C. i. I'RENCH 



453 



600 



700 



750 



650 



Wavelength, mp 



Fig. 5. The derivative absorption spectrum of a culture of Ochromonas danica 

 having a large amount of a chlorophyll a form with an absorption peak at about 

 712 m^. (Unpublished measurements of M. B. Allen and J. S. Brown). 



pheophytin rather than of chlorophyll. Kok (38, 39) found re- 

 versible changes of absorption at 705 m^u, on illumination of cells. 



Whether these different forms of chlorophyll may have their own 

 specific functions in photosynthesis is a problem of major interest 

 to our group at the present time. 



Chloropliyll b 



In ether, chlorophyll b has absorption bands at 644, 595, 549, 455, 

 and 430 m^. (55). The "644" band is recognizable in plants at about 

 650 niyu. The absorption spectra of plants usually have a shoulder at 

 480 niyu, which is generally attributed to carotenoids. Barer (4) has 

 suggested that the 480 mfx band in vivo may be primarily due to the 

 chlorophyll /; band found in ether solution at 455 m^. This idea 

 may be possible in spite of the unusually large wavelength shift. 

 The other chlorophyll b bands are not generally recognizable in 

 spectra of whole plants. Even the 650 ni/x band is only a shoulder 

 on the side of the red chlorophyll a absorption. In Ulva, but in no 

 other plant studied, there are two forms of chlorophyll b, or else 

 there is some other unrecognized pigment absorbing near 650 m^ 

 in this species (22, 23) . 



