1 14 SEX IN MICROORGANISMS 



in all cases, the cells may have built up, during an extended period of 

 illumination, a supply of the agent exceeding the threshold for 100 

 per cent gamete mating; and that it is only when the level of gene- 

 tyllin falls below this threshold that mating activity declines. Sus- 

 pensions of cells containing various amounts of reserve genetyllin 

 were therefore prepared (different pre-illumination periods being 

 used) and were mixed with suspensions of sexually inactive cells. In 

 no case was there evidence that activity could be transmitted to in- 

 active cells by this means; and one may conclude that genetyllin can 

 probably not be transmitted from cell to cell through the medium. 



Genetyllin may prove to be as mythical as the Genetylhdes 

 themselves. The concept has been introduced, with some misgivings, 

 in an attempt to indicate a less orthodox approach to the subject of 

 sex substances than is provided by a search for soluble hormones. 



Sex Substances 



A few authors have claimed to have demonstrated the presence 

 of "sex substances" in culture media from sexually active cells. A 

 clear distinction should be drawn here between at least four different 

 actions attributed to such agents. 



1. Positive chemotaxis, drawing gametes of one mating type or 

 sex toward their prospective partners (see page 116), 



2. In heterothallic species, the induction of clumping in a clonal 

 suspension by treatment with filtrate from cells of opposite mating 

 type. 



3. The sexual activation of non-sexual cells by treatment with 

 filtrate from sexually active gametes of the same mating type. 



4. The induction of the formation of gametes which behave tem- 

 porarily as a single mating type by treating cells of a homothallic 

 strain ("phenotypically dioecious") with filtrate from the appropri- 

 ate mating type of a heterothallic species. 



Sex substances of type (2) were reported in the supernatant 

 medium after centrifuging gamete suspensions of Tetraspora (Geit- 

 ler, 1931 ). In T. lubrica, which is regularly heterothallic and appro- 

 priately lubricous, Geitler found that a certain amount of intraclonal 

 clumping could be induced in cultures by the addition of concen- 

 trated "extracts," practically free from cells, prepared from suspen- 



