SECTION UI. 
PHYSIOLOGY OF THE NUTRITIVE 
ORGANS. 
235. VeGETABLEs consist principally of carbon (charcoal), 
oxygen, and hydrogen; they also contain small quantities 
of nitrogen, lime, magnesia, &c. They derive the principal 
_ part of their nourishment from the soil. The porous 
_ extremities of the rootlets absorb the fluids with which they 
come in contact. These fluids consist chiefly of water, hold- 
ing in solution decayed animal and vegetable substances, and 
various earthy matters, as silica, alumina; and lime, magnesia, 
soda, potassa, in union with caronic, sulphuric, hydrechloric, 
and acetic acids. 
236. The animal and vegetable matters are sami form- 
ing the main substance of the food of the plant. Hence 
lands which have been covered with wood afford excellent 
crops. The action of the earthy matters on the plant is not 
so well ascertained. It is most probable that they act as a 
stimulus to the absorbing fibres of the root ; and within the 
plant, as a condiment, by their stimulating properties assist- 
ing to keep up the action of the solids in elaborating the 
food; and also forming an important part of the secre-: 
tions. In the soil the different earths and salts assist in de- 
composing the animal and vegetable remains. 
237. To certain plants, particular earthy substances or 
salts are essential, as chloride of sodium (common salt) to 
those which vegetate near the sea-coast, nitrates of lime or 
potassa to borage and nettles: sulphate of lime tolegumi- 
nous plants, siliceous earth to those of the grasses irae a2 
firm rigid culm. ; eae 
matter. Hence there is no need of teeth for the purpose of _ 
mer! gS If a germinating plant be placed in a 
water containing a known quantity of very 
288. The food of vegetables must always be Six = 
fluid form, as the spongioles are incapable of absorbing solid = 
