POTAMOGETON. 
351 
2. RuppiA. Fl. perfect. Perianth 0. Stam. 2, the cells 
considerably separated; filaments veiy short, scalelike. 
Ovaries 4. Styles 0. Nuts 4, with long stalks. — Fl. about 
2 together. 
3. Zannichellia. Fl. monoecious, axillary. Barren with 1 
stam., and no perianth. Fertile wdth a bellshaped perianth, 
persistent style, and peltate stigma. Nuts 3—5 or more, 
very shortly stalked. 
1. Potamoge'ton Linn. Pondweed. 
• L. alternate, floral I. floating and sometimes opposite; stipules 
free. 
1. P.niHans (L.); 1. all stalked, upper coriaceous floating 
ovate or elliptic folded at the base, lower leafless petioles linear 
or setaceous, fr. (larr/c) rounded on the back lohen fresh keeled 
when dry, pedimcle equal.— J?. .5. 1822. R. vii. 50.— 'St. creeping 
below, simple. Petioles plane-concave ; lowermost limbless and 
often slender. L. subcordate below, when pressed flat a ridge 
is formed on each side of the base, jointed to their stalks a 
little below the limb. Sep. stalked, roundly rhomboidal. Auth.- 
cells not parallel. Fr. greenish, slightly compressed, \\ — 2 lin. 
long. — Ponds, ditches, and slow streams. P. VI. VII. E. S. I. 
2. P. poh/ffonifSliits (Pourr.); 1. all stalked, upper subcori- 
aceous floating oolong-eUiptic subcuspidate, no leafless petioles, 
lower 1. linear-lanceohxte, fr. minute blunt and rounded on the 
back, pedimcle equal. — P. oblongus Viv., E. B. S. 2849. — St. 
creeping below. Petioles longer than leaves, plane-concave. 
Lower 1. often very naiTOW. Spikes rather short and in-egular. 
Sep. transversely elliptic, stalked. Fr. reddish scarcely com- 
fressed, 1 lin. long ; a faint keel and lateral ridges when di-y. — 
)itches, small streams, and ponds. P. VII. E. S. I. 
3. P. planfagin'eus (Ducr.) ; I. all shortly stalked meinhranons 
and pellucid blunt not cuspidate nor plicate, upper elliptic, lower 
1. oblong, fr. minute roimded on the back when fi-esh keeled 
when dry, peduncle equal. — F. B. S. 2848. R. vii. 45. — St. 
creeping below, branched, sometimes throwing out long runners 
from its upper axils. L. all beautifully transparent and netted 
with veins, the upper often almost sessile and nearly. orbicular, 
sometimes slightly cuspidate. Petioles plane-concave above. 
Spikes long, cylindrical. Anth. -cells nearly parallel. Sep. 
ovate. Fr. greenish, f lin. long. — Stagnant peaty water. P. 
VI. VII. E. S. I. 
4. P. rufes'cens (Schrad.); submersed I. lanceolate narrowed 
at both ends subsessile membranous pellucid entire not apictdate 
with chainlike network near the midrib, floating 1. subcoriaceous 
