EUGENE RAiil NO WITCH AND CXJVJNDJEE 



381 



New Observations 



Action Spcchti of the Emerson Effect 



The hyi)othcsis that two (or more) lornis ol chlorophyll a, with 

 cliftereiu photochemical properties, are present in vivo was confirmed 

 by new and more precise measurements of the action spectrum of 

 the Emerson effect (Figs. 3. A, B) . Fig. 3 A applies to the green 

 alga, Chlorella. It shows the extent to which the quantimi yield of 

 photosynthesis produced by the absorption of light in a "far red" 

 band (685-700 ni/x) is enhanced by monochromatic supplementary 

 light of different wavelengths. The curve has two sharp maxima. 

 The one at 650 m^ (already observed by Emerson) must belong to 

 chlorophyll b; the other, at 670 m/x, not noted by Emerson, indicates 

 the existence of a chlorophyll a form having an absorption peak in 

 this region — a form whose excitation can supplement that in the far- 

 red band as effectively as does the excitation of chlorophyll b. 



Fig. 3B refers to the diatom Navicula. The action spectrum of the 

 Emerson effect in this diatom shows three peaks, at 535 m^ (attributa- 

 ble to fucoxanthol — this is not the peak of the fucoxanthol band, but 

 tlie region of maximum participation of fucoxanthol in total absorp- 



a. 



< 



u. 



650 690 530 570 



m;j SUPPLEMENTARY LIGHT 



610 



650 



690 



FijT. 3. A, Action spectrum <j[ Emerson cflet t in Chlorelln (after Coxindjce and 

 Rabinowitch, 17). B, Action spectrinn of Emerson effect in Navicula (after Gov- 

 indjee and Rabinowitcfi, 17). 



