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CHAPTER XX 



GROWTH 



IN studying the growth of plants we must bear in mind 

 the relation which it bears to the processes of metabolism 

 which we have already discussed. We have seen that the 

 constructive processes, partly anabolic and partly kata- 

 bolic, are much greater than those which lead to the 

 disappearance of material from the plant-body. The result 

 of this is that there is a conspicuous increase in the 

 substance of the plant, as well as an accumulation of 

 potential energy which can be made use of by the plant 

 through various decompositions which its protoplasm can 

 set up. The great permanent accumulation of material is 

 what we associate with the processes of growth. Here 

 however we must distinguish between the increase of the 

 living substance, which is essentially an anabolic process, 

 and that of the manufacture of the framework, the con- 

 struction of cellulose, wood, cork, and other products, which 

 is the result of katabolism. 



The growth of the living substance is always the result 

 of constructive metabolism, and is attended by an increase 

 of bulk and weight. The growth of an organ sometimes 

 appears to be independent of such increase of weight : 

 indeed, a diminution of the weight of the whole structure 

 is sometimes noticeable. Thus in the case of a potato 

 tuber allowed to germinate under such conditions as 

 prevent the absorption of food materials from without, we 

 meet with a marked change of form, but, owing to the loss 

 of moisture by transpiration, and of carbon dioxide as a 

 consequence of its respiration or the katabolic processes 



