THE NATURE OF PHOTOSYNTHESIS 147 



tion. Willstatter and Stoll in discussing the theoretical value of Pc 

 emphasize the temperature factor; but it seems essential to define the car- 

 bon dioxide-concentration, for different plants show specific differences in 

 the concentration of carbon dioxide they can utilize. In Willstatter and 

 Stoll's experiments some of the leaves which had a very low chlorophyll- 

 content did not attain maximum photosynthesis tecause the light intensity 

 was not sufficiently high. 



In Table 24 are given the values of Pc for normal leaves, that is, 

 excluding those low in chlorophyll, young and old leaves. Approximately 

 constant values of Pc for a given temperature would indicate that under 

 these conditions the rate of photosynthesis was determined by the 

 chlorophyll-content. 



The values of Pc in the first section of Table 24 shows a fair constancy, 

 for 25° ranging from 5.2 to 7.7, for 30° from 6.5 to 9.1. In these cases 

 there is a rough parallelism between the rate of photosynthesis and 

 chlorophyll-content. In the lower section of Table 24 are given the values 

 of Pc for plants which have a notably rapid growth and high photosynthetic 

 rate. In these Pc is considerably higher. It is already evident from these 

 values that there is no simple quantitative ratio between chlorophyll-content 

 and rate of phv^tosyntl-c ■'. 



In this coni.L\:tior .t has been an interesting question as to what are the 

 relations in very young leaves between the rate of photosynthesis, chloro- 

 phyll formation and respiration. The latter activity is notably high and 

 decreases with time and the development of the leaf.^^^ Under favor- 

 able conditions of temperature and light the development of chlorophyll 

 is quite rapid. Thus, for example, Willstatter and Stoll observed increases 

 in chlorophyll-content, at 25° and 48,000 Lux, in 80 minutes as follows: 

 Tilia cordata, 32 per cent of the original, Acer negundo, 29 per cent, 

 Quercus Robur, 22 per cent, Popuhis pyramidaUs hort., 15 per cent, Acer 

 Pseudoplatamis, 10 per cent. With this increase in chlorophyll-content 

 there is also an increase in photosynthesis. There is, however, not a 

 direct proportionality between chlorophyll-content and photosynthetic rate. 

 The latter, 8 to 10 days after the first determination, made when the leaves 

 were just unfolding, show about a constant value for equal areas but a 

 decreased value on the basis of dry weight. On the basis of chlorophyll- 

 content after about nine days there is a decrease in photosynthesis, that is, 

 Pc decreases. These relations are given in Table 25 which show an in- 

 crease in Pc after about nine days and thereafter again a decrease. The 

 table is taken from the results of Willstatter and Stoll. 



A perusal of Table 25 will show an increase with time of the dry weight 

 of the leaves ; on the basis of the dry weight there is a decrease in photo- 

 synthesis. The leaves also show a consistent increase in chlorophyll 

 content, but this is not associated with an increase in photosynthesis after 

 the first nine days. This results in a considerable variation of the Pc. 



'"Willstatter and Stoll, 1. c, p. 87. 



