CHYTRIDIALES 449 



SUBFAM. POLYPHAGOIDEAE 



Reproductive rudiment formed as an outgrowth from the body of 

 the encysted zoospore; resting spore sexually produced by conjugation 

 of directly adnate thalli or thalli joined by a conjugation tube; parasitic 

 on fresh-water algae. 



POLYPHAGUS Nowakowski 



Cohn, Beitr. Biol. Pflanzen, 2: 203. 1876 



(Figs. 4 Z-Z', p. 72; 5, p. 80; 29 F-J, p. 450) 



Thallus generally lying free in the medium, monocentric, eucarpic, 

 consisting of an expanded central part, the rudiment of the pro- 

 sporangium, from which arise from two to three or more rhizoidal axes, 

 the rhizoids profusely developed, much branched, strongly polyphagous, 

 only the tips endobiotic; sporangium inoperculate, formed as an out- 

 growth from the prosporangium, from which it is cut off at maturity 

 by a cross wall; zoospores posteriorly uniflagellate, with a single 

 globule, completely formed in the sporangium, liberated through a 

 pore produced in the wall of the sporangium; resting spore thick- 

 walled, with a large globule, produced by the fusion of two anisogamous 

 aplanogametes in the distal part of a conjugation tube formed generally 

 by the smaller of two thallus-like gametangia, upon germination 

 functioning as a prosporangium. 



The species have thus far been found as parasites of Euglena, Chlamy- 

 domonas, Tribonema, and Sphaerocystis. 



Through the early researches of Nowakowski (1876b; 1878), supple- 

 mented by later accounts of the morphology and cytology by Dangeard 

 (1886a; 1900-1901c), Wager (1899a; 1913), Scherffel (1925b), and 

 Bartsch (1945), Polyphagia has become one of the best known of the 

 chytrids. The strongly polyphagous thallus of P. euglenae is ordinarily 

 profusely developed, and both nonsexual and sexual reproductive 

 organs are readily formed. Since the resting spore germinates after a 

 relatively brief period of quiescence the whole life cycle can be easily 

 followed in a short time, a situation of uncommon occurrence among 

 the chytrids. 



The most ubiquitous species of the genus is Polyphagus euglenae. 



