PERSPIRATION OP LEAVES. 185 



rope for the food of silkworms only, bears 

 wonderfully the loss of its foliage three or 

 four times a year. How far the fruit is in- 

 jured nobody thinks it worth while to in- 

 quire, as it is never eaten, but it certainly 

 does not fall off prematurely. 



That Leaves imbibe and give out moisture 

 has been long known, this being one of the 

 most obvious facts belonging to them. Dr. 

 Hales thought they might probably imbibe 

 air; but since his time more certain disco- 

 veries have been made concerning this point, 

 as well- as the effects of light upon leaves, 

 which also did not escape the consideration 

 of that great philosopher. All these subjects 

 w r e shall mention in their turn. 



That Leaves give out moisture, or are or- 

 gans of insensible perspiration, is proved by 

 the simple experiment of gathering the leafy 

 branch of a tree, and immediately stopping 

 the wound at its base with mastick, wax, or 

 any other fit substance, to prevent the ef- 

 fusion of moisture in that direction. In a 

 very short time the leaves droop, wither and 

 are dried up. If the same branch, partly 

 faded, though not dead, be placed in a very 



