PHOTOSYNTHESIS OF GREEN PLANTS IN ULTRAVIOLET AND INFRARED 1155 



A similar decline of X above 630 m/n was noted by Blinks and Haxo 

 (1950) in the green alga Ulva taniata (fig. 30.11A), by Emerson and Lewis 

 (1941) with the blue-green alga Chroococcus (fig. 30.10A) and by Tanada 

 (1950) with the diatom Navicula minima (fig. 30. 9A). Ehrmantraut (1950) 

 noted the same phenomenon in the Hill reaction in Chlorella, Livingston 

 (c/. chapter 23, p. 752) noted a drop in the yield of the chlorophyll fluo- 

 rescence (in ether and acetone) in the same spectral region. 



Emerson and Lewis suggested that the decline in quantum yield on the 

 infrared side of the absorption maximum of chlorophyll a (at 680 m/x) is 

 repeated on the red side of the absorption peak of chlorophyll h, and that 

 this is the explanation for the shallow minimum in the y ciu've that figure 

 30.1 showed near 660 mn. (The absorption maximum of chlorophyll h in 

 vivo must be situated at about 648 m^u; cf. chapter 22, page 702.) 



It may be pointed out in passing that the quantum yield curve of Emerson and 

 Lewis provides a direct argument against Seybold's (1941) hypothesis that chlorophyll b 

 does not act as a sensitizer in the reduction of carbon dioxide at all, but is a specific sen- 

 sitizer for the polymerization of sugars to starch. 



In sharp contrast to the results of Emerson and Lewis are those of 

 Noddack and Eichhoff (1939) and Eichhoff (1939), who found (cf. Table 

 30.11) that the quantum yield of Chiordla remains high even at 832.5 mju. 



Table 30.11 

 Quantum Yields of Chlorella According to Eichhoff 



van 



m/i 



832.5 0.164 



780 0.204 



750 0.244 



725 0.228 



685 0.179 



650 0.204 



622 0.228 



598 0.238 



576.5 0.263 



558 0.238 



542 0.204 



527.5 0.232 



515 0.222 



Figure 30.4 shows a comparison of the action spectrum with the absorp- 

 tion spectrum of Chlorella, according to Eichhoff; the two curves remain 

 closely parallel far above 680 mix. Even if we doubt the correctness of the 

 absolute values of Eichhoff' s quantum yields (cf. page 1098), i\\ewave length 

 dependence of these values could be significant — e. g., it would not be af- 

 fected by an error in calibration (suggested on page 1098). One possible — 

 but not very probable — explanation of the differences between the two y 

 curves in the far red is that only Noddack and Eichhoff have measured 

 true absorption, while others have related the yield to the sum of absorp- 

 tion and scattering. The elucidation of this point is particularly desirable 

 because of the theoretical implications of a decline in y with wave length, as 



