PERONOSPORA LES \ 035 



13 by 8 y when motile, 8-9 y in diameter when 

 encysted; in water (Fig. 86 H) 



P. dissotocum Drechsler l , p. 28m 

 Oospore wall not appreciably thickened 

 Antheridium monoclinous or diclinous, one to five 

 to an oogonium, terminal on lateral distorted 

 branches, the blunt apex making broad contact 

 with oogonium; zoospores 8.5 by 5 y; oogonia 

 12.6-27.0 y. (av. 19.8 y) in diameter; oospore 

 10.8-25.2 (av. 18 y.) in diameter, wall 1-1.8 u 

 thick; in fresh-water green algae (Figs. 84 C-H; 



86 B ) P. angustatum Sparrow, p. 35m 



Antheridium diclinous, never monoclinous, single; 

 zoospores 8.4 by 4.8 y; oogonia 11-20 y in 

 diameter; oospore 9-17 y in diameter, wall 0.6- 

 0.8 (x in thickness; in fresh-water green algae 



P. apleroticum Tokunaga, p. 36m 

 Oospore wall reticulate, sheathed with a gelatinous mate- 

 rial, golden; antheridium monoclinous and diclinous, 

 one to two to an oogonium, clavate, crooknecked, 

 making narrow contact with oogonium; parasitic in 

 fresh-water green algae P. dictyosporum Raciborski, p. 36m 

 Antheridium not delimited by a septum, one to two to an 

 oogonium, mostly monoclinous, clavate, slightly swollen, 

 terminal; oogonium 7.2-15.6 y (mean 10.3 y) diameter; 

 oospore thin-walled, aplerotic, 6-12 y in diameter; par- 

 asitic in fresh- water green algae (Fig. 86 G) 



P. tenue Gobi, p. 38m 

 Wall of oogonium papillate, oogonia often catenulate, one to 

 five, 16.8-26.4 y in diameter, thin-walled, smooth or with 

 one to two papillae; oospore plerotic except for oogonial 

 neck and papillae, single, occasionally two, moderately thin- 

 walled; antheridia lacking; zoospores 12 by 7.2 y; in soil 



P. papillatum Matthews, p. 39m 

 Sex organs lacking; mycelium of irregular width, forming numer- 

 ous spherical or elliptical swellings 9-27 y in diameter, de- 

 limited by remote septa from the hyphae; zoospores 8-10 y in 

 diameter when encysted ; on fresh-water green algae 



P. afertile Kanouse and Humphrey, p. 39m 

 Sporangium somewhat differentiated from the vegetative hyphae, 

 usually consisting of a more or less complex series of lobulate 

 elements and a discharge tube 



1 Includes P. perigynosum Sparrow (1936a). 



