CHYTRIDIALES 47 



of the morphology of the zoospore will probably afford one of the 

 more fundamental bases of separation, since this structure is 

 presumably primitive. It is of interest to note in this connec- 

 tion that in the Woroninaceae alone is this cell biciliate as in 

 the higher orders. The Chytridiales are of special interest to 

 that group of students who beheve that the higher fungi arose 

 from the lower (Atkinson 1909 6). By other students they are 

 regarded as degenerate unicellular green algae or degenerate 

 Oomycetes. Although the writer is inclined to the belief that 

 the fungi have arisen from unicellular non-chlorophyll bearing 

 organisms and that the group is phylogenetically a unit, it seems 

 evident that certain lines of development have progressed a 

 relatively short distance. The terminations of several such 

 lines apparently exist today in the Chytridiales, while one or 

 more other lines may be assumed to have produced the higher 

 forms. 



The order Chytridiales embraces approximately two hundred 

 known species. The majority were described first from Central 

 Europe and may not have been encountered elsewhere. The 

 group has been studied relatively httle, and numerous unde- 

 scribed species doubtless await the attention of the investigator' 

 in all parts of the world. Many are probably cosmopohtan. 

 Most of the known species are true parasites in plants or animals. 

 Of those in plants fully half occur in fresh-water algae, almost 

 as many Uve in higher plants, while the remainder occur in marine 

 algae, aquatic fungi, and in pollen grains, rust spores, and other 

 similar bodies which fall into the water. A few species are 

 parasitic in Protozoa, and some are saprophytic in submerged, 

 decaying plant or animal remains. All the species are micro- 

 scopic, though in some cases their presence stimulates the host 

 to form noticeable galls, swellings or discolorations. In the 

 treatment which follows, the effort is made to include all known 

 genera. The miscellaneous character of the literature, has made 

 this difficult, however, and it is to be expected that some forms 

 have been overlooked. 



Key to Families of Chytridiales 



I. Mycelium wholly lacking; thallus always intramatrical. 



A. Thallus existing, through early stages at least, as a naked, more or 

 less amoeboid protoplast, often somewhat obscured by the 

 protoplasm of the host cell, finally (in most cases) fragmenting 



