922 AQUATIC PHYCOMYCETES 



KEY TO THE GENERA OF THE OLPIDIOPSIDACEAE 1 



Parasitic in aquatic Phycomycetes or in fresh-water or marine algae 

 Thallus completely filling the host cell, the sporangia at maturity 



single or in linear series Rozellopsis, p. 922 



Thallus not completely filling the host cell 



Sporangia unlobed, not tubular; with one (rarely more) discharge 

 tube 

 Resting spore sexually formed after conjugation of thalli, or 

 parthenogenetically developed; sporangia predominantly 



spherical or ellipsoidal Olpidiopsis, p. 926 



Resting spore lacking; sporangia as above . . . Pseudolpidium, p. 955 

 Sporangia predominantly irregularly lobed or tubular, with more 



than one discharge tube Petersenia, p. 957 



Parasitic in Euglenophyceae or Cryptophyceae .... Pseudosphaerita, p. 961 



ROZELLOPSIS Karling 



Mycologia, 34:205. 1942 



(Fig. 75 G, I, p. 939) 



"Thallus intramatrical, holocarpic, more or less indistinguishable 

 from but apparently immiscible with the host protoplasm; becoming 

 invested with a wall at maturity and forming one sporangium, or cleaving 

 (?) into several segments which become separated by host walls, mature 

 in basipetal succession, and develop into sporangia or resting spores. 

 Sporangia terminal or intercalary, variable in size and shape, with one 

 to several exit papillae which extend through the host wall; usually 

 filling the host sporangia or the hypertrophied portions of the hyphae 

 completely; sporangium wall tightly pressed against, seemingly fused 

 with, and usually indistinguishable from that of the host. Zoospores 

 slightly variable in size and shape, with one to several minute globules, 

 bifiagellate and heterocont, shorter flagellum usually extending forward 

 and the longer one backward in swimming; zoospores swirling in the 

 sporangium before emerging fully formed and swimming away; con- 

 tents flowing into host cell through an infection tube in germination, 

 leaving the empty zoospore case on the outside. Resting spores unknown 

 in monosporangiate species; solitary in septigenous species, lying free 

 within host cell and separate from host wall, variable in size, brown, 



1 See also recently described taxa, p. 953. 



