pyrenoids; asexual reproduction by large globose, multiflagellate 

 zoospores cut off singly at the ends of clavate branches; thick-walled 

 akinetes at the ends of branches, or in the tubes of some species; 

 sexual reproduction oogamous; oogonia globose or ovate, sessile, on 

 pedicels, or on long stalks, containing a single egg which may 

 completely fill the oogonium; antheridia on the same or different 

 filaments, clavate, cylindrical, or subcylindrical, coiled or straight, 

 usually reflexed with the terminal opening directed toward the 

 oogonium, borne near the oogonia or at the end of a series, producing 

 many biflagellate, ovoid to fusiform antherozoids; oospores with 

 thick walls, sometimes completely filling the oogonia and the same 

 shape. 



Key to the Species 



1. Oogonia 262-289/ix in diameter V. Nicholsii 



1 . Oogonia smaller „ 2 



2. Oogonia sessile on the main filament 3 



2. Oogonia on a pedicel or on a lateral branch 5 



3. Oogonia obliquely o\ate, large, up to 160/ot high 



and 220fj. long; wall 6m thick V. pachydermum 



3. Oogonia more nearly erect, smaller; wall not thick _ 4 



4. Oogonia erect, the pore vertically directed V. orthocarpa 



4. Oogonia with the pore directed obliquely upward V. sessilis 



5. Oogonia on a short pedicel, sometimes nearly sessile 6 



5. Oogonia at the end of a long or short lateral branch, stalked 10 



6. Oospores not filling the oogonia; oogonia usually 



in pairs, the pores directed oppositely V. aversa 



6. Oospores filling the oogonia; arranged otherwise 7 



7. Pedicel very short, scarcely evident; oogonia 



broadly ovate, the pore nearly erect -V. sessilis 



7. Pedicel evident; oogonia narrowly ovate or ellipsoid, 



the pore oblique or more nearlv horizontal 8 



8. Oogonia in pairs, or several on a short pedicel, 



the antheridium between V. geminata 



8. Oogonia arising singly, near the antheridium. 9 



9. Oogonia 80-150^ in diameter, the pore directed 



horizontally or obliquely downward *V. ornithocephala 



9. Oogonia 60-65^ in diameter; pore directed obliquely upward.V. polysperma 

 10. Oogonia 2 to several on the end of a lateral branch 



a millimeter or more in length V. longipes 



10. Oogonia solitary, on a much shorter branch -11 



11. Oogonia 60-103/x in diameter, 85-21 1^ long, without a pedicel 



from the branch, arising near the base of the antheridia V. terrestris 



11. Oogonia averaging smaller, 60-75^ in diameter, 75-90^ long, with 



a pedicel, placing it well above the associated antheridium V. hamata 



Vaucheria aversa Hassall 1843, p. 429 

 PI. 66, Figs. 9, 10 

 Coarse filaments, freely branched and readily collapsing upon 

 being handled, 65-100/i. in diameter; oogonia usually in pairs or 



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