LEAVES OX THE ATMOSPHERE. 165 



the existence of such wonderful powers in so small 

 and seemingly simple an organ as the leaf of a plant. 

 The agency of the vital principle alone can account 

 for these wonders, though it cannot, to our understand- 

 ing, explain them. *' The thickest veil," says Dr. 

 Thomson at the end of his chapter on vegetation, 

 *^ covers the whole of these processes ; and so far have 

 philosophers hitherto been from removing this veil, 

 that they have not even been able to approach it. All 

 these operations, indeed, are evidently chemical de- 

 compositions and combinations ; but we neither know 

 what these decompositions and combinations are, nor 

 the instruments in which they take place, nor the 

 agents by which they are regulated." 



The vain BulFon caused his own statue to be in- 

 scribed " a genius equal to the majesty of nature," 

 but a blade of grass was sufficient to confound his 

 pretensions. 



