ASSIMILATION OF CARBON 1 7 



The presence of oxygen is an additional condition necessary for greening. 

 Etiolated leaves in an oxygen-free chamber remain yellow, even in light. This 

 is also true when the amount of oxygen is small; greening demands an excess 

 of this gas. 



Ville 1 was able to show that the absence of necessary mineral salts in the 

 soil results in the diminution of the chlorophyll and carotin contents of leaves. 

 Lesage and Schimper 2 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, Palladin 3 pointed out that carbohydrates are essential to the 

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



Pig. 9 — Gingko leaf in which autumnal coloration has been prevented in the upper part, 



by an incision. (After Stahl.) 



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 yellow. 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 light 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 4 

 under these conditions. The concentration of these substances is important 



1 Ville, Georges, Recherches sur les relations qui existent entre la couleur des plantes et la richesse des 

 terres en agents de fertilite. Compt. rend. Paris 109 : 397-400. 1889. 



2 Schimper, A. F. W., Die Indo-Malayische Strandfiora. Jena, 1891. P. 9. 



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

 1891. 



* Palladin, W., Recherches sur la formation de la chlorophylle dans les plantes. Rev. gen. Bot. 9: 385— 

 394. 1897- 

 2 



