LAGENIDIALES 917 



maturation of resting spores without previous conjugation, has led him 

 to conclude that sex, at least in O. achlyae, is phenotypically, not geno- 

 typically, determined. 



Sexual reproduction in the Lagenidiaceae is well known, although 

 cytological details concerning it are for the most part lacking. Zopf 

 (1884) showed that adjacent cells of the linklike thallus of Myzocytium 

 conjugated. One cell, the antheridium, produced a tube which pierced 

 the walls separating it from the oogonium. The contents of the female 

 structure contracted, moved toward the tip of the tube, and exhibited 

 relatively lively amoeboid motion. With the passage of the protoplasm 

 into the oogonium the female gamete became rounded and nearly 

 quiescent. After fusion the zygote was surrounded by a thick double 

 wall, and a large central globule was formed in the contents. In Zopf's 

 material the oospore always remained attached to the fertilization tube. 

 Karling ( 1944g) noted a somewhat similar sexual process in Myzocytium 

 (Lagenidium) microsporum. In this species, however, the male and 

 female gametangia occur in single pairs and only a fertilization pore is 

 formed, not a tube. 



Dangeard (1903b) studied cytologically the sexual stage of Myzocyt- 

 ium vermicola. The gametangia are multinucleate, the somewhat cylin- 

 drical male bearing two nuclei, the more rotund female, about eight. 

 The antheridial cell penetrates the female gametangium by means of a 

 tube and discharges its contents. By this time the protoplasm of the 

 female gametangium has contracted and become vacuolate. One male 

 and one female nucleus persist, but the others degenerate. No coen- 

 ocentrum is visible. After plasmogamy the zygote rounds off in the 

 gametangium, a thin smooth surrounding wall is formed, and the 

 nuclei approach one another. Later, karyogamy occurs and a reticulate 

 exospore is formed. At germination the single large fusion nucleus is 

 replaced by several smaller ones. Meiosis was not observed, although 

 it presumably took place at this time. 



Sexual reproduction in Lagenidium humanum Karling (1947c) is 

 quite like that in Myzocytium microsporum. In no instance was there 

 significant morphological differentiation of the gametangia or a special- 

 ized fertilization tube. In Lagenidium rabenhorstii (Zopf, 1884), the 

 thalli, in contrast to those of Myzocytium, are ordinarily dioecious, the 



