ORDER 134. NAIAD ACE JE. 675 



7 P. obriitus. Lvs. linear-lanceolate, sessile, rather acute, only the midvein con- 

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

 late; ped. not enlarged upwards; ach. inflated, margined on the back, beak in- 

 curved, both sides conspicuously urabilicate. 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 tho slightly clasping base, 

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

 as shown by the pits of the fruit. 



8 P. praelongus "Wolfg. Lvs. oblong or ovate, obtuse, many-veined, with threo 

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

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

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

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

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



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

 spikes terminal ; fls. alternate ; fruit not keeled. A common species growing in 

 ponds and slo',7 waters, wholly below tho surface except the purplish flowers. 

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

 fbliate near the base, IV long, ^ as wide, obtuse, pellucid. Spadix on a short 

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



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

 linear, alternate, sessile ; fls. few in the spike, p3d. 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 line wide, 3-veined, of a bright green 

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

 water, but ripening tho seeds below. (P. gramineum MX.) 



11 P. compressus L. St. compressed, ancipital, flexuous ; Ivs. broad-linear, ob- 

 tuse; spike short, pedunclo elongated. A very distinct species in ponds and 

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

 stipules above tho nodes. Leaves 3 4' in length, 2" wide, closely sessile, re- 

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

 ^ 1' long, on a pedunclo 1 2' long, and bearing 5 25 flowers. Jl. (P. zos- 

 terifolium Schum.) 



12 P. pusillus L. St. filiform, flcxuoust, branched; Ivs. linear-subulate, mem- 

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

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

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

 2' by ", a little longer than tho intcrnodes. Spikes 3 5-flowered, the pe- 

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



13 P. Tuckermani Bobbins ? St filiform, with capillary branches ; Ivs. few, all 

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

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

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

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

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

 long. 



14 P. pectinatus (and P. marinus L.) St. slender, branched, striate, fiexuous ; 

 Ivs. numerous and fascicled in the axils, long, narrowly linear, acuminate, oa 

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

 Plant submersed in deep water, bushy and very leafy, N. Eng. ? Middle States 1 

 W. to Wis. (Lapham ?) Leaves 4 7' by (less than) 1", thin, the midvein scarcely 

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

 nor umbilicate. 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. Bobbins in Pondicherry 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. 



