1182 THE LIGHT FACTOR. III. COLOR CHAP. 30 



and Blinks (1950) with very striking results. The polarographic method 

 (page 850) was used, with occasional checks by oxygen determination and 

 manometric measurements. Light intensities used were low enough (about 

 twice the compensating intensity) for the results to approximate the maxi- 

 mum quantum yields. In the green alga Ulva taeniata (fig. 30. 11 A) the 

 action spectrum was found to follow closely the absorption spectrum, with 

 the exception of a yield deficiency of up to 100% in the far red (>700 m/x), 

 already noticed by Emerson and Lewis (c/. fig. 30.3), and of a certain 

 yield deficiency around 480 van, also noticed before, and interpreted as evi- 

 dence of partial inactivity of the carotenoid pigments in green cells. It is, 

 however, to be noted that the yield deficiency disappears at 415 m/i, al- 

 though a considerable proportion of light (over 50% in extracts) must be 

 absorbed in this region by carotenoids. 



In the brown Coilodesme (fig. 30.1 IB), the action spectrum also paral- 

 leled rather closely the absorption spectrum with a moderate deficiency 

 (of up to 20%) in the region of strong carotenoid absorption. In the red 

 algae Delesseria decipiens (fig. 30.11C), Porphyra nereocystis (fig. 30.11D), 

 Porphyra naiadum (fig. 30. HE) (purple, indicating relatively high content 

 of phycocyanin) and Porphyra perforata (fig. 30.1 IF, G) (a slate-green 

 vegetative section containing mainly phycocyanin, and a red carposporic 

 section) the action spectra Avere strikingly different from the absorption 

 spectra. They showed unmistakable maxima corresponding to the ab- 

 sorption peaks of phycoerythrin, at 500 and 565 m/x, and also to those of 

 phycocyanin at 620 m^u (fig. 30. HE, F), but only very little of the chloro- 

 phyll maxima in the red as well as in the violet. The quantum yield was 

 estimated to be the order of 0.06 in the phycoerythrin bands, and as low as 

 0.02 in the chlorophyll bands. Similar results were obtained with several 

 other Bangiales and Florideae. The absorption by carotenoids appeared to 

 be as little effective as that by chlorophyll. A slight increase in activity 

 shown by some species at X = 440 mju, coinciding as it did with an increase 

 in the absorption of the aqueous phycobilin extract, could not be inter- 

 preted as sign of photosynthetic activity of the chlorophylls or the caro- 

 tenoids. 



These unexpected results indicate that in contrast to all other plants 

 direct sensitization by chlorophyll plays only a subordinate role in at least 

 some of the red algae, and that photosynthesis in them is sensitized pri- 

 marily by phycobilins. If this is the case, it would seem unlikely that the 

 energy quanta absorbed by the phycobilins are transmitted to chlorophyll, 

 since how could indirectly produced excitation of chlorophyll be more 

 effective than excitation due to energy absorbed directly by chlorophyll? 

 Rather, these results would seem to indicate that the phycobilins are 

 sensitizers of photosynthesis in their own right, and that their presence 



