1120 



THE LIGHT FACTOR. II. QUANTUM YIELD 



CHAP. 29 



The quantum yields obtained in these experiments scattered consider- 

 ably — from 0.01 to 0.1 — but never exceeded the latter limit. Still lower 

 quantum yields (0.002 to 0.027) were obtained in experiments in white 

 light; in this case, however, about ten times higher intensities of incident 

 light were used, so that saturation effects appeared possible. Experiments 

 with a different technique (closed reaction bottles, no stirring, analytical 

 determination of the change in [O2] in solution by Winkler's method) 

 yielded 7 values between 0.02 and 0.065. 



In another paper from the same laboratory, Manning, Juday and Wolf (1938) de- 

 scribed experiments in which bottles containing Chlorella suspensions were deposited at 

 different depths in a lake, and thus exposed to different intensities of illumination, rang- 

 ing from full sunlight (600 kerg./cm.'' sec, not counting the infrared) down to 6 kerg/cm.* 

 sec. The change in color of the light with depth (cf. Table 22. XI) complicated the calcu- 

 lation of the number of absorbed quanta; the results were therefore less exact than 

 those of the first paper. However, the approximate magnitude of 7 values was the 

 same as in other experiments — about 0.05 at the lowest light intensities (at 10 meter 

 depth); c/. figure 29.5. 



0.07 





O 



UJ 



3 

 f- 



< 

 3 

 O 



0.1 0.2 0.4 



10 20 40 



100 



LIGHT INTENSITY, (erg/cm^ sec.) x 10" 



Fig. 29.5. Quantum efficiencies for Chlorella (after Manning, Juday, 

 and Wolf, 1938). Curve A, 3.17 hr., cell concn. 3,250,000/ml.; B, 1.03 

 hr., cell concn. 718,000/ml.; C, 4.00 hr., cell concn. 331,000/ml.; D, 4.00 hr. 

 cell concn. 718,000/ml.; E, 4.05 hr., cell concn. 1,900,000/ml.; F, 3.30 hr., 

 cell concn. 1,210,000/ml. 



(6) Polar ographic Method 



In a third investigation from the Wisconsin laboratories. Petering, 

 Duggar and Daniels (1939) applied the polar ogra phi c meOiod {cf. page 850) 

 because it permitted the determination of respiration immediately before 

 and after a period of photosynthesis, without the delays (illustrated by fig. 

 29.1) inherent in the manometric method. Figure 29.(» shows the polaro- 



