SAPROLEGNIALES 825 



with thick walls which spread apart the valves of the host; resting spores 

 (oospores?) thick-walled, with eccentric globules and peripheral refrac- 

 tive spots, without periplasm, one or several formed, apparently asex- 

 ually, in an expanded part of the thallus, germination not observed. 



In fresh-water diatoms and desmids. 



Tokunaga (1934a: 232) proposed the transference of the genus to the 

 Lagenidiaceae on the following grounds: ". . .(1) absence of a typically 

 [well-?] developed mycelium. (2) Thallus completely transformed into 

 the reproductive organs at maturity." While it is unquestionably true 

 that the thallus of Aphanomycopsis is of limited extent and that all of 

 it is transformed into a reproductive structure, the method of zoospore 

 formation is markedly different from that found in the Lagenidiaceae, 

 with one exception (noted by Scherffel, 1925a: 112). Further, the cyto- 

 plasm is typically saprolegniaceous, rather than lagenidiaceous. Then, 

 too, the form studied by Tokunaga is quite different from Scherffel's in 

 that the thallus is septate (see discussion under Aphanomycopsis bacil- 

 lahacearum). Hence, Karling's (1942e) expansion of the genus to include 

 Tokunaga's fungus is not followed here. 



KEY TO THE SPECIES OF APHANOMYCOPSIS 



Parasitic in diatoms; thick-walled forcing apparatus at base of dis- 

 charge tube usually present A. bacillariacearum, p. 825 



Parasitic in desmids; forcing apparatus absent A. desmidiella, p. 827 



Aphanomycopsis bacillariacearum Scherffel 



Arch. Protistenk., 52: 14, pi. 1, figs. 31-35, pi. 2, figs. 36-48. 1925 



(Fig. 64, p. 826) 

 Sporangium 6-10 \x in diameter, unbranched or, more frequently, 

 richly branched, the branches of variable length, discharge tubes one or 

 several, slightly tapering, occasionally branched, up to 240 \x long; cysts 

 of the primary zoospores variable in number, 8-10 jjl in diameter, 

 secondary zoospores grape-seed-like in shape, 10-12 u, long by 7-8 \i 

 broad, anterior flagellum short and active, posterior one long and pas- 

 sive, movement even, in a zigzag line; oospores one or several, lying 

 loosely in an expanded part of the thallus, spherical (20 u. in diameter) 

 or broadly ovoid (24 by 20 \x), colorless, wall thick, smooth, germination 

 not observed. 



