22 SECTIONAL ADDRESSES 



succulents does not come from malic acid, for the rate of carbon dioxide 

 evolution is not proportional to the concentration of malic acid. 

 Bennet-Clark's view of the breakdown of sugar by succulents is thus 

 represented by the scheme : 



sugar 



intermediate products 



of glycolysis -^ malic acid -> polysaccharide 



Y 



and the malic acid is thus an intermediate product of anabolism. 



Lack of time prevents a further discussion of this interesting subject 

 of the part played by organic acids in plant metabolism : it must suffice 

 to say that in other plants besides succulents evidence is accumulating 

 which indicates that the part played by these acids in oxidative anabolism 

 may be quite a general phenomenon. 



While then data are accumulating which indicate the linkage of anabolic 

 processes with those of the breakdown of sugar, it is important to note that 

 there is no evidence of the formation of products other than carbohydrates. 

 Is it possible, however, that syntheses of more complex substances are 

 indeed involved, and that we have here a dim glimpse of the mechanism 

 for the production of these substances, and that along with the formation 

 of sugar or some intermediate there may be also the formation of protein 

 or other complex substances ; that, indeed, we have here the mechanism 

 by which the carbohydrate is brought into a suitable form for combination 

 with nitrogenous and other compounds ? If this is so we should expect to 

 find the strongest evidence of oxidative anabolism in actively growing 

 material. It is therefore disappointing that in tissues such as those of 

 germinating seeds the indication of oxidative anabolism is often wanting. 

 In work by Leach on the respiration of germinating seeds of different 

 types it was found that in those seeds storing carbohydrate as their chief 

 food reserve the ratio of anaerobic to aerobic respiration was about i : 3 or 

 less, so that in these the experimental data suggest that the same amount 

 of carbohydrate is broken down to carbon dioxide and water in presence 

 of air as is broken down to carbon dioxide and alcohol in absence of 

 oxygen. In seeds which contain a considerable amount of fat the ratio 

 of the initial rate of anaerobic to the previous rate of aerobic respiration 

 was found to be greater than 0-33, and in these, therefore, some oxidative 

 anabolism might take place. On the other hand, a high rate of anaerobic 

 respiration has been observed in other fruits besides apples, and it is 

 curious that the indications of anabolism should appear in just those 

 materials where it would seem to have least meaning. However, many 

 seeds contain a considerable reserve of protein which suffers break- 

 down, at least in part, during germination. Thus Isaac has shown 

 that in the seeds of the same variety of sweet pea in which Leach found 

 a ratio of anaerobic to aerobic respiration of only about 0-2, there is a 

 continuous breakdown of reserve protein during the first ten days of 

 germination, over a third of the protein disappearing in this period. 



