074 ORDER 13 NAIADACE^E. 



and submersed, only the flowers arising above the surface of the water. 

 Spadix (or spike) pedunculate, 3 10-flovvered. Lvs. stipulate, par- 

 allel-veined, lower alternate, the upper mostly- opposite. Fls. small, 

 greenish. 



5 Leaves of two kinds ; the floating, oval-elliptical, coriaceous petiolate, stipules free 

 from the petiole, connate; submersed leaves thin, (*) 



* Floating leaves broader than the submersed ones, (a) 



a Leaves all conspicuously stipulate Nos. 1, 2 



a Leaves (the submersed ones) almost destitute of stipules Nos. 8, 4 



* Floating leaves smaller than the ample submersed ones No. 5 



Leaves of one kind only, all growing beneath the water's surface. (*) 



* Stipules entirely free from the petiole or leaf, (a) 



a Leaves lanceolate, petiolate or merely sessile Nos. 6, 7 



a Leaves oval or oblong, broad and clasping at base Nos. 8, 9 



a Leaves linear, Stems evidently compressed more or less. Nos. 10, 11 



Stems terete, very slender Nos. 12, 13 



Stipules united with the sheathing base of the leaf Nos. 14, 15 



1 P. nataiis L. BROAD-LEAVED POND-WEED. Floating Ivs. coriaceous, oblong, 

 or elliptic-ovate, acute or obtuse or cordate at base, on long petioles, submersed 

 cues linear-lanceolate, membranous, elongated, attenuated to petioles at base, 

 lowest reduced to mere petioles ; stipules connate, distinct from the petiole, 

 elongated ; spikes rather dense, shorter than the peduncles ; fruit somewhat 

 semi-globous, roughish, more or less carinate at the back. A very common 

 species, in slow waters or ponds, N. Eng. to Wis. St. slender, 1 to 3f long, ac- 

 cording to the depth of the water, branched. Upper Ivs. 2 to 4' long, about 

 half as wide; petioles 2 to 8', submersed. Spike 1 to 2' long. Jh, Aug. 



2 P. heterophyllus Schreb. Floating Ivs. lanceolate or oblong, 5 to 7-veined, 

 tapering to the petioles, scarcely coriaceous, submersed Ivs. long, narrowly linear, 

 membranous, acute, 1-veined, slightly tapering to the sessile base ; stip. nearly 

 distinct, resembling the Ivs. ; spikes dense, on thickened peduncles ; fr. com- 

 pressed, suborbicular. Ponds and slow waters, frequent. St. round, slender or 

 filiform, often branched. Lower Ivs. 3 to G' by 1", remote, upper about 2 to 3' 

 by J'. Spikes 1' long, peduncles 2 to 4'. (P. Claytonia Tuckerman.) 



3 P. diversifolius Bart. St. filiform, branching ; upper Ivs. oval or lance-oval, 

 5-veined, on short petioles, lower ones submerged, sessile, filiform, alternate, often 

 densely fascicled, not at all reticulated, obtuse. Common in pools and ditchea 

 A very slender and delicate species, only the upper Ivs. arising to the surface. 

 These are 6 to 10" by 2 to 4", acute at each end, on hair-like petioles 3 to G" long. 

 Spadices dense, short, 5 to G-flowered. Jl. (P. setaceum Ph.) Yaries with the 

 leaves nearly all of either kind. 



4 P. hybridus MX. Floating Ivs. elliptic-oblong, coriaceous, scarcely veined, 

 longer than their petioles ; submersed Ivs. long-linear, thin, sessile ; stipules above 

 equaling the petioles, those of the submersed Ivs. very short or wanting ; spikes 

 cylindric, dense, on short, thkSkerted ped. ; fruit keeled on the back, seed coiled 

 into a ring. Pools and slow waters, S. ? and "W. States. Sts. mostly simple, very 

 slender, 1 to 3f long. Lower Ivs. 3 to 5' long, alternate, upper opposite, 1' to 18". 

 Spike about 1'. A handsome species. 



5 P. fluitaiis Roth. Floating Ivs. opposite, oval-lanceolate, coriaceous, acute at 

 each end, shorter than the petioles ; submersed Ivs. larger than the floating, lan- 

 ceolate, sessile, short-acuminate, strongly veined, wavy, thin, not shining, faintly 

 reticulated; stip. large, connate; ped. thickened, cylindric. In clear, deep 

 waters, N". New Eng. and Can. Sts. simple or branched, several feet long. Sub- 

 mersed Ivs. 5 to 7' long, a third as wide, the floating 2 to 3' long. Stip. 2 to 3' 

 long. Spikes 2' long, rather dense-flowered. Aug. 



*6 P. liicens L. Lvs. shining, oblong-lanceolate, acuminate, flat, large, the short 

 petioles continuing in a thick midvein ; spikes long, cylindric, many -flowered ; 

 ped. thickened upward; fr. slightly keeled. It Can,, N". Eng., &c. Rivers and 

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

 shining above, conspicuously cross-veined, 3 to 5' long, an inch or more wide, 

 each with a lanceolate, double stipule above its base. Spadix 2' long, of nu- 

 merous green flowers, on a peduncle 2 or 3 times as long, thick and enlarged up- 

 wards. Jn. 



