CHYTRIDIALES 257 



brownish, surrounded by a halo or beset with strands of mucilaginous 

 (?) material; content [with] numerous small globules. Rhizoidal sys- 

 tem as for sporangium; germination unknown" (Canter, loc. cit.). 



Parasitic on the planktonic desmids Staurastrumjaculiferum and Arth- 

 rodesmus sp., Great Britain. 



As in Rhizophydium sphaerocystidis the entire sporangium wall dis- 

 appears. In this species, however, the zoospores are mature when 

 liberated. Although no evidence of the sporangium remains after dis- 

 charge, infected host cells are readily recognized by their reddish 

 content, the remains of the chytrid rhizoidal system, and a slight thicken- 

 ing of the desmid wall at the point of infection. The curious gelatinous 

 halo around the sexually formed resting spore recalls R. coronum 

 Hanson (p. 251). 



Rhizophydium cyclotellae Zopf 

 Abhandl. Naturforsch. Gesell. Halle, 17: 94, pi. 2, figs. 13-22a. 1887 



(Fig. 17 G, p. 228) 



Sporangia sessile, single or in groups, subspherical or broadly ob- 

 pyriform, up to 12 (jl in diameter, with a smooth delicate wall which 

 collapses and disappears after spore discharge; rhizoidal system well 

 developed, extremely delicate, with branches arising from a main axis; 

 zoospores spherical, 1.8-2.5 \l in diameter, with a relatively large ec- 

 centric colorless globule and a delicate flagellum, escaping through 

 from one to three very small sessile pores, capable of amoeboid move- 

 ment; resting spore not observed. 



Parasitic on Cyclotella sp. in culture dishes; not capable of infecting 

 Melosira or naviculoid or synedroid diatoms, pine pollen, or Lyco- 

 podium spores. Zopf {loc. cit.), in a Stinkhaale (= 'sulphurous' or 

 'salt pool'?), Germany; Cyclotella chaetoceras, Domjan (1936: 42, pi. 

 1, fig. 171), Hungary. 



Infection always took place along the silica-free region between the 

 girdle band and valve, obviating the necessity for penetration of the 

 siliceous wall of the diatom. The contents of the latter, with the ex- 

 ception of the brown remains of the chromatophores, were all con- 

 sumed. 



