230 AQUATIC PHYCOMYCETES 



tractive globule, and one or two oscillating granules in small vacuoles. 

 Resting spore extramatrical, stipitate, with a golden wall, . 746 to 1 \x 

 thick, ornamented with irregular lobes, spherical at maturity, 16.4 

 to 33.6 [x, rarely elliptical, 11.9 x 16.4 to 15.4 x 19.4 \l, containing 

 one very large globule of refringent material 10.4 to 12.6 \i in diameter; 

 formed as a result of lateral fusion of isomorphic motile gametes 

 [gametangia], one of which has previously come to rest and germinated; 

 germination not observed" (Hanson, be. cit.). 



Parasitic on all parts but the purely vegetative cells and thick- 

 walled oospores of Volvox carteri, United States. 



RHIZOPHYDIUM Schenk 1 



Verhandl. Phys.-Med. Gesell. Wurzburg, A.F., 8: 245. 1858 

 (Fig. 17, p. 228; also, Figs. 4 B-O, p. 72: 8 F-H, p. 97; 10 A-L, p. 108; 18 



A-E, F, H-J, p. 286; 20 F, p. 330) 



Chytridium subgen. Sphaerostylidium Braun, Abhandl. Berlin Akad., 1855: 



75. 1856. 

 Rhizophyton Zopf, Nova Acta Acad. Leop.-Carol., 52 (7): 343. 1888. 



Thallus epi- and endobiotic, monocentric, eucarpic, generally monoph- 

 agous; the epibiotic part forming the rudiment of the sporangium 

 or resting spore, the endobiotic, the branched (rarely unbranched) 

 rhizoidal system; sporangium inoperculate, sessile, or rarely on an 

 extramatrical stalk, uni- or multiporous, the wall occasionally deli- 

 quescing wholly or in part; zoospores formed within the sporangium, 

 posteriorly uniflagellate, generally with a single globule; resting spore 

 thick-walled, contents with one or more globules, borne like the spo- 

 rangium, asexually formed or sexually afler receiving the contents of 

 a small adnate contributing thallus which persists as a cyst, upon 

 germination functioning as a sporangium or prosporangium. 



Parasites and saprophytes on a wide variety of plant and animal 

 substrata. 



This is the largest and most complex genus of the chytrids, one in 

 which extensive morphological studies and cross-inoculation work will 

 be necessary before the limits of the species can be established. One, 

 Rhizophydium graminis Ledingham (1936), is parasitic on the roots of 



1 See also Sparrow (1957a) for the new species R. elyensis and R. stipitatum. 



