LESSON 27.] MOVEMENTS. 171 



light ; this is especially the case with those that cling to walls 01 

 trunks by sucker-like disks, as Virginia Creeper, p. 38, fig. 62. 

 When an active tendril comes into contact with a stem or any such 

 extraneous body, it incurves at the point of contact, and so lays hold 

 of the support : the same contraction or tendency to curve affecting 

 the whole length of the tendril, it soon shortens into a coil, part coil- 

 ing one way, part the other, thus drawing the shoot up to the sup- 

 porting body ; or, if the tendril be free, it winds up in a simple coil. 

 This movement of tendrils is so prompt in the Star-Cucumber (Sic- 

 yos) in Echinocystis, and in two sorts of Passion-flower, that the 

 end, after a gentle rubbing, coils up by a movement rapid enough to 

 be readily seen. In plants that climb by their leaf-stalks, such as 

 Maurandia and Tropaeolum, the movements are similar, but much 

 too slow to be seen. 



491. The so-called sleep of plants is a change of position as night 

 draws on, and in different ways, according to the species, the 

 Locust and Wood-Sorrel turning down their leaflets, the Honey 

 Locust raising them upright, the Sensitive Plant turning them for- 

 wards one over another ; and the next morning they resume their 

 diurnal position. One fact, among others, showing that the changes 

 are not caused by the light, but by some power in the plant itself, is 

 this. The leaves of the Sensitive Plant close long before sunset; 

 but they expand again before sunrise, under much less light than 

 they had when they closed. In several plants the leaves take the 

 nocturnal position when brushed or jarred, in the common Sensi- 

 tive Plant very suddenly, in other sorts less quickly, in the Honey 

 Locust a little too slowly for us to see the motion. The way in 

 which blossoms open and close, some when the light increases, some 

 when it diminishes, illustrates the same thing. The stamens of the 

 Barberry, when touched at the base on the inner side, as by an 

 insect seeking for honey, or by the point of a pin, make a sudden 

 jerk forward, and in the process commonly throw some pollen 

 upon the stigma, which stands a little above their reach. 



492. In many of these cases we plainly perceive that a useful end 

 is subserved. But what shall we say of the Venus's Fly-trap of 

 North Carolina, growing where it might be sure of all the food a 

 plant can need, yet provided with an apparatus for catching insects, 

 and actually capturing them expertly by a sudden motion, in the 

 manner already described (126, Fig. 81) ? Or of the leaflets of the 



