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.

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