3. Oogonium opening by a pore Sec. 5. p. 195 



3. Oogonium opening by a lid Sec. 8. p. 201 



4. Plants gynandrosporous only .._. 5 



4. Plants both idioandrosporous and gynandrosporous 6 



5. Oogonium opening by a pore Sec. 6. p. 197 



5. Oogonium opening by a lid . Sec. 9. p. 203 



6. Oogonium opening by a pore Sec. 7. p. 199 



6. Oogonium opening by a lid Sec. 10. p. 207 



7. Plants monoecious 8 



7. Plants dioecious 9 



8. Oogonium opening by a pore Sec. 2. p. 176 



8. Oogonium opening by a lid Sec. 4. p. 189 



9. Oogonium opening by a pore Sec. 1. p. 165 



9. Oogonium opening by a lid- Sec. 3. p. 182 



Key to the Species 



1. Dwarf male plants present (nannandrous species), attached 



on or near oogonia (rarely scattered )._ - 2 



1. Dwarf male plants absent, antheridia in filaments approximately 



the same size as those bearing oogonia (macrandrous species) 50 



2. Oogonia opening by a pore (poriferous) 3 



2. Oogonia opening by a lid (operculate) — 28 



3. Pore superior or supramedian 4 



3. Pore median or inferior .__ 19 



4. Oospore wall layers smooth - 5 



4. Oospore wall layers decorated ( ribs, spines, scrobiculations, etc. ) 13 



5. Oogonia globose or subglobose 6 



5. Oogonia obovoid, quadrangular- or sexangular-ovoid, or ellipsoid 10 



6. Vegetative cells 10-20/a in diameter 8 



6. Vegetative cells more than 20,11 in diameter 7 



7. Idioandrosporous; oospores ellipsoid-globose 



to angular-globose Oe. idioandrosporum 



7. Gynandrosporous; oospores ellipsoid to globose Oe. crassiusculum 



8. Oospore 27— 30m in diameter Oe. multisporum 



8. Oospore 36— 42yu in diameter 9 



9. Pore distinctly superior; oospore filling oogonium Oe. irregulare 



9. Pore supramedian ( sometimes median ) ; oospore 



not filling oogonium --Oe. magnum 



10. Pore supramedian ( sometimes median ) ; 



oogonia sexangular-ellipsoid— , Oe. sexangulare 



10. Pore distinctly superior; oogonia obovoid, 



subovoid, or quadrangular-ellipsoid 11 



11. Oogonia 24-35ai in diameter Oe. multisporum 



11. Oogonia larger 12 



12. Oospores 49-65^1 in diameter; oogonia 



53-68m in diameter Oe. Westii 



12. Oospores 35-46^ in diameter; oogonia 



(33)— 40— 50/A in diameter Oe. Borisianum 



13. Oospore wall (middle layer) decorated with 



pits in longitudinal series Oe. concatenatum. 



13. Oospore wall decorated with ridges or ribs 14 



14. Outer spore wall decorated with spiral ridges 15 



14. Outer or middle wall with longitudinal ribs or ridges 16 



[157] 



