THE GREEN ALGAE OF NORTH AMERICA 19 



2. Vegetative cells 9-12 M diam. 2. D. americana. 



2. Vegetative cells 15 M diam. or more. 3. 



3. Cells 16-20 M diam., chromatophores 2, stellate. 3. D. decussata. 

 3. Cells 20-26 M diam., chromatophore an axial plate. 4. D. laevis. 



1. D. GLYPTOSPERMA (De Bary) Wittrock, 1872, p. 35 ; 

 P. B.-A., No. 1419 ; Mougeotia glyptosperma De Bary, 1858, 

 p. 78, PI. VIII, figs. 20-25 : Wolle, 1887, p. 229, PI. CXLVI, 

 figs. 6-9. Filaments crisped, lubricous, 10-15 //. diam., cells 

 6-12 diam. long, fertile cells still longer ; spores ovoid, 42-49 X 

 30-40 n, with smooth, saccate, yellowish, translucent outer 

 membrane and yellowish-brown median membrane, with three 

 longitudinal parallel ridges connected by fine radial cross lines. 

 Fig. 9. Mass., Minn., Fla. Europe, New Zealand. 



Var. FORMOSA Transeau, 1915, p. 18. Vegetative cells 

 7-5-9 ^ diam., spores 30-42 X 24-30 /*, steel blue. Among 

 Zygnema peliosporum in P. B.-A., No. 808, Cal. 



2. D. AMERICANA Transeau, 1915, p. 18. Vegetative cells 

 9-12 X 27-120 p., constricted at the dissepiments, chromatophore 

 a two-lobed axial plate with two pyrenoids ; zygospores ovoid 

 or quadrate-ovoid, 20-40 X 30-40 /*, with angles rounded, pro- 

 duced or retuse ; parthenospores 15-20 X 20-30 ft, unilaterally 

 ellipsoid with retuse ends ; median spore wall minutely and 

 irregularly verrucose, yellow brown at maturity. Ontario, 

 A. B. Klugh. 



3. D. DECUSSATA Transeau, 1915, p. 19. Vegetative cells. 

 16-20 X 25-50 /*, cylindrical ; chromatophores two, stellate, each 

 with a pyrenoid ; zygospores ovoid, quadrate-ovoid or irregular, 

 24-30 X 30-48, with rounded, retuse or produced angles ; aplano- 

 spores unilaterally ovoid, 17-25 X 20-40 p ; parthenospores 

 15-20 X 20-30 ft ; median membrane scrobiculate, yellow brown ; 

 akinetes with smooth, heavy walls, 18-20 X 20-30 ft. Pa., 111., 

 Mich., Minn., Ont. Transeau. 



4. D. LAEVIS (Kiitz.) W. & G. S. West, 1897, p. 476; 

 Zygogonium laeve Kiitzing, 1845, p. 225. Vegetative cells 

 20-26 p. diam., 1-5 diam. long; fertile cells often much longer; 

 spores broadly ellipsoid to ovoid, 42-50 ft long, 20-30 ft thick ; 

 median membrane thick, brown, scrobiculate. Wis., G. M. 

 Smith. 



Page 122, and p. 75 of supplement, for Key to the Species of 

 Mougeotia, substitute, 



i. Fructification by zygospores ; aplanosphores unknown. 2. 



i. Zygospores exceptional ; usual reproduction by aplanospores. 22. 



2. Spore bounded by 2 cells. 3. 



2. Spore normally bounded by more than 2 cells. 15. 



