434 MANUAL OF BOTANY 



discharge of these functions makes it rather difficult at first to 

 appreciate their independence. In the animal body 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 may take place in it side by side with 

 the digestive ones and at almost the same time. True, a certain 

 division of labour can be noted, but it is not very clearly as- 

 sociated with particular structures. Thus the leaf is especially 

 concerned in the processes of anabolism, but it is mainly so by 

 virtue of the chloroplasts which its cells contain. These pro- 

 cesses can go on perfectly Avell in other parts than leaves ; 

 indeed, wherever there are chloroplasts we know they do. Thus, 

 though we associate the leaf with anabolism, it would be wrong to 

 say that it is the organ to which this process is referred. We can 

 say with greater accuracy that the chloroj^last is the organ con- 

 ducting these preliminary anabolic processes, and that they take 

 place wherever the chloroplasts are found. Their wide distribu- 

 tion, however, shows us that there is not a specially differentiated 

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

 In the same way, a catabolic process, the digestion of stored 

 products, goes on wherever there are reservoirs of such bodies, 

 and there, and there only, unorganised ferments or enzymes are 

 found, instead of being located in particular glands, as in the 

 animal body. These reservoirs, we have already seen, and shall 

 see again later, are found in the most varied regions of the 

 plant's substance— regions, moreover, which vary considerably 

 in different plants. 



Starting, then, with the intricacy of the metabolic processes 

 placed before us, and with their relations to each other, we may 

 begin the consideration of them in detail with an inquiry into 

 the introductory absorption of the materials from which the 

 food is ultimately made. Even here we meet with some com- 

 plexity, as the ordinary green plant shows marked differences in 

 behaviour from its parasitic relation, and from the great class 

 of fungi, which possess no chlorophyll. It will be best to con- 

 sider first the ordinary terrestrial green plant, noticing in passing 

 differences in behaviour shown by aquatic and epiphytic forms. 



