ACTION SPECTRUM OF RED AND BLUE ALGAE 11S5 



cemed with the other aspect of the same phenomenon — chromatic adapta- 

 tion as a factor enabhng plants to make better use of available light energy. 

 It was mentioned in chapter 15 that Oltmanns (1893) and others (most 

 recently, von Richter 1912, and Sargent 1934) objected to Engelmann's 

 theory (as well as to its extension by Gaidukov to color changes induced 

 artificially in blue-green algae) and insisted that algae responded only to 

 changes in light intensity, and not color. 



\m\ Richter (1912) raised a further objection and asserted that "chro- 

 matic adaptation" could not achieve the purpose that was suggested by 

 Engelraann, because phycobilins do not act as sensitizers in jjliotnsynthe- 

 sis. Although, in comparing the ratio of the photosynthetic productions 

 of the green alga Ulva lactuca in red and green light with the corresponding 

 ratios for Plucaniiiim, CallUhamnion, Delesseria and other red algae, von 

 Richter could not help confirming the results of Engelmann and finding 

 that red algae are two or three times as eflicient in green light as the green 

 algae, he nevertheless denied that this proved the photosynthetic activity 

 of the red pigments. He pointed out that similar differences are obtained 

 also by changing the intensity of light, and suggested that the red algae 

 utilize green light better not because of its wave length but because it is 

 only weakly absorbed by chlorophyll — and red algae are adapted to weak 

 light. 



However, the views of von Richter have not been confirmed by later 

 investigators. Wurmser and Ducleaux (1921) compared the photosyn- 

 thetic eflSciencies of red and green fronds of Rhodymenia palniafa and 

 Chondrus crispus and found that the red varieties give yields two or three 

 times greater than the green ones. Wurmser (1921) compared the photo- 

 synthesis of the green alga Ulva lactuca with that of the red alga Rhodymenia 

 palmaia in red, green and violet light. He found that, if the rate in red is 

 taken as imitj^ that in green is 0.24 in Ulva and 0.49 in Rhodymenia, and 

 that in violet 0.81 and 0.16, respective^ (for equal intensity of incident 

 light). Thus, the red algae are more eflScient in the green, but le::s ef- 

 ficient in the violet than the green ones. Wurmser pointed out that, even 

 if von Richter's intensity effects are real, this does not mean that color ef- 

 fects are only indirect consequences of changes in absorption intensity. 



Similar results were obtained by Harder (1923), who concluded that 

 both intensity adaptation and color adaptation are real phenomena. He, 

 as well as Ehrke (1932), interpreted the result of the rate measurements 

 with red algae as indicating active participation of the phycobilins in photo- 

 synthesis, and the same conclusions were reached by Montfort (1936) and 

 Schmidt (1937), who found the spectral maximum of the efficiency of phyco- 

 cyanin algae in yellow light, and that of phycoer>'thrin algae in green 

 light. 



