HYPHOCHYTRIALES 751 



Parasitic in Stigeoclonium subuligerum, Stigeoclonium sp., and Drap- 

 arnaldia plumosa Canter (he. cit.), Great Britain; Stigeoclonium sp., 

 Karling (1941c: 357), Stigeoclonium sp. (Michigan), United States. 



As indicated by Canter, the zoospores take a relatively long time to 

 become delimited and to mature (up to 30 minutes). Even longer times 

 have been noted in the Michigan material. 



RHIZIDIOMYCETACEAE 



Thallus eucarpic, monocentric, composed of an extramatrical fertile 

 part and an intramatrical apophysate or nonapophysate part bearing 

 a branched rhizoidal system, walls containing both cellulose and chitin ; 

 zoospores anteriorly uniflagellate, usually with one or more small 

 refractive globules or granules formed within the sporangium, or dis- 

 charged in a more or less amorphous mass and completing maturation, 

 sometimes in a vesicle, at the orifice of the discharge tube; resting spore, 

 where known, thick-walled, like the sporangium in position and rhizoid- 

 al system, germination not observed. 



Parasitic on oogonia and eggs of Phycomycetes, on algae, and sap- 

 rophytic in soil. 



Separation at the family level of the fungi with endogenously formed 

 zoospores from those in which they are developed at the orifice of the 

 discharge tube may in the future prove feasible. 



RHIZ1DIOMYCES Zopf 



Nova Acta Acad. Leop. -Carol., 47: 188. 1884 

 (Fig. 55 E-G, p. 752) 



Thallus monocentric, eucarpic, composed of an extramatrical part, 

 converted at maturity into an apophysate or nonapophysate sporangium, 

 and an intramatrical branched rhizoidal system; sporangium sessile, 

 inoperculate, with a pronounced discharge tube; zoospores possibly 

 delimited in part within the sporangium, discharged as an amorphous 

 mass and undergoing maturation at the orifice of the discharge tube 

 where they may be surrounded by a vesicle, somewhat ovoid or spher- 

 ical, often bearing a refractive globule, anteriorly uniflagellate; resting 

 spore not observed. 



