1040 AQUATIC PHYCOMYCETES 



ately applied terminally to the oogonium; oogonium 

 spherical, ovoid, or irregular, when unisporous 18.9- 

 39.9 jjl (av. 30.4 y) in diameter, when multisporous 

 26.4-48.4 \x by 39.6-74.8 y.; sporangia spherical, sub- 

 spherical, occasionally ellipsoidal or pyriform, ter- 

 minal on lateral branches, 29.5-55 p. (av. 42.8 y) in 

 diameter, proliferous, secondary sporangia nested 

 within primary; zoospores 8.4-10.5 y by 10.5-16.8 y 



when encysted; in soil P. multisporum Poitras l 



Oospore wall reticulate, oospore aplerotic; oogonium spherical, 

 terminal or intercalary; antheridia diclinous, one to three, 

 borne terminally on branches of varying length; sporangia 

 spherical; zoospores 8-16 y long; parasitic in Lemna spp. 

 and Riccia fluitans 



P. cystosiphon (Roze and Cornu) Lindstedt, p. 106m 2 

 Oogonium wall echinulate 

 Odspore plerotic 



Oogonial protuberances 2.7-6.0 y. (av. 4.4 fx) long, conical, 

 oogonium spherical, typically terminal, 13-19.3 y. (av. 

 16.4 y) in diameter, exclusive of protuberances ; oospore 

 with moderately thick wall; antheridium usually single, 

 monoclinous, arising in close proximity to oogonium, 

 stalk short, cell clavate with apex moderately applied to 

 oogonium; sporangia spherical, 14.3-20.7 y (av. 16.3 y) 

 in diameter, terminal or intercalary; in soil 



P. mammillatum Meurs, p. 109m 

 Oogonial protuberances 5-8 y long, digitate or blunt, conical, 

 odgonia spherical to subspherical when terminal, some- 

 times limoniform when intercalary, 13.2-27.4 y (av. 18.2 

 y) excluding spines; oospore 10.1-25.3 y. (av. 16.7 y.) in 

 diameter, wall moderately thick; antheridia terminal, 

 typically monoclinous, sometimes diclinous, one, rarely 

 two, originating close to oogonium, 12-32 y by 3-5 y; 

 sporangia spherical to subspherical when terminal, spher- 

 ical to spindle-shaped when intercalary, 14-33 y. (av. 

 22.4 y), wall usually smooth, occasionally with digitate or 

 blunt conical spines; zoospores rare, germination usually 



by germ tubes; in soil P. spinosum Sawada, p. 111m 



Oospore aplerotic 



Oospore 14-24 y (av. 20 y) in diameter, one to two in an 

 oogonium; oogonium spherical to cylindrical, terminal 



l Mycologia, 41: 171, figs. 1-17. 1949. 



2 According to Miss Waterhouse (comm.), P. pythioides (Roze and Cornu) 

 Ramsbottom. 



