180 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 go 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 
Jatter, 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 
