SUPPLEMENT 41 



and under the influence of light (SCHIMPER, 1888, 1890). This view can no 

 longer be held, for the fact that further working up of nitrates may occur in 

 non-green cells has been proved beyond a doubt by several investigators 

 (ZALESKI, 1900 ; SUZUKI, 1898 ; GODLEWSKI, 1903). It has been shown, it 

 is true (GODLEWSKI, 1903), that the amount of the proteid formed in light is 

 markedly greater than in darkness, and doubtless the foliage leaf takes an 

 important share in the synthesis. Further, it must be noted that the favourable 

 effect of light in proteid formation is direct according to GODLEWSKI, and not 

 merely conditioned by the contemporary carbon assimilation going on, although 

 it cannot be doubted that the products of CO 2 -assimilation are required in 

 the synthesis. In the dark proteid synthesis takes place only when sugar is 

 plentifully supplied. 



We are as little acquainted with the seat of the working up of ammonia 

 as we are with regard to that of nitrates. No ammonia is accumulated, as we 

 have seen to take place often in the case of nitrates ; on the contrary, it 

 appears to be rapidly altered wherever it occurs, and this rapid transforma- 

 tion must be of importance, seeing that salts of ammonia are poisonous. Where 

 it takes place, and whether light is an essential or helpful agent in the matter, we 

 have no certain knowledge (LAURENT and MARCHAL, 1904 ; HANSTEEN, 1899). 



In the absence of any positive data on the subject, we must content 

 ourselves with hypotheses as to the nature of the chemical processes taking 

 place in proteid synthesis. It is highly probable that the construction of 

 proteid consists essentially in an inversion of hydrolytic decomposition. Amino- 

 acids must first arise, and from them, through polypeptids, peptones, and 

 albuminoses, arises the proteid. There is a possibility that the ammonia of 

 the nitric acid at once unites with carbon in CO 2 -assimilation, and then per- 

 haps hydrocyanic acid might appear from nitric acid and formaldehyde as the 

 first nitrogenous assimilation product, as TREUB (1895, 1905) has in detail 

 attempted to show. Possibly also carbohydrates or their derivates may take 

 up the nitrogen as ammonia, and so form amino-acids, and it must be remem- 

 bered that ERLENMEYER junior (1912) has obtained glycocoll, the simplest 

 amino-acid, from glyoxylic acid. ABDERHALDEN (Phys. Chem. p. 330) has 

 shown how glycerose (C 3 H 6 O 3 ) may form a point of departure of the amino- 

 acids, and he also shows how glucose may give rise to amino-acids through 

 glycosamin. In every case, the nitric acid must first of all be reduced, and such 

 reduction occurs in the plant not only frequently, but readily. 



It seems natural to ascribe to the light a reducing power, especially as 

 it has been certainly shown to possess such a capacity in CO 2 -assimilation. 

 Since, however, further metabolism of nitrates can take place also in dark- 

 ness, and since, on the other hand, also, light is possibly useful in the assimila- 

 tion of ammonia, the influence of light cannot be limited to the reduction of 

 nitric acid, and it might be capable of being replaced by other sources of energy. 

 Primarily, one thinks of the chemical energy released in the oxidation of 

 carbohydrates, which we have discussed already in Lecture XVI. If that be so, 

 then the carbohydrates are essential to proteid synthesis, not only because 

 they take part as such in the construction of the proteid, but also indirectly, 

 inasmuch as they supply the energy necessary for their actual construction. 

 While CO 2 -assimilation in the green plant is dependent on solar energy, N- 

 assimilation can be carried out by means of chemical energy which the plant 

 itself has accumulated. CCX-assimilation is a photosynthetic process, while 

 N-assimilation is a chemosynthetic one. 



If we regard the amino-acids as the first stage in protein synthesis, we 

 have then to find whether these bodies occur in the plant to any degree worthy 

 of mention. As a matter of fact, they are found quite generally, wherever 

 indeed one looks for them, but unfortunately we have no certain means of 



