ATMOSPHERIC ELECTRICITY. MOTIONS OF PLANTS. 265 



warmth of the sun, are causing the vegetation of the land to 

 possess an opposite condition. " How wonderful," it has been 

 remarked, " are the operations of nature ! The silent and peace- 

 ful growth of a vegetation, whose splendour fascinates the eye, 

 develops an agency, which, opposed to that produced by the 

 rapid but unobserved evaporation from the surface of the sur- 

 rounding ocean, tends to load the atmosphere with conflicting 

 elements, from the depth of whose strife issues thunder proclaim- 

 ing the approach of the hurricane and tornado." 



Of the Motions of Plants. 



416. The gradual movements of the parts of plants, which 

 occur as a part of the natural changes involved in their growth, 

 such as the extension of their roots beneath the ground, and the 

 elevation of their leaves and flowers by the upward growth of 

 their stems and branches, have been already noticed; and the 

 causes which influence th|m have been assigned, as far as our 

 knowledge of them extends (. 107, 309). A curious experi- 

 ment has been recently performed, which proves in a remarkable 

 manner the influence of light, on the direction of the growth of 

 these parts. Some seeds of Cabbages, Mustard, and Kidney- 

 beans, were placed in Moss ; and were so arranged, that the 

 only light they could receive was from a mirror, which threw 

 the solar rays upon them from below, upwards ; the natural 

 direction of their growth was in this manner completely changed, 

 the stem being sent downwards, and the roots upwards. 



417. We have here to notice, however, another set of move- 

 ments displayed by Plants ; in which an evident change of place 

 occurs, whilst they are being observed for a short time. One of 

 these is known as the sleep of plants, from the circumstance of 

 its generally occurring in the evening. This consists sometimes 

 in the folding-together of the leaves, in other cases in their 

 drooping, and occasionally in their clasping the stem ; it is most 

 displayed in Leguminous plants having pinnate leaves (. 238.) ; 

 and in them the lateral leaflets commonly fold together, whilst 

 the leaf-stalks are bent downwards on the stem. Many flowers, 

 also, exhibit a regular movement of the same description; 



