G4 



PHYCOMYCETEAE 



Fig. 18. Chytridiales, Family Cladochytriaceae. Catenomyces persicinus Hanson. 

 Portion of plant showing coarse rhizomycelium and zoosporangia with endo-operculate 

 exit tubes. (Courtesy, Hanson: A7n. J. Botany, 32(7):431-438.) 



large sporangium from whose sides arise many moderately stout rhizoidal 

 tubes with occasional constrictions and septa, and fusiform swellings, 

 some of which may become large or small zoosporangia or resting spores. 

 The latter act as prosporangia when they germinate. In S. variabile 

 Berdan, Miss Berdan (1939) demonstrated that the sporangial walls and 

 intercalary swellings give a pronounced violet color on treatment with 

 chloriodide of zinc, indicating the presence of cellulose. This reaction is 

 absent in most of the members of the family. M egachytrium differs from 

 the two foregoing genera in the possession of a very coarse, tubular, 

 branched rhizomycelium instead of fine tapering threads. The swellings 

 of this rhizomycelium become operculate sporangia or resting spores. The 

 latter act as prosporangia when they germinate. The genus Catenomyces 

 (Hanson, 1945) is quite similar to the three foregoing genera but has an 

 endo-operculum deep down in the exit tube, not at its apex. Resting 

 spores have been doubtfully observed. The zoosporangia may be terminal 

 or intercalary, with one to several exit tubes. The rhizomycelium is stout 

 but tapers to slender rhizoid-like tufts. (Fig. 17D-F, Fig. 18.) 



The inoperculate genus Catenaria, assigned by Sparrow (1943) to the 

 subfamily Catenarioideae, has been shown by Couch (1945) to be proba- 

 bly more closely related to Order Blastocladiales and will accordingly be 

 discussed in the next chapter. 



Family Physodermataceae. Two genera, Physoderma and Uro- 

 phlyctis are usually included in this family, but since the only constant 

 difference is the effect upon the host the validity of this distinction is 

 doubtful. Both are parasitic on and in higher plants. Physoderma may 

 discolor and eventually kill the infected tissues without causing marked 

 hypertrophy, while Urophlyctis induces strong gall formation. Tentatively 



