g6 PROCESS OF NUTRITION. CHAP. HI 



by the upper surface is all that is necessary to herbs, 

 being but low in stature, and near the surface of the 

 earth, where the dews and exhalations are yet so 

 much condensed and so slow of ascent, that absorp- 

 tion by the under surface of the leaf would but 

 drench and destroy them. There may possibly be 

 some truth in this conjecture, though it rests on a 

 foundation rather too slight to be much trusted to ; 

 as the same mode of argumentation would have 

 suited a reversed order of the absorbing capacity of 

 surfaces, if viewed with regard to the rains that 

 descend from the atmosphere. 

 Observa- But as the foregoing experiments upon leaves 



living 011 were ma( ^ e on suc h on ty as were detached from the 

 plants. plant, it may be said that they are not well calcu- 

 lated to become the ground of any general conclu- 

 sion, and that they do not represent to us the actual 

 phenomena of vegetation. To the actual phenomena 

 of vegetation therefore let us now appeal, in as far at 

 least as they are applicable to the present subject. 

 They will be found fully to confirm the fact of the 

 absorption of moisture by the leaf. If, after a long 

 drought, a fog happens to take place before any rain 

 falls, so as to moisten the surface of the leaves, the 

 plant begins to revive and to resume its verdure long 

 before any moisture can have penetrated to the root. 

 Hence it follows incontestably that moisture has been 

 absorbed by the leaf: because it is impossible to 

 account-for the change that has been effected, except 

 by such absorption. But the efficacy of rains them- 



