ABSORPTION OF CARBON 33 



always higher. Willstatter observed in one of his experiments 

 that the rate of assimilation was the same in the dark as in 

 the pale variety of elms, though in the former the chlorophyll 

 content was ten times greater. A similar relation was obtained by 

 Lubimenko with shade and light plants, the first of which had 

 darker leaves. The considerable increase of the assimilation 

 number, coincident with the decrease in amount of chlorophyll, 

 shows that there is always a certain surplus of chlorophyll in the 

 leaf. 



The selective absorption of light by the chlorophyll indicates 

 that the assimilation process is not equal in the different parts of 

 the spectrum. It has been established, long ago, that in the green 

 rays, which are feebly absorbed by chlorophyll, assimilation is 

 comparatively insignificant. By placing assimilating leaves under 

 double-walled bell jars where the space between the walls was filled 

 with colored liquids of different composition, Senebier noted, 

 early in the nineteenth century, that in the yellow-red half of the 

 spectrum, under a solution of potassium bichromate, the plants 

 were assimilating more intensely than in the blue-violet half 

 under a solution of cupro-ammonium. 



The most detailed studies on assimilation in different rays have 

 been carried out by Timiriazeff, who has proved that the maximum 

 of assimilation lies in the red rays (between the Frauenhofer lines 

 B and C), which are most completely absorbed by chlorophyll. 

 The blue-violet rays, though strongly absorbed, have, however, a 

 considerably smaller assimilative effect. This is due to the fact 

 that they carry much less energy. And since the energy quanta 

 peculiar to the red rays are considerably smaller, these rays, with 

 an equal number of irradiated calories, carry a greater number of 

 quanta and, therefore, induce the breaking down of a larger num- 

 ber of molecules and, consequently, also a greater energy of assimi- 

 lation. 



Marine algae, whose chloroplasts are not green but of other 

 colors, show a maximal absorption of light in other spectral por- 

 tions than the green leaves of land plants. According to the theory 

 of Engelmann, these changes in absorption are connected with 

 differences in the composition of light, resulting from its passing 

 through the water. In sea water, which is of blue-green color, 

 the red rays are absorbed already at a depth of 35 m., while the 

 green rays penetrate to a depth of 350 m. Therefore, the red algae, 



