Vaticheria sessilis (Vauch. ) De Candolle 1805, p. 63 



PL 68, Fig. 5 



Aquatic or terrestrial; filaments somewhat slender, 50-58/x in 

 diameter, with irregular branching; monoecious; oogonia usually 

 in pairs, ovoid to subglobose with the pore in a short beak and 

 directed obliquely upward, 70-85/^ in diameter, as much as lOO/x, 

 long; antheridia on a short pedicel between 2 oogonia, either 

 stiaight or circinate, but usually with the opening directed toward 

 the pore of an oogonium, about 25/x in diameter; oospore with a 

 3-layered membrane, filling the oogonium. 



A common species but infrequently found in our collections; 

 forming a felt-like mat on submerged rocks and on sandy bottoms 

 of springs; on rocky outcrops where there is trickling water. Mich., 

 Wis. 



Vaucheria sessilis fa. clavata ( Klebs ) Heering 1921, p. 88 



PI. 67, Figs. 3, 4 



Filaments stouter than in the typical, 77-1 lO^a in diameter; oogonia 

 broadly ovate with the beak directed vertically; oospore 49.5-66.5/x 

 in diameter, 66-88.5//. long. 



Mich. 



Vaucheria terrestris (Vauch.) De Candolle 1805, p. 62 



PI. 68, Fig. 4 



Either aquatic or terresti'ial, usually forming floating clots; fila- 

 ments rather slender, 50-80/x in diameter, branching dichotomous, 

 or at right angles to the main filament ( as in the case of the relatively 

 long branches which bear the sex organs); monoecious; oogonia 

 subglobose to ovoid, at the end of a slightly bent stalk, with the 

 pore directed downward, exceeding the antheridium and appearing 

 to be terminal on the branch, 60-1 03/x in diameter, 85-211/^ long; 

 antheridia stiongly circinate, 15-20/x in diameter, terminating the 

 branch but appearing to arise beneath the oogonium; oospore with 

 a thick, 4-layered membrane, completely filling the oogonium which 

 falls with the oospore. 



Floating in hard or soft water lakes and small ponds, becoming 

 mature and fruiting abundantly at low temperatmes. This species 

 is also found on moist soil, especially in well-shaded habitats. Mich., 



Wis. 



ORDER ZYGNEMATALES 



Except for the desmid famihes in which there are unicellular 

 genera (See Appendix) plants in this order are unbranched 

 filaments without basal-distal differentiation. Rarely, incidental 

 rhizoidal branches may be formed where filaments come in contact 



[294] 



