ACTION SPECTRUM OF BROWN ALGAE 1177 



quanta. Moatfort and Schmidt concluded from these results that, of all the carotenoids, 

 only fucoxanthol is able to assist in the sensitization of photosyntlu^sis, whereas the 

 carotenoids of green algae are inactive (for a criticism of their methods, sec Emerson 

 1937). 



Table 30. VI 

 Energy Yield of Algae in Light of Different Colors" (after Schmidt 1937) 



P /I (green) P/I (blii^ 

 Alga P/I (red) P/I (red) 



Green ^ „^ 



Cladophora 0-49 0.80 



Ulva laduca 0.46 0.82 



Brown 



Laminaria digitata 



Strong light (1) 1.29 



Medium light (Vs) 0.91 1 .32 



Weak light Qi) 1-00 1 .23 



Phyllilis fascia — 1-40 



Dictyota dichotoma . 90 1 . 48 



Fucus vesiculosus (brown, but with low fucoxanthol content) 0.38 0.59 



" P/I for equal incident intensities. 



A certain improvement of methods was attempted by Montfort later (1940). The 

 pigments were extracted from the algae and their absorption curves determined (in 

 methanol solution), with results shown in figure 22.45A,B {cf. also Table 22.VIII). These 

 absorption data were applied to the results of Gabrielsen and Steemann-Nielsen (1938), 

 who found that, for equal incident light intensity, the rate of oxygen production by di- 

 atoms is consistently higher in the blue than in the red. (A similar difference was re- 

 ported earlier by Mothes, Baatz and Sagromsky 1939.) The difference is particularly 

 strong in low light, as shown by Table 30. VII. The table describes a perfectly under- 



Table 30.VII 



Ratios of Rates of Photosynthesis by Diatoms in Blue and Red Light 

 (after Gabrielsen and Steemann-Nielsen 1938) 



Incident light, PjblueJ Incident light. ^r^.v 



cal/cm.2 sec. P (red) cal/cm.2 sec. P (red) 



0.25 1.8 1.7 1.4 



0.5 l.fi 2.4 1.3 



1.0 1.5 3.7 1.1 



standable transition from the conditions at low light intensities (where the yield is pro- 

 portional to absorption, and may therefore be higher in the blue than in the red, if the 

 absorption in the blue is so nmch sti'onger as to overbalance the laiger size of the quanta) 

 to the conditions in strong (saturating) light, where the rate must be (and apparently is) 

 independent of wave length. Montfort (1940) preferred, however, to average all the 

 ratios in Table 30.VII and concluded that a ratio of 1.5 between the rates in blue light 

 and red light indicates an active participation of carotenoids in photosynthesis. Using 

 the absorption curviis of methanolic extracts he calculated that the energy conversion 

 rate in blue light is 1.03 times larger than in red light, referred to absorption by all pig- 



