LEPTO MIT ALES 861 



and could even fertilize their own oogonia. Since all the cultures used 

 for critical experimental work were derived from single zoospores, which 

 have been shown by Kevorkian (1935), using cytological methods, to 

 be uninucleate, the older theory postulating that each nucleus possesses 

 the potentialities of but one sex could not be applied here to explain 

 the sexual phenomena found in Sapromyces elongatus. On the basis of 

 the results of these investigations Bishop concluded that the theory of 

 "relative sexuality" proposed by Hartmann (1925), rather than the 

 "heterothallism" of Blakeslee, best explained the observed facts. He 

 pointed out that heterothallism implied the strict unisexuality of the 

 individual, whereas relative sexuality postulated that there were: 



. . .even in single nuclei, male potencies (A) and female potencies (G) under 

 the control of male realisators (alpha) and female realisators (gamma). In the 

 male strains of haplogenotypic, heterothallic organisms, the male realisator 

 (alpha) is at once the means of activation of the male potency (A) and the 

 inhibition of the female potency (G). The reverse is true in the female strains 

 of such organisms, where the female realisator (gamma) activates the female 

 potency (G) at the expense of the male potency (A) 



On this hypothesis Bishop has indicated that the following types of 

 sexuality may be present in S. elongatus: pure male (MM), male with 

 latent femaleness (Mf), neutral, strongly sexed (ME), neutral, weakly 

 sexed (mf), female with latent maleness (mF), and pure female (FF). 

 Of the seventeen single-zoospore cultures studied by Bishop, there were 

 five of the MM type, seven of the mF type, and five of the mf type. He 

 suggests that further collections may reveal the FF, Mf, and MF types. 



Cytology 



Representatives of all genera of the Leptomitales save Mindeniella 

 have been studied cytologically and their nuclear behavior, consequently, 

 is well known. 



In the types examined (Leptomitus lacteus, Apodachlya brachynema, 

 Sapromyces elongatus, Araiospora pulchra, and Rhipidium interruption) 

 the thallus is multinucleate, with the nuclei scattered throughout a 

 peripheral layer of cytoplasm lining a central vacuole. Nuclei are espe- 

 cially abundant in the growing apices. Kevorkian (1935) states that the 

 numerous nuclei found in the basal cell of S. elongatus result from the 



