VEGETABLE lEEITABILITY. 385 



lected from the pitcher before the lid opened. It is probable that the 

 pitchers of Dischidia and Cephalotus may contain similar fluids, and 

 may act in the same manner on insects. 



Irritability exists in the stems of twining plants and in tendrils. 

 The coiling of tendrils seems to be due to the same cause as the closing 

 of the leaves of the sensitive plant on being touched. Hofmeister says 

 that the shoots and leaves of all plants, while young, move after being 

 shaken ; and it is almost invariably young petioles and young tendrils, 

 whether formed of modified leaves or flower-peduncles, which move 

 on being touched. The young flower-peduncles of Maurandia semper- 

 florens spontaneously revolve in very small circles and bend them- 

 selves, when gently rubbed, to the touched side. Asa Gray found that 

 the tendrils of many common plants coiled up more or less promptly 

 after being touched or brought with a slight force into contact with a 

 foreign body. In some plants the coiling is rapid enough to be directly 

 seen by the eye. The tendril of Sicyos angulatus, one of the Cucurbi- 

 tacese, when touched, will uncoil into a straight position in the course 

 of an hour, and will again coil up at the second touch. This may be 

 repeated three or four times in the course of six or seven hours. A 

 certain temperature seems to be necessary. Gray experimented at 

 77° F. A tendril that was straight, except a slight hook at the top, 

 on being gently touched once or twice with a piece of wood on the 

 upper side, coUed at the end into 2^ or 3 turns within a minute and 

 a half. The motion began after an interval of several seconds, and 

 fully half of the coiling was quick enough to be very distinctly seen. 

 After little more than an hour had elapsed, it was found to be straight 

 again. The contact was repeated, timing the result by the second- 

 hand of a watch. The coiling began in four seconds, and made one 

 circle and a quarter in four seconds. It had straightened again in an 

 hour and five minutes, and it coiled the third time, on being touched 

 rather firmly, but not so quickly as before — viz. 1^ turn in half-a- 

 minute. The same movements have been observed in the tendrils of 

 the grape-vine and of other plants. The coiling is perhaps caused 

 by the contraction of the cells on the concave side of the coil. — 

 (Gray, Proc. Amer. Acad, of Arts and Sciences, iv. Aug. 12, 1858, 

 p. 88.) 



Darwin has given a valuable paper on climbing plants in the 

 Journal of Proceedings of the Linneam Society, ix. p. 1. 



Climbing plants are thus divided by him :— 



1st. Those which twine spirally round a support. 



2d. Those which ascend by the movement of the foot-stalks or tips 

 of their leaves. 



3d. Those ascending by true tendrils, which are either modified 

 leaves or flower-peduncles, or perhaps branches or stipules. 



■ith. Those furnished with hooks or rootlets for climbing. 

 ■ 2o 



