CHAP. 5. 2. ON VITAL FUNCTIONS. 19.5 



as demonstrating an unusual state of the atmo- 

 spheric electricity. The succeeding summer, 

 that is, in 1811, some of the same species of 

 Plane Trees were again diseased, and a few 

 died. I am informed, that some years ago a 

 similar, though not so extensive a mortality, 

 prevailed among the smoothrined Plane Trees 

 From hence it would appear, that there were 

 particular states of atmosphere which become 

 specific stimuli to diseased actions of particular 

 plants. Abundant ^ proof of the fact, that 

 particular seasons destroy particular tribes of 

 vegetables, may be collected from gardeners 

 and nurserymen. 



A phaenomenon exists in plants which I have 

 never seen fully treated of in any work on the 

 physiology of vegetables, and on which I shall 

 therefore offer a few observations. I allude to 

 the periodical opening and shutting of flowers, 

 and to its particular cause. For example, some 

 flowers are open all day, while others expand 

 only in the evening. There are likewise 

 noctiflorous plants, which close their flowers in 

 the morning. 



In the above cases the degree of heat might be 

 alleged as the exciting cause of the expansion 

 of the flowers : but this will not hold good 



o 2 



