ASSIMILATION OP CAEBON 1 7 



Lesage and Schimper^ found that an excess of mineral substances reduces the 

 chlorophyll content, an effect that may be observed not only in halophytes, 

 growing normally upon soils rich in salts, but also in other plants when watered 

 with strong salt solutions. 



Finally, PaUadin^ pointed out that carbohydrates are essential to the 

 formation of chlorophyll. As wiU be seen farther on, plants fall into two 

 groups according to the carbohydrate content of their etiolated leaves; in one 

 group (for example, wheat), such leaves contain much soluble- carbohydrate 

 material, while in etiolated leaves of the other group (such as bean and lupine) 

 carbohydrates are almost entirely absent. If etiolated leaves of these plants 

 are removed and floated upon water in light, those of barley become green, while 

 almost all the bean leaves and all those of lupine remain yeUow. If the latter 

 are floated, not upon water but upon a saccharose or glucose solution, then 

 they also all become green. The greening of entire, completely etiolated bean 

 plants in Ught is explained in this way, that carbohydrates migrate into the 

 leaves from the stems. ■ Besides saccharose and glucose, such substances as 

 raffinose, fructose, maltose, glycerine, and some others, also produce greening' 

 under these conditions. The concentration of these substances is important 

 in this connection.* 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 algfe are particularly well adapted to the study of the im- 

 portance 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.' 



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. Ac- 

 cording to Monteverde and Liubimenko,^ 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,'' of which little more is 



' Schimper, A. F. W., Die Indo-Malayische Strandflora. Jena, iSgi. P. 9. 



2 Palladin, W., Ergrunen und Wachsthum der etiolirten Blatter. Ber. Deutsch. Hot. Ges. 9: 229-232. 

 1891. 



' Palladin, W., Recherches sur la formation de la chlorophylle dans les plantes. Rev. g^n. Bot. 9 : 38s- 

 394- 1897. 



* Palladin, W., Einiiuss der Concentration der Losungen auf die Chlorophyllbildung in etiolirten Blattern. 

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



' Artari, Alexander, Ueber die Bildung des Chlorophylls durch grvine Algen. Ber. Deutsch. Bot. Ges. 

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

 I'influence du milieu nutritif. Rev. gdn. bot. 40: 114-130. 254-268. 1902. 



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

 plantes. [Text in Russian.] Bull. Acad. Imp. Sci. St.-P^tersbourg F/, s : 73-ioo; 191 1. 



' Sachs, J., Ueber das Vorhandensein eines farblosen Chlorophyll-Chromogens in Pflanzentheilen, welcho 

 fahig sind grun zu werden. Lotos 9: 6-r4>^ 1859. Idem, same title. Chem. Centralbl., n. F. 4: 145- 

 153. 1859. 



