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 
