54 PHYCOMYCETEAB 



or three sporangia, is external to the host cell instead of internal as in 

 Micromyces. He points out that though in general the cell walls of the 

 Synchytriaceae do not show a cellulose reaction, yet the wall of the 

 sporangial sorus and of the tube on which this is borne becomes red-violet 

 in color with iodine in potassium iodide solution, in Micromycopsis cristata 

 Scherffel and also in Synchytrium mercurialis (Lib.) Fuckel. Miss Canter 

 (1949) has described a third genus in this family parasitic in fresh-water 

 algae, the genus Endodesmidium, parasitic in Desmids. Like the two fore- 

 going genera this is endobiotic and holocarpic. The prosorus of the only 

 recognized species is smooth-walled, not spiny as in Micromyces and most 

 species of Micromycopsis. The relatively large sorus grows out of one end 

 of the prosorus within the cavity of the host cell. The contents divide into 

 numerous, movstly spherical sporangia which escape through papillae into 

 the cavity of the host wall or into the surrounding medium if the papilla 

 pierces the cell wall. These sporangia occasionally possess a posterior 

 flagellum which is feebly active. They produce 2 to 5 minute, posteriorly 

 uniflagellate zoospores which swim actively. (Fig. 13.) 



The eucarpic, monocentric Chytrids fall into two families according 

 to Miss Whiffen and three according to Sparrow, who sets the operculate 

 forms apart from the inoperculate as a distinct family. In general the 

 fungus body can be distinguished into a uninucleate enlargement and a 

 non-nucleate haustorial or rhizoidal system attached directly or indirectly 

 to the former. This varies from a short peg to an extensive mass of usually 

 tapering and more or less branched rhizoids. These may be entirely 

 intramatrical or, except for the tips of the branches, may be entirely 

 extramatrical. The body of the encysted zoospore may enlarge and be- 

 come the sporangium or it may become a prosporangium from whose apex 

 the sporangium arises. On the other hand an enlargement of the germ 

 tube may be formed, the contents of which eventually pass into the 

 sporangium which arises by enlargement of the original zoospore cyst. 

 In Miss Whiffen's family Entophlyctaceae the zoospore cyst empties 

 itself completely into the subjacent portion of the germ tube, this enlarge- 

 ment becoming the sporangium or a prosporangium out of which the 

 sporangium buds. The old zoospore cyst falls away or remains only as an 

 empty fragment. 



The eucarpic monocentric families may be distinguished as follows 

 according to Miss Whiffen: 



Rhizidiaceae: zoospore cyst enlarging into a sporangium or prosporangium. 

 Entophlyctaceae: zoospore cyst not further functional; the upper part of the 

 germ tube enlarging into a zoosporangium or prosporangium. 



Both of these families as delimited by Miss Whiffen contain operculate 

 as well as inoperculate genera. Sparrow segregates the operculate forms 

 into the family Chytridiaceae. He divides the inoperculate genera on the 



