Page:Darwin - On the movements and habits of climbing plants.djvu/40

fully to examine them. They never act as tendrils: I repeatedly placed thin sticks in contact with young and old peduncles, and I allowed nine vigorous plants to grow over an entangled mass of branches; but in no one instance did a peduncle bend round any object. It is indeed in the highest degree improbable that this should occur, for the flower-peduncles are generally developed on branches which have already securely clasped a support by their petioles; and when borne on free depending branches, they are not produced by the terminal portion of the internode which alone has the power of revolving; so that they can only accidentally and rarely be brought into contact with any surrounding object. Nevertheless (and this is the remarkable fact) these flower-peduncles, whilst young, exhibit feeble revolving powers, and are slightly sensitive to a touch. I selected some stems which had firmly clasped a stick by their petioles, and, placing a bell-glass over them, traced the movements of the young flower-peduncles. Some days these moved over a short and extremely irregular line, making little loops in their course. One day a young peduncle 1½ inch in extreme length was carefully observed, and it made four and a half narrow, vertical, irregular, and very short ellipses—each at an average rate of about 2 h. 25 m.; an adjoining peduncle described during the same time similar, but fewer, ellipses. As the plant had for some time occupied exactly the same position, these movements could not be attributed to the varying action of the light. Peduncles, old enough for the coloured petals to be just visible, do not move. With respect to irritability, I rubbed a few times very lightly with a thin twig two young peduncles (1½ inch in length), one on the upper side and the other on the lower side, and they became in between 4 h. and 5 h. plainly bowed towards the rubbed sides; in 24 h. 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 bowed towards each other, that the arcs of the bows stood at nearly right angles to their previous positions; 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 l½ inch in length required to be rubbed two or three times, and then became only just perceptibly curved. Loops of thread suspended on the peduncles pro-