168 Important New Theories in Agricultural Science. 
constituents—so far at least as they are soluble in water, or through 
continued action of carbonic acid; and the more abundant and va- 
rious these solutions, the more fruitful is the ground.’ Arguing 
from this view, it is not richness of soil or humus that produces the 
multiplied varieties of alpine plants in Germany, or the absence of 
it that produces but few. ‘‘ Soluble mineral constituents” are 
shewn to be the characteristic of our cultivated field ; and ‘‘ an agri- 
cultural plant” is defined as one, ‘‘ distinguished from wild in- 
dividuals of the same species, by peculiar qualities, which constitute 
its fitness in culture, and which depend upon a modification of che- 
mical action.”” The amazing yield of Indian corn in Mexico—from 
200 to 600 fold—is something which, with all our skill, we cannot 
accomplish, and is a fact in favour of the argument, ‘ that in no case 
do the organic substances contained in the ground perform any direct. 
part of the nutrition of plants.” The annual destruction of organic 
matter all over the earth is estimated at 146 billions of pounds, equal 
to 24 billions of cubic feet ; and if all vegetation depends on organic 
matter for nutrition, to satisfy this consumption, ‘‘ there must have 
been, five thousand years back, ten feet deep of pure organic sub- 
stance on its surface.” Another illustration is furnished by taking 
the number of cattle and other animals in France in a given year 
(1844), and observing the amount of food they consume. The pro- 
cess of nutrition would require 76,789,000,000 pounds of organic 
matter-—six times more than the whole number contribute of organic 
matter towards the reproduction ; and in 100 years “ the whole or- 
ganic material of the country would be consumed!” 
Again ; look at a farm.—How much more is carried off from it 
than is given back again; generally the amount of its yield is three 
times greater than that of the organic matter it receives: while of 
the manure applied, the greater part is not taken up, but imperceptibly 
decomposed. Carbon is the most important of the constituents of 
plants. An acre of sugar plantation produces 7500 pounds of cane, 
of which 1200 pounds are carbon; and yet sugar ‘plantations are 
rarely manured, and then only with the ashes of the burnt canes. 
With bananas, the result is still more striking :—the yield is 98,000 
pounds of fruit in a year from a single acre; and of this 17,000 
pounds—more than a fifth—is carbon ; and the same acre will give 
the same return, year after year, for twenty or thirty years; and 
the ground at the end of that time will be richer than at the com- 
mencement, from nothing more than the decay of the leaves of the 
plant. Here in Europe, too, the difference in weight and in carbon 
between the seed and the produce has often been noted: in wheat, 
89 per cent.; in red clover, 158 per cent.; in peas, 361 per cent. 
‘These facts afford evidence of a supply of carbon derived from other 
sources than those commonly supposed to exist; and while we know 
that seeds will germinate and become vigorous plants i in pure quart- 
zose sand, or in cotton wool, or on a board, we seem to have proof 
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