60 PHYCOMYCETEAE 



some species. In E. vaucheriae (Fisch) Fischer the latter acts as a prospo- 

 rangium, giving rise to a thin-walled spherical sporangium. Sexual repro- 

 duction is not known. In Endochytrium the exit tubes are operculate, 

 otherwise the fungus is like Entophlyctis. In Diplophlydis the germ tube 

 enlarges as in the two foregoing genera but this enlargement is a prospo- 

 rangium from which grows out an external inoperculate sporangium. The 

 resting spores in D. intestina (Schenk) Schroet. are formed, according to 

 Sparrow (1936), by the anastomosis of the rhizoidal systems of two plants, 

 the contents of the smaller passing into the larger which becomes thick- 

 walled and covered externally by minute short sharp spines. They may 

 function directly as zoosporangia or as prosporangia. In Phlyctorhiza 

 (Hanson, 1946) the rhizoids radiate from the germ tube, branching freely 

 and anastomosing to form a reticulum. The proximal portions of these 

 rhizoid branches form, at first, a thin, angular sporangium which even- 

 tually becomes a round, shallow^, somewhat lenticular, thin-walled zoospo- 

 rangium lying underneath the radiating branches. Through a low, 

 inoperculate papilla the zoospores escape into a vesicle where they soon 

 become active and swim away. Thick-walled somewhat tuberculate 

 resting spores may be formed, apparently asexually, in place of the 

 zoosporangia. In germination they act as prosporangia. Rarely some of 

 the rhizoid branches produce secondary zoosporangia so that such indi- 

 viduals are polycentric. The only known species, P. endogena Hanson, 

 grows in the basement membrane of insect integuments. 



Nephrochytrium, saprophytic mostly on algae or grass leaves in water, 

 corresponds to Diplophlydis except that the exit tubes are operculate. 

 Whether its resting spores are produced by a sexual process or not is 

 unknown. 



Macrochytrium may possibly belong in the Entophlyctaceae but needs 

 further study. The zoospore gives rise to a stout germ tube which produces 

 a cluster of coarse rhizoids. Laterally from the germ tube, near its point 

 of origin, arises the subspherical sporangium which may attain a diameter 

 of 0.5 mm. It opens at the apex by a large operculum allowing the escape 

 of up to a thousand zoospores. This has been found in Europe and in the 

 United States, saprophytic on submerged fruits or twigs. Whether this is 

 a typical member of the Chytridiales or not is uncertain. The coarse 

 rhizoidal system suggests the possibility of a coenocytic mycelial structure 

 with many nuclei instead of an enucleate system. 



The polycentric, eucarpic Chytridiales are placed by some students 

 in one, two, or three families. Until their life histories and cytology are 

 known more completely any classification of these genera will have to be 

 tentative. The author recognizes two families as well distinguished, with 

 the probability that more may have to be recognized when the life 

 histories of the members of the group are better known. 



