ACTION OF LEAVES ON THE ATMOSi'HRRE. 211 



Kezo. V. 3. t. 13. An impression made even 

 in the most gentle manner, upon one of their 

 leanets, is commnnicated in succession to all 

 of them, evincing an exquisite irritability, 

 for It is in vain to attempt any mechanical 

 solution of this phenomenon. Oo.e of this 

 tribe, Hedijsarinn gyrans^ has a spontaneous 

 motion in its leaves, independent of any ex- 

 ternal stimulus, even of light, and only re- 

 quiring a very warm still atmosphere to be 

 performed in perfection. Each leaf is ter- 

 natc, and the small lateral leaflets are fre- 

 quently moving up and down, either equably 

 or by jerks, without any uniformity or co- 

 operation among themselves. It is difficult 

 to guess at the purpose which this singular 

 action is designed to answer to the plant it- 

 self; its effect on a rational beholder cannot 

 be indifferent. 



The chemical actions of light, heat, and 

 the component parts of the atmospheric air, 

 upon leaves, and, where the latter are want- 

 ing, on the green stems of plants, are now, 

 as far as concerns all plants in common, tole- 

 rably well understood. The observations and 

 experiments of Priestley and Ingenhousz hsLve 



p 2 



