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 



