1864.] CHEMISTRY OF MANURES. 117 



was imbibed by the roots plunged therein, and so conveyed as food 

 to the living tissues. According to this view, plants were supposed 

 to live like animals, on organic food, more or less resembling ip 

 chemical composition the tissues which it nourished. This was 

 the old organic or humus theory of plant-nutrition, referred to 

 above as having been attacked and demolished by the great author 

 of the mi 'cral theory, now universally accepted. Liebig indeed 

 proved, in the clearest manner, partly by data ready to his hand^ 

 partly by his own incomparable researches, that it is not possible 

 for plants to oi>tain their nutriment in the form of organic matter. 

 He showed that the "Vegetal kingdom of nature is interposed be- 

 tween the Mineral and the Animal Kingdoms, with the special 

 function of elaborating from the former the food of the latter. 



Thus, for example, with reference to carbon, the weightest 

 solid constituent of plants, Liebig proved it to be absolutely im- 

 possible that a sufficient supply of this element should reach them 

 in the form of dissolved organic matter, or humus. In this de- 

 monstration Liebig took as his data, first, the ascertained solubility 

 of humus in rain water ; secondly, the known average quantity of 

 rain-water fulling annually on an acre of land ; and lastly, the 

 quantity of carbon annually yielded by the average crop of that 

 area, whether in the form of hay, timber, or corn and straw, 

 With these elements of calculation, Liebig demonstrated irrefrag- 

 ably that humus, as such, is not soluble enough to serve as plant- 

 food ; seeing that the whole annual rainfall, even if completely 

 saturated with humus, and entirely absorbed by the growing 

 wheat-plants, grass, or trees, would not supply a fourth part of the 

 carbon removed from the farm in those crops. Liebig showed 

 further, that the growth of perennial plants (forest trees, for ex- 

 ample), so far from exhausting the soil of humus, tends on the 

 contrary, to occasion its accumulation therein ; vegetation, in point 

 of fact, being a condition precedent of humus, not humus of vege- 

 tation. 



Supply op Carbon to Plants. — Pursuins; a chain of aroru- 

 ment in which the researches of De Saussure, Boussinsrault, and 

 many others, were, by a masterly and luminous induction, brought 

 to bear in support of his own conceptions, Liebig established the 

 fact, now universally received, that carbon is conveyed to plants, 

 not in any org nic combination whatever, but as a mineral gas, 

 formed by the aid of atmospheric oxygen, and termed carbonic 

 acid. 



