NAIADACE.E. (PONDWEi:i> FAMILY. ) 563 



the face arcliing ami terminated by the short st} le ; snininit of the large embn/o 

 li/inrj transverse to the fruit. (P. compressus, Fries ; not L.f) — Still and slow- 

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



-0. P. Hillii, Morong. Stem slender, tr/c/e/y branr.hin(j,Jinttish; leaves 

 linear, (iciUe (1 -:2^' long by i- 1 i" wide), S-iierced, 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. — Mirli. and western N. V. 



21. P. obtusifdlius, Mortens & Koch. Stem flattened, vcrij hranchiug ; 

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

 3- (rarely 5-) nerved; stipules elongated, yery obtuse; spike ovate, continuous, 

 5 - S-tiowered, about the length of the peduncle ; fruit oval, apiculate with the 

 style, uot keeled when iresh, upper portion of embryo coWed 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, Pursh. Stem flUformJhittish and very branching; 

 leaves narroa-ly linear (1-2' long and seldom 4" 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. !N"iagar6nsis, Gray. Stem often longer (1 - 3°) ; leaves larger ( 1^ - 

 3y long by 1" wide or less), 3-.'>nerved at base, very acute and mucronate, 

 narrowed to the subpetiolate base. (P. Niagarcnsis, Tuckerm.) — Running 

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



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

 branching; lea res iiarrow- 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, N. Scotia to N. J., west to 

 Minn, and Mo., and westward. — Leaves sometimes almost setaceous (var. 

 tenuissimus. Knrh). 



y-cXT. poly phallus, 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 imbricated leaves. — In a shallow pool, S. Natick, Mass. 



24. P. mucron^tUS, Schrad. Resembling V. pusillus, but stem less 

 branching; leaves hroadrr (almost 1" wide), o/?r// ry-nerved ; sj)ikes interrupted. 

 (P. pusillus, var. major, Fries.) — N. Brunswick to western N. Y., ^lich., and 

 Minn. July. (Eu.) 



25. P, gemmiparus, Bobbins. Stem filiform, branching, terete, varying 

 greatly in lieiglit ; Icarcs hair-like, sometimes not as broad :is the stem, often 

 witli no apparent midrib, tapering to the flue st point (1 - 3' long), bi-glandular at 

 base; stipules \-V long; spikes few (3-6-flowcred), interrupted, on long fili- 

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

 very rare. (P. pusillus, var. 1 gemmiparus, Rubbins.) — Slow-moving streams 

 and still water, Mass. Auc.. JSept. 



