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Jack Myers 



across an algal film of any appreciable absorption. The I1/I2 

 ratio necessarily varies considerably within the film. The curves 

 show the requirement for most instructive study of spectra. En- 

 hancement in the >.i region (Ei) is seen most clearly in an excess 

 of A.2, practically a very high P2/P1 ratio. Enhancement in the ?^2 

 region (E2) is seen most clearly in an excess of ^i, practically 

 requiring only a rather modest pi/p2 ratio. 



Enhancement Spectra 



Fig. 2 and 3 present enhancement spectra obtained under condi- 

 tions meeting the requirements noted above. In Chlorella (Fig. 2) 

 the Xi and Xg regions intersect at about 685 m^i. The Xg region^ _^ 

 has been associated with chlorophyll b and chlorophyll a-673. ' 

 The question of role of carotenoids does not seem answerable. 

 Fig. 3, taken from the recent work of Jones"^"^ on Anacystis, shows 

 spectra for two kinds of cells of widely differing pigmentation. 

 Cells grown under usual tungsten illumination (w) and with a "nor- 

 mal" phycocyanin/chlorophyll ratio show a >.2 region of about 530 

 to 655 mja. There are two segments to the Xi region, < 530 and 

 >655 mil. If cells are grown under red light > 660 mjJ. (practically 

 under BCJ dark room lamps with necessary addition of a small 

 amount of clear tungsten illiimination), they show a much reduced 

 chlorophyll. Such cells (curve R, Fig. 3) show decreased Ei and 

 increased E2 enhancements together with broadening of the ^-2 re- 

 gion. From the Ei enhancement at 460 to 510 mji a case can be made 

 for carotenoid participation in system 1. However, the case can- 

 not be made from casual Inspection of the curves. These are not 

 action spectra and enhancement cannot be related to absoi^jtion by 

 any one pigment alone; it can be related only to absorption ratios 

 between different active pigments. 



Though there are important differences from the spectrum reported 

 by Blinks^ for Anabaena, the curves for Anacystis confirm his 

 finding that the 'h.x region may have two segments, one in the blue 

 and the other in the far red.^ Hence it is clear that the Xi 

 region is related to pigment absorption and not to some peculiar 

 character of long wavelength. 



DISTRIBUTION OF LIGHT QUANTA 



I turn now to the problem of distribution of light quanta be- 

 tween the two phot oreact ions or, in the casual language of Kok, 

 how the carburetor of photosynthesis works. Enhancement in 

 intact- cell photosynthesis is regarded as a tool for study of 

 quanta distribution as viewed by the over-all rate. Suppose that 



