74 BOAKD OF AGRICULTURE 



ing in the atmosphere, are seized upon by the aqueous vapor, 

 which, when condensed into snow, rain or dew, brings them to the 

 ground, and to the rootlets of the plants, and imbibed bj^ these it 

 is conveyed through the stem and into the leaves where the super- 

 fluous water is. restored to the atmosphere by exhalation, while 

 the residue is converted into the substance of the vegetable. The 

 water exhaled may be again absorbed by the roots laden with a 

 new supply of the otiier elements from the air again exhaled, and 

 so on. In this way the atmosphere is I'epeatedly purified by the 

 rain, and those -gases and vapors washed out, which else by their 

 accumulations, would prove injurious to man and animals, and are 

 conveyed to the absorbents of plants which they are adapted to 

 nourish. 



Carbonic acid gas contains just its own bulk of oxygen, and by 

 the decomposition of this gas in the leaves of plants, pure oxygen 

 is returned to the air. Vegetation alone in nature operates to 

 give to the air free oxygen, which is indispensable to animals at 

 every moment of their lives. While animals consume the oxygen 

 of the air, and give back carbonic acid, which is injurious to their 

 life, this carbonic acid is the principle element of the food of vege- 

 tables, is consumed and decomposed by them, and its oxygen 

 returned for the use of animals. Here is seen the perfect adapta- 

 tion of the two great kingdoms of living beings to each other ; 

 each removing from the atmosphere that which is noxious to the 

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

 continued existence of the other. 



How dependent is man upon vegetation I While the vegetable 

 kingdom is independent and did exist alone for ages, yet it is 

 absolutely essential to the life of man. 



In this brief view of some of the wonderful processes in nature, 

 we see that a beautiful harmony exists between animal and vege- 

 table life, and that action and reaction takes place between them ; 

 thus preserving through the centuries of a geological period, that 

 balance of the elements favorable to liunmn life. Man, as an actor 

 upon the scene, is a power of sufficient magnitude to work local 

 irregularities, if not an appreciable change in the whole vital 

 economy. The destruction of a large portion of the forests of a 

 continent in a brief period, is an act that cannot pass without being 

 noted in the account current of pliysical nature. 



A great many facts have been recorded that are of interest as 



