178 PHYSIOLOGY OF NUTRITION 



are tested for solubility in a saturated solution of asparagin, which dissolves 

 all crystals but those of this substance. 



§6. Protein Synthesis in Plants.*'— It has already been stated (page 31) 

 that the primary protein synthesis occurs in leaves. The nitrogen necessary 

 for such synthesis is mainly derived from the soil, as nitrates. Investigations 

 upon the distribution of nitrates 1 in the plant have shown that they reach the 

 leaves through the water-conducting system. Nitrates are found in leaves 

 only in exceedingly small amounts, however, or else they are entirely absent, and 

 it is therefore suggested that a transformation of nitrates must take place in 

 these organs. Schimper 2 has proved, moreover, that the transformation of 

 nitrates in leaves is connected with the photosynthetic assimilation of carbon. 

 Accumulation of nitrates occurs in plants that have been kept in darkness, 

 and these salts are used up afterwards, when the plants are exposed to light. 

 Also, in chlorotic leaves, which are incapable of photosynthesis, no transforma- 

 tion of nitrates occurs in the light. Experiments with variegated leaves are 

 especially convincing in this connection. The green as well as the white parts 

 of such leaves are filled with nitrates in the dark. After subsequent illumination 

 only the green portions are found to be without nitrates; in the colorless parts 

 the amount of nitrate remains unchanged. 



From such experiments it has been concluded that protein synthesis in leaves 

 occurs only in light. It must be noted, however, that in these experiments of 

 Schimper a deficiency of carbohydrates surely occurred in the absence of light. 

 This consideration is of great importance, since Zaliesskii 3 was able to demon- 

 strate protein synthesis from carbohydrates and nitrates when darkened leaves 

 were supplied with carbohydrates by means of a nutrient solution. It thus 

 appears that protein synthesis in leaves is only indirectly dependent upon light. 

 Only in light is the formation of carbohydrates possible, and these substances 

 are necessary for the formation of proteins. It is quite possible, however, that 

 with an adequate supply of carbohydrates, protein synthesis may go on more 

 rapidly in light than in darkness. 



1 Wulfert, H., Ueber die Bestimmung der Salpetersaure bei Gegenwart organischer Substanzen. Landw. 

 Versuchsst. 12: 164-184. 1869. Monteverde, Arbeit. Naturforscherges St. Petersburg. 1882.* Berthe- 

 lot, [Marcellin], and Andre, [Gustave], Sur l'existence et stir la formation des azotates dans le regne vege- 

 tal. Ann. chim. et phys. VI, 8: 5-8. 1886. Idem, Les azotates dans les veg6taux. I. Methodes 

 2'analyze. Ibid. VI, 8: 8-25. 1886. Idem, same title. II. Leur presence universelle. Ibid. VI, 8: 

 d6-3i. 1886. Idem, Les azotates dans les plantes aux diverses periodes de la v£g6tation. Plante 

 totale. Ibid. VI, 8: 32-63. 1886. Idem, Les azotates dans les difterentes parties des plantes. Ibid. 

 VI, 8: 64-115. 1886. Idem, Sur la formation de salpetre dans les v6g6taux. Ibid. VI, 8: 116-128. 

 1886. — Berthelot, [Marcelin], and Andre, [Gustave], Recherches sur la vegetation. Sur les carbonates dans 

 les plantes vivantes. Ann. chim. et phys. VI, 10: 85-107. 1887. Idem, Recherches sur l'acide oxalique 

 dans la vegetation. I. Methodes d'analyze. Ibid. VI, 10: 289-308. 1887. Idem, same title. II. 

 Etude de diverses plantes. bid. VI, 10: 308-350. 1887. Idem, Sur une relation entre la formation de 

 l'acide oxalique et celle des principes albuminoides dans certains v6g£taux. Ibid. VI, 10: 350-353- 1887. 



2 Schimper, A. F. W., Ueber Kalkoxalatbildung in den Laubblattern. Bot. Zeitg. 46: 65-69, 81-89. 

 97-107. 113-123. 129-139, 145-153- 1888. 



s Zaleski, W., Die Bedingungen der Eiweisssynthese in Pflanzen, p. 53- 1900.* Idem, Zur Kenntniss 

 der Eiweissbildung in den Pflanzen. Ber. Deutsch. Bot. Ges. 15: 536-542. 1897. 



o This method is very unsatisfactory for several reasons. For better methods see Molisch, 

 1013. [See note i, p. 90.] — Ed. 



p The section is numbered §7 in German; the numbering of the 7th Russian edition is 

 here followed. — Ed. • 



