OEDER 134. NAIAD ACE M. 675 



7 P. obrutus. Lvs. linear-lanceolate, sessile, rather acute, only the uiidveia 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, botli sides conspicuously umbilicate. 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, 1 J' long, ped 3'. Seed coiled into a ring 

 as shown by the pits of the fruit. 



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

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

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

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

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

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

 peduncle (12'), few-flowered. Jl. 



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

 linear, alternate, sessile; fls. few in the spike, psd. 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 tho 

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



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

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

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

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

 terifolium Schum.) 



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

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

 few-flowered; fr. ovoid-compressed, umbilicate 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 internodes. Spikes 3 5-flowered. the pe- 

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



13 P. Tuckermani Robbins ? 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 the 

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

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

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

 long. 



14 P. pectinatua (and P. marinus L.) St. slender, branched, striate, flexuous , 

 Ivs. 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 7' by (less than) 1", thin, tho midvein scarcely 

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

 nor umbilicate. Jn. 



15 P. Robbmsii Oakos. Lvs. lance-linear, approximate, sheathing the stem 

 with the adnafe 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 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. 



