sometimes giving rise to branches (akinetes wanting in young 

 plants). Chloroplast a parietal net, sometimes close and dense, 

 covering the entire wall, containing many pyrenoids. 



Under some environmental conditions (particularly in aquaria) 

 plants develop luxuriantly without forming akinetes, but akinetes 

 are so generally present that they constitute an identifying character. 

 The akinetes may be intercalary or both intercalary and terminal. 

 Branching is frequent, but there is no definite order or basal-distal 

 differentiation in the thallus. 



Key to the Species 



1. Filaments slender, up to lOfj. in diameter; 



akinetes all cask-shaped P. oedogonia 



1. Filaments stouter; akinetes cylindrical, ovoid, or irregular 2 



2. Akinetes all the same shape in the filament, alternating with the 

 vegetative cells throughout much of the plant; filaments 



95-140/t in diameter P. Mooreana 



2. Akinetes variously shaped within the same filament, 1-3 in a 



series; filaments 75-1 00,u in diameter P. varia 



Pithophora Mooreana Collins 1912, p. 97 

 PI. 22, Figs. 5, 6 

 Filaments highly branched to the third order, (65) -95-1 40//, in 

 diameter; tertiary branches about 50/a in diameter. Both terminal 

 and intercalary akinetes cylindrical, those terminating the branches 

 becoming acuminate, the tips broadly rounded, 95/a in diameter, up 

 to 215/A long. 



Floating mats in shallow pond. Wis. 



Pithophora oedogonia ( Mont. ) Wittrock 1877, p. 55 

 PI. 22, Figs. 7-10 

 Filaments slender, 45-70/i, in diameter; branching mostly solitary, 

 rarely opposite. Cells long and cylindrical, as much as 20 times their 

 diameter in length. Akinetes cylindrical or slightly swollen to cask- 

 shaped, conical, or more often acuminate, when terminal, 57-144/a 

 in diameter, 95-380/x long. 



Forming tangled mats in quiet water. Yellow River, Wisconsin. 



Pithophora varia Wille 1902, Phyc. Bor.-Amer. No. 983 



PL 24, Figs. 5,6 

 Filaments with branches about the same diameter as the main 

 axis, 75-105/i, wide, narrowing to 43-70/i, at the apices. Akinetes 

 variable within the same filament; ovate, cylindrical or irregularly 

 ovate; 1-3 in a series; 60-1 12/a in diameter, 70-240fjt. long. 

 Mich. 



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