80 THE TISSUES OF PLANTS 



to the motions visible in the lowest and simplest animal, 

 which are equally destitute of a nervous and muscular 

 system. ^ 



The sensitive plant of the conservatories does not greatly 

 exceed in irritability the shrankia, or wild sensitive plant 

 of the Southern States, the leaves of which promptly close 

 when touched by the hand or the foot of the traveller. 

 Indeed, there is more than one sensitive plant in the 

 world J the vegetable creation teems with these faint fore- 

 shado wings, as it were, of those higher powers of life 

 manifested by animals. 



To the same cause, that is to say, vegetable irritability, 

 or the contractility of the tissues, is to be attributed, the 

 curvature of the tendrils or even of the stems of weak 

 plants around the objects to which they become attached. 

 In cases where tendrils only are put forth, the irritability 

 appears to be confined to them ; but when, the whole stem 

 acts as a tendril, it seems to be diffused through its entire 

 length. 



That the irritability of the tendrils produces the spiral 

 attachment of themselves to the bodies with which they 

 are brought into immediate contact, is capable of direct 

 experimental proof. All tendrils are first put forth in a 

 right line, which is curved into a sort of hook at its apex. 

 If, whilst the tendril is in the condition, a twig or young 

 shoot be rubbed against it a little below the hook, in a few 

 minutes, the tendril will be seen to be curving round the 

 twig, and if the friction be continued, the regular spiral 

 attachment will be ultimately formed. These phenomena 

 must therefore be classed with the movements of the . 

 mimosa, as they are probably only feebler manifestations 

 of the same principle. 



All the movements executed by vegetables are only par- 



