XI.

INSECTIVOROUS AND CLIMBING PLANTS.*

(THE NATION, January 6 and 18, 1876.)

"MINERALS grow; vegetables grow and live; animals grow, live, and feel;" this is the well-worn, not to say out-worn, diagnosis of the three kingdoms by Linnæus. It must be said of it that the agreement indicated in the first couplet is unreal, and that the distinction declared in the second is evanescent. Crystals do not grow at all in the sense that plants and animals grow. On the other hand, if a response to external impressions by special movements is evidence of feeling, vegetables share this endowment with animals; while, if conscious feeling is meant, this can be affirmed only of the higher animals. What appears to remain true is, that the difference is one of successive addition. That the increment in the organic world is of many steps; that in the long series no absolute

1 "Insectivorous Plants. By Charles Darwin, M. A., F. R. S." With Illustrations. London: John Murray. 1875. Pp. 462. New York: D. Appleton & Co.

"The Movements and Habits of Climbing Plants. By Charles Darwin, M. A., F. R. S., etc." Second Edition, revised, with Illustrations. London: John Murray. 1875. Pp. 208. New York: D. Appleton &

Co.

lines separate, or have always separated, organisms which barely respond to impressions from those which more actively and variously respond, and even from those that consciously so respond-this, as we all know, is what the author of the works before us has undertaken to demonstrate. Without reference here either to that part of the series with which man is connected, and in some sense or other forms a part of, or to that lower limbo where the two organic kingdoms apparently merge or whence, in evolutionary phrase, they have emerged-Mr. Darwin, in the present volumes, directs our attention to the behavior of the highest plants alone. He shows that some (and he might add that all) of them execute movements for their own advantage, and that some capture and digest living prey. When plants are seen to move and to devour, what faculties are left that are distinctively animal?

As to insectivorous or otherwise carnivorous plants, we have so recently here discussed this subject-before it attained to all this new popularity—that a brief account of Mr. Darwin's investigation may suffice.' It

1 The Nation, Nos. 457, 458, 1874. It was in these somewhat light and desultory, but substantially serious, articles that some account of Mr. Darwin's observations upon the digestive powers of Drosera and Diona first appeared; in fact, their leading motive was to make sufficient reference to his then unpublished discoveries to guard against expected or possible claims to priority. Dr. Burdon-Sanderson's lect ure, and the report in Nature, which first made them known in England, appeared later.

A mistake on our part in the reading of a somewhat ambiguous sentence in a letter led to the remark, at the close of the first of those articles (p. 295), that the leaf-trap of Dionea had been paralyzed on one side in consequence of a dexterous puncture. What was commu nicated really related to Drosera.

is full of interest as a physiological research, and is a model of its kind, as well for the simplicity and directness of the means employed as for the clearness with which the results are brought out-results which any one may verify now that the way to them is pointed out, and which, surprising as they are, lose half their wonder in the ease and sureness with which they seem to have been reached.

Rather more than half the volume is devoted to one subject, the round-leaved sundew (Drosera rotundifolia), a rather common plant in the northern temperate zone. That flies stick fast to its leaves, being limed by the tenacious seeming dew-drops which stud its upper face and margins, had long been noticed in Europe and in this country. We have heard hunters and explorers in our Northern woods refer with satisfaction to the fate which in this way often befalls one of their plagues, the black fly of early summer. And it was known to some observant botanists in the last century, although forgotten or discredited in this, that an insect caught on the viscid glands it has happened to alight upon is soon fixed by many more—not merely in consequence of its struggles, but by the spontaneous incurvation of the stalks of surrounding and untouched glands; and even the body of the leaf had been observed to incurve or become cup-shaped so as partly to involve the captive insect.

Mr. Darwin's peculiar investigations not only confirm all this, but add greater wonders. They relate to the sensitiveness of these tentacles, as he prefers to call them, and the mode in which it is manifested; their power of absorption; their astonishing discernment of

the

presence of animal or other soluble azotized mat ter, even in quantities so minute as to rival the spectroscope that most exquisite instrument of modern research-in delicacy; and, finally, they establish the fact of a true digestion, in all essential respects similar to that of the stomach of animals.

Sensi

First as to sensitiveness and movement. tiveness is manifested by movement or change of form in response to an external impression. The sensitiveness in the sundew is all in the gland which surmounts the tentacle. To incite movement or other action, it is necessary that the gland itself should be reached. Anything laid on the surface of the viscid drop, the spherule of clear, glairy liquid which it secretes, produces no effect unless it sinks through to the gland; or unless the substance is soluble and reaches it in solution, which, in the case of certain substances, has the same effect. But the glands themselves do not move, nor does any neighboring portion of the tentacle. The outer and longer tentacles bend inward (toward the centre of the leaf) promptly, when the gland is irritated or stimulated, sweeping through an arc of 180° or less, or more-the quickness and the extent of the inflection depending, in equally vigorous leaves, upon the amount of irritation or stimulation, and also upon its kind. A tentacle with a particle of raw meat on its gland sometimes visibly begins to bend in ten seconds, becomes strongly incurved in five minutes, and its tip reaches the centre of the leaf in half an hour; but this is a case of extreme rapidity. A particle of cinder, chalk, or sand, will also incite the bending, if actually brought in contact with the

gland, not merely resting on the drop; but the inflection is then much less pronounced and more transient. Even a bit of thin human hair, only go of an inch in length, weighing only the 78t of a grain, and largely supported by the viscid secretion, suffices to induce movement; but, on the other hand, one or two momentary, although rude, touches with a hard object produce no effect, although a repeated touch or the slightest pressure, such as that of a gnat's foot, prolonged for a short time, causes bending. The seat of the movement is wholly or nearly confined to a portion of the lower part of the tentacle, above the base, where local irritation produces not the slighest effect. The movement takes place only in response to some impression made upon its own gland at the distant extremity, or upon other glands far more remote. For if one of these members suffers irritation the others sympathize with it. Very noteworthy is the correlation between the central tentacles, upon which an insect is most likely to alight, and these external and larger ones, which, in proportion to their distance from the centre, take the larger share in the movement. The shorter central ones do not move at all when a bit of meat, or a crushed fly, or a particle of a salt of ammonia, or the like, is placed upon them; but they transmit their excitation across the leaf to the surrounding tentacles on all sides; and they, although absolutely untouched, as they successively receive the mysterious impulse, bend strongly inward, just as they do when their own glands are excited. Whenever a tentacle bends in obedience to an impulse from its own gland, the movement is always