894 



AQUATIC PHYCOMYCETES 



septate at their point of origin on the edge of the platform, or appear- 

 ing lateral by sympodial branching of the supporting filaments, the 

 whole thallus anchored in the substratum by a branched system of 

 filamentous holdfasts; zoosporangia borne singly or in umbellate clus- 

 ters, with a single discharge papilla; zoospores reniform, laterally 

 biflagellate, contents with numerous coarse refractive granules, formed 

 within the sporangium, emerging in a cylindrical group upon the 



Fig. 71. Rhipidium 



A-C. Rhipidium americanum Thaxter: A, habit of plant with zoosporangia 

 and sex organs; B, discharge of zoospores; vesicle surrounding emerged 

 spores has just split; C, sex organs, showing androgynous antheridium and 

 oospore in surface view. D. Rhipidium thaxteri Minden, habit of sex organs, 

 showing oogonium with apically applied antheridium. E. Rhipidium interrup- 

 tum Cornu, habit of diclinous sex organs. F. Rhipidium sp., zoospore (freehand 

 drawing). 



(A, C, Sparrow, 1932b; B, after Thaxter, 1896b; D-E, after Minden, 1916) 



