STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 73 



amino-acids than the water extract. This gives an indication of the 

 amount of protein in the leaf as compared with the amino-acids. A 

 considerable number of analyses such as the one just described were 

 carried out, all of which represented about the same proportions, but 

 as the results have not a real quantitative value they are omitted here. 



Special tests were also made to determine whether there was an 

 accumulation of nitrates in the leaves which had been kept in the 

 dark. However, no indication could be found that this was the 

 case. In fact, no tests for nitrates could be obtained in the water 

 extracts. Similarly, the amount of ammonia was so small that it can 

 be considered as insignificant. The ammonia was determined by 

 treating the leaf powder, suspended in water, with magnesium oxide 

 and distilling in a stream of air at 35° to 40° under reduced pressure, 

 15 mm. The distillate was taken up in standard acid solution. 



It is well known that with an ample supply of carbohj^drates, 

 protein synthesis can take place in the leaf in the dark from in- 

 organic nitrates.^ The observation that light acts favorably on 

 protein synthesis — more than three times the amount which is 

 formed in the dark — has been made by a number of workers, ^ 

 Since it had been shown that protein synthesis from inorganic nitrogen 

 compounds occurs only in the presence of an abundance of carbo- 

 hydrates, the beneficial influence of light was attributed to photo- 

 synthetic elaboration of carbohydrates by means of light. That this 

 was not the only interpretation to be given to experiments showing 

 the favorable action of light on protein syntheses was made evident 

 by the experiments of Godlewski.^ He showed that protein synthesis 

 from nitrates was very much greater in the light, even when photo- 

 synthesis was largely excluded by keeping the plants in a carbon- 

 dioxid-free atm.osphere, and that his wheat seedling grown under 

 these conditions contained not only as much protein as was in the 

 original seeds, but had formed a certain amount over and above 

 this. Such was not the case with the seedHngs grown in the dark. 

 Evidently, then, light exercises a very direct influence on protein 

 synthesis. These observations have led to much experimentation 

 and extensive speculation in an endeavor to ascertain the mode of 

 synthesis of the complex proteins. 



Emmerling^ and others consider that amino-acids are the first 

 products of nitrogen assimilation in the leaves. However, this part 

 of the problem is still largely in the speculative stage and little 

 direct experimxcntal evidence is available. That leaves take up 

 amino-acids and, in the presence of sugar, increase in protein- 

 content was demonstrated in a qualitative m anner by Hansteen.^ 



' Zaleski.W. Ber. deutsch. hot. Ges., 15, 536-542 (1897). Prianischn'ikow, D. lbid.,17,151 (1899). 

 - Laurent, E., and M. Mahchal. Bull, de I'Acad. Roy. de Belgique, 32, 55 (1903). 

 » GoDLEWSKi, E. Bull. Acad. Science de Cracovie, 313 (1903). 



* Emmerling, E. Landw. Versuch. Stat., 34, 113 (1880). 



* Hansteen, B. Jahrb. wiss. Bat, 33 417 (1899). 



