116 PHOTOSYNTHESIS 



synthesis are concerned, both "Hght" and "shade" varieties. ^^ By cultivat- 

 ing the same alga under different intensities of light, Harder found that 

 the plants grown under light of low intensity can utilize lower intensities 

 of light for their photosynthetic work than plants grown under high light 

 intensity, while plants grown in light of high intensity attain a higher rate 

 of photosynthesis in light of high intensity than those grown in light of 

 low intensity. The color of the plant, i.e., the presence of phycocyanin or 

 phycoerythrin seems to be of little significance herein. This adaptation or 

 accommodation to light of different intensity is not recognizable by any 

 outward appearance of the plant, but is a more important factor than color. 

 For this reason it is extremely important that it be taken into consideration 

 in all determinations of the rate of photosynthesis. Just what the nature 

 is of these accommodations to light of different intensities it is difficult 

 to tell. Presumably it is associated with the chlorophyll-content and pos- 

 sibly also with internal plasmatic factors. 



There exists, it is evident, a contradiction between the conclusions of 

 Richter and those of Harder. The former regards that the color of the 

 plant or the presence of pigments besides chlorophyll is of no consequence 

 to photosynthesis. Harder considers that this is an extreme view. There 

 is no doubt that the light to which the plants are accommodated is an im- 

 portant factor. This is evident from the following extreme conditions : 

 plants which have been raised in weak red light (blue-green "shade" plants) 

 show relatively higher photosynthesis in weak blue light than in strong 

 red light, and plants raised in strong blue light (red "light" plants) show 

 relatively higher photosynthesis in strong red light than in blue light of 

 low intensity. That is, the typical behavior of "light" and "shade" plants 

 is maintained even when the light is not complementary to the color of the 

 plants. This would be quite in agreement with Richter's claims. How- 

 ever, Harder points out, that when the light intensity is duly taken into 

 consideration, the factor of wave-length is always discernible, in the sense 

 that the plants show relatively higher photosynthesis in those wave-lengths 

 which are complementary to the color of the plant. This action is often 

 covered by results of differences of intensity. Harder comes to this 

 conclusion from the following facts. Photosynthesis of different colored 

 plants in light of different wave-lengths, hut of the same intensity, is 

 highest in those wave-lengths which are complementary to the color of 

 the plant. Also, when plants are accommodated to light of different wave- 

 lengths but of the same intensity, photosynthesis is highest in those wave- 

 lengths which are complementary to the color of the plant, no matter what 

 intensities of other wave-lengths are used. 



Harder's conclusion that "light" plants show greater photosynthesis 

 in light of high intensity than "shade" plants and the latter greater photo- 

 synthesis in light of low intensity than "light" plants, is in apparent con- 

 tradiction to the conclusions of Warburg and Negelein, already referred 



"Lubimenko, W., Ann. sci. not. (9), 7, 321 (1908). Rose, ibid. (9), 17, 1 

 (1913). 



