310 VEGETABLE PHYSIOLOGY 



CHAPTEK XIX 



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 dis- 

 appearance 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 construction 

 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. For instance, 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 



