64 THE PHYCOMYCETES 



tion within sporangia of anteriorly uniflagellate zoospores. Un- 

 fortunately this feature is not easy to determine. 



Sparrow (1943) divides the chytrids into two groups, Inoper- 

 culatae and Operculatae. The sporangia of the Operculatae 

 open by means of a lid or operculum, while those of the Ino- 

 perculatae lack this device to free the uniflagellate zoospores. 

 The Inoperculatae include the Olpidiaceae, Achlvogetonaceae, 

 Svnchvtriaceae, Phlyctidiaceae, Rhizidiaceae, Cladochvtriaceae, 

 and Physodermataceae; the Operculatae include the Chytri- 

 diaceae and Megachytriaceae. 



The thallus either (1) is naked at first (plasmodial), later be- 

 coming walled, and is entirely transformed into a sporangium or 

 a cluster (sorus) of sporangia, or else (2) is walled from the 

 first and differentiated into a vegetative and a fertile portion. 

 The vegetative portion is a delicate, branched structure of 

 rhizoidal appearance and has been appropriately designated a 

 rhizomycelium. Among older systems of chytrid classification 

 and on the basis of these two types of thaUi the Chytridiales are 

 divided into the suborders Myxochytridiales and Mycochytri- 

 diales. In the Myxochytridiales are the Olpidiaceae, Synchytria- 

 ceae, and (doubtfully) Woroninaceae; in the Alycochytridiales, 

 the Rhizidiaceae, Cladochytriaceae, and Hyphochytriaceae. 



Amoncr the older taxonomic treatises are those of Schroeter 

 (1892) and von Minden (1911). Although these r^vo works are 

 basic, numerous species have been described subsequently, and 

 these publications, especially the ones by Scherffel (1925) and 

 Sparrow (1935, 1943), and the numerous reports by Couch, 

 should be consulted in connection with the taxonomy of chy- 

 trids. 



Occurrence and cultivation. A large proportion of the re- 

 ports on chytrids have been concerned with the description of 

 new species. Although many occur on algae, flowering plants, 

 and other fungi, some are free-living in the soil. Recent evidence 

 [Whiff en (1941)] from growth in culture on cellulose indicates 

 that they may function in cellulose decomposition in the soil. 

 Inability to isolate chytrids in pure culture has been a material 

 obstacle in the acquisition of knowledge of their activities. For 

 a time Sparrow (1931) cultivated Cladochytrhnn noivako^Li'skiu 

 mixed with bacteria, on bacto-corn-meal agar. Butler and 

 Humphries (1932) grew Catenaria migidlhdae, parasitic on the 



