1096 THE LIGHT FACTOR. II. QUANTUM YIELD CHAP. 29 



in yellow sodium light, the yields were approximately independent of the 

 initial carbon dioxide concentration (1-9%), and of temperature (17-25° 

 C). The light curves remained fairly straight up to 10 or 20 kerg/cm.^ 

 sec. The quantum yields were calculated from the rates observed at 10 

 kerg/cm.2 sec. The resulting 7 values are given in Table 29.11. The 

 smallest I/7 values measured were of the order of 11, corresponding to 

 7 < 0.09. 



Table 29.11 

 Quantum Yields of Oxygen Production by Horticultural Plants" 



(after Wassink 1946) 



Nunaber of 

 Plant 1/7 mea'surements 



Strawberry 12 . 1-17 .8 23 



Kohlrabi 13.5-15.4 5 



Chinese cabbage 10 . 8-14 . 7 8 



White succory 13 . 6-16 . 8 4 



Tomato 16.0-43.5 17 



Cucumber 13 . 8-24 . 6 5 



Endive 21.8 2 



Asparagus 14 . 6-18 . 2 4 



" At 10 kerg/cm.2 sec. 



The significance of the variations of the quantum yield of Chlorella 

 with wave length will be discussed in chapter 30, primarily from the point 

 of view of the function of carotenoids in photosynthesis. Most experi- 

 ments on the quantum yield of photosynthesis of ''colored" algae (brown, 

 red or blue-green) were carried out with a similar aim in mind — elucidation 

 of the role of phycobilins and carotenoids. As far as the absolute value 

 of the maximum quantum yield is concerned, there seems to be no funda- 

 mental difference between these algae and the green plants, as is shown by 

 the following observations : 



Emerson and Lewis (1941, 1942) measured manometrically the quan- 

 tum yield of photosynthesis by the blue-green unicellular alga Chroococcus, 

 and found a maximum 7 value of about 0.08 in red Hght. Working with a 

 suspension of diatoms {Nitzschia closterium) , Button and Manning (1941) 

 found an average quantum yield of 0.063, with single 7 values up to 0.1. 

 Wassink and Kersten (1944) used another diatom, Nitzschia dissipata, and 

 calculated the quantum yields from manometric measurements, with il- 

 lumination periods of 30-60 min., in sodium light of about 10 kerg/cm.^ sec. 

 (The light curves obtained by these authors showed only small deviations 

 from linearity at these comparatively high intensities; of. fig. 28.5). 

 From one third to one half of the incident light was absorbed in the vessel. 

 In five experiments at 25° C, and one at 6° C, I/7 values from 11.4 to 

 13.9 \ver(; obtained, witli an average of 12.9, or 7 = 0.078, and 7,„ax = 

 0.09. 



