PoTAMOGETON. CXXXVII. NAIADACEE. 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. Tuckerman. (P. fluitansl Ph., Bw., Torr., <f-t:.) 

 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 — 6' by 1^", remote, upper about 2 — 3' by J'. Spikes 1' long, pedun- 

 cles 2 — 4' 



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

 late; ped. shorter. — Uxbridge, Mass., Rickard ! Probably common. A beauti- 

 ful variety. Fruit not seen. 



3. P. DivERSiFOLius. Bart. (P. setaceum. Ph.) Setaceous-leaved Pond-weed. 



Upper Irs. 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. 



p. Submersed leaves few, not fascicled in the axils. 



§ 2. Leaves all subniersed, uniform. 



4. P. LucENS. Skining Pond-weed. 



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

 vein; 5pi//cs 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, beautil'uUy veined, 3 — 5' long, acuminate, \ — 1' wide, each 

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

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



5. P. oBRUTus. Wood. L/yndon Pond-icccd. 



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

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

 culate; achcma inflated, subhemispherical, margined on the back, beak incurved 

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

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

 Stem round, slender, simple. Leaves uniform, 3 — 4' by J', tapering to the 

 slightl}-- clasping base, the two upper opposite. Spike dense, 1 J' long, peduncle 

 3' in length. Fruit with 2 little pits. 



G. P. pr.s;longus. Wolff". Long-sUdked Pond-weed. 



L/vs. oblong or ovate, obtuse, many-veined, with 3 stronger veins, all reticu- 

 lately connected, base amplexicaul; 7;e^. very long; spike cylindrical, many- 

 flowered; fr. ventricose, 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. I have gathered it in Niagara 

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



7. P. PERFOLiATUs. Perfoliate ur Clasping Pond-weed. 



Lvs. cordate, clasping the stem, uniform, all immersed; spikes terminal; fls. 

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

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

 long. Leaves alternate, apparently perfoliate near the base, IJ' long, \ as wide, 

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



8. P. PtOBBiNsii. Oakes. Rnbbins' Pond-v-eed. 



Lvs. lance-linear, approximate, sheathing the stem with the adnate stipules, 

 lamina auriculate at base, margin minutely ciliate-serrulate ; spikes oblong, 

 small and few-floM'ered ; psd. shorter than the leaves. — First discovered by Dr. 

 Rohbinsl in Pondicherrv Pond. Jefferson, N. H. Since found in manv other 



