Plants. 191 



est, depending much on the vital ener- 

 rgy. Excessive perspiration seems to 

 hurt, and even sometimes to destroy, veg- 

 etables ; defective perspiration is equal- 

 ly injurious. It is also found, that this 

 function is performed, chiefly, if not al- 

 together, by the leaves and young shoots* 

 That it may be properly carried on, all 

 leaves are deciduous ; in those trees cal- 

 led ever-greens, there being a constant 

 succession of leaves, to prevent the or- 

 gan of perspiration from becoming rigid* 

 A quantity of moisture is absorbed by 

 plants, when exposed to a humid atmos- 

 phere. This absorption, as well as the 

 perspiration, is performed by the leaves $ 

 but in what manner has not yet been as- 

 certained. Experiments made by M, 

 Guettard shew, that perspiration is more 

 considerable from the upper, than from 

 the under, surface of the leaves. 



Plants in general are known to receive 

 and transpire more, in equal time, than 

 large animals. It has been found by ac- 

 curate calculation, and repeated experi- 

 ments, that a plant of the sun-flower re- 

 ceives and perspires in twenty-four hours 

 seventeen times more than a man, 



