CHYTRIDIALES 549 



from the center of which one or two tenuous generally feebly developed 

 branched rhizoids emerge; zoospores from four to forty in a sporangium, 

 asymmetrically ovoid, sharply acuminate posteriorly, with a single 

 anterior colorless refractive globule and a long fiagellum, emerging 

 after the dehiscence of the strongly convex operculum, movement 

 hopping; "male" thallus (dwarf sporangia?) pyriform, 4-5.4 \x in diam- 

 eter, the expanded endobiotic part with or without rhizoids, copulation 

 tube basal or lateral, usually one (rarely two), up to 45 \x long by 1-2 \x 

 in diameter, refractive, with a narrow lumen, making contact with the 

 lower half of the receptive thallus, if not conjugating functioning as a 

 sporangium; receptive thallus large, spherical or subspherical, the knob- 

 like endobiotic part with or without rhizoids, after conjugation forming 

 a subspherical resting spore 8-11 \l in diameter by 7-10 \x high, with a 

 thick smooth colorless or brownish wall, contents with numerous large 

 refractive often centrally disposed globules, germination not observed. 



On Cylindroeystis brebissonii, possibly only saprophytic, Lowenthal 

 {he. cit.), Norway; Mougeotia parvula, Mougeotia sp., Scherffel {he. 

 cit.), Spirogyra longata, Mougeotia sp., Zygnema sp., Domjan ( 1 936 : 5 1 , 

 pi. 1, figs. 128-129, 138), Hungary; Mougeotia sp., Canter (1947c: 128, 

 fig. 2, pi. 11, figs. 1-2), Great Britain; Zygnema sp., Sparrow and 

 Barr (1955: 554), United States. 



The nonsexual thalli observed by Scherffel on Mougeotia differed from 

 those on Cylindroeystis in that they lacked an endobiotic knob and 

 formed instead a group of very short rodlike rhizoids. They also differed 

 in that they caused a marked bending of the long host cell and stimulated 

 it to form a protective plug of wall material. It is possible that this 

 reaction of the host may account for the absence of the characteristic 

 knob. 



Scherffel's contention that the fungus called Rhizophydium sphaero- 

 carpum Zopf by Atkinson (1909a) was Zygorhizidium willei is open to 

 question (see Sparrow, 1943: 365). 



Zygorhizidium willei was investigated cytologically by Lowenthal. 

 He found the young thallus to be uninucleate at first and the cytoplasm 

 strongly alveolate. As the plant increases in size the plasma becomes 

 denser and the spherical (0.5-0.1 \i in diameter) generally homogeneous 

 nuclei are more numerous as well as smaller and less distinct. Mitotic 



