THE STORAGE OF RESERVE MATERIALS 223 
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 is 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, keeping pace with the 
parts aboveground. 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 construction there is 
almost always an excess of such matter formed, which is 
partly deposited in the chloroplasts in the form of small 
granules of starch. These afford us an instance of a very 
