POTAMOGETON. RTTPPIA . 
355 
apiculate or acuminate 3 — 5-veined with transverse veins,^<rf- 
iiiff I. uaiTow acute 3-vei»ed, fr. (2 lin. long) broadly |-obovate 
inner edge near!)/ straight but gibbous near the top rounded on 
the back, nut -with a promineut keel. — Phijtol. iv. 1158. P. zos- 
teraceus Bab. (not Fr.). — Rhizome spreading, from a tuber that 
has outlived the winter. Floating st. branched, spreading like 
a fan. Broad lower 1. usually decayed at the time of flowering. 
Lateral veins of upper 1. at tlie marrin, of lower 1. distant from 
it. Spikes slightly interrupted. Back of fr-. without ridges, 
rounded when fresh : inclosed nut with faint lateral ridges. — 
Ponds aud ditches. P. VI. VII. E. 
20. P. pedindtus (L.) ; I. fomied of 2 iiiierrupted tubes, lower 
nan-owly linear flattened slightly grooved above, upper setaceous, 
fr. (2 lin. long) broadly i^-obovate inner edge rather convex 
roimded on the back, nut icith 2 iateral ridges bat (usually) »o 
Jceel — _g. .323. H. vii. 19. — St. branched, forming linear masses. 
L. very gradually acute, all 1-veined, no marginal veins and 
scarcely thickened there ; upper 1. with an oval section. Spikes 
slightly interrupted. Back of fr". without ridges and rounded 
when fresh; nut with strong lateral ridges. Varying greatly 
in length and size of st. and leaves. — Ponds and streams. P. 
VI. VII. E. S. I. 
21. P.Jilifor'mis (Nolte !) ; 1. linear-setaceous 1-veined with 
transverse veins, spikes greatly interrupted, fr. (1| lin.) obovate 
rugose rounded on the back without keel or ridges when dry, nut 
roimd-backed. — L. like those of the preceding but longer. Fr. 
smaller. "\Miorls very distant on the spikes. Peduncles verj- 
long. — Rare. Forfarshire and Berwickshire. P. VI. VTI. S. 
***** L. all opposite, submersed ; stipules none. 
22. P. den'sus (L.) ; I. all ojyposite pellucid clasping elliptic- 
lanceolate or lanceolate, spikes shoitly stalked ultimately reflexed. 
— E. B. .397. R. vii. t. 28. — L. crowded, rather recurved. Spike 
■l-flowered. Sep. triangular. — Ditches. P. VI. VII. E. S. I. 
2. Rup'piA Linn. Tassel-Pondweed. 
1. R. marit'ima (L.) ; ped. long spirally twisted, anth. -cells 
oblong Ij times as long as broad, nut ovoid rather obliquely 
erect. — R. vii. 17. — Whole plant stronger than the next. L. very 
narrowly linear, foimed as in Potamogeton pectinatus. Sheaths 
large, inflated. — Salt marshes in the South. P. VII. ^ ill. E. I. 
2. R. rostelldta (Koch) ; ped. short not spiral, anth.-eells 
squarish as long as broad, nut gibbous at base obliquely ascend- 
ing when v'oung. — E. B. 13G ? R. vii. 17. — Whole plant very- 
slender. L. rather filiform than linear. Sheaths small, close. 
—Salt marshes. P. VU. VIH. E. S. I. 
