130 FOOD OP PLANTS AND ANIMALS COMPARED. 



amount of organic matter would be continually diminishing. 

 But Vegetables, holding an intermediate station between the 

 Mineral and Animal creation, bring them, as it were, into con- 

 nexion with each other ; preparing, from little else than the air 

 and the water of the globe, the materials for the sustenance of 

 the countless millions of beings, which move upon its surface, 

 and which, when their allotted period of existence has expired, 

 restore, by their decay, the elements that are required for the 

 support of Vegetable life. 



189. No organic substances can be said to serve as food 

 to Vegetables, in the same manner as to Animals ; for they 

 all need to be separated into nearly their simplest forms, before 

 they can be reunited into the peculiar compounds, which are 

 required by the tissues of the Plant for their nourishment and 

 extension. If it were otherwise, we should expect that those 

 would act as most serviceable manures, which are most similar 

 in composition to vegetable tissue ; just as animal flesh is the 

 most easily digested, of all food, by the animal. But this is not 

 the case ; for the richest manures are well known to be those, 

 which (supplying also certain ingredients presently to be men- 

 tioned) are continually evolving, by their decay, a large quan- 

 tity of carbonic acid. It is in part, by hastening the separation 

 of the elements of some substances, which might otherwise resist 

 decay for a long time, that lime acts as a valuable manure ; and 

 yeast is a still more powerful agent of the same kind, occasion- 

 ing a kind of fermentation in the vegetable matter of the soil, by 

 which a large quantity of carbonic acid is liberated. On the 

 other hand, the carbonic acid produced by a manure may be too 

 rapidly set free ; and thus the plant may become, as it were, 

 gorged with food ; whilst, at a subsequent time, it is starved by 

 the deficiency occasioned by the too great energy of the change 

 at its commencement. In such cases, the addition of some sub- 

 stance (such as charcoal made from bones), which has the power 

 of retarding decomposition, renders the operation of the manure 

 more equable, and more correspondent with the progress of vege- 

 tation. In general, rich manures are most serviceable to plants 

 which, being only annual, naturally grow rapidly ; and those 



