C. S. FRENCH 455 



certain green bacteria. Not only arc the iiulivickial carotenoids im- 

 possible to identify in spectra ot intact plants, l)ut they seriously ob- 

 scure the shorter wavelength chlorophyll bands. Some brown algae 

 and diatoms, ho^\■ever, have broad absorption bands in the 480-550 

 m^u, region attributable to the carotenoid fucoxanthin in combination 

 with a protein. 



Pliycobili7is 



Unlike chlorophylls and carotenoids, the phycobilins — red phyco- 

 erythrin and blue phycocyanin — occur as water-soluble pigment pro- 

 tein complexes. The spectra of the extracted and purified substances 

 may be compared directly, without wavelength shifts, with spectra of 

 intact plants. Both phycoerythrins and phycobilins come in several 

 different types characterized by their spectra. References 1, 2, 5, 28, 

 30, 31, 32, 34, 35, 40, 50, 51 discuss the properties of some phycobilin 

 pigments studied since the work of Lemberg and Legge (45) . Evi- 

 dence for the participation of the phycobilins in photosynthesis has 

 been reviewed (5, 15, 30). 



Since the phycobilins are highly fluorescent, their fluorescence spec- 

 tra may also be used for identification in intact plants, if the dis- 

 tortion of the spectrum by reabsorption within the sample is avoided 

 by using very thin layers (20) . Phycoerythrin has a fluorescence peak at 

 578 rufx with a broad shoulder around 625 m^, phycocyanin fluoresces 

 at 637 m^, and allophycocyanin at 663 m^^ (28) . The main absorp- 

 tion bands by which the common photosynthetic pigments may be 

 identified in live plants are shown in Fig. 6. 



Action Spectra of Photosynthesis 



The Participation of Accessory Pigments Shozun by 

 Action Spectra of PJiotosynthesis 



The fact that chlorophyll is the primary light absorber for photo- 

 synthesis was guessed long ago from the observation that only green 

 parts of plants produce oxygen. The only clear evidence for this 

 function of chlorophyll is, however, the qualitative agreement of the 

 absorption spectrum of chlorophyll in vivo with the action spectrum 

 for photosynthesis. 



A large number of action spectra for photosynthesis have been 

 measured for many species, Avith techniques varying from some of 

 remarkable ingenuity and high precision to some of ridiculous in- 

 adequacy. Comparatively crude action spectra showing the partici- 



