Okdke 134.— NAIADACKffi. C75 



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

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

 late ; ped. not enla^g6d upwarJs ; 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 the 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. praelongus Wolfg. Lvs. oblong or ovate, obtuse, many-veined, with three 

 stronger veins, all reticulately connected, base amplexioaul ; ped. very long; spiko 

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

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

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

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



9 P. perfoli^tus L. Lvs. cordate, clasping the stem, uniform, all immersed; 

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

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

 Stem diohotomous, 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. paucifl6ni3 Pursh. St. dichotomous, slightly compressed, filiform; lvs 

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

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

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

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

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



11 P. compressus L. St. compressed, ancipital, flexuous ; lvs. broad-lmear, 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 codes. Leaves 3 — i' in length, 2" wide, closely sessile, re- 

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

 4 — 1' long, on a peduncle 1 — 2' long, and bearing 5 — 25 flowers. Jl. (P. zos- 

 terifolium Sehum.) 



12 P. pusillua L. St. filiform, flexuous, branched; lvs. 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. 

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

 — 2' by J", u, little longer than the internodes. Spikes 3 — 5-flowered, tho pe- 

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



13 P. Tuckerm^iii Kobbins ? St filifoi-ra, with capillary branches ; lvs. few, all 

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

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

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

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

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

 long. 



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

 lvs. numerous and fascicled in tho axUs, 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 I 

 W. to Wis. (Lapham ?) Leaves 4 — 1' by (less than) 1 , thin, the mid vein 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 aurioulate 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, JeSerson, N. H. Since 

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

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

 what crowded. 



