136. Oogonia 43-60/i in diameter 137 



136. Oogonia smaller 138 



137. Oogonia 52-60^ in diameter ..Oe. iowense 



137. Oogonia 43-50m in diameter Oe. Welwitschii 



138. Oogonia pyriform Qe. Sancti-thomae 



138. Oogonia ellipsoid, globose, ovoid, or oblong _._ _ 139 



139. Oogonia oblong, or oblong-ellipsoid to fusiform 140 



139. Oogonia globose, depressed-globose, or ellipsoid ____ _.141 



140. Oospores ( 17.5)-23-24a by 25-28m Oe. porrectum 



140. Oospores 24-30m by 48-62m Oe. inclusum 



141. Oogonia obovoid-globose, or subovoid to depressed-globose 142 



141. Oogonia ovoid to ellipsoid-ovoid. 144 



142. Opening supramedian Oe. spurium 



142. Opening superior 143 



143. Oogonia 35-43m in diameter, subo void-globose; 



oospore globose _..__ Oe. Pringsheimii 



143. Oogonia 28-37— (40) m in diameter, obovoid to depressed 



globose; oospores similar in shape to the oogonia Oe. abbreviatum 



144. Basal cell elongate ...Oe. pisanum 



144. Basal cell subhemispheric Oe. nanum 



145. Outer wall of oospore with 12-15 longitudinal ribs Oe. spheroideum 



145. Oospore wall smooth 146 



146. Opening median or inframedian 147 



146. Opening supramedian or superior 154 



147. Opening inframedian; wall of oogonium with 



lateral conical projections Oe. Itzigsohnii 



147. Opening median; oogonium wall without lateral projections 148 



148. Oogonia subbiconic-ellipsoid to subbiconic-globose 



( often dioecious ) Oe. pusillum 



148. Oogonia globose, elhpsoid, or pyriform 149 



149. Vegetative cells subhexagonal to subelliptic 



(barrel-shaped) in same filament Oe. Reinschii 



149. Vegetative cells not subhexagonal or barrel-shaped 150 



150. Vegetative cells capitellate 151 



150. Vegetative cells cylindric _ . 152 



151. Oospores globose, 25-S9fi in diameter Oe. minisporum 



151. Oospores depressed-globose, 30-42/x in diameter Oe. minus 



152. Vegetative cells 9-10/^ in diameter; oogonia 



broadly pyriform-globose Oe. psaegmatosporum 



152. Vegetative cells averaging narrower; oogonia ellipsoid, 



globose, or depressed-globose _ 153 



153. Vegetative cells 6-8^ in diameter, 20^7^ long; oospores 



ellipsoid, not quite fiUing oogonia Oe. poecilosporum 



153. Vegetative cells averaging sHghtly wider, 6-9/u in diameter, 30-85ai 



long; oospores subdepressed-globose, filling the oogonia .. .. Oe. Gtinnii 



154. Vegetative cells with 2 undulations or constrictions Oe. nodulosum 



154. Vegetative cells without undulations 155 



155. Oogonia 13-30m in diameter.— 156 



155. Oogonia larger 160 



156. Oospores 13-17/x in diameter Oe. gracilimum 



156. Oospores larger 157 



157. Oogonia subglobose to depressed-globose Oe. spurium 



157. Oogonia ellipsoid or oblong. _ .158 



[164] 



