130 VEGETABLE PHYSIOLOGY 



The absence of well- differentiated organs set apart for 

 the discharge of these separate functions makes it rather 

 difficult at first to appreciate their independence. In most 

 animal organisms such a differentiation is easily seen, but 

 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 manu- 

 facture of food, but it is mainly so by virtue of the chloro- 

 plasts which its cells contain. These processes can go on 

 perfectly 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 

 chloroplast is the organ which conducts these preliminary 

 constructive 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 differen- 

 tiated 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 many 

 cases 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 more- 

 over which differ considerably in situation in different 



