?P#f vife. ^hfiology of. Plants; ^%X^ 

 and even fometimes to deftroy vegetables; de* 

 feftive perfpirauon is equally injurious. It i^ 

 alfo found, that this fundlion is performed 

 chiefly, if not altogether, by the leaves anj 

 young (hoots. That it may be properly carried 

 on, all leaves are deciduous i in thofe trees 

 called ever-greens, there being a conftant fuc* 

 ceOion of leaves, to prevent the organ of per- 

 Ipiration from becomine rieid. 



Dr. Hales firft obferved, that a quantity of 

 moifture is abforbed by plants when expofed to 

 a humid atmofphere. This abforption, as well 

 as the perfpiration, is performed by the leaves; 

 but in what manner has not yet been afcertained! 

 Experiments made by M. Guettard* Ihew, that 

 perfpiration is more confiderable from the upper, 

 than from the under, furface of leaves, and thofe 

 of the fame author, of Buhamel, t and Bonnet, % 

 demon (Irate, that abforption, on the contrary, 

 is much greater at the inferior furface than at 

 the fuperior. To prove this, the fuperior fur- 

 face of one leaf, and the inferior furface of ano- 

 ther, were covered with varnifh, and the con- 

 fequcnce was, that the former, in a given time, 

 fufFrred little diminution of weight, but the lat- 

 ter became much lighter. Again, fimilar leaves 



* Memolres de I'Acad. des Sciences, 1749. 

 t Phyr. des Arbres, Tom. I. p. ijg. 

 J Tr;iitc des feuilles, Mem. l. 



were 



