298 AQUATIC PHYCOMYCETES 



Rhizophydium fusus (Zopf) Fischer 



Rabenhorst. Kryptogamen-Fl., 1 (4): 99. 1892 



(Fig. 17 X, p. 228) 



Rhizidium fusus Zopf, Nova Acta Acad. Leop. -Carol., 47: 199, pi. 18, 

 figs. 9-12. 1884. 



Sporangium sessile or borne on a short stalk, narrowly to broadly 

 fusiform, usually slightly tilted, 10.4-20 u. high by 3-8 u, in diameter 

 in mid-region, wall thin, smooth, colorless; rhizoids extensive, much 

 branched, monophagous or polyphagous, arising from a relatively 

 stout central axis; zoospores spherical, 2-2.5 u, in diameter with a 

 colorless globule and a flagellum, emerging through a small apical 

 often slightly protruding pore; resting spore not observed. 



Parasitic on Synedra sp., Zopf (loc. cit.), Germany; various diatoms, 

 de Wildeman (1890: 12), Belgium; Melosira, de Wildeman (1894: 

 156), France; Cymbella, Gomphonema cons trie turn, Scherffel (1902a: 

 [106]), Hungary; Melosira various, Sparrow (1932b: 276, fig. 2a-b; 

 1933c: 519), United States; Surirella sp., Pinnularia sp., Tokunaga 

 (1934b: 389, pi. 11, fig. 4), Japan; Melosira various, Sparrow (as 

 Rhizophydium lagemda, 1936a: 439, fig. 4 k-m), Great Britain; 

 Synedra sp., coll. P. W. Richards, Sparrow (1938a: 148, fig. 2d), 

 Sarawak; Melosira ambigua, Rohde and Skuja (in Skuja, 1948: 381, 

 pi. 39, figs. 22-25), Sweden; Melosira sp., Litvinow (1953: 81), Latvia. 

 Doubt exists as to whether or not Zopf's species is identical with 

 Braun's Chytridium lagenula on Melosira (Braun, 1856a: 31, pi. 2, 

 figs. 2-3). Scherffel (1926a, see C. lagemda, p. 504) believes that two 

 distinct fungi were grouped under this name by Braun, one occurring 

 on Melosira and the other on Tribonema. Since the rhizoids were not 

 observed by Braun in either form, it is difficult to attempt an analysis 

 of his species. Zopf's specific name is preferred for the parasite of dia- 

 toms, because it applies to a more completely known organism. 



Rhizophydium fusus is parasitic and, as Zopf noted, consumes the 

 nucleus and plasma of the host cells, leaving only an olive-green or 

 brownish residue of chloroplast material. On Melosira the rhizoids 

 may ramify through several (five to six) cells of the host. The sporangia 

 described by Rohde and Skuja are the largest yet reported for the 

 species; they are 15-25 [x long by 5-9 \x broad. 



