CHYTRIDIALES 



77 



two genera are evidently very closely related and should perhaps 

 be merged. The first species enumerated below (Fig. 12) is the 

 type of the genus. In it the resting spore is smooth- walled. 

 The other species possess spiny-walled resting spores and have 

 not been studied sufficiently to warrant their certain inclusion 

 here. All of the species occur in green algae. 



F. schenkiana (Zopf) v. Mindcn— in the filaments and zygospores of 

 Spirogyra, Mougentia, and Me.socarpus. Anotlicr form, 1\ parasitica (Fisch) 

 V. Minden, said to differ in having several companion cells on the resting 

 spore is perhaps the same. 



P. zopfii (De Wild.) v. Minden and P. fibrillosa (De Wild.) v. Minden 

 occur in Spirogyra and differ chiefly in the character and arrangement of the 

 spines which ornament the resting spore. 



P. appendicvlata (De Wild.) v. Minden and P. ellipticd (Schroter) v. 

 Minden occur in Mesocarpus. The companion cell of the first is vermiform, 

 that of the latter globose. 



v/- 



S^^miim^^j//i9M«mie^^M 



Fig. 1.3.^ — Ectrogella haciUariacearum Zopf in the diatom Pinnularia. (a) 

 Young ellipsoidal thallus. (6) Germinating swarmsporangium provided with 

 four exit tubes. (.After Zopf 1884.) 



In this genus, as in Olpidiopsis and other genera of the Chytri- 

 diales in which sexuality occurs, the resting spore has received 

 various names (e.g., resting sporangium, oospore, oosporangium), 

 but it should be noted that the wall of the mature spore is merely 

 the thickened or modified membrane of the female gametangium. 

 An oospore lying free in the oogonium, as in the Ancyhstalcs 

 and Oomycetes, is never formed. 



5. Ectrogella Zopf (1884: 175). 



Erected on E. haciUariacearum Zopf, parasitic in diatoms and 

 first observed by Zopf near Berlin. It also occurs in America 



