Chap, hi The absorption of Nitrogen 351 



A similar effect of light was noticed in the case of 

 nitrates. In 1875 Sorokine found a smaller percentage 

 of nitrates in the leaves of the buckwheat than in the 

 rest of the plant, while Pagnioul in 1879 went further and 

 demonstrated not only the disappearance of nitrates, but 

 also the formation of organic nitrogenous compounds in 

 the leaves of the beet, when they were exposed to the sun. 

 Emmerling (1880), Molisch (1883), Berthelot and Andre 

 (1884), and Capus (1886), confirmed Pagnioul. 



These researches appeared to point to the importance 

 of light being as great in these processes as in those con- 

 nected with carbohydrate formation. More exact investi- 

 gations later brought to light some features which showed 

 the two syntheses to be indirectly connected. 



In 1896 Laurent, Marchal, and Carpiaux showed that 

 appropriation of nitrate nitrogen by green plants does not 

 occur in darkness, but requires the ultra violet rays ; that 

 it is most active in green leaves, and only feeble in etio- 

 lated ones, and that it is accompanied by an intermediate 

 production of ammonia. Godlewski, who followed them 

 in the next year, working upon seedlings of wheat, threw 

 more light upon the problem. He supplied some of his 

 seedlings with nitrates, and left others without any ; grew 

 some in light and others in darkness ; arranged his experi- 

 ments so that the plants received no free carbon dioxide, 

 but were compelled to use only the carbohydrates of their 

 endosperms. He found that with access of light the seed- 

 lings produced abundant protein, but scarcely any in the 

 dark, a noteworthy quantity of amido-compounds replacing 

 it. The light appears accordingly to be necessary to the 

 synthesis of protein but not of amido-bodies. The process 

 appeared to Godlewski to take place in two stages, light 

 being unnecessary for the first one which terminates with 

 the amides, but being indispensable for the synthesis of 

 protein from the latter. 



