490 AQUATIC PHYCOMYCETES 



KEY TO THE SPECIES OF CHYTRIDIUM l , 2 



Occurring in fresh-water or inland salt pools 



Rhizoids arising directly from the tip of the penetration tube, 

 branched or unbranched 

 Rhizoids branched or, if unbranched, tapering and delicate 

 Sporangium ovoid or urceolate at maturity 



Sporangium ovoid or narrowly urceolate, with a rounded 

 base; operculum usually umbonate; on green algae 

 Sporangium 1 1.9-100 \± high by 10.6-55 \j. in diameter; um- 

 bo, when present, not prolonged C. olla, p. 493 



Sporangium smaller, about 16 y. in diameter; umbo dis- 

 tinct and prolonged C. acuminatum, p. 495 



Sporangium broadly urceolate with a concave base; oper- 

 culum smoothly convex, 20 y. in diameter; on cysts of 



Vampyrella C. lateoperculatum, p. 495 



Sporangium distinctly pyriform, citriform, obpyriform, pestle- 

 shaped, or cylindrical 

 Sporangium pyriform or citriform 



Sporangium distinctly pyriform; rhizoidal axis elongate 

 Sporangium predominantly narrowly pyriform, asym- 

 metrical (tilted); operculum inconspicuous; rhizoids 



tenuous; on green algae C, sphaerocarpum, p. 497 



Sporangium broadly and symmetrically pyriform; oper- 

 culum conspicuous, solid; rhizoids stout; on dia- 

 toms C. perniciosum, p. 498 



Sporangium pyriform to citriform; rhizoidal axis short or 

 wanting 

 Rhizoidal axis short ; on Stigeoclonium . . C. papillatum, p. 499 

 Rhizoidal axis lacking, rhizoids arising from one or 

 several places on the base of the sporangium; on 



sheath of Microcystis C. microcystidis, p. 500 



Sporangium elongate-citriform to obpyriform, pestle-shaped, 

 or cylindrical 

 Sporangium elongate-citriform to obpyriform; rhizoid 

 needle-like or finely branched; on sporangia of Rhi- 



zophydium C. rhizophydii, p. 500 



Sporangia obpyriform; not on chytrids 



Sporangium with a knoblike or slightly prolonged base, 

 borne usually on a short extramatrical stalk; on 

 diatoms 



1 See also Fott (1957) for two new species on phytoplankton, C. telmatoskenae 

 and C. mallomonadis and recently described taxa, p. 528. 



2 Note that this key is not strictly dichotomous. 



