]£3 



CHAPTER XVI. 



OF THE FUNCTIONS OF LEAVES. 



The knowledge of the functions of leaves, 

 and their real use with regard to the plant, is a 

 curious branch of vegetable physiology, which 

 made but a slow progress long after the na- 

 ture of many other parts had been deeply 

 scrutinized and thoroughly explained. 



Caesalpinus {De Plant is, p. 6.) thought 

 leaves merely a clothing, or a protection 

 against cold and heat. He conceived that 

 the rays of the sun, being moderated in 

 passing through them, were prevented from 

 acting too violently on the fruit and young 

 buds. " Accordingly," says he, " many 

 trees lose their leaves in autumn, when 

 their fruits are perfected, and their buds 

 hardened, while such as retain the fruit 

 long, keep also their leaves ; even till a new 



