322 
POTAME.E. 
lous. Albumen 0. Embryo straight or curved, with a lateral 
cleft. 
1. Potamogeton. Fl. perfect. Perianth 4-parted. Anth. 
4, sessile, opposite to the divisions of the perianth. Ova- 
ries 4, styles 0. Drupes or nuts 4, sessile. 
2. Ruppia. Fl. perfect. Perianth 0. Stam. 2, the cells 
considerably separated, filaments very short scalelike. 
Ovaries 4, styles 0. Nuts 4, with long stalks. 
3. Zannichellia. Fl. imperfect. Male fl. with 1 stam. 
and no perianth. Fern. fl. with a bellshaped perianth, per- 
sistent style, peltate stigma. Nuts 3 — 5 or more, very 
shortly stalked. 
4. Zostera. Stam. and pistils inserted in 2 rows upon one 
side of a spadix. Spath linear, terminating in a leafy point. 
Fl. naked. Anth. 1. Ovary 1, style 1, stigmas 2. 
1. Potamogeton Linn. Pondweed. 
* L. alternate, upper I. floating and sometimes opposite, sti- 
pules free. 
1. P. nutans (L.) ; 1. all stalked, upper coriaceous floating ovate 
or elliptical, lower 1. linear or lanceolate or setaceous, petioles 
plano-concave above, nuts (large) rounded on the back when fresh 
keeled when dry, peduncles equal. — E. B. 1822. — A creeping 
rhizoma at the bottom of the water. Lowermost 1. often quite 
setaceous ; upper 1. more or less cordate at the base, when 
pressed flat a ridge is formed on each side of the base. Nuts 
2 lines long. — P.flidtans (Roth) according to Koch differs from 
this by having its petioles convex above and its fresh nuts rather 
acute on the back. It is probably a native. — Ponds, ditches, 
and slow streams. P. VI. VII. 
2. P. oblongns (Viv.) ; I. all stalked, upper coriaceous floating 
oblong-elliptical, lower 1. linear-lanceolate, petioles plano-con- 
cave above, nuts minute always obtuse and rounded on the back, 
peduncles equal. — E. B. S. 2849- — St. creeping below. Lower 
1. often very narrow. Nuts not exceeding 1 line in length, 
rounded on the back in the fresh and dry state. — Ditches, small 
streams, ponds. P. VII. 
3. P. plantagineus (Ducr.) ; I. all stalked membranous and pel- 
lucid blunt entire, upper elliptical, lower 1. oblong, petioles plano- 
concave above, nuts minute rounded on the back when fresh 
acutely keeled ivhen dry, peduncles equal. — E. B. S. 2848. — St. 
creeping below, branched, sometimes throwing out long scions 
from its upper axils. L. all beautifully transparent and netted 
with veins, the upper often nearly sessile and nearly orbicular. 
