ACTION SPECTRUM OF BROWN ALGAE 1175 



(However, the latter value was derived from a small shoulder on the 

 absorption curve, and is not precise.) The absorption peak of fucoxanthol 

 in vivo was calculated from the difference between the absorption curves 

 of the cells before and after extraction with aqueous methanol ; it indicated 

 a red shift by as much as 40 m/x for this pigment — from 445 mn in methanolic 

 solution, to 485 mju in vivo. The blue peak of chlorophyll c was calculated 

 similarly from the difference between the spectra of cells before and after 

 extraction with 50% methanol; a red shift of 20 m/x was deduced in this 

 way. 



(The shifts deduced by Tanada for the four blue-violet bands — 8 m/x 

 for chlorophyll a, and 40 mju for fucoxanthol — can be compared with those 

 derived in chapter 22, on pages 705-706, from earlier investigations. 

 The agreement is good for chlorophyll a; for fucoxanthol, the shift found 

 by Tanada — 40 m/x — is about twice that estimated previously by Wassink 

 and Kersten.) 



When the blue-violet solution bands of all pigments present in the 

 diatoms were shifted as indicated, and superimposed, a composite absorp- 

 tion curve was obtained (see fig. 30.9C). (No attempt was made by 

 Tanada to analyze the region > 620 mju, where all absorption is due to the 

 chlorophylls.) The quantitative agreement is not too good, the composite 

 curve having a higher peak, and a lower valley in the green than the actual 

 absorption cui-ve of the cells. This may be due, at least in part, to scatter- 

 ing — although the cell cur\^e was obtained on Hardy spectrophotometer 

 equipped with an integrating sphere, and with cells immersed in glycerol to 

 reduce scattering. Another likely source of discrepancies is the broadening 

 of the absorption bands in vivo (particular^ of that of fucoxanthol) . 



The uncertainty implied in the discrepancy between the two curves, 

 had to be accepted in estimating the contribution of the several pigments 

 to total cell absorption at any given wave length. The results of this 

 estimate are shown by fig. 30.9D. It indicates that in the region 500- 

 550 ran, fucoxanthol takes up most of the quanta absorbed; and yet, fig. 

 30. 9A shows no drop in yield in this region — except below 520 mju, where 

 absorption by "other carotenoids" sets in. The simplest explanation of the 

 results is that three pigments — chlorophylls a and c and fucoxanthol — are 

 fully effective in photosynthesis (70 — 0.11), while the other carotenoids 

 are either altogether ineffective or have a much smaller efficiency. 



Tanada found further that 70 of Navicula minima was the same at 1.5, 

 10, and 20°C., and that 7 was a smooth function of light intensitj' between 

 0.9 and 6.9 X 10 ~* einstein/cm.^ min., the curvature becoming noticeable 

 >2 X 10~* einstein/cm.2 min. Points obtained in red, orange, blue and 

 green light all fell onto the same slightly curved line, similar to that found 

 for ChloreUa by Emerson and Lewis (fig. 30.5). 



