146 LEAVES. 



sistent with the observations of many of his predeces 

 sors, and of some who have succeeded him. They 

 do not explain why the air we breathe is constantly pure, 

 notwithstanding the unequivocal and decidedly bad ef- 

 fects of respiration. They point to no renovating 

 cause ; and if true, they must subvert one of the most 

 beautiful explanations of modern science ; one which 

 has long been sanctioned by high authority, and will 

 long be remembered with delight, even if it should be 

 proved erroneous. Speaking on this subject, Sir Hum- 

 phry Davy makes the following observations. " It can- 

 not be supposed that the production of oxygen from the 

 leaf, which is known to be connected with its natural 

 colour, is an exertion of diseased action, or that it can 

 acquire carbon in the day time, during its most vigorous 

 growth, and when all its powers for obtaining nourish- 

 ment are exerted, merely for the purpose of exhaling 

 it at night." He concludes that in proportion to the ex- 

 igencies of any plant, will be the rapidity of its absorb- 

 ing carbon ; that if one be made to grow in pure water, 

 and another be placed in carbonaceous earth, the leaves 

 of the former will derive from the atmosphere, what 

 the roots of the latter absorb from the ground ; and 

 tinally that when the leaves of vegetables perform their 

 healthy functions, they purify the air. And their in- 

 fluence on the temperature of the atmosphere, is one 

 of those extraordinary provisions of Nature, which 

 claims the attention and the gratitude of man. Were it 

 not for this, the summer's wind would become a Siroc- 

 co, and the breeze of health would be converted into 

 a pestilential blast. We have already recited the ob- 

 servations of Sonnerat, who found plants comparatively 

 cool, although the heat of the earth from which they 



