens, the tendril has clasped the plant's own stem.
+
+{34}  Prof. Asa Gray informs me that the tendrils of P. sicyoides
+revolve even at a quicker rate than those of P. gracilis; four
+revolutions were completed (the temperature varying from 88 degrees-
+92 degrees Fahr.) in the following times, 40 m., 45 m., 38.5 m., and
+46 m.  One half-revolution was performed in 15 m.
+
+{35}  See M. Isid. Leon in Bull. Soc. Bot. de France, tom. v. 1858,
+p. 650.  Dr. H. de Vries points out (p. 306) that I have overlooked,
+in the first edition of this essay, the following sentence by Mohl:
+"After a tendril has caught a support, it begins in some days to wind
+into a spire, which, since the tendril is made fast at both
+extremities, must of necessity be in some places to the right, in
+others to the left."  But I am not surprised that this brief
+sentence, without any further explanation did not attract my
+attention.
+
+{36}  Sachs, however ('Text-Book of Botany,' Eng. Translation, 1875,
+p. 280), has shown that which I overlooked, namely, that the tendrils
+of different species are adapted to clasp supports of different
+thicknesses.  He further shows that after a tendril has clasped a
+support it subsequently tightens its hold.
+
+{37}  Annales des Sc. Nat. Bot. 4th series, tom. xii. p. 89.
+
+{38}  It occurred to me that the movement of notation and that from a
+touch might be differently affected by anaesthetics, in the same
+manner as Paul Bert has shown to be the case with the sleep-movements
+of Mimosa and those from a touch.  I tried the common pea and
+Passiflora gracilis, but I succeeded only in observing that both
+movements were unaffected by exposure for 1.5 hrs. to a rather large
+dose of sulphuric ether.  In this respect they present a wonderful
+contrast with Drosera, owing no doubt to the presence of absorbent
+glands in the latter plant.
+
+{39}  Text-Book of Botany, 1875, p. 779.
+
+{40} Journal of Linn. Soc. vol. ix. p. 348.  Professor G. Jaeger has
+well remarked ('In Sachen Darwin's, insbesondere contra Wigand,'
+1874, p. 106) that it is highly characteristic of climbing plants to
+produce thin, elongated, and flexible stems.  He further remarks that
+plants growing beneath other and taller species or trees, are
+naturally those which would be developed into climbers; anti such
+plants, from stretching towards the light, and from not being much
+agitated by the wind, tend to produce long, thin and flexible shoots.
+
+{41}  Professor Asa Gray has explained, as it would appear, this
+difficulty in his review (American Journal of Science, vol. xl. Sept.
+1865, p. 282) of the present work.  He has observed that the strong
+summer shoots of the Michigan rose (Rosa setigera) are strongly
+disposed to push into dark crevices and away from the light, so that
+they would be almost sure to place themselves under a trellis.  He
+adds that the lateral shoots, made on the following spring emerged
+from the trellis as they sought the light.
+
+{42}  Mr. Spiller has recently shown (Chemical Society, Feb. 16,
+1865), in a paper on the oxidation of india-rubber or caoutchouc,
+that this substance, when exposed in a fine state of division to the
+air, gradually becomes converted into brittle, resinous matter, very
+similar to shell-lac.
+
+{43}  Fritz Muller informs me that he saw in the forests of South
+Brazil numerous black strings, from some lines to nearly an inch in
+diameter, winding spirally round the trunks of gigantic trees.  At
+first sight he thought that they were the stems of twining plants
+which were thus ascending the trees:  but he afterwards found that
+they were the aerial roots of a Philodendron which grew on the
+branches above.  These roots therefore seem to be true twiners,
+though they use their powers to descend, instead of to ascend like
+twining plants.  The aerial roots of some other species of
+Philodendron hang vertically downwards, sometimes for a length of
+more than fifty feet.
+
+{44}  Quoted by Cohn, in his remarkable memoir, "Contractile Gewebe
+im Pflanzenreiche," 'Abhandl. der Schlesischen Gesell.  1861, Heft i.
+s. 35.
+
+{45}  Such slight spontaneous movements, I now find, have been for
+some time known to occur, for instance with the flower-stems of
+Brassica napus and with the leaves of many plants:  Sachs' 'Text-Book
+of Botany' 1875, pp. 766, 785.  Fritz Muller also has shown in
+relation to our present subject ('Jenaischen Zeitschrift,' Bd. V.
+Heft 2, p. 133) that the stems, whilst young, of an Alisma and of a
+Linum are continually performing slight movements to all points of
+the compass, like those of climbing plants.
+
+{46}  Mr. Herbert Spencer has recently argued ('Principles of
+Biology,' 1865, p. 37 et seq.) with much force that there is no
+fundamental distinction between the foliar and axial organs of
+plants.
+
+{47}  Annales des Sc. Nat. 4th series, Bot. tom. vi. 1856, p. 31.
+
+{48}  Moquin-Tandon (Elements de Teratologie. 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 completely disappeared
+and the stipules grew to an enormous size.
+
+
+
+
+
+End of The Project Gutenberg Etext of Climbing Plants by Charles Darwin
+
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