242 VEGETABLE PHYSIOLOGY 
CHAPTER XVI 
DIGESTION 
We have noticed in studying the deposition of reserve food- 
stuffs that the forms in which they exist in the reservoirs 
differ in many respects from those which they assume for 
purposes of transport or translocation. They are generally 
insoluble in water or cell-sap, and almost always indiffu- 
sible, whereas they travel in the form of soluble, diffusible, 
bodies. The removal of them from the seats of storage 
takes place at times which are dependent on the resump- 
tion of activity of growth or development; and as such a 
removal involves the resumption of the travelling forms, 
they must undergo a process which, from analogy with 
similar processes in the animal body, may be described as 
digestion. Tach must, after such treatment, be presented 
to the protoplasm of the growing cells in much the same 
form or condition as that in which it was first constructed 
from the simple bodies which the plant absorbed from its 
environment. This is necessary in all cases, because, 
as we have already noticed, the storage forms are not 
directly assimilable by the protoplasm, but have under- 
gone a certain modification in the process of their deposi- 
tion. 
The process of digestion in plants is chiefly intra- 
cellular, and takes place in all cells in which reserve 
materials occur. It is only occasionally that we find it 
taking place on the exterior of the plant—that is, not in 
the interior of a cell. In a few cases we find it carried 
on in connection with the absorption of nitrogenous or 
protein food, as has been already shown in a preceding 
