THE NATURE OF PHOTOSYNTHESIS 143 



Lubimenko endeavored to correlate with differences in chlorophyll-con- 

 tent, for he found that "shade" plants contain more chlorophyll than 

 the "light" plants. The "shade" plants show an optimal light intensity 

 for photosynthesis; if the light intensity is increased above this optimal 

 intensity the rate of photosynthesis decreases. This, it is assumed, is 

 due to the fact that the "shade" plants have a high chlorophyll-content 

 and consequently a high absorption coefficient. On the other hand, "light" 

 plants, with a low chlorophyll-content show maximum photosynthesis 

 at the highest light intensities. This can be interpreted, that in "light" 

 plants the amount of light absorbed when illuminated by highest light 

 intensities, is not sufficient to produce an inhibition in the activity of 

 the chloroplasts. The optimum temperature and optimum light intensity 

 for photosynthesis of a plant decreases with increasing chlorophyll-content 

 according to this view. In the course of its development a plant can 

 regulate the amount of light it absorbs by changes in its chlorophyll- 

 content. It is, however, not only the light intensity which determines 

 the chlorophyll-content, but also temperature. With increasing tempera- 

 tures the intensity of light required for maximal chlorophyll formation 

 decreases. 



Plester^*^ studied the relation of carbohydrate formation (by means 

 of the half leaf method) to the chlorophyll-content of the light green or 

 yellow and normal varieties of a number of plants. He found that the 

 light green varieties have a lower chlorophyll-content than the normal 

 varieties per equal area of leaf surface; the former ranged from about 

 30 to 50 per cent of the latter. From Plester's results it cannot be 

 concluded that there is any direct ratio between the rate of photosyn- 

 thesis and chlorophyll-content. The light green varieties showed a lower 

 rate of photosynthesis than the normal varieties, ranging from 34.2 to 

 59.5 per cent. On the other hand in some cases the light green or 

 yellow varieties showed a much higher rate of photosynthesis than would 

 correspond to their chlorophyll-content. This points to the fact that other 

 factors besides chlorophyll-content are playing a role. Also, the light 

 green varieties had a lower rate of respiration than the normal plants, 

 though there was no direct parallelism between respiration and chlorophyll- 

 content. A closer relationship seems to exist between the rate of photo- 

 synthesis and that of respiration. Hence, to a measure at least, the lower 

 rate of photosynthesis in the light green varieties is compensated for 

 by a lower rate of carbohydrate consumption. It is, however, still a 

 question whether the lower rate of respiration is simply the result of a 

 lower supply of carbohydrates, or whether the other conditions or fac- 

 tors which produce a higher rate of respiration (protoplasmic factors, 

 enzymes) do not also affect the rate of photosynthesis. 



Plester also found, contrary to Willstatter and Stoll (see below) that 

 plants which contain besides chlorophyll admixtures of red pigments, had 

 a lower rate of photosynthesis than the same species without these pig- 



"' Plester, Beitr. Biol. d. Pflansen, 11, 249 (1912). 



