860 AQUATIC PHYCOMYCETES 



formed oogonial initials. When sterile plants, developed from isolated 

 male and female basal cells, were placed in the same culture in such a 

 manner that their branches were interwoven, an abundance of sex organs 

 resulted. Plants forming antheridia could be traced to male basal cells, 

 whereas those forming only oogonia had developed from the female 

 basal cells. In addition to the aberrant female strain previously mention- 

 ed, certain of Jordan's gross cultures were composed of strains which 

 never produced sex organs. Some of these when isolated and paired 

 with strains of known sexual potentiality proved to be male, others, 

 female, but there remained a few which showed no sexual potentiality 

 whatsoever. Jordan's preliminary work, therefore, established experi- 

 mentally what had been suspected as being the reason for the sterile 

 strains reported from time to time by various investigators and so 

 frequently found in nature, that is, that S. elongatus, like Dictyuchus 

 of the Saprolegniaceae (Couch, 1926b), was heterothallic. It also showed 

 that there existed in nature a female strain which could form oogonial 

 initials without contact with the opposite sex, as well as other strains 

 which under ordinary conditions showed no reactions to either sex. 

 Bishop (1940), starting from single-zoospore isolations, extended the 

 study of this fungus and grew it in pure artificial culture. Thirty-nine 

 pure cultures derived from single zoospores were obtained. Of these, 

 seventeen were intensively studied. Four were found to be strongly male 

 and could be distinguished not only by the formation of antheridial 

 branches but by their greater rate of growth. One was classified as 

 "weakly male," five were neuter or neutral, one "weakly female," and 

 six "strongly female." The strongly male and strongly female strains 

 when mated formed reproductive organs (the former, antheridia, the 

 latter, oogonia); the eggs were fertilized, and normal oospores were 

 developed. There was some evidence that the formation and direction 

 of growth of the antheridial branches were positive responses to sub- 

 stances diffusing from the female; this suggests a hormone-control 

 mechanism similar to that found in Achlya by J. Raper (1939a, 1939b, 

 et seq., see p. 798). Evidence derived from various combinations indi- 

 cated also that, whereas the male strains never showed signs of latent 

 femaleness when grown alone, all female strains under such conditions 

 exhibited undoubted latent maleness, could form antheridial branches, 



