428 Dr. Bell on the Phyfiology of Plants: 



were laid upon a furface of water, and it foN 

 lowed, that thofe which had their fuperior fur- 

 face inverted gained little weight, and for the 

 moft part died in a few days ; while fuch as had 

 their inferior furface applied to the water be- 

 canrie much heavier, and flourifhed many months. 

 Thefe fa6ts make it evident, that perfpiration, 

 and abforption, are not performed by the fame 

 VcfiVls, but that each has its peculiar organs. 



It has been commonly fuppufed, that per- 

 fpiration takes place, chiefly, when the air is 

 ■warm ; and abforption, on the other hand, when 

 it is cold and moift. But unlcfs the veflels, pe- 

 culiar to abforption, which are placed in the 

 under furface of the leaves, were kept conftantly 

 in adlion, they would ncceiTarily collapfe or 

 decay. All abforbing organs have a peculiar 

 ftrudure, and an a<ftion depending on life : that 

 fuch an organization is prefent in the leaves of 

 plants, it is reafonable to conclude, becaufe dried 

 leaves do not abforb. The fame reafoning is 

 applicable to the abforption performed by the 

 roots: for when a fmall portion of the root of a 

 hyacinth, growing in water, is cut off, the whole 

 root dies, and new roots are fhot out, having 

 their extremities peculiarly adapted to the ab- 

 forption of nourifhment. 



The noxious matter, carried off by perfpira- 

 tion, requires large dilution to prevent its hurtr 

 ing the delicate (tru6ture of the leaves, and in 



this 



