THE STOBAGE OF EESEKVE MATEBIALS 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 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, 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 



