328 HOW CROPS GROW. 
cells; they also imbibe such salts as the water of' the soil 
holds in solution; they likewise act directly on the soil, 
and dissolve substances, which are thus first made of avail 
to them. The compounds that the plant must derive from 
the soil are those which are found in its ash, since these 
are not volatile, and cannot, therefore, exist in the atmos- 
phere. The root, however, commonly takes up some other 
elements of its nutrition to which it has immediate access, 
Leaving out of view, for the present, those matters which, 
though found in the plant, appear to be unessential to its 
growth, viz., silica, soda and manganese, the roots absorb 
the following substances, viz. : 
Sulphates ] Potash. 
Phosphates Lime. 
Nitrates and i = Magnesia and 
Chlorides Tron. 
These salts enter the plant by the absorbent surfaces of 
the younger rootlets, and pass upwards through the active 
portions of the stem, to the leaves and to the new-forming 
buds. 
The Leaves, which are unfolded to the air, gather from 
it Carbonic Acid Gas. This compound suffers decompo- 
sition in the plant; its Carbon remains there, its Oxygen 
or an equivalent quantity, very nearly, is thrown off into 
the air again. 
The decomposition of carbonic acid takes place only by 
day and under the influence of the sun’s light. 
From the carbon thus acquired and the elements of wa- 
ter with the codperation of the ash-ingredients, the plant 
organizes the Carbohydrates. Probably glucose, perhaps 
dextrin or soluble starch, are the first products of this 
synthesis. 
The formation of carbohydrates appears to proceed in 
the chlorophyll-cells of the leaf. 
The Albuminoids require for their production the pres- 
ence of a compound of Nitrogen. The salts of DWitria 
