324 PLANT GROWTH SUBSTANCES 



female culture grown in red light and exposed it to blue light until it 

 contained the end substance (trans-crocetm dimethyl ester). This filtrate 

 did not induce sexuality in darkness but an addition to it of a cis/ trans 

 mixture of the proper proportion did induce sexuality in darkness. 

 From this he argues that the filtrate contains a sexual substance in 

 addition to the sexual substance {cis/ trans mixture) inactivated by blue 

 light. This argument seems inconclusive when one takes into considera- 

 tion the fact that cisj trans mixtures in distilled water also can induce 

 sexuality in darkness. 



TABLE 3 



Table showing the correlation between cis/ trans ratios of the five sexual types 



of the Chlamydomonas eugametos group and Bergmann-Niemann ratios 



Moewus obtained more convincing evidence for the presence of 

 termones in his study of homothallic strains. When taken from darkness 

 and exposed to light for an hour the cells of a homothallic clone become 

 motile, aggregate in clumps, and fuse in pairs. Moewus (12) placed 

 homothallic clones in darkness, flooded them with a solution of picro- 

 crocin and allowed them to remain in darkness for 20-25 minutes. 

 These cultures were then taken to Hght but there was no gametic union 

 of the cells even after illumination for an hour or more. However, when 

 the cells had been standing in light for an hour and were tested against 

 functional male and female gametes they reacted sexually with the 

 male but not with the female gametes. The picrocrocin makes all cells 

 in a homothallic culture function as female gametes. Solutions with a 

 concentration of from 8 x 10^ to 8 x lo^^ molecules of picrocrocin per zc. 

 produce this effect, but those with a concentration greater than 8 x \o^'^ 



