THE GREEN ALGAE OP NORTH AMERICA 59 



17. Oogonium 40 ^ diam. or less. 18. 



17. Oogonium 42-50 M diam. 10. Oe. fragile. 



18. Vegetative cells 10-14 /* diam. loa. Oe. giobosum. 



18. Vegetative cells 15-18 M diam. 75. Oe. intermedium. 



19. Monoecious. 14. Oe. geniculatum. 



19. Dioecious. 20. 



20. Oogonium one-third to one-half wider than vegetative cells. 



15. Oe. capilliforme. 



20. Oogonium scarcely wider than vegetative cells. 16. Oe.capillare. 

 21. Oogonium swollen to twice the diam. of filament or more. 22. 

 21. Oogonium less swollen ; average less than double the filament. 33. 



22. Membrane of oospore smooth. 23. 



22. Membrane of oospore ribbed or pitted. 27. 



23. Monoecious. 25. 



23. Dioecious. 24. 



24. Vegetative eel Is 25-30 n diam. 7. Oe. cardiacum var. carbonicum. 



24. Vegetative cells 35-45 M diam. 19. Oe. rivulare. 



25. Division of antheridial cell vertical. 17. Oe. upsaliense. 



25. Division of antheridial cell horizontal. 26. 



26. Oogonium largest near base, oospore filling lower part. 



2ia. Oe. pseudoboscii. 



26. Oogonium ellipsoid, quite filled by oospore. 



18. Oe. Richterianum. 



27. Membrane of oospore ribbed. 28. 



27. Membrane of oospore areolate or pitted. 31. 



28. Ribs continuous and entire. 29. 



28. Ribs not continuous and entire. 30. 



29. Monoecious. 20. Oe. paludosum. 



29. Dioecious. 21. Oe. Boscii. 



30. Ribs composed of elongate dots. 22. Oe. margaritiferum. 



30. Ribs distinctly dentate. 23. Oe. crenulato-costatum. 



31. Membrane of oospore areolate. 



23. Oe. crenulato-costatum. var. aureum. 

 31. Membrane of oospore pitted. 32. 



32. Oogonium 38-48 M diam. 25. Oe. punctatum. 



32. Oogonium 70-83 M diam. 24. Oe. taphrosporum. 



33. Membrane of oospore smooth. 34. 



33. Membrane of oospore pitted. 70. Oe. giganteum. 



34. Monoecious. 26. Oe. martinicense. 



34. Dioecious. 35- 



35. Oogonium usually 65-75 M diam., rarely to 63 M. 3 6 - 



35. Oogonium 65 M diam. or less. 37. 



36. Vegetative cells 31-40 M diarn. 27. Oe. Landsboroughii. 



36. Vegetative cells 40-49 /* diam. 88. Oe. crassum. 



37. Vegetative cells 3-9 diam. long. 38. 



37- Vegetative cells 1.75-3 diam. long. 31. Oe. mexicanum. 



