SEX IN UNICELLULAR ALCAE 



109 



(sec Alocwus, 1939c, 1940c, 1950b, for example); the possibility that 

 chlorophyll may be involved is discussed briefly below. 



Provasoli and Pintner (sec Hutner and Provasoli, 1951) found 

 tliat liolit was required for the mating of C. vwcunisii. Preliminary 

 experiments indicated that any wavelengths within the visible range 

 Mere acti\c in promoting sexual clumping and pairing, and they con- 

 cluded that at a sufficient intensity all qualities of light were stinui- 



400 



500 



600 



700 



WAVELENGTH (m;)) 



Fic. 1. Action spectrum for sexual induction in C moeioiisii Gerloff. 



latory. It has since been shown (Lewin, unpublished) that in this 

 species light is required for the sexual activation of both mating types, 

 and unless both gametes have received illumination no mating takes 

 place. Not all wavelengths are equally effective: an action spectrum 

 for sexual induction in C. 7iioewusii is presented in Fig. 1. It will be 

 observed that the form of this curve is not dissimilar to the absorp- 

 tion spectrum of chlorophyll. The suggestion is therefore made that 

 the action of light on mating in Chlamy domonas is mediated by the 

 chloroplast, and that sexual activity is promoted by some product or 



