C. S. FRENCH 



461 



in 050 u\fi. legion. Siuli a pair ol cuiacs, aiiloniatically recorded for 

 Chlorella, is given in Fig. 12. The diiference between the curves 

 in ihe sliorter wavelength region gives enhancement spectra similar 

 to those ol Emerson suggestive ol chlorophyll b. The difference be- 

 tween the curves in the long wavelength region gives the action spec- 

 triuii ol the long wavelength partner. The difference ciuve for one 

 of the active components has its peak at 695 m^. This active pigment 

 is believed to be the chlorophyll a form, C;,695, found in the absorp- 

 tion spectrum of Euglena and in smaller amounts also in Chlorella 

 (11). This part of the spectrum was checked by individual point-by- 

 point measurements (Fig. 13). It thus appears that enhancement of 

 photosynthesis by light absorbed by chlorophyll b is somehow due 

 to the simultaneous light activation of C,,650 and of 0^695. Chloro- 

 phyll a 695 and Ci,650 act as a mutually enhancing pair. Similar 

 measinements by McLeod and by Fork (as reported by Haxo, 3) 

 have sho^vn enhancement of chlorophyll a j^hotosynthesis by the ac- 

 cessory phycobilin pigments, and vice versa (27) . 



Enhancement thus looks like a two-way balanced affair. We see 

 no reason to suppose that either of the two pigments involved plays 

 a primary role and the other a secondary or "accessory" role. 



Action Spectra for Chlorella Photosynthesis 



X700 background 



T 1 r 1 1 



X650 background 

 / 



600 



700 



650 

 Wavelength , mp 



Fig. 12. Action spectra for photosynthesis by Chlorella pyrenoidosa. Dashed 

 curve: no extra light. Other two upper curves with background light as indicated. 

 Lower curve: difference between 700 and 650 m/i background curves. The part of 

 this curve below 683 mm represents the action spectrum for chlorophyll b, one of 

 the mutually enhancing pair of pigments, while the part at longer wavelengths 

 than 683 m^ is the action spectrum for the other partner, C,695. (From 27). 



