PoTAMOGETON. CXXXVII. NAIADACE.ffi. 525 



1 — 3f long according to the depth of the water, branched. Upper leaves 2 — 4' 

 by 8—16", petioles 2 — 8', submersed about ^ as wide. Spike 1 — 2' long, 

 20— 40-flowered. Jl. Aug. — Varies with the lower leaves all reduced to peti- 

 oles. In the Wisconsin plant the leaves are all subcordate, fruit acutely cari- 

 nate but not lunate. 



2. P. Claytonii. Tiickerman. (P. fluitans'? PA., Dii\, Torr., (f-c.) 

 Floating; lis. lanceolate or oblong, tapering to long petioles (sometimes 



on short petioles, E. T.), scarcely coriaceous, submersed leaves long, narrowly 

 linear, membranaceous, acute, 1-veined, slightly tapering to the sessile base ; 

 spikes rather loose, on long peduncles; fr. compressed, suborbicular. — Ponds and 

 slow waters, frequent. Stems round, slender or filiform, often branched. Lower 

 leaves 3— G' by U", remote, upper about 2 — 3' by \'. Spikes 1' long, pedun- 

 cles 2—4' 



/? 1 (P. heterophyllus. Torr.) Lower Ivs. approximate, lowest slightly petio- 

 late ; ped. shorter.— Uxbridge, Mass., Richard \ Probably common. A beauti- 

 ful variety. Fruit not seen. 



3. P. DivERsiFOLius. Bart. (P. setaceum. PA.) Setaceous-leaved Pond-weed. 



Upper Ivs. lanceolate, opposite, 5-veined, on short petioles, lower ones sub- 

 merged, sessile, filiform, alternate, dense, axillary. — Common in pools and 

 ditches. A very slender and delicate species, only the upper leaves arising to 

 the surface. These are 6—10" by 2—4", acute at each end, on hair-like peti- 

 oles 5 — 6" long. Spadices dense, short, 5 — 6 flowered. July. 



/?. Submersed leaves few, not fascicled in the axils. 



§> 2. Leaves all submersed, uniform. 



4. P. i.ucKNS. Sklning Pond-weed. 



Lvs. lanceolate, flat, large, the short petioles continuing in a thick mid- 

 vein ; spikes long, cylindric, many-flowered. — % Can., N. Eng., &c. Rivers and 

 lakes. Distinguished for its large leaves which are very pellucid, and, when 

 dry, shining above, beautifully veined, 3—5' long, acuminate, l—V wide, each 

 with a lanceolate bract above its base. Spadix 2' long, of numerous, green 

 flowers, on a peduncle 2 or 3 times as long, thick and enlarged upwards. June. 



5. P. OBRUTUS. Wood. Lyndon Pond-nxed. 



Lvs. glossy, linear-lanceolate, sessile, rather acute, only the midvein con- 

 spicuous, alternate, approximate, the lower stipules wanting; spikes long-pedun- 

 culate; «cAt'?«fi? inflated, subhemispherJcal, margined on the back, beak incurved 

 both sides, con.spicuously umbilicate. — Passumpsic river, Lyndon, Vt.! A 

 remarkable species, differing widely from any other with which I am acquainted. 

 Stem round, slender, simple. Leaves unilorm, 3—4' by i', tapering to the 

 slightly clasping base, the two upper opposite. Spike dense, li' long, peduncle 

 3' in length. Fruit with 2 little pits. 



6. P. PR^:i.ONGUs. Wolff. Long-stalked Pond-u-ecd. 



Lvs. oblong or ovate, obtuse, many-veined, with 3 stronger veins, all reticu- 

 lately connected, base amplexicaul; ;;er/. very long; spike cylindrical, many- 

 flowered; //•. ventrico.se, lunate, acutely carinafe 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. I have gathered it in Niagara 

 river, growing in depths of 6 or 8f, July, Aug. 



7. P. PERFOLiATUS. Perfoliate or Clasping Pond-weed. 



Lvs. cordate, cla.sping tlie stem, uniform, all immersed ; spikes terminal ; fls. 

 alternate. — A common species growing in ponds and slow waters, wholly below 

 the surface except the jjurplish flowers. Stem dichotomous, very lealy, 6—10' 

 long. Leaves alternate, apparently perfoliate near the ba.se, 1^' long, i as wide, 

 obtuse, pellucid. Spadix on a short peduncle (1 — 2'), few flowered. Jl. 



8. P. RoBBiNsir. Oakcs. Robl/ins' Pond-weed. 



I/vs. lance-linear, approximate, sheathing the .stem with the adnate stipules, 

 lamina auriculate at ba.sc, margin minutely ciliate-serrulale; spikes oblong, 

 small anil few-flowered; prd. shorter than the leaves. — First discovered by Dr. 

 Robhins! in Pondieherrv Pond. Jeffer.son. N. H. Since found in many other 



