NAIADACE^.. (PONDWEED FAMILY.) 563 



the face arching aud terminated by the short style ; suminit of the large embryo 

 lying transverse to the fruit. (P. corapressus, Fries ; not L. ?) — Still aud slow- 

 flowing waters, N. Eng. to N. J., Iowa, and Minn. Aug., Sept. (Eu.) 



20. P. Hillii, Morong. Stem slender, w.v'c/e/^ branching, fatt i sh ; leaves 

 linear, acute (1 -2|' long by |- 1^" wide), 3-nerved, the lateral nerves delicate 

 and near the margin ; stipules whitish, striate, obtuse (3 - 5" long) ; spikes 

 capitate (3-6-fruited), on short spreading or recurved peduncles ; fruit as in 

 the last. — Mich, and western N. Y. 



21. P. obtusifollUS, Mertens & Koch. Stem flattened, very branching ; 

 leaves linear, tapering toward the base, obtuse and mucronate or very acute, 

 3- {rarely 5-) nerved; stipules elongated, \Qxy obtuse; spike ovate, continuous, 

 5 - 8-flowered, about the length of the peduncle ; fruit oval, apiculate with the 

 style, not keeled when fresh, upper portion of embryo coiled inward and lying 

 transverse to the fruit. — Slow streams and ponds, Canada and X. Eng, to west- 

 ern N. Y. and Mich. Sept., Oct. (Eu.) 



22. P. pauciflorus, Tursh. Stem filiform, flattish and very branching ; 

 leaves narrowly linear (1-2' long and seldom -J"" wide), acute, obscurely 3- 

 nerved ; stipules obtuse; spikes capitate, 1-4- (usually 2-) flowered, on short 

 club-shaped peduncles ; fruit roundish-lenticular ; the back more or less crested ; 

 upper portion of the embryo incurved in a circle. — Still or stagnant waters, 

 N. Brunswick to Ga., Iowa, Minn., and westward. 



Var. Wiagarensis, Gray. Stem often longer (1 -3°) ; leaves larger {\\- 

 3|' long by V wide or less), 3-.5-nerved at base, very acute aud mucronate, 

 narrowed to the subpetiolate base. (P. Niagareusis, Tuckerm.) — Kunning 

 water, Great Lakes to S. C. ; also in Cal. 



23. P. pusillus, L. Stem slender, flattish or nearly cylindrical, often very 

 branching; leaves narroio- or setaceous-linear, acuminate, acute or subacute, 1 - 

 3-nerved, furnished with translucent glands on each side at the base ; stipules at 

 first obtuse; spikes interrupted or capitate, 2 -8-flowered, on rather long pe- 

 duncles ; fruit obliquely elliptical, scarcely keeled ; apex of embryo incurved and 

 directed obliquely downward. — Pools and ditches, X. Scotia to X. J., west to 

 Minn, and ]\Io., and Avestward. — Leaves sometimes almost setaceous (var. 

 tenuissimus, Koch). 



Var. poly phyllus, Morong. Dwarf form (3 - ,5' high), divaricately branch- 

 ing from the base, very leafy throughout ; leaves very obtuse, not cuspidate, 

 3-nerved ; non-flowering but abundantly provided with propagating buds which 

 are formed on the thickened and hardened ends of the branches and closely 

 invested by iml^ricated leaves. — In a shallow pool, S. X'atick, Mass. 



24. P. mucronatus, Schrad. Resembling P. pusillus, but stem less 

 branching; leaves broader (almost \" wide), o/'Cen 5-nerved ; spikes interrupted. 

 (P. pusillus, var. major. Fries.) — X'. Brunswick to western X. Y., Mich., and 

 Minn. July. (Eu.) 



2.5. P. gemmiparus, Robbins. Stemfiliform,branching, terete, varying 

 greatly in height ; leaves hair-like, sometimes not as broad as tlie stem, often 

 with no apparent midrib, tapering to theflnest point (1 - 3' long), bi-glandular at 

 base; stipules |-1' long; spikes few (3-6-flowered), interrupted, on long fili- 

 form peduncles; propagating buds very numerous ; fruit like that of P. pusillus, 

 very rare. (P. pusillus, var. ? gemmiparus, Robbins.) — Slow-moving streams 

 and still water, Mass. Aug., Sept. 



