124 VEGETABLE PHYSIOLOGY 



in plants the cellular structure is so prominent, and the 

 life of the protoplasm is so closely related to its condition 

 in the cell, that attention needs to be specially directed to 

 the point. Each protoplast is dependent upon the contents 

 of its own vacuole, and the early constructive processes in 

 the metabolism, including the manufacture of food in such 

 cells as carry out this process, may take place in it side 

 by side with the digestive changes and at almost the same 

 time. True, a certain division of labour can be noted, but 

 it is not very clearly associated with particular organs. The 

 leaf, for instance, is especially concerned in the manufacture 

 of food, but it is mainly so by virtue of the chloroplasts 

 which its cells contain. These processes can go on per- 

 fectly well in other parts than leaves ; indeed wherever 

 there are chloroplasts we know they do. Thus, though we 

 associate the leaf with this manufacture, it would be wrong 

 to speak of it as the organ to which this process must be 

 referred. We can say with greater accuracy that the chloro- 

 plast is the organ which conducts these preliminary con- 

 structive processes, and that they take place wherever the 

 chloroplasts are found. The wide distribution of the latter, 

 however, shows us that there is no specially differentiated 

 member of the plant set apart to be an organ for this 

 function. In the same way the digestive process, or the 

 utilisation of stored products, goes on wherever there are 

 reservoirs of such bodies, and takes place in the cells of 

 which such reservoirs consist. There, and there only for 

 the most part, unorganised ferments or enzymes are found, 

 instead of being located in particular glands, as in the 

 animal body. These reservoirs, as we have already seen, 

 and shall see again later, are found in the most varied 

 regions of the plant's substance, regions moreover which 

 differ considerably in situation in different plants. We 

 cannot therefore speak of a differentiated organ of 

 digestion. 



Starting, then, with the intricacy of the metabolic 

 processes placed before us, and with their relations to each 



