108 LETTER XXXVI. 



observer at every step. Plants are Nature's eternal 

 laboratories for the decomposition of all that would 

 be injurious to man and other animals — the means 

 by which the nicest equipoise is maintained between 

 two most important opposite principles. Hence it is, 

 that the most tiny blade of grass, or the most obscure 

 weed, becomes in the hands of Providence an effi- 

 cient means of working out the great design of the 

 creation. 



This is not a phenomenon liable to derangement or 

 interruption, but arranged with the most admirable 

 precision in every portion of its details. Thus, for 

 example, although it is through the agency of leaves 

 that the salubrious effect upon the air is brought 

 about ; yet we are not to suppose, that when the 

 leaves have dropped from the trees, and the forest 

 exhibits nothing but bare and naked branches, this 

 agency is diminished. Leaves fall off indeed in win- 

 ter, but at that time the corruption of the air, by the 

 putrefaction of organized matter, is either arrested 

 or very much diminished, and the green carpet which, 

 even in the driest countries, springs up at that season, 

 presents an elaborating surface of immeasurable ex- 

 tent, and amply sufficient to consume such gaseous 

 impurities as may then be engendered. On the other 

 hand, in the spring, when an elevated temperature sets 

 rapidly at liberty the elastic impurities that the winter 

 had bound in chains, leaves, too, are again produced 

 with renewed vigour, and still carry off from the atmo- 

 sphere all that the rapidly decaying matter is mingling 

 with it, separating for themselves what man is inca- 



