274 AQUATIC PHYCOMYCETES 



gia which possess a broad discharge papilla have been referred to it. 

 The above diagnosis does not include types with a well-developed 

 much-branched rhizoidal system or those growing on organisms other 

 than algae. These limitations may subsequently be shown to be too 

 restrictive and the extent of rhizoidal development a poor specific 

 character (see, for example, Chytridium lagenaria, p. 522). 

 The following have been excluded : 



1. De Wildeman (1893b: 61, pi. 6, figs. 13-16, pi. 7, fig. 18), on 

 Mougeotia and Spirogyra, Belgium. The sporangia resemble those 

 of the present species, but no rhizoidal system was observed. De 

 Wildeman noted that on Mougeotia the fungus caused marked bending 

 of the host cells. 



2. Raitschenko (1902: 124, figs. 1-8), on the heterocysts of Ana- 

 baena flos-aquae, Russia. The endobiotic part is a stout unbranched 

 peg (see Phlyctidium megastomum, p. 214). 



3. Valkanov (1931a: 362, fig. 1), on Mougeotia sp., Bulgaria. From 

 the figures, the sporangia are nearly or completely spherical and the 

 rhizoids much branched. No discharge of the zoospores was observed. 

 The fungus stimulated the host to form a protective plug of wall 

 material. 



4. Skvortzow (1927:206), on Spirogyra, Manchuria. No mention 

 is made of the character of the rhizoids. 



5. Sparrow (1933c: 519, pi. 49, fig. 1; 1936a: 442, pi. 19, figs. 15-18), 

 on nematodes, United States, Great Britain (see R. vermicola, p. 277) 

 Though resembling Rhizophydium sphaerocarpum in the shape of its 

 sporangium, in its rhizoid, and in the method of spore discharge, 

 Sparrow's fungus differs in several particulars. The zoospores in both 

 the American and the British collections were about 4-5 a in diameter 

 and formed in a thin-walled sporangium, whereas, to judge from 

 Zopf's figures, the sporangium in his species is thick-walled and the 

 zoospores are estimated to be about 2.5 \i in diameter. Another differ- 

 ence is the type of substratum. How far we are justified in supposing 

 that a single species of chytrid is capable of penetrating all types of 

 walls — cellulose, chitinous, or siliceous — cannot at present be said 

 with certainty. R. gibbosum, the peculiar sporangia of which cannot 

 be confused with those of any other species, was observed by Zopf 



