TKANSLOCATION OP NUTEITIVE MATEKIALS 215 



These considerations lead us to the conclusion that when 

 the absorption of food or food materials by a plant is pro- 

 ceeding, the probabilities are decidedly in favour of such 

 an absorption being much greater than the immediate 

 need for direct consumption. The constructive process, 

 followed by the accumulation of its products, is certainly 

 the leading one in the history of the different members 

 of the vegetable kingdom. Most of it is ultimately devoted 

 to the increase of the framework which attends upon the 

 multiplication of the protoplasts, which we commonly speak 

 of as growth, and proceeds for such long periods that there 

 is accumulated in such a structure as a forest tree an enormous 

 amount of material and of potential energy. 



But this latter, form of accumulation, devoted especially 

 to the production and maintenance of a very large plant- 

 body, differs materially from the storage of a quantity of 

 food which is temporarily a surplus, but which is destined 

 for subsequent consumption by the protoplasts. This is 

 a feature of the life of all plants in varying degrees, whether 

 they form a large plant-body or not. We must turn to 

 examine this surplus production in more detail. 



In an earlier chapter we alluded to the very marked 

 division of labour which we can observe in such a com- 

 munity of protoplasts as form a large plant. We have 

 since studied certain of the different processes which are 

 carried on by particular tissues or collections of protoplasts, 

 rendering them unable to perform other necessary duties. 

 It is evident that to enable them to discharge their special 

 functions they must be fed and nourished. It is equally 

 clear that they are not living under conditions which enable 

 them to construct food for themselves. We see that it is 

 consequently necessary for food to be transported to them 

 from the seat of its construction. 



There is in every green plant a localised, though fairly 

 widespread, region in which construction is taking place, 

 and there are other equally well-defined regions which 

 must be supplied with food transported from the seats of 



