294 AQUATIC PHYCOMYCETES 



to the female by a narrow cylindrical conjugation tube 2 y. diameter 

 and up to 38 u. long" (Canter, loc. cit.). 



Parasitic on Spirotaenia condensata, Great Britain. 



Canter noted that the fungus seemed specific to Spirotaenia since 

 other associated members of the Conjugatae were not attacked. Her 

 observations on sexuality in this species give further support to the 

 idea, first proposed by her in the case of Zygorhizidium, that the 

 nature of the thallus produced by the zoospores (whether asexual or 

 sexual) is determined by the environmental conditions and not by any 

 inherent difference in the swarmers that develop upon germination of 

 the resting spores. 



Rhizophydium ephippium Canter 



Ann. Bot. London (N.S.), 14: 273, figs. 5-6. 1950 



(Fig. 10 B, p. 108) 



"Thallus eucarpic, epibiotic, sporangium saddle shaped, 8 u. broad 

 by 4 \x high to 15 [jl broad by 5 [x high, containing 8 to 30 zoospores. Zoo- 

 spores spherical, 2u. in diameter, uniguttulate, posteriorly uniflagellate, 

 emerging singly after dissolution of two oppositely directed lateral pa- 

 pillae. Intramatrical rhizoidal system composed of one or a few short 

 threads. Resting spores oval to subspherical, 5 \x broad by 3.7 \i high to 

 7 [j. broad by 5 u. high, arising from fusion of the content of a small male 

 with a larger female thallus, the former remaining as an appendage 

 to the mature resting spore. Wall smooth, colourless, beset with a 

 narrow central projecting band of wall material, content consisting 

 of two large refractive globules, germination unknown" (Canter, loc. 

 cit.). 



Parasitic on Stylosphaeridium stipitatum, Great Britain. 



While the sporangial stage undoubtedly resembles that of Rhizo- 

 phydium transversum, this species differs in having the resting spore 

 sexually formed. 



The saddle-shaped sporangium perched on the apex of the host cell 

 is a striking object. 



