330 PHOTOSYNTHESIS 



the value for the Hmiting case, where E is equal to zero, was calculated. 

 In view of the fact that the course of the ratio U/E with changing light 

 intensity was known for only two points, the values obtained by extrapola- 

 tion must be subject to some error. This method of calculation was later 

 altered in a subsequent publication. Some typical results are given m 



Table 38. 



TABLE 38 



Values of U/E Obtained by Warburg and Negelein. 



Incident ^ . 100 



Radiation, tt inn .. 



Cal. per sq. cm 



U . 100 lim 



permi. X "lO-^' E U E E = 



0.162 0.136 0.078 57 79 



0.327 0.275 0.116 42 



0.203 0.171 0.096 56 57 



0.406 0.341 0.155 45 



0.215 0.181 0.099 55 



0.430 0.362 0.147 41 



69 



As an average, it was found that 70 per cent of the absorbed radiant 

 energy was utilized in photosynthesis. A later recalculation gave a mean 

 value' of 59 per cent and a maximum value of 63.5 per cent in red light. 

 These results are of quite a different order from those obtained by Brown 

 and Escombe and by Puriewitsch. They are, however, hardly comparable, 

 for while the authors just mentioned used solar radiation, Warburg and 

 Negelein worked with a limited portion of the spectrum, 570-645 ^[x, also 

 the plants in the two series of investigations were very different. Warburg 

 and Negelein used very low light intensities and this factor was probably 

 in relative minimum; their results also show an increasing percentage of 

 energy utilized in photosynthesis with decreasing incident radiation. The 

 results given in the table may be taken as the highest values obtained, for 

 the amount of energy utilized in photosynthesis depends to a large extent 

 upon the condition of the plants and the conditions under which these 

 were cultivated. This applies especially to the chlorophyll-content of the 

 algae used. Plants were kept under culture conditions of low light in- 

 tensity and thus developed the capacity for utilizing the high percentage 

 of absorbed radiant energy given in the table. 



Warburg and Negelein ^^ also determined the per cent of absorbed 

 radiant energy utilized in photosynthesis with incident radiation of different 

 frequencies. A quartz mercury vapor lamp was used as a source of light 

 and the following lines were isolated : the yellow line 1 = 578 |.i[x, the green 

 line 1 r= 546 \Ji\i, and the blue line X = 436 ^ijx. These lines were obtained 

 by the use of filters prepared according to the instructions of Hiibl.^® A 

 red portion of the spectrum l = 610-690 ti[i with maximum intensity at 

 660 nn was also used. 



"Warburg and Negelein, Zcit. physik. Chcm., 106, 191 (1923). 

 " Hubl, "Die Lichtfilter," Halle, 1921. 



