Oeder 134.— NAIADAOEiE. 6*75 



7 P. obriitus. Lva. linear-lanceoiAte, sessile, rather aouto, only the midrein con- 

 spiououa, alternate, approximate, the lower stip. wanting ; spikes long, peduncu- 

 late ; pad. not enlarged upwards ; aoh. inflated, margined on the back, beak in- 

 curved, both sides conspicuously umbilioate. — A. remarkable species, first found 

 at Lyndon, Vt., since seen southward to Ga.; in slow waters. St. round, slender, 

 simple. Lvs. uniform, 3 to 4/ by 4 to 6", tapering to the slightly clasping base, 

 the two upper opposite. Spike dense, 1 j' long, ped 3'. Seed coiled into a ring 

 as shown by the pita of the fruit. 



8 P. prselongus "Wolfg. Lvs. oblong or ovate, obtuse, many-veined, with three 

 stronger veins, all reticulately connected, base amplexicaol ; ped. very long ; spike 

 cyhndrical, many-flowered ; fr. ventricous, lunate, acutely carinate on the back. — 

 Ponds and rivers, Korthern States and Can. The plant is wholly submersed, 

 sending up its spike to the surface on a very long stalk. We have gathered it in 

 Niagara river, growing in depths of G or 8f. July, Aug. 



9 P. perfoliktus L. Lvs. cordate, clasping the stem, uniform, all immersed; 

 spikes terminal ; fls. alternate ; frail not kcolcd. — A common species growing in 

 ponda and slow waters, wholly below the surface except the purplish flowers. 

 Stem dichotomous, very leafy, 6 — 10' long. Leaves alternate, apparently per- 

 foliate near the base, IJ' long, J as wide, obtuse, pellucid. Spadix on a short 

 peduncle (1 — 2'), few-flowered. Jl. 



10 P. pauciflorus Pursh. St. dichotomous, slightly compressed, filiform; lvs, 

 linear, alternate, sessile ; fls. few in the spike, pad. short ; fruit distinctly crested 

 on the back. — A delicate species, in rivers, &c. Leaves numerous, obtuse, taper- 

 ing to the stipulate base, 2 — 3' long, a hno wide, 3-veined, of a bright green 

 color. Peduncle an inch long, terminal, bearing 3 — 5 greenish fls. above the 

 water, but ripening the seeds below. (P. gramineum Mx.) 



11 P. compressus L. St compressed, ancipital, flexuous ; lvs. broad-Unear, ob- 

 ■ tuse; spike short, peduncle elongated. — A very distinct species in ponds and 



rivers. Stem 1 — 2f long, branching, weak, flattened, green, with sheathing 

 stipules above the nodes. Loaves 3 — i' in length, 2" wide, closely sessile, re- 

 mote, the margins perfectly parallel, ending in an abrupt point. Spadi.Y terminal, 

 -J — 1' long, on a peduncle 1 — 2' long, and bearing 5 — 25 flowers. Jl. (P. zos- 

 terifolium Schum.) 



12 P. pusillus L. St. fihform, flexuous, branched; lvs. linear-subulate, mem- 

 branaceous, very acute, sessile, not narrower than the stipules; spikes capitate, 

 few-flowered; fr. ovoid-compressed, umbilioate each side. — Shallow waters, N. 

 Eng. to Ohio and Can. A very delicate species, wholly submersed. Leaves 1 

 — 2' by J", a little longer than the intemodes. Spikes 3 — 5-flowered, the pe- 

 duncles i' long. Fruit with sharp pits, as in P. obrutus, and rather inflated. 



13 P. Tuokermani Robbins ? St filiform, with capillary branches ; lvs. few, all 

 capillary and coufervoid, with minute, membranous stipules ; spikes few (6 to 9)- 

 flowered, oblong, on a long, filiform peduncle, which is slightly thicker than the 

 stem ; (fruit immature). — In clear water, XJxbridgo, Mass. (Ricard) (White Mts., 

 Alleghany Mts. Tuokerman? in Gray's Manual.) An exceedingly delicate species. 

 The leaves taper to the fineness of cobwebs. Spike 4" long, the ped. about 5' 

 long. 



14 P. peotinatus (and P. marinua L.) St. slender, branched, striate, flexuous ; 

 lvs. numerous and fascicled in the axils, long, narrowly linear, acuminate, on 

 sheathing stipules ; spikes cylindrical, the lower fls. remote ; ped. filiform, long. 

 — Plant submersed in deep water, bushy and very leafy, N. Eng. ? Middle States ! 

 W. to Wis. (Lapham ?). Leaves 4 — V by (less than) 1", thin, the midvein scarcely 

 perceptible. Fruit large, purplish, rough, a little compressed, neither carinate^ 

 nor umbilioate. Jn. 



15 p. Robbinsii Oakes. Lvs. lance-linear, approximate, sheathing the stem 

 with the adnate stipules, lamina auriculate at base, margin minutely ciliate-ser- 

 rulate; spikes oblong, small and few-flowered; ped. shorter than the leaves. — 

 First discovered by Dr. Robbins in Pondioherry Pond, Jefferson, N. H. Since 

 found in many other ponds in N. H., Mass. W. to Ohio. St. long, branched, 

 almost wholly enclosed in the sheaths. Lvs. 2 to 4' by 2 to 3", very acute, some- 

 what crowded. 



