ABSORPTION BY CAROTENOIDS IN BROWN ALGAE 725 



this absorption by 40 to 00% in the region 500-550, and by 30% in the 

 region 450-500 mn. In bro^vn algae and diatoms, the absorption increase 

 due to the carotenoids is much larger, from 160% to 400%. This is a 

 consequence of the absence of chlorophyll b and the presence of fucoxanthol ; 

 these two pigments substitute for each other, despite their difference in 

 color. 



Table 22.VIII 



Ratio of Absorption by Individual Pigments in Methanol or Benzene and by 

 THE Total Pigment in Methanol" (after Montfort 1940) 



550-500 m^ 500-450 iiim 



X. X. 



(including f including 



Organisms Clil. F.) pl> Clil. F.) C. /3 b 



Diatoms 0.34 0.40^ 3 0.20 0.82 0.24 5 



Phaeophijceae 



Laminaria digitata 

 taken from 12 m. 

 depth 0.38 0.69= 2.6 0.32 0.93 0.33 3.1 



Fucus vesiculatus 



from the surface . 0.24 0.80 4.2 0.22 0.91 0.30 4.5 



(0.33)'= (0.47)"= 



Chlorophyceae 



Ulvalactuca 0.73'' 0.34 1.37 0.75'' 0.56 0.25 1.33 



(0.19)^ 



Leaves 



Phaseolus vulgaris^ . — — 1.6 — — 1-3 



" The figures in the table do not add to unity because they do not represent the 

 proportions in which the energy absorbed by the pigment mixture is divided between the 

 individual pigments, but rather the ratios (.absorption by the separated pigments): 

 (, absorption by the mixture). Chi. = chlorophyll (in methanol), X. = carotenols (in 

 methanol), F. = fucoxanthol (in methanol), C. = carotene (in benzene). 



* /3 = factor by which total absorption is increased by the presence of carotenoids. 



" F. alone. 



'' Chi. a + b. 



« Chi. a alone. 



/ According to page 684, the leaves of this species contain a considerable quantity 

 of water soluble yellow pigments. 



A considerably more detailed analysis of the absorption by diatom pig- 

 ments was made by Button and Manning (1941); the results are repro- 

 duced in figure 22.46. They are based on measurements with acetonic pig- 

 ment extracts from Nitzschia closterium. In constructing the figure, 

 Button and Manning postulated a shift of all absorption bands, those of 

 chlorophyll as well as those of the carotenoids, by 20 m/z. (They based 

 this assumption on the observation that, in the spectrum of this diatom, the 

 maximum of the red chlorophyll band was recognizable at 680 m^; the 

 maximum of the blue-violet band, although not distinct in the cell spectrum 



