GILBERT M. SMITH 3^5 



do not. When treated in similar manner with safranol all cells of a homo- 

 thallic clone functioned as male gametes. This takes place in safranol 

 solutions with 5 x 10^ to 5 x 10® molecules per cc. but not in solutions 

 of higher concentration. 



From the foregoing experiments Moewus concludes that picrocrocin, 

 or a closely related compound, is the female sex-determining substance 

 (gynotermone) and that safranol is the male sex-determining substance 

 (androtermone). As already noted, picrocrocin is derived from proto- 

 crocin; and safranol, in turn, is derived from picrocrocin, a change 

 brought about by a specific enzyme (14). Female cells of heterothallic 

 species lack this enzyme and so have no conversion of the picrocrocin 

 into safranol. Male cells of heterothallic species produce this enzyme 

 and so have a conversion of all the picrocrocin into safranol. Homothallic 

 species have a conversion of only a part of the picrocrocin into safranol 

 and so have both picrocrocin and safranol within their cells. Cells with 

 more picrocrocin than safranol are female; those with more safranol 

 than picrocrocin are male. 



Cultures of members of the eugametos group have not been available 

 to others studying the sexuality of Chlamydomonas and so there has 

 been no confirmation or extension of the striking results reported for 

 this group by Moewus. However, studies on sexuality in other species 

 of Chlamydomonas do afford a certain amount of data for comparison 

 with the results reported for the eugametos group. 



Plus and minus clones of seven heterothallic strains, none of which is 

 interfertile with any other, and several homothallic strains have been 

 isolated at Stanford University. The heterothallic strains include C. 

 Reinhardi Dang., C. intermedia Chodat., C. minutissima Korshikov, and 

 a strain superficially resembling C. minutissima but not interfertile with 

 it. One of the homothallic strains has been identified as C. Snowiae 

 Printz. 



The behavior of the Stanford strains with respect to light and darkness 

 is quite different from that of the eugametos group. When motile 

 sexually functional cells of Stanford strains are taken from light to 

 darkness the cells remain motile and sexually functional for several 

 hours, and in certain cases for a day or two. When palmella cultures of 

 both homothallic and heterothaUic Stanford strains are grown in hght 

 and then kept in darkness for 24 hours before flooding, the cells become 

 motile within an hour or two after flooding. If plus and minus clones 



