l8 PHYSIOLOGY OF NUTRITION 



in this connection. 1 Greening occurs quickly with a saccharose solution of 

 low or medium concentration. If the concentration is previously increased 

 to 35 per cent., in darkness, the leaves remain yellow for several days when 

 subsequently brought into the light, but greening occurs quickly in these leaves 

 if they are transferred from the strong solution to one having a concentration 

 of from 5 to 10 per cent. 



Single-celled algae are particularly well adapted to the study of the 

 importance of various substances in the formation of chlorophyll. Cultures in 

 light exhibit a considerable range of color (from yellow-green to intense, dark 

 green) according to the composition of the nutrient solution used. 2 



Thus greening, or the accumulation of chlorophyll, is a physiological process 

 that proceeds only in living cells and under conditions favorable to life. The 

 substance from which chlorophyll arises has not yet been isolated, but the 

 existence of such a substance may be inferred from various observations. 

 According to Monteverde and Liubimenko, 3 a pigment called chlorophyllogen is 

 formed, independently of light, in the chromatophores of all green plants. It is 

 said to arise from a colorless chromogen, leucophyll, 4 of which little more is 

 known. Chlorophyllogen is a very unstable substance, and its absorption spec- 

 trum shows a great similarity, in the red region, to that of chlorophyll. 

 Attempts to isolate it result in an artificial transformation-product, the proto- 

 chlorophyll of Monteverde. 5 Like chlorophyll, protochlorophyll is a deep green 

 pigment, which is fluorescent, appearing red by reflected light. The spectrum 

 shows four absorption bands. The absorption spectra of alcoholic solutions of 

 protochlorophyll on the one hand, and of alcoholic chlorophyll on the other, 

 are different in that the absorption band between B and C in the second is absent 

 in the first, and the one between C and D in the first appears slightly displaced 

 toward the left in the second; the other bands practically agree. Although 

 protochlorophyll is a transformation-product, it is still of interest, in so far as 

 its existence indicates the presence of a mother-substance for chlorophyll; 

 protochlorophyll itself cannot change into chlorophyll. Protochlorophyll 

 arises independently of light, from chlorophyllogen. As to its presence in 

 living cells, it is normally found in large quantities in the inner seed-coats of 

 the Cucurbitaceae, especially in Luffa. 



1 Palladin, W., Einfluss der Concentration der Losungen auf die Chlorophyllbildung in etiolirten Blat- 

 tern. Ber. Deutsch. Bot. Ges. 20: 224-228. 1902. 



2 Artari, Alexander, Ueber die Bildung des Chlorophylls durch griir.e Algen. Ber. Deutsch. Bot. Ges. 

 20: 201-207. 1902. Matruchot, L., and Molliard, M., Variations de structure d'une algue verte sous 

 l'influence du milieu nutritif. Rev. gen. bot. 40 : 1 14-130, 254-268. 1902. 



3 Monteverde, N. A., and Lubimenko, N. V., Recherches sur la formation de la chlorophylle chez les 

 plantes. [Text in Russian.] Bull. Acad. Imp. Sci. St.-Petersbourg VI, 5: 73-100. 1911. 



4 Sachs, J., Ueber das Vorhandensein eines farblosen Chlorophyll-Chromogens in Pflanzentheilen, welche 

 fahig sind griin zu werden. Lotos 9: 6-14. 1859. Idem, same title. Chem. Centralbl., n. F. 4: 145- 



153- 1859. 



6 Monteverde, 1894. [See Note, 1, p. 9.] Monteverde, N. A., Der Einfluss des Lichts auf die Gesch- 

 windingkeit der Chlorophyllbildung in Blattern etiolirter Pflanzen. Trav. Soc. Imp. Nat. St.-Petersbourg 

 27J: 131-142 [Russian], 143-145 [German abstract]. 1896. Idem, Das Protochlorophyll und Chlorophyll. 

 [Title and abstract in German, article in Russian.] Bull. Jard. Imp. Bot. St.-Petersbourg 2: 179-182. 

 [Abstract, p. 181-182.] 1902. Idem, Ueber das Absorptionsspectrum des Protochlorophylls. I. [Title 

 and abstract in German, article in Russian.] Ibid. 7: 37~42 [Abstract, p. 42], 47-58. [Abstract, p. 55-58J. 

 1907. 



