324 PROTEINS 



can take place in the dark and in tissues free from chloro- 

 phyll, provided that an adequate supply of carbohydrate be at 

 hand.* Zaleski and Suzuki f found that the leaves of the 

 sunflower floating upon a solution containing sugar and nitrate 

 produced considerable quantities of proteins in the dark, from 

 which it appears that nitrate assimilation is not a photo- 

 chemical process, and that light is only of indirect import- 

 ance in providing one of the means for the formation of 

 carbohydrates.! The synthesis of proteins is conditioned by 

 the available supply of carbohydrate, and since photosynthesis 

 is a daylight process, it is not surprising to find that the pro- 

 duction of proteins may be four or five times as great in the 

 light as in darkness. § Baudisch j| is of the opinion that the 

 formation of protein under abnormal conditions in the dark is 

 no proof that the process is not a photochemical one under 

 normal conditions ; he considers that the synthesis may in 

 this case be due to anaerobic respiration or some other ab- 

 normal chemical processes which reduce the nitrates and so 

 aid in the production of proteins. It has also been stated 

 that if but small quantities of carbohydrate are available, the 

 synthesis of proteins, in darkness, may stop at the formation 

 of amides,1F which some plants, e.g.. Algae such as Pleurococcus 

 and Raphidimn, and the Fungi Etirotiuin and Penicillium, can 

 directly assimilate.** 



Evidence is not wanting to show that nitrates are reduced 

 to nitrites in the plant,ff but much uncertainty exists as to the 

 further fate of the nitrite. To obtain some insight into this 



*Jost: " Biol. Centrlbl.," 1900, 20, 625. 



tZaleski and Suzuki: " Ber. deut. bot. Gesells.," 1897, 15, 536; " Bot. 

 Centrlbl.," 1901, 87, 281 ; Suzuki, " Bull. Coll. Ag. Tokyo," 1898, 2, 409 ; 3, 241. 



t Zaleski : " Ber. deut. bot. Gesells.," 1909, 27, 56. 



§ Montemartini ; " Atti. R. Inst. Bot. Pavia," 1905, II, 10, 20. 



II Baudisch; "Zentr. Bakt. Parasit.," 1912,32, 520. 



H Jakobi : " Biol. Centrlbl.," 1898, 18, 593- 



** Lutz : "Bull. Soc. Bot. France," 1902, 48, 118. 



tt Pertiabosco and v. Rosso : " Staz. sperim. Agrar. Ital.," 42, 5 ; Aso : 

 " Beih. bot. Centrlbl.," 1900, 15, 208. 



Since plants absorb their nitrogen chiefly in the form of nitrates, there 

 should be some means of reducing them to nitrites. According to Irving and 

 Hankinson (" Biochem. Journ.," 1908, 3, 87) such an enzyme occurs in many 

 plants, chiefly aquatic, examined by them. These plants gave off nitrogen ; 

 but oxygen, owing to the reducing agent, was not evolved. The sequence of 

 events which they suggest is as follows: — 



