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CHAPTER XVL 



OF THE FUNCTIONS OF LEAVES. 



XiiE 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 pro- 

 gress long after the nature of many other })arts had 

 been deeply scrutinized and thoroughly explained. 



Caesalpinus (Be Flantis, 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 crop is pro- 

 duced, and longer, as in the Fir, the Arbutus, and the 

 Bay. It is reported that in hot climates, where there 

 is almost perpetually a burning sun, scarcely any trees 

 lose their leaves, because they require them for shade." 

 C?esalpinus goes on to show that leaves proceed from 

 the bark, with some remarks on the pith, (in which 

 we m.ay trace the origin of the Linnaean hypothesis of 

 vegetation,) but which are now superseded by more 

 accurate inquiries. 



A 



