112 SEX IN MICROORGANISMS 



Ondratschek, 1939). According to Moewus (1935c, 1950a), the sex 

 ratios among gametes formed by certain homothallic Protosipho?i 

 strains and by C. eiigametos alpina are markedly affected by pH. 



Warming for short periods tends to stimulate gametogenesis in 

 Protosiphon (Klebs, 1896; Maher, 1946-47). It was found that aera- 

 tion promotes sexual activity in the heterotrophic flagellate Folytovia 

 (Moewus, 1933; Pringsheim and Ondratschek, 1939), but its action 

 in illuminated suspensions of photosynthetic algae is probably less 

 marked. 



It has been found (Lewin, unpublished) that sexual clumping 

 and pairing in Chlamy dojnonas moewusii are dependent on the con- 

 centration of the Ca-' ion in the medium. Sexually active cells lose 

 their ability to mate after washing in distilled water but regain it 

 when CaCl2 is added. The optimum range of Ca • • for mating lies 

 around 3 to 30 ppm, being higher in media containing much phos- 

 phate or amino acids, which combine with a proportion of the free 

 cations. Mating is also inhibited when the Ca • • is removed by such 

 agents as citrate or oxalate. Inhibition by 0,02 M. citrate may be re- 

 versed by washing the cells in mineral media, or by the addition of 

 0,001 M CaCl2, and may be slightly alleviated by higher concentra- 

 tions of MgCls or SrCh, Since, once the cells have paired, citrate 

 does not reverse the mating reaction, it appears that the Ca • • is con- 

 cerned primarily in the specific agglutination which occurs between 

 the flagella of mating cells (see page 117), Loeb (1915) and Vasseur 

 (1949) showed that the presence of Ca- • was required for the agglu- 

 tination of spermatozoa and for fertilization in certain echinoderms. 

 Possibly this requirement is related to the free superficial amino 

 groups, which, as indicated by Metz and Donovan (1951), take an 

 active part in this process. The phenomenon may also be in some 

 ways compared with that of the adsorption of bacteriophage by host 

 bacteria (Puck and co-workers, 1950). 



"Genetyllin" 



To provide a material basis for discussion of the experiments 

 described in this section (Lewin, unpublished), it has been postulated 

 that in Chhmiydovionas moeuousii there is a specific agent or hormone 

 responsible for sexual activity. We shall refer to this hypothetical 

 agent as genetyllin. Genetyllin is formed within the cells under the 



