TRANSLOCATION OF NUTRITIVE MATERIALS 223 



the absorption of food or food materials by a plant is 

 proceeding, 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. The increase of the framework 

 which attends upon the multiplication of the protoplasts, 

 which we commonly speak of as growth, proceeds for such 

 long periods, moreover, that there is stored up in such a 

 structure as a forest tree an enormous amount of material 

 and of potential energy. 



But this latter form of storage, devoted especially to 

 the production and maintenance of a very large plant-body, 

 differs materially from the accumulation 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 trans- 

 ported 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 

 its manufacture. The cell or protoplast, which contains a 



