1864.] CHEMISTRY OF MANURES. 123 



Whether free atmosplieric nitrogen is assimilable by plants is a 

 moot-point. M. G. Ville and others maintain that it is: M. 

 Boussingault, from the results of experiments extending over 

 twenty years, draws the oj>posite conclusion. Messrs, Lawes, Gil- 

 bert, and Pugh, in an elaborate paper lately published,* record the 

 result of a series of valuable experiments on this point ; and their 

 conclusions are confirmatory of M. Boussingault's view. This 

 therefore appears to be the opinion supported by the prepondera- 

 ting weight of experimental evidence ; a circumstance which ren- 

 ders Schonbein's observation, and the conclusion to which it points, 

 doubly interesting and important. 



Atmospheric Derivation of Plants and Humus. — Thus 

 far the atmosphere, and the moisture and gases it contains, supply 

 the food on which plants live ; the soil serving merely as a sponge 

 to bring into contact with the roots their share of this air-derived 

 food. Even the carbon yielding humus, though it immediately 

 surrounds the roots, supplies them not directly, but only 

 through the intervention of what has been above termed the under- 

 ground atmosphere, by which it is slowly burned. Each successive 

 generation of plants leaves its roots and other debris behind it ; 

 thus replenishing the soil with a fresh stock of air-derived humus, 

 •eremacausis, or decay, in its turn. Every shower washe> down 

 nitrouen, in its acid or alkaline form, from the air; and the same 

 cloud-supplied water furnishes the crops with their oxygen and hy- 

 drogen. It is evident that from centuries of such plant-growth 

 as this no exhaustion of the soil would ensue. 



There is certainly no result of modern investigation more calcu- 

 lated to strike the mind with wonder and admiration than this 

 fact,— that the mighty forests which clothe the earth, and all the vast 

 expanse of herbage and waving crops, and all the living animals 

 which feed on these and each other, including man himself, the 

 lord of all, are built up, so far as concerns nineteen-twentieths of 

 their weight, entirely of invisible gases and vapor supplied by the 

 atmosphere. 



Thus upheld, and moving with the wind, the carbon and nitro- 

 gen compounds chiefly diffused below, the watery clouds suspended 

 above to wash them down, these, the materials of the whole or- 

 ganic kingdom, hover invisible around us ; and by a distributive 

 mechanism the most grand and simple that can be conceived, all 



* Lawes, Gilbert, and Pugh, ''Phil. Trans." vol. cli, p. 431, 1861. 



