342 AQUATIC PHYCOMYCETES 



arising from the base or the sides of a spherical (about 7 \i in diam- 

 eter), broadly ellipsoidal, or somewhat irregularly saclike subsporan- 

 gial apophysis, sometimes apparently absent; zoospores spherical or 

 somewhat ovoid, 3-4 \x in diameter, with a conspicuous eccentric 

 colorless globule and a long flagellum, emerging in a compact mass, 

 probably surrounded by the inner layer of sporangium wall, through 

 an apical pore, movement hopping; resting spore not observed. 



On Zygnema cruciatum, Z. stellinum, Rosen {Joe. cit.), France 

 (Strasbourg); Minden (1915:343), Germany; Zygnema sp., Berczi 

 (1940: 84), Hungary; zygospores of Spirogyra sp., Sparrow (1952a: 

 36), Cuba. 



The sporangium in this species tends to be more spherical and the 

 teeth are more shallowly cleft than in Phlyctochytrium quadricome 

 or P. dentation. 



Rosen's rather complete investigation of his species established the 

 fact that the apophysis is a secondarily formed structure which appears 

 on the endobiotic system after the establishment of the rhizoids. 

 Remarkable variations in the character and the position of the apoph- 

 ysis and rhizoids were also noted. Abnormal forms with more than 

 one apophysis, others with the apophysis outside the substratum rather 

 than inside it, and so on, were described and figured. Smaller "Frost- 

 sporangien" frozen in the ice but still viable were found. Rosen's 

 fungus only attacked filaments of Zygnema which were in a moribund 

 or enfeebled condition, and it could not be transferred to other, as- 

 sociated, algae. 



Phlyctochytrium magnum Under 



Nat. Museum Canada, Bull. No. 97, Biol. Ser. No. 26, p. 243, pi. 12, fig. H 



1947 



"Sporangia extramatrical, obovoid [basally expanded], 23.8 X 18.5 

 \i, ornamented below the apex by four pairs of short, relatively stout, 

 bluntly pointed, divergent spines, which are up to 4 jx long, and which 

 are joined at the base; within the host is formed an irregular, broadly 

 pyriform vesicle that measures up to 12.5 u. in diameter" (Linder, 

 loc. cit.). 



Parasitic on Zygnema sp. (F. slide No. 2718, Type), Canadian 

 Eastern Arctic. 



Known only from preserved material. 



