gS PROCESS OF NUTRITION. CHAP. III. 



ture better by the one surface than the other : and 

 it is known that some surfaces do actually repel it ; 

 as may be seen in the case of Cabbage-leaves in 

 the time of rains and dews, when the drops roll 

 along the upper surface without wetting it, or lodge 

 in its folds and hollows like globules of quicksilver, 

 conglomerated together without being absorbed. 

 This is the case also with all such plants as are 

 covered with bloom. It is probable therefore that 

 all such surfaces as repel moisture are fitted rather 

 for the inhalation of air which they have long been 

 regarded as capable of effecting; and in times in 

 which it was fashionable to look for analogies 

 between the plant and animal in every thing what- 

 ever, leaves were even regarded as being the lungs 

 Though of plants. The notion seems to have arisen as 

 noUungs. follows : Grew thought he had discovered in the 

 leaves a number of little bags or bladders filled 

 with air : the air was supposed to have entered by in- 

 halation ; and the bags or bladders were supposed to 

 be analogous in their office to the cells of the lungs 

 of animals. This was at the time a sufficiently 

 plausible conjecture, but was not enough to prove 

 that leaves are lungs. Accordingly it became ne- 

 cessary to look out for some further arguments in 

 defence of the doctrine, and one of the first that 

 was discovered was that of the experiment of M. 

 Papin, who, with a view to ascertain the point in 

 question, introduced into the receiver of an air- 

 pump an entire plant, root, stem, and leaf. The 



