PHYSIOLOGICAL BOTANY. 



imperceptible manner. In these latter cases, the effect 

 is denominated the sleep of plants, and may be more 

 especially witnessed in the leguminose tribes, whose 

 leaves remain folded during a certain portion of tin- 

 day, and assume an appearance of languor and inaction 

 singularly analogous to the periodical state of repose 

 exhibited in the animal kingdom. In cases therefore, 

 where similar effects are brought about by the action of 

 certain stimuli, in a yet more violent or rapid succession, 

 we may imagine that they are nevertheless the results 

 of the same vital property, which is here exhibited 

 under some peculiar degree of excitement. 



(149.) Examples of Vegetable Irritability. As 

 some of the phenomena exhibited by vegetable irrita- 

 bility are very striking, we shall here insert a brief 

 uotice of a few of the most interesting examples. 



(1.) Sensitive- Plants. There are several species 

 of sensitive-plants, which 

 possess the property of 

 moving their leaves 

 when they are touched, 

 or otherwise stimulated. 

 The most common is an 

 annual (Mimosa pudica}, 

 with compound digitate 

 leaves, with four pinnules 

 (_/?</.! 4*9.); each partial 

 petiole being furnished 

 with numerous pairs of 

 leaflets, expanded hori- 

 zontally as at (a). One 

 of the most striking 

 means of eliciting the phenomenon in question, is by 

 scorching a single leaflet in a candle, or by concen- 

 trating the sun's rays upon it with a lens. This 

 leaflet will immediately move, together with the one 

 opposite to it, both bringing their upper surfaces 

 into contact, and at the same time inclining forwards, 





