72 BIOLOGY OF PLANTS. 



of the possibility and utility of supplying these conditions of 

 vegetable life. 



It is on this account that I would urge upon the young far- 

 mer to study this subject, to obtain a scientific knowledge of 

 it, that he may be able to exhibit a practical application of the 

 principles here suggested, when he settles down to the great 

 business of life. 



CHAPTER II. 



INFLUENCE OF THE ATMOSPHERE, WATER AND OTHER 

 AGENTS UPON THE VITAL PRINCIPLE AS CONNECTED 

 WITH THE PHENOMENA OF VEGETATION. 



Some of these agents have already been alluded to when 

 treating of the vital principle, considered as the principal 

 cause of vegetable productions. It is proposed now to con- 

 sider more particularly the degree in which they favor or re- 

 tard the process of nutrition, with the mode in which they act, 

 in order more fully to explain the philosophy of the subject, 

 and to point out suitable methods, to be employed by the ag- 

 riculturist in the culture of his crops. These agents are 

 the atmosphere, water, gravity, cohesion, affinity, heat, light, 

 electricity, and the agency of man. 



Sect. 1. Agency of the Atmosphere. 



The atmosphere is that gaseous fluid which surrounds the 

 earth, and extends to a distance of forty or forty-five miles 

 above it. It is composed essentially of oxygen and nitrogen 

 in the proportion of 21 parts of the former, to 79 of the latter 

 in 100. The atmosphere also contains variable quantities of 

 watery vapors, ytj^uiy part by volume of carbonic acid, a 

 smaller quantity of ammonia, and several other gaseous com- 



