LKCT. XI.] ANATOMY OF LEAVES. 621 



All animals that require the presence of air 

 for their existence, have some peculiar apparatus 

 for producing that change in the blood which has 

 been termed its oxygenizement ; and the change, 

 so termed, is said to be the result of respiration, 

 whether it be performed by lungs or by spira- 

 cula. Plants, also, require the presence of air; 

 vitiating it, under certain circumstances, in the 

 same manner as animals, but, under others, in- 

 creasing the proportion of its oxygen : hence 

 plants may properly be said to respire, and the 

 question arises, by what organs is this function 

 performed? Phytologists have generally agreed, 

 that the leaves are the lungs of plants ; but still it 

 may be inquired, does the whole of the leaf act, 

 or in what part of it are the respiratory organs si^ 

 tuated ? My answer is, that the foliar apertures 

 are the actual breathing organs of the plant. In 

 support of this position I refer to the situation of 

 these apertures, which are never seen on leaves that 

 are not exposed to the air ; for the leaves of sub- 

 mersed aquatics are devoid of them; even the 

 leaves of plants which are not naturally aquatics, 

 if they be submersed, soon lose them ; and al- 

 though some plants of the higher classes, which 

 grow in the air, have no leaves, yet, these have 

 apertures on the stem, which, in such instances, 

 perform the respiratory function. But the most 

 perfect plants are furnished with leaves which, 



