CHYTR1DIALES 231 



wheat; another, R. fungicola Zimmerman (1902), on the hyphae of 

 Gloeosporium. Mastigochytrium saccardiae Lagerheim (1892), which is 

 parasitic on perithecia of Saccardia durantae, may possibly be refer- 

 able to Rhizophydium. 



It is well realized that the present treatment of this most difficult 

 genus is far from adequate. Characters which appear from the original 

 description of a species to be fixed, well marked, and distinctive are 

 usually found, upon careful investigation of a great many individuals, 

 to be subject to wide variation. Thus, the number of discharge pores, 

 the size and shape of the sporangium, the extent of the rhizoidal system, 

 the nature of the substratum, and so forth, do not always prove con- 

 stant or decisive. Before much reliance can be placed on an analytical 

 key, such as the one immediately following, for the identification of 

 a member of the genus, the whole complex of the "species" should be 

 studied, the original papers consulted, and the figures compared. 



In this treatise those species with a tapering unbranched rhizoid have 

 been placed in Rhizophydium rather than in Phlyctidium, where at first 

 sight they might seem to belong. 



The treatment of such collective species as Rhizophydium globosum, 

 R. sphaerocarpum, and so on, has been a subject for much deliberation. 

 There has been no attempt to solve with finality the many problems 

 associated with them. An effort has been made, however, to adhere 

 to the original conception of these species as much as possible. This 

 has left some well-described forms without names. It is hoped that 

 further study will show either that they are worthy of specific rank 

 or that they should be placed under an already described species. 



KEY TO THE SPECIES OF RHIZOPHYDIUM l 



Sporangium predominantly spherical, subspherical, or ovoid, occa- 

 sionally broadly obpyriform 2 or angular and upright 



Section I 3 , p. 237 



In fresh-water or inland salt pools 

 Sporangium wall smooth 



1 Note that this key is not strictly dichotomous. 



2 That is, having the distal part broadest (reverse of British usage). 



3 See also recently described taxa at end of each section. 



