THE GREEN ALGAE OF NORTH AMERICA 423 



4. Dioecious ; oogonia sessile. 5. V. dichotoma. 



4. Monoecious; oogonia somewhat stipitate. 2. V. Tluirefii. 



5. Oogonia facing in opposite directions. 4. V. aversa. 



5. Oogonia single, or several facing one way. 6. 



6. Oogonium usually single. i. V. Dillwynii. 



6. Oogonia in series of 2-6. 3. V. ornithocephala. 



7. Oogonia sessile on the main filament or very shortly stipitate. 



SESSILES. 8. 



7. Oogonium on a branch or distinct pedicel, antheridium terminal. 



RACEMOSAE. 10. 



8. Oogonia straight. 8. V. orthocarpa. 



8. Oogonia oblique. 9. 



9. Filaments 33-50 ,u diam. 6. V. repens. 



9. Filaments 50-85 M diam. 7. V. sessilis. 



10. Oogonium sessile on the branch, or nearly so. 



10. V. terrestris. 

 10. Oogouia stipitate. n. 



ii. Oogonium usually solitary. 9. V. hamata. 



ii. Oogonia usually 2-6. 12. 



12. Pedicels of oogonia and antheridia arising from same point on 



main filament. 13. V. Gardneri. 



12. Pedicels of oogonia and antheridia arising near the end of a 



branch. 13. 



13. Branch short ; antheridium usually surpassing oogonia. 



11. V. getninata. 

 13. Branch long; antheridium not surpassing oogonia. 



12. V. longipes. 



14. Oogouium separated from filament by an empty cell. 



1 8. V. litorea. 



14. Oogonium not separated from filament by an empty cell. 15. 

 15. Oogoninm with many fecundation tubes. 17. V. coronata. 



15. Oogonium with only one fecundation tube. 16. 



16. Oospore spherical. 17. 



16. Oospore lentiform. 14. V. piloboloides. 



17. Antheridium truncate. 16. V. intermedia. 



17. Antheridium acute. 15- V. sphaerospora. 



i. V.DILLWYNII (Web. and Mohr) Agardh, 1810, p. 21; 

 Wittr. and Nordst., Alg. Exsicc., No. 1583; V. p&chyderma 

 Walz, 1866, p. 146, PI. XII, figs. 1-6. Terrestrial; filaments 

 60-100 p. diam.; oogonia globose or ellipsoid, sometimes sub- 

 reniform, sessile, rostrate, generally solitary, occasionally two 

 together, about 150 ^ diam.; membrane with fine dots; ripe 

 oospore with brown spots, with thick wall, manifestly lamellate, 

 sometimes up to 7 layers ; antheridia saccate, formed at the ends 

 of short, hooked lateral branches, 20 p. diam., near the single 

 oogonium, or between two approximate oogonia. Me., N. J. 



Europe. 



