t 153 ] 



CHAPTER XVI, 



OP 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 nature of many other parts had been deep- 

 ly scrutinized and thoroughly explained. 



Caesalpinus {De Plantis, 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 produced, 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." Caesalpinus goes on to show 



that leaves proceed from the bark, with some remarks 



on the pith, (in which we may trace the origin of the 



Linnean hypothesis of vegetation,) but which are now 



superseded by more accurate inquiries. 



The above is certainly a very small part of the use of 



leaves. Yet the observations of this writer, the father of 



botanical philosophy among the moderns, are so far CQr- 

 u 



