70 ON VEGETABLE PHYSIOLOGY. 



being amply balanced by the renovating opera- 

 tions of the day. In the winter, when foliation 

 is suspended, the absence of vegetation is sup- 

 plied by the agitating storms of the season, bring- 

 ing with them purifying breezes from the ocean; 

 or rendering less stationary the deleterious exha- 

 lations of the land. 



Thus in the natural as in the moral world, 

 occurrences, which individually appear to be 

 very striking evils, collectively are productive of 

 the greatest degree of good; and the functions 

 of organic substances, which from their primary 

 effects carry with them strong features of simila- 

 rity, when more closely investigated, are found to 

 be productive of very opposite consequences. 



Before we quit the physiology of leaves (though 

 irrelevant to the subject we have just been treat- 

 ing,) it will be proper to mention, that particular 

 plants and flowers in general close their foliage 

 during the night ; and this has been erroneously 

 termed the sleep of plants. Sleep, as applied 

 to the animal kingdom, more especially the hu- 

 man subject, we know, consists of a suspension 

 of most of the active functions to afford repose to 

 the body, more or less exhausted by the exertions, 

 mental and corporeal, of the preceding day. In 

 plants, deprived as they are of all power of loco- 

 motion, and exposed to no mental excitements, 

 none of the exhausting causes which operate upon 

 Animals prevail, and therefore they seem to need 



