PoTAMOGKToy. CXXXVII. NAIADACE^. 5% 



1 — 31" long according to the depth of the water, branched. Upper leaves 2 — i' 

 by 8 — 16", petioles 2 — 8', suhincrsed al)out i as wide. Spike 1—2' long, 

 20— 40-flowcred. JI. Aug.— Varies with the lower leaves all reduced to peti- 

 oles. In the Wisconsin jjlnnt the leaves arc all subcordiite, iVuit acutely cari- 

 nate but not lunate. 



2^ P. Ci.AYTONir. Tuckermnn. (P. tluitansl P//., /,'//;., Tarr., tf^c.) 

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

 on short petioles, E. 7'.), scarcely coriaceous, submersed leaves long, narrowly 

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

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

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

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

 cles 2 — 4' 



(31 (P. heterophyllus. Torr.) Z>?/7cr Zr.s. approximate, lowest slightly petio- 

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

 I'ul variety. Fruit not seen. 



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

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



rnergcd, 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 den.se, short, 5 — 6 flowered. July. 

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



^ 2. Leaves all submersed^ uniform. 



4. P. I.UCENS. Skiniiig Pond-tceed. 



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

 vein ; spi/ics 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, ^—1' 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. L/ijndoti Pond-icecd. 



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

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

 culate; achenia 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 i', tapering to the 

 slightly clasping base, the two upper opposite. Spike dense, 1^' long, peduncle 

 3' in length. Fruit with 2 little pits. 



6. P. PR^LONGus. Wolff. Long-stalked Pond-weed. 



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

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

 flowered; fr. ventricose, lunate, acutely carinate^on the back. — Ponds aiid 

 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. PERFOLiATirs. Perfoliate; or Clasping Pond-weed. 



Lvs. cordate, clasping the stem, unilbrm, all immersed ; spikes terminal ; fis. 

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

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

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

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



8. P. RoBBix.sii. Oakes. Robt/ins' Pond-v^eed. 



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

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

 small and few-flowered ; pc.d. shorter than the leaves. — First discovered by Dr. 

 Rohbins! in Pondicherrv Pond, .Teffl-rson. N. H. Since found in ma nv other 



