76 PLANT LIFE ON THE FARM. 
to the light. The starch in a wheat grain, for instance, 
is not actually formed within the seed—it is formed in 
the leaves and conveyed from them to the seed. But 
starch is insoluble; therefore, before it can be conveyed 
from the place where it is formed to the place where it is 
to be stored, it must be rendered soluble, and this change 
is effected by a process of fermentation resulting in its 
conversion into soluble “‘ glucose.” Arrived at the seed, 
the glucose is turned back into insoluble starch to be 
reserved for use when required. The process is essentially 
the same in the case of the tuber of the potato, the 
“bulb” of the turnip, or the root of the mangel: All 
these organs are severally storehouses wherein food is ac- 
cumulated for future use. The food is neither made nor 
elaborated in them, but simply stored, having been 
formed in the leaves and conveyed to the storehouse. 
At one time, therefore, the leaves and stem may be full 
of starch, at another, they may be destitute of it, owing 
to its having been transferred to the seed or the bulb. 
While the origin of the starch is now well known and 
the processes connected with its formation and transport 
fairly understood, it is not so with the nitrogenous mat- 
ters. The nitrogen, as we have seen, enters the plant by 
the root, and is, therefore, not directly dependent on 
light or chlérophyll action. Nitrogenous compounds are 
not formed in the seed, but conveyed to them just as the 
starch is. 
The carbonaceous reserve-materials—that is, the starch, 
the sugar, the oil, the coloring matters—are all the direct 
result of the action of the green matter acted on by light; 
the starch and the sugar are essential requisites for the 
building up of the cell-membrane, the albuminoid or 
nitrogen-containing substances being, in their turn, es- 
sential to the formation of the protoplasm, and of the 
chlorophyll. 
