338 CHEMISTRY IN AGRICULTURE AND PHYSIOLOGY. 
Both these functions of the leaf are exerted by the same 
cause, viz., light. 
From these experiments we may infer that the leaf prepares 
all the nutriment upon which root and branch and every 
other part of a plant depends; this is quite in contradiction 
to the commonly admitted notion that the root directly nou¬ 
rishes the leaf, and not the leaf the root. I shall now attempt 
to show that the ashes of plants are their true food. 
In 1846 I prepared an artificial soil—of burnt clay, sixty- 
two parts; ashes of mustard, one part. In this earth I 
planted mustard, the vessel containing this soil was put out 
into the open air, receiving nothing but the ordinary rains 
during the summer; in due season the mustard produced 
fine, healthy plants, yielding perfectly mature seed. 
The Rev. Mr. Huxtable has grown turnips weighing four 
pounds in holes made in a plank, filled with nothing but the 
ashes of turnip and sawdust. If any one doubts the truth 
of this statement, I ask: From whence do our “ maiden 
forests” obtain their organic matter ?—not from the soil, for 
here it is constantly accumulating. This question is one of 
great importance to the agriculturist, especially those using 
artificial manures. 
If we have in the atmosphere an inexhaustible supply of 
the element of which organic matter is formed, and it is 
proved that the air is the source from which plants obtain it, 
all that is required of the tiller of the earth is to supply or 
return to the soil the inorganic substances, the ashes. 
The perfect development of a plant, according to this view, 
is dependent upon the presence of certain salts and earths ; 
when these substances are wanting, its growth must be 
arrested. 
If we examine those plants growing on barren soils, we find 
they contain but little inorganic matter; a hundred pounds 
of the wood of fir yield but six ounces of ash, oak, four pounds, 
wheat straw, seven pounds, hops, twelve pounds; the fir 
grows on a rock, or nearly barren sand, oak on good clay, 
wheat a rich loam, and hops on the best soils, requiring 
more skill and capital than any other plant. 
Now it is well known that plants are incapable of forming 
these inorganic substances; hence the soil must be the source 
from whence they were obtained, and the rigid analysis of 
all soils known to be fertile without manure prove such to 
be the fact. 
Wheat straw has a perfect coating of silica, and yields 7 
per cent, of ashes, the grain only 2 per cent.; the ashes of 
the straw contain 65 percent, silica and 8 per cent, phosphc- 
