138 LEAVES. 



those countries where the heat is always intense, trees 

 never part with their leaves. The correctness of an 

 opinion, confirmed by arguments like these, was for a 

 while unquestioned, but subsequent observations have 

 shewn, that leaves are subservient to other and more 

 important ends. It is true, they defend the fruit from 

 the intense heat of summer, and at the same time, pro- 

 tect animals and even men from the parching rays of 

 noon-day. And in cultivating the plants of warm cli- 

 mates, naturally pleased with a greater degree of heat, 

 it is often expedient to remove the leaves, so as to ex- 

 pose the flowers and fruit to the full influence of the 

 sun. This practice, fatal if carried too far, when ju- 

 diciously adopted, will restore to their native flavour, 

 the Melon, the Orange, and the Grape. 



It has long been known, that leaves are organs of 

 Exhalation, from which an invisible vapour continually 

 escapes, capable of being collected, condensed, and 

 accurately examined. The fact is illustrated by a 

 very simple experiment, and we all know that when a 

 branch is separated from its parent stock, it will shortly 

 droop, wither and die. Its weight is diminished, for it 

 is no longer filled with those fluids on which its firmness 

 and elasticity depend. They have been discharged 

 through the pores of the leaves, which, being cut off 

 from all further supply, are sooner or later entirely ex- 

 hausted. But if a leafy stem be placed in a small ves- 

 sel of water, its freshness will be preserved a much 

 longer time, though the perceptible and rapid diminu- 

 tion of the water, will prove that the leaves have been 

 the outlet, through which it has escaped. If the same 

 branch be placed in a close tin box, its freshness will 

 be still longer preserved. Here are no fluids for the 

 stem to absorb, but by confining the air which is al- 



