346 SPONTAXKOUS MOVEMENTS IN PLANTS. 



ville, North Carolina, where it is exceedingly abundant ; but it is 

 not elsewhere found. 



674. A familiar, although less striking, instance of the same kind 

 is seen in the stamens of the common Barberry, which are so excit- 

 able, that the filament approaches the pistil with a sudden jerk, when 

 touched with a point, or brushed by an insect, near the base on the 

 inner side. The object of this motion seems plainly to be the dis- 

 lodgement of the pollen from the cells of the anther, and its projec- 

 tion upon the stigma. But in the D'.onrca it is difficult to conceive 

 what end is subserved by the capture of insects. In a species of 

 Stylidium of New Holland, not uncommon in conservatories, the 

 column, consisting of the united stamens and styles, is bent over to 

 one side of the corolla ; but if slightly irritated, it instantly springs 

 over to the opposite side of the flower. These are among the more 

 remarkable cases of the kind, but by no means the only ones. 

 Anatomical investigation brings to view no peculiarity in the struc- 

 ture of such plants which might explain these movements. Some 

 other movements, which have been likened to these, are entirely 

 mechanical ; as that of the stamens of Kalmia, where the ten an- 

 thers are in the bud received into as many pouches of the mono- 

 petalous corolla, and are carried outwards and downwards when the 

 corolla expands. In this way the slender filaments are strongly re- 

 curved, like so many springs ; until at length, when the anthers are 

 liberated by the full expansion of the corolla, or by the touch of a 

 large insect or other extraneous body, they fly upwards elastically, 

 projecting a mass of pollen in the direction of the stigma. 



675. The twining of stems round a support, and the coiling of 

 tendrils, are attributed by Mohl to a dull irritability ; and this is the 

 most plausible explanation that has been offered. The inner side, 

 which becomes concave and has smaller cells, is in this, as in other 

 cases, the irritable portion. When a foreign body is reached, a 

 contraction of this side causes the tendril partially to embrace the 

 support : this brings the portion just above into contact with it, 

 which is in like manner incited to curve ; and so the hold is secured, 

 or the twining stem continues to wind around the support. In ten- 

 drils this irritability, propagated downward along the concave side, 

 would appear to cause its contraction, which throws the whole into 

 a spiral coil, or, when fixed at both ends, into two opposite spiral 

 coils, thus approximating the growing stem to the supporting 

 body. 



