620 CONSERVATIVE ORGANS. [LECT. XI, 



was absorbed by the under surface; but if, by 

 thus placing such leaves, we obstruct the exhaling 

 pores, we can readily see why the leaves will be 

 longer withering, since no exhalation takes place ; 

 while in those placed on the opposite disk, the ex- 

 halants are free to perform their functions, and 

 thus empty the foliar cells of their aqueous con- 

 tents more quickly than the absorbents of the 

 upper disk can supply them. In stating this ar- 

 gument, I do not feel bound to point out by what 

 media leaves absorb : although I have already 

 hinted my opinion, that this function in the suc- 

 culent plants of arid soils is performed by a dis- 

 tinct set of organs. A further proof of the truth 

 of this conclusion is, that the leaves of herbs, as 

 Bonnet himself observed, remain fresh nearly the 

 same length of time when placed on either sur- 

 face; for these apertures are present on both 

 surfaces; and, besides, these leaves sooner wither, 

 whichever surface is in contact with the water, 

 than the leaves of trees which are laid with 

 their inferior surface upon that fluid. 



Were I now to enter fully into the proofs, that 

 the foliar apertures are, also, respiratory organs, I 

 should be anticipating the arguments which must 

 be again detailed, when we come to the consider- 

 ation of the general functions of the leaves ; and, 

 therefore, I shall at this time, as briefly as possible, 

 examine those proofs only which are connected 

 with the structure of these organs. 



