Page:Darwin - On the movements and habits of climbing plants.djvu/83

 considerably elongated and had completely wound round sticks, exactly like true tendrils. The whole length of another sub-peduncle bearing only eleven flower-buds quickly became curved when slightly rubbed; but even this scanty number of flowers rendered the stalk less sensitive than the other branch, that is, the flower-tendril; for the latter after a lighter rub became curved in a greater degree and more quickly than the sub-peduncle with its few flowers. I have seen a sub-peduncle thickly covered with flower-buds, but with one of the higher lateral branchlets bearing from some cause only two buds, and this one branchlet had become much elongated and had spontaneously caught hold of an adjoining twig; in fact, it formed a little tendril. The increase of length in the sub-peduncle (C) with the decreasing number of its flower-buds is a good instance of the law of compensation. Hence it is that the whole ordinary tendril is longer than the whole flower-peduncle; thus, on one and the same plant, the longest flower-peduncle (measured from the base of the common peduncle to the tip of the flower-tendril) was 8½ inches in length, whilst the longest tendril was nearly double this length, namely 16 inches.

The gradation from the ordinary state of the flower-peduncle, as represented in the drawing (fig. 10), to that of the true tendril (fig. 9) is perfect. We have seen that the sub-peduncle (C), whilst still bearing from thirty to forty flower-buds, may become somewhat elongated and partially assume all the characters of the corresponding branch of the true tendril. From this state we can trace every stage till we come to a full-sized common tendril, bearing on the branch which corresponds with the sub-peduncle one single flower-bud! Hence there can be no doubt that the tendril is a modified flower-peduncle.

Another kind of gradation well deserves notice. The flower-tendril (B, fig. 10) sometimes produces a few flower-buds; I found thirteen and twenty-two on two flower-tendrils on a vine growing against my house; in this state they retain their characteristic qualities of sensitiveness and spontaneous movement, but in a somewhat lessened degree. On vines in hothouses, so many flowers are occasionally produced by the flower-tendrils that a double bunch of grapes is the result; and this is technically called by gardeners a "cluster." In this state the whole bunch of flowers presents scarcely any resemblance to a tendril; and, judging from the facts already given, it would probably possess little power of clasping a support, or of spontaneous movement. Such flower-peduncles closely resemble in structure those borne