524 
FOOD OF PLANTS. 
ceasing rotation. Anaximenes also believed that all bodies 
were formed of air, or of aerial matters. Among the moderns, 
Lawrence contended for fire, Helmont for water, Bradley 
for air, and others for earth and nitre; and this uncertainty 
continued till more recent discoveries found that liquids, 
carbonaceous, gaseous, and other substances entered into the 
food of plants, and that water and air are compound sub¬ 
stances—the former consisting of two elastic fluids or gases, 
viz., inflammable air or hydrogen, and vital gas or oxygen, 
or the oxide of hydrogen, and in weight 1 +8 of oxygen ; and 
the latter of two gases, oxygen and azote, and small quanti¬ 
ties of aqueous vapour and of carbonic acid gas—this last 
substance being itself a compound elastic fluid, consisting 
of charcoal dissolved in oxygen. Tull thought that the 
earth reduced to very minute particles supplied the nourish¬ 
ment to vegetables, by attracting much moisture in that 
comminuted state; and that manures only acted mechani¬ 
cally in improving the texture and in crumbling the particles, 
and thus increasing the power of attraction. Duhamel 
adopted these opinions, and thought manures unnecessary ; 
but he lived long enough to abandon that notion, and he 
finally concluded that no single material composed the food 
of plants. Succeeding philosophers have made many ex¬ 
periments on the growth of vegetables in different situations, 
in light and in darkness, and placed in substances of different 
qualities; and the results satisfied them that light and atmo¬ 
spheric air have great influence, and that water is essentially 
necessary to organized bodies, as without it no circulation of 
juices can be carried on, though it be only reckoned a vehicle, 
and not to constitute any part of the food itself. Ingenhousz 
contended for atmospheric air by many very ingenious 
reasonings, which have not yet been clearly proved or under¬ 
stood. Hassenfratz argued for carbon or charcoal being the 
chief food of plants, and derived from the soil by the roots, 
supplied to them in a state of solution or suspension from 
the brown sediment of dung after evaporation. This opinion 
was adopted by Kirwan, with the difference of supposing 
that plants derived carbon from the air by the act of vegeta¬ 
tion, as carbonic acid gas is easily resolved into its two in¬ 
gredients, oxygen and carbon. But common air has been 
shown to contain only a thousandth part of its bulk of car¬ 
bonic acid gas, or, according to Lavoisier, none at all; and 
carbon forms only one fourth part of the fixed air itself. 
And it is doubtful if the brown mud of dung remaining 
after evaporation can be reckoned real coal without under¬ 
going the action of fire; it may rather be called an extract, 
