GILBERT M. SMITH 319 



dividing cells do not accumulate these substances in sufficient concen- 

 tration before the amount is halved or quartered by division to form 

 two or four daughter cells. 



The most extensive studies on sexual substances of Chlamydomonas 

 are those of Moewus on three interfertile species, C. eugametos, C. 

 Braunii, and C. dresdenensis. These three species and mutants derived 

 from them are collectively known as the eugametos group. When a 

 palmella culture of any member of the series is flooded with water in 

 light the cells become motile, but if this is done in darkness they do not 

 become motile. Transfer of motile cells from light to darkness is soon 

 followed by a loss of motihty. On the other hand, Moewus (8,11) finds 

 that both cells which have become immobile in darkness and palmella 

 cultures flooded in darkness do become motile when various sugars are 

 added to the liquid. Although members of the eugametos group can be 

 made motile in darkness by means of sugars the cells do not react sexually 

 when mated with sexually functional cells of opposite sex. 



When palmella cultures standing in darkness are flooded with the 

 filtrate from a culture standing in light and containing sexually functional 

 cells the eff'ect is different. Here the cells in darkness become both motile 

 and sexually functional (8). This is due to the fact that the cells in 

 darkness have absorbed both motility-inducing and sexuality-inducing 

 substances excreted by cells swimming in light. However, a filtrate from 

 an illuminated culture will only induce sexuality when applied to a 

 culture of the same sex. That is, a filtrate from a female culture will 

 induce sexuality in a female culture but not a male culture. The reverse 

 is true for filtrates from male cultures. 



Having shown that sexual substances of the eugametos group are 

 formed only in light, Moewus then proceeded to determine more pre- 

 cisely the conditions under which they are formed and the nature of the 

 substances. He soon found that for both male and female cells the sexual 

 substances are formed only in light from the blue end of the spectrum. 

 Sexual substances are formed in light of 4358 and 4961 A, but there is 

 no formation of them in light of 5461, 5770, 5791, 5890, or 6430 A (10). 



The effect of light upon sexual substances excreted from motile 

 sexually functional cells was also studied. This was done by obtaining a 

 filtrate containing the sexual substances, exposing the filtrate to light 

 for a specific time, flooding cells in darkness with the illuminated filtrate, 

 and then noting whether or not this procedure induced sexuality in 



