MATERIAL TRANSFORMATIONS IN THE PLANT 1 63 



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 syntheses is mainly derived from the soil, as nitrates. Investigations 

 upon the distribution of nitrates^ 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^ has proved, moreover, that the transformation of 

 nitrates in leaves is connected with the photosynthetic as.similation 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' was able to demonstrate 

 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. 



* Wulf ert, H., Ueber die Bestimraung der Salpetersaure bei Gegenwart organischer Substanzen. Landw. 

 Versuchsst. 12: 164-184. i86g. MontSverde, Arbeit. Naturforsoherges St. Petersburg. 1882.* Berthe- 

 lot, [Marcellin], and Andr€, [Gustave], Sur I'existence et sur la formation des azotates dans le regne v6g6- 

 tal. Ann. chim. et phys. F/, 8: s-8. 1886. Idem, Les azotates dans les v6g6taux. I. M^thodes 

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

 26-31. 1886. Idem, Les azotates dans les plantes aux diverses periodes de la v6g6tation. Plante 

 totale. Ibid. VI, 8: 32-63. 1886. Idem, Les azotates dans les diff6rentes parties des plantes. Ibid. 

 VI, 8: 64-iis. 1886. Idem, Sur la formation du salp^tre clans les v6g4taux. Ibid. VI, 8: 116-128. 

 1886. — Berthelot, [Marcelin], and Andr€, [Gustave], Recbercbes sur la v6g6tation. Sur les carbonates dans 

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

 dans la vigdtation. I. M^thodes d'analyze. Ibid. VI, 10: 289-308. 1887. Idem, same title. II. 

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

 I'acide oxalique et celle des principes albuminoides dans certains v6g6taux. Ibid. VI, xo: 350-353. 1887. 



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

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



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

 der Eiweissbildung in den Pflanzen. Ber. Deutsch. Bot. Ges. is : S36-542. 1897. 



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

 1913. See note I, p. 84.] — Ed. . _ 



" This section is numbered §7 in the German; the numbering of the 7th Russian edition is 

 here followed. — Ed. 



