420 AQUATIC PHYCOMYCETES 



undergone by this species and about 4 per cent of the thalli were even 

 polycentric rather than monocentric! 



RECENTLY DESCRIBED TAXON J 



Rhizidium richmondense Willoughby 

 Trans. Brit. Mycol. Soc, 39: 128, figs. 1-3. 1956 



Thallus monocentric, eucarpic, interbiotic, consisting of a globose or 

 subglobose sporangium and branching rhizoids which arise from one 

 point; sporangium 9.5-35 \x in diameter, bearing an obtuse apiculus, 

 discharging upon the rupturing of the sporangium wall near the 

 apiculus; zoospores globose, 3-3.3 jx in diameter, or ovate and 3-3.3 by 

 2.5-3 u., with a large or small oil globule and posterior flagellum, 

 18-23 fj. long; when discharged from the sporangium undergoing a 

 period of collective swarming, possibly within a vesicle; resting spores 

 not observed. 



In onion-bulb epidermis and cellophane bait in a soil culture (Herb. 

 I. M. I. 60445), Great Britain. 



Although the apiculus of the sporangium strongly resembled an 

 operculum it was, rightly, not so regarded by Willoughby. 



IMPERFECTLY KNOWN SPECIES OF RHIZIDIUM 



? Rhizidium lignicola Lindau 

 Verhandl. Bot. Vereins Prov. Brandenburg, 41: xxvii, figs. 1-12. 1900 



Sporangium usually more or less flattened, ellipsoidal, pyriform, or 

 saclike, rarely spherical, sometimes with a narrow stalklike base, 

 rounded at the top, often irregular with hornlike outgrowths, 25-75 u, 

 long by 20-25 \i broad, wall thickened, colorless or somewhat brownish, 

 resting on a vesicular apophysis formed from the body of the encysted 

 zoospore, discharging by the deliquescence of an apical pore after the 

 expulsion of a plug (operculum?); zoospores spherical, 2-3 \x (up to 8 

 jjl in culture) in diameter, with a posterior flagellum 40-50 \i long and 

 an oil drop, discharge not observed. 



Saprophytic on twigs of horse chestnut, Germany. 



From the description given by Lindau, the fungus appears to have 



1 Not included in the key. 



