56. Oogonia 32-38/^ in diameter. Oe. laeve 



56. Oogonia smaller ___. 57 



57. Oogonia solitary, 23-29^ in diameter Oe. cryptoporum 



57. Oogonia nearly always in a series up to 5; 



averaging smaller, 18-25/* in diameter Oe. vulgare 



58. Pore supramedian _ 59 



58. Pore superior (species in the following group are separable 



by a combination of characteristics) 61 



59. Oospores 40-48/* in diameter Oe. tyrolicum 



59. Oospores smaller 60 



60. Oospores 31-41/i in diameter; vegetative cells 



31-144/1 long; pore nearly superior Oe. varians 



60. Oospores 34-45/i in diameter; vegetative cells 



24-77/1 long, pore nearly median Oe. plusiosporum 



61. Oospore wall with longitudinal ribs or costae 62 



61. Oospore wall smooth 63 



62. Oogonia 39-48/t in diameter Oe. paludosum 



62. Oogonia 54-63/4 in diameter Oe. carolinianum 



63. Vegetative cells capitellate 64 



63. Vegetative cells not capitellate 65 



64. Vegetative cells 8— 13ai in diameter; oogonia 32— 37m in 



diameter (cells sometimes somewhat capitellate) Oe. Hirnii 



64. Vegetative cells 13-15/i in diameter; oogonia 



38— 40/x in diameter Oe. patulum 



65. Oospores elHpsoid or subellipsoid 66 



65. Oospores globose, subglobose, ovoid, or subovoid 69 



66. Vegetative cells 20-24/* in diameter Oe. Sodiroanum 



66. Vegetative cells smaller 67 



67. Vegetative cells 8-14/i in diameter; 



oogonia 75-105/* long Oe. pseudo-Boscii 



67. Vegetative cells larger 68 



68. Vegetative cells 12-21/* in diameter; oospores 



subellipsoid, 48-74/* long Oe. Richterianum 



68. Vegetative cells 44-52/* in diameter; oospores 



subglobose, 80-93- ( 98 )/* long.... Oe. Kurzii 



69. Vegetative cells spirally punctate Oe. curtum 



69. Vegetative ceUs with smooth walls 70 



70. Filaments (mature) relatively short, not more than 20 cells long; 

 oogonia usually in a series up to 4 Oe. curtum 



70. Filaments longer; oogonia solitary (rarely 2). 71 



71. Oogonia 32-36/t in diameter .'. 72 



71. Oogonia larger 74 



72. Vegetative cells 15—18/* in diameter Oe. intermedium 



72. Vegetative cells narrower 73 



73. Oospores 28-31/i in diameter, 32-39/* long Oe. Hirnii 



73. Oospores 30-37/t in diameter, 32-46/* long Oe. globosum 



74. Oospores globose or subglobose 75 



74. Oospores obovoid or ovoid 76 



75. Vegetative cells 20-30/* in diameter Oe. Vaucherii 



75. Vegetative cells 17-19/i in diameter -...Oe. fennicum 



76. Oogonia oblong or elongate-onovoid; oospores 



42-47/* in diameter _ -Oe. upsaliense 



76. Oogonia obovoid to ovoid — 77 



[160] 



