1052 AQUATIC PHYCOMYCETES 



Mycelium much branched, the branching frequently monopodial and 

 at nearly right angles, often constricted at the base, sometimes bearing 

 spherical or ellipsoidal or irregular swellings, groups of irregular bud- 

 like outgrowths, or involved torulose complexes, becoming septate with 

 age, when parasitic, intra-and intercellular and often bearing haustoria, 

 protoplasm refractive, pallid, sometimes bearing occasional conspic- 

 uous granules, walls giving a modified cellulose reaction, occasionally 

 forming terminal or intercalary, spherical, ellipsoidal, or irregular chlam- 

 ydospores; zoosporangia borne on more or less well-defined spo- 

 rangiophores which are sometimes slightly swollen near point of origin 

 on hypha, usually ovoid or limoniform, pyriform or bluntly ellipsoidal, 

 occasionally slender, with either a prominent, broad hyaline apical 

 papilla or a blunt nonpapillate apex, persistent on the sporangiophore 

 or abscissing sometimes with an attached, usually short hyphal pedicel, 

 capable of renewed growth by internal proliferation of secondary spo- 

 rangia which may be sessile and "nested" within the primary or borne 

 on a sporangiophore which extends through the discharge orifice, or by 

 the production of compound sympodial sporangiophores, germinating 

 indirectly by zoospores or directly by germ tubes; zoospores completely 

 formed within the sporangium, emerging individually or in a quickly 

 dissociating mass either upon the dissolution of the sessile or slightly 

 elevated apical papilla or by the papilla forming a very quickly evanescent 

 vesicle around the emerging spores, encysting and germinating after 

 a period of swarming or capable of repeated emergences before 

 germinating; plants usually monoecious, antheridia usually amphigy- 

 nous, sometimes paragynous or both; oogonium usually terminal, 

 somewhat spherical, forming a single egg; oospore single, aplerotic or 

 sometimes plerotic, wall 1 -3 \x thick, usually with a large reserve globule, 

 germinating by one or more hyphae or by zoospores. 



Parasitic on flowering plants and saprophytic on debris in water. 



Blackwell, Waterhouse, and Thompson (1941) confirmed Buisman's 

 (1927) contention that species of Pythiomorpha are in reality members 

 o\' Phytophthora and established that Phytopltflwra megasperma and P. 

 cryptogea occur in nature living as water molds. The success of Hickman 

 (1940) in growing the strawberry parasite, P.Jragariae, on hempseed in 

 liquid medium and the ease in general practice of obtaining Phytoph- 



