THE STORAGE OF RESERVE MATERIALS 229 
made for storage. The storage forms, whether retained in 
the cells of construction or transferred to others, are different - 
from and more complex than the originally prepared ones, 
and further energy has to be expended on them, either. 
where they are made, or in the place of storage itself. 
As we shall see later, when they come to be utilised in 
after time, a converse process takes place, which is com- 
parable to the digestion which they undergo when, as so 
frequently happens, they are eaten by an animal. 
The surplus food of the plant exists thus in two conditions, 
the one suitable for travelling, the other for storage. The 
former is characterised by solubility and diffusibility, the 
latter generally by insolubility in the cell-sap, and always 
by an absence of the power to pass through the protoplasmic 
membranes. The former usually consists of such substances 
as can at once be assimilated by the living material; the 
latter does not, but requires the digestive changes to take 
place before it becomes so. 
The places where these reserve materials are deposited 
are more numerous than we are apt to suppose. Parts of 
the plant, or definite structures which ultimately serve as 
reproductive organs, readily occur to us as reservoirs which 
are adapted for a somewhat prolonged storage. Seeds, 
tubers, fleshy roots and branches, bulbs, corms, and rhizomes 
are instances of these, and in the short-lived plants which we 
group together roughly as herbaceous in their habit, these are. 
necessarily the most important reservoirs. But it ig different 
with trees and shrubs which live for many years, and which 
do not form fleshy receptacles. We have in these forms 
stout stems or trunks, with numerous branches; large 
woody roots which continue to grow year after year, keep- 
ing pace with the parts above ground. Though the primary 
use of these members is not to store food products, yet they 
have work of this kind to do. We have seen that in the 
cells which are the original seats of carbohydrate construc- 
tion there is almost always an excess of such matter formed, 
which is partly deposited in the chloroplasts in the form 
