42a 



Dr. Bell on the Fhyfiokgy of PJants. 



the branches only expofcd to the air. They 

 remained in this fituation during the following 

 fummer, when feme of them lived, though in a 

 languid (late, and put out a few leaves; but 

 thofe from which the air had been more accu- 

 rately excluded, died without a fingle exception, 

 2. Trees over- grown with rnofs have few leaves, 

 weak ftioots, and no fruit. The pradice of 

 gardeners is therefore to be commended, who, 

 in the fpring, ftrip the rnofs from the bark of 

 aged trees, and thus admitting the accefTion of 

 the air, reftore them to verdure and fruitfulnefs. 



Haviny: confidered the courfe of the fluids in 

 vegetables, we next proceed to examine the 

 powers by which thefe fluids are moved. 



Capillary atrradion has generally been ac- 

 counted the caufe of the motion of the juices 

 of plants; and the permanence of the action of 

 this power has been fuppofed to depend on the 

 evaporation from the leaves. Qf late years, 

 indeed, botanifts have afcribed to plants a vital 

 power, which they believe afllfts the flow of the 

 juices i and to this opinion I accede, for the folr 

 lowing reafons. i. The defcent of the juices, 

 that is, their return from the branches to the 

 roots, cannot be explained without the fup- 

 pofition of a vital power regulating the motion. 

 A flow of fluids, through capillary tubes, will 

 only take place, v/hen the refiftance, at the one 

 end, is dirniniftied. This might account for 



