174 METABOLISM 



quantity. If we now compare the amides appearing in a darkened seedling 

 with those which may be obtained from the decomposition of proteid outside 

 the plant by the aid of acids or enzymes, we find them to exhibit several remark- 

 able differences. In the first place we generally find an abundance of asparagin 

 and glutamin in the plant, whilst the related aspartic and glutaminic acids 

 appear outside. Then again the proportional amounts of the several amino- 

 acids in the plant and outside it are by no means the same ; in the plant, one 

 is generally predominant, and the greatest differences present themselves in 

 different plants in this respect. Thus we find in the seedlings of Leguminosae 

 and Gramineae that asparagin is especially abundant, whilst in Cruciferae, 

 Ricinus, and Cucurbita, glutamin, and in Coniferae, arginin is the dominant 

 compound. These differences are not to be explained by assuming a different 

 composition in the reserve proteid of the seeds concerned ; since in the individual 

 species one does not find as a rule the substances under discussion always in the 

 same relation. E. Schulze (1898), who has gone most deeply into these 

 questions, formulates the hypothesis that the same decomposition products 

 arise from proteid in the plant and apart from it, but that in the plant a further 

 alteration takes place which affects the individual products of the hydrolytic 

 decomposition in varying degree. Changes in the composition of the mixture 

 of organic nitrogenous bodies can be determined directly by analysis. This 

 is apparent in a comparison, for example, of an analysis of pea-seedlings one week 

 old with those three weeks old : — 



Leucin. Tyrosin. Arginin. Asparagin. 



1 week abundant little present absent 



3 weeks much less absent almost absent very abundant 



Further, Schulze was able to demonstrate the presence of arginin and 

 amido-acids only in the cotyledons of the lupin, but he could find no asparagin, 

 while this latter substance was present in the stem of the seedling ; similarly, 

 the cotyledons of the cucumber contained no glutamin although that substance 

 collects abundantly in the stem. Finally, it would appear from quantitative 

 analyses that the occurrence of asparagin goes hand in hand, not with the dis- 

 appearance of proteid, but with that of amino-acids. 



Schulze assumed that the amino-acids first arising from the proteid sub- 

 stances, in addition to which perhaps also primarily asparagin and glutamin 

 may arise, break down further into ammonia, and from this, in presence of 

 a suitable carbohydrate — perhaps glucose — asparagin and glutamin are con- 

 structed. These amides would be thus, not the main products of decomposition, 

 but rather the first stages in a higher synthesis, and their formation from this 

 point of view is not inconceivable. According to Hansteen's experiments 

 the amino-acids appear, so far as they have been investigated, much less adapted 

 for the formation of proteid than ammonia or the two amides above mentioned ; 

 an accumulation of ammonia would be a disadvantage, however, because that 

 substance, which can be detected only in traces, readily acts as a poison in 

 larger quantities. This hypothesis of Schulze, which has been recently sup- 

 ported by Balicka-Iwanowska (1903) [and also by Prianischnikow, 1904, 

 and earlier], appears to us to explain best the facts known to us at the present 

 time in this difficult region of investigation ; much still remains to be done, 

 however, quite apart from the fact that the mode of origin of asparagin from 

 ammonia and glucose in a purely chemical manner cannot be discussed at all at 

 present. 



A new difficulty presents itself when we attempt to investigate how proteid 

 arises from amino-acids or amides. It cannot be doubted that the process 

 takes place in light, and Pfeffer (1873) has further given proof that light acts 

 indirectly in the process. Balicka-Iwanowska (1903), however, shows that 

 in all likelihood light has also a direct influence. Illumination in conjunction 

 with an atmosphere free from carbon-dioxide does not result in the disappearance 



