Page:Darwin - On the movements and habits of climbing plants.djvu/56

 them; but these objects were not well seized. The tendrils, after clasping an upright stick, repeatedly loosed it again; often they would not seize it at all, or their extremities did not coil closely round it. I have observed hundreds of tendrils in 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; and one or both regularly seized an adjoining, thin, upright stick, not high up as with the three previous species, but in a nearly horizontal plane; thus the non-twining stem was enabled to ascend the stick.

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

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