RELATIONS OF THE VEGETABLE AND ANIMAL KINGDOMS. 201 



sources, and for the restoration of its oxygen. The needful com- 

 pensation is found in the vegetable kingdom. Wliile animals con- 

 sume the oxygen of the air, and give back carbonic acid which is 

 injurious to their life, this carbonic acid is the principal element of 

 the food of vegetables, is consumed and decomposed by them, and 

 its oxygen restored for the use of animals. Hence the perfect adap- 

 tation of the two great kingdoms of living beings to each other ; — 

 each removing from the atmosphere what would be noxious to the 

 other; — each yielding to the atmosphere what is essential to the 

 continued existence of the other.* 



361. The relations of simple vegetation, under this aspect, to the 

 mineral kingdom on the one hand, and the animal kingdom on the 

 other, are simply set forth in the first part of the diagram placed at 

 the close of this chapter. 



362. But, besides this remotely essential office in purifying the 

 air, the vegetable kingdom renders to the animal another service 

 so immediate, that its failure for a single year would nearly depop- 

 ulate the earth; namely, in providing the necessary food for the 

 whole animal Idngdom. It is under tliis view that the great office 

 of vegetation in the general economy of the world is to be contem- 

 plated. Plants are the sole producers of nourishment. They alone 

 transform mineral, chiefly atmospheric materials, they condense air, 

 into organized matter. While they thus produce upon a vast scale, 

 they consume or destroy comparatively little ; and this never in 

 proper vegetation, but in some special processes hereafter to be con- 

 sidered (370). Often when they appear to consume their own pro- 

 ducts, they only transform and transfer them, as when the starch 

 of the potato is converted into new shoots and fohage. 



363. Animals consume what vegetables produce. They them- 

 selves produce nothing directly from the mineral world. The 

 herbivorous animals take from vegetables the organized matter 

 which they have produced ; — a part of it they consume, and in 

 respiration restore the materials to the atmosphere, from which 



* It is plain, however, that, while the animal kingdom is entirely dependent 

 on the vegetable, the latter is independent of the former, and might have 

 existed alone. The decaying races of plants, giving back their carbon to the 

 air and to the soil by decay, would furnish food for their successors. And since 

 all the carbonic acid which animals render to the air in respiration they have 

 derived from their vegetable food, this would in time have found its way back to 

 the air, for the use of new generations of plants, without the intervention of 

 animals. At most, they merely expedite its return. 



