£>OTAiioGETnK. CXXXVII. NAIAD ACEJE. B2ii 



a — 3f long according to the depth of the v/ater, branched. Upper leaves 2 — i' 

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

 20— 40-flowered. JL Aug. — Varies v/ith the lov/er leaves all reduced to peti- 

 oles. In the Wisconfiin plant the lea\'-es are all subcordate, fruit acutely cari- 

 iiate but not lunate. 



2. P. Claytonii. TucKerman. (P. fluitansl Pk., Biv., Tarr., c^'C.) 

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



on short petioles, _E. T.), scarcely coriaceous, submersed feaves long, narrowly 

 linear, membranaceous, acute, 1-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 — 6' by IJ", remote, upper about 2—3' by J-'. Spikes 1' long, pedun- 

 cles 2 — 4' 



^"2 (P. heterophyllus. Toir.) Z.-<?w5er Zi75. approximate, lowest slightly petio- 

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

 ful variety. Fruit not seen. 



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

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



■oierged, 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 — G flowered. July. 

 ,0. Submersed leaves iew, not fascicled in the axils. 



^ 2. Leaves all sitb/nerscd, vMifornt. 



4. P. LUCEN.S. Shining Pond-^ceed. 



L/DS. lanceolate, flat, large, the short petioles continuing in a thick mid- 

 ^'■eia; &pikes 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 ^reined, 3 — 5' Icng, 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. Jime, 



5. P. OBRUTUs. Wood. Lyndon Pond-u-eed. 



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

 spicuous, alternate, approximate, the lov/er stipules wanting; spj'Acs long-pedun- 

 ;cu)ate; achenia inflated, subhemispherical, margined on the back, beak incurved 

 both sides, conspicuously umbilicate. — Passumpsic river, L3mdon, Vt. ! A 

 remarkable species, difiering widely from any other v.ith which I am acquainted. 

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

 sligktly clasping base, the tv^o upper opposite. Spike dense, li' long, peduncle 

 3' in length. Fruit with 2 little pits. 



6. P. PR.EL0NGUS. WclflT. Long-stolked Pond-weed. 



Lvs. oblong or ovate, obtuse, many-veined, v/ith 3 stronger veins, all reticu- 

 lately connected, base amplexieaul; 7;erf. very long; spike cylindrical, many- 

 flowered; //•. ventriccse, lunate, acutely carinate on the back. — Ponds and 

 rivers, Northern Slates 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 

 i-iver, growing in depths of 6 or 8f. July, Aug. 



7. P. PERFOLiATUs. PerfoliaU or Clasping Pond-weed. 



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

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

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

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

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



8. P. RoEBiNSii. Oakes. Robbins^ Poiidr-wced. 



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

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

 small and fev/-fiowered ; fed. shorter than the leaves. — First discovered by Dr. 

 Mokbins! in Pondicherry Pond, Jeflerson, N. H. Since found in many other 



