CHYTRIDIALES 483 



bearing turbinate cells and numerous thick-walled resting spores which 

 germinate by zoospores to form the thin-walled epibiotic sporangia. 



Obligate parasites, primarily of angiospermous marsh and aquatic 

 plants. 



The genus Physoderma as presently understood is coextensive with 

 the family. Because certain members are parasitic on submerged aquatic 

 flowering plants and many others (the majority, in fact) on marsh plants, 

 mention here of the family and genus is logical. 



Any classification of this group of fungi now attempted would, of 

 necessity, be both makeshift and temporary. No arrangement based on 

 host relationships alone (lacking knowledge of life cycles and proven 

 host ranges) could be truly authoritative. The genus is being currently 

 investigated and it is hoped that a sound taxonomic scheme will 

 eventually result. Meanwhile, descriptions of the family and genus are 

 given in this treatise. Concerning the species, interested students are 

 referred to Karling's (1950) account of the genus, but references to a few 

 aquatic forms described since his paper are included. 



PHYSODERMA Wallroth 



Flora Crypto. Germ., 2: 192. 1833 



(?) Urophlyctis Schroeter, in Cohn, Kryptogamen-Fl. Schlesien, 3 (1): 196. 

 1885 (1889). 



Monocentric thallus consisting of an epibiotic part, derived from the 

 expanded body of the zoospore and an endobiotic part of bushy, stubby, 

 or more or less prolonged rhizoids of limited extent, usually confined 

 to one host cell, which either arise directly from the tip of the germ 

 tube or from a small apophysis, epibiotic part becoming converted into 

 a sporangium with a discharge papilla which after deliquescence 

 liberates small zoospores; sporangia internally proliferous; polycentric 

 thallus entirely endobiotic, exceedingly extensive, ramifying through 

 many host cells, consisting of delicate freely branching rhizoids which 

 bear intercalary, usually once- or twice-septate, turbinate cells; resting 

 spores numerous, disproportionately large, thick-walled, dark-colored, 

 somewhat spherical or ellipsoidal, or assuming the shape of the host 

 cell, often flattened on one surface, formed either from one of the 



