158 AQUA TIC PH YCOM YCETES 



zoospores multiplying in host hyphae and carried by plasma currents 

 of host to the distal parts of hyphae. Sporangia formed in cylindrical 

 compartments, the latter resembling in shape, size, and position the 

 sporangia of the host. Compartments separated from healthy host 

 hypha by cross wall. Each sporangium in a sorus developing from a 

 separate thailus and forming an emergence papilla upon maturity. 

 Sporangia spherical to oval or polygonal from pressure, 16-21 [x thick, 

 with a cellulose membrane. Zoospores very minute, 1.8-3 x 3 \x, 

 spherical or slightly elongated, with one minute glistening globule, 

 and a single posterior flagellum, moving directly away after a brief 

 pause at the sporangial mouth. Resting bodies (zygotes) formed only 

 where two sexually opposite or sexually compatible strains are brought 

 together, spherical, 15-17 [x thick, golden brown with an eccentric 

 globule and a minutely rough or reticulate membrane, formed within 

 a larger cell which is polygonal from pressure. Containing cell 25-30 u, 

 thick; sometimes larger and containing as many as six zygotes. Ger- 

 minating by uniflagellate zoospores after six weeks' rest" (Couch, 

 he. cit.). 



Parasitic in Achlya dioica, Pringsheim (1860: 21 1, pi. 23, figs. 1-5), 

 Germany; Achlya sp., A. ftagellata, coll. J. N. and A. B. Couch, 

 Ward, Shanor, United States. 



The species is dioecious, resting spores being formed only in cultures 

 containing compatible or sexually opposite strains. 



PLEOTRACHELUS Zopf 

 Nova Acta Acad. Leop.-Caro)., 47: 173. 1884 

 (Fig. 12 E, p. 124) 

 Thailus endobiotic, holocarpic, without a specialized vegetative 

 system, unwalled at first, with pseudopodia, forming the rudiment 

 of the zoosporangium at maturity, causing hypertrophy of the host; 

 zoosporangium inoperculate. lying free in the host cell, with many 

 (rarely from one to two) discharge tubes; zoospores posteriorly uni- 

 flagellate, formed in the sporangium; resting spore not (?) observed. 

 In Phycomycetes. algae, and rhizoids of mosses. 

 Petersen (1905) included in this genus a number of Pleotrachelus- 



