SFX IN UNICFLI.Ul.AR Al.CAF. 115 



sions of opposite niaring r\pc. Unlike the noniuil scxiuil reaction, 

 such clumping was not followed l)\' the formation of gamete pairs. 

 Though he considered the possibility that this effect might be due 

 to cell breakdown products, he decided that this was unlikely. In 

 1933 and 1934, Aloewus reported a similar phenomenon in contami- 

 nated cultures of Cblaviydovwiicts engLinictos and in Protosiphov and 

 Stcpbiinospbiie)\i. He found that the acti\e agent did not diffuse into 

 cotton or agar, and evidence for its insoluble nature lay in the fact 

 that activity could be removed by filtration through membranes with 

 0.01 [}- mean pore size, though not by coarser membranes with 0.7 5 -[i- 

 pores. When such intraclonal mating responses were induced, Moe- 

 wus observed that the cells in each clump appeared to have aggre- 

 gated around a central point, which he suspected might be a bac- 

 terium, though he \\as unable to confirm this. It may be noted that 

 Pringsheim and Ondratschek (1939) were able to induce aggregation 

 of various flagellates by the addition of bacteria alone. (Moew^us also 

 reported that solutions containing active sex substance did not freeze 

 when cooled to —10°, but that, when the agent was removed by 

 filtration, the filtrate froze normally — a phenomenon inexplicable on 

 simple physicochemical grounds.) Lerche (1937) was able to demon- 

 strate sex substance activity in centrifugates from Dunaliella; but in 

 this case she found that filtration through a membrane with 0.75-!x 

 pores M'ould remove the active agent, again suggesting that large par- 

 ticles, rather than a solute, were responsible for the effect. 



Jollos (1926) reported that filtrates from "strong" phis gametes 

 of Dasycladiis tended to augment the sexual response of "weak" 

 plus gametes, and to reverse that of weak vnmis gametes {mutatis 

 mutandis, strong mimis gametes behaved similarly) ; but he did not 

 exclude the possibility that such changes could be attributed to 

 non-specific alterations in the composition of the medium. 



On the other hand. Smith (1946) and Hutner and Provasoli 

 (1951) were unable to demonstrate the presence of any soluble sex 

 substances in three species of Chlaiuydomonas and in C i/ioeuiisii 

 respectively. E. Hinreiner (Al. Starr, in litt., July and September 

 1952) found no flavones in culture filtrates from C. moewusii or C. 

 eugametos, despite the activity claimed for certain compounds of 

 this sort in C. eugametos (Aloewus, I950a,b). Attempts to demon- 

 strate the activity of specific water-soluble sex substances in Farame- 



