221 



CHAPTEK XV 



THE STORAGE OF RESERVE MATERIALS 



WE have seen that the large amount of food which is 

 continually being manufactured by a normal green plant is 

 very greatly in excess of its immediate requirements, and 

 that there is a very extensive system of storage in such an 

 organism, by the aid of which it is enabled to survive 

 periods, often of some duration, in which the manufacturing 

 processes are entirely suspended. We have considered 

 further the mechanisms of transport, by which the various 

 nutritive substances are transferred from the seats of their 

 manufacture to the places in which they are laid up for 

 longer or shorter periods. 



The questions of transport and of storage are very inti- 

 mately connected. Food once formed is not always moved 

 at once to some place where, after a period of storage, it 

 will be ultimately consumed. It is often transferred more 

 than once, and may occupy several places in succession 

 as the demand for it varies. Indeed, we may regard the 

 surplus manufactured food, that is the quantity which is 

 in excess of the immediate requirements of the construc- 

 tive cells, as a single store, part of which is travelling 

 about the plant, and part of which is from time to time 

 withdrawn from the travelling stream and laid down in 

 particular cells, either to rejoin the travelling current after 

 a longer or shorter time, or to be separated from the parent 

 plant, and serve as a starting point for the growth and 

 nutrition of its offspring. 



A very little consideration will show us that the forms 

 in which the various food- stuffs are packed away in the 



