CONTROL BY LIGHT 219 



totaxis and plioto-orientations of all kinds in protista and other 

 organisms (Bendix, 1960; Mast, 1911); pigmentation, morphogenesis, 

 and sporulation in fungi (Bonner, 1959; Cantino and Turian, 1959; 

 Cochrane, 1958); pigmentation in bacteria (Baker, 1938; Kreitlow, 

 1941); protoplasmic streaming (Haupt, 1959); and respiration 

 (Fockler, 1938). 



As with photoperiodism, studv of blue-light effects in many ani- 

 mals is complicated by the presence of vision, although there is, 

 again, evidence that morphologicallv specialized photoreceptor or- 

 gans need not be involved. In a sea-anemone (North, 1957) and a 

 starfish, for example, the skin itself appears to be light-sensitive; in 

 the latter, the same blue-absorbing pigment occurs both in the skin 

 as a whole and in specialized pigment bodies (Rockstein, 1956). 

 However, work on the identification of possible blue-receptive pig- 

 ments has been most intensively carried out by investigators of pho- 

 totropism in the higher plants and the fungi, and it is such studies 

 we must now consider briefly. (General references for the follow- 

 ing discussion on phototropism are the four given above. ) 



For a long time, /S-carotene or related carotenoids were believed 

 to be the only possible photoreceptors in phototropism. This belief 

 was based on action spectra, on the appropriate distribution of caro- 

 tenoids in the sensitive tissues, and also on the known role of such 

 compounds in vision. Some ten years ago, however, flavine com- 

 pounds were suggested, and the situation is no longer as clear as it 

 appeared to be. 



In various published action spectra, single, double, or even triple 

 peaks in the blue are found. In addition, a peak near 3800 A, in 

 the near-ultraviolet, may be evident. The presence of multiple 

 peaks in the blue has been taken (e.g., Curry and Gruen, 1959) as 

 evidence for the functioning of carotenoids, since the absorption of 

 riboflavin and certain related compounds in water solution generally 

 shows a single broad peak or a peak and a shoulder. However, this 

 argument against flavine involvement has been weakened by demon- 

 strations that certain flavoproteins in water, or simpler flavine com- 

 pounds in various other solvents, can show multiple peaks in the 

 blue (Asomaning, 1960; Beinert and Crane, 1956; Searls and Sanadi, 

 1959). On the other hand, the action-spectrum peak in the near- 

 ultraviolet has been used to support the flavine hypothesis, since it 

 fits the absorption of many flavine compounds very well. An ob- 



