76 NAJADACEAE (PONDWEED FAMILY) 



24. P. strictifblius Benn. Stems slender, wiry, simple below, freely and 

 stiffly branched above, the ascending branches mostly tipped by large winter- 

 buds; leaves spreading-ascending, very rigid, 2-3.5 cm. long, 0.4-1 mm. wide, 

 revolute, 3-nerved, the central nerve prominent ; stipules as long as the upper 

 internodes, appressed and veiny; peduncles rigid; spikes slightly interrupted, 

 6-10 mm. long, 3-8-fruited ; fruit obliquely ellipsoidal, 2 mm. long, plump and 

 rounded on the back, the style nearly in line with the straightish ventral face. 

 (P. pusillus, var. pseudo-rutilus Benn.) Que. to e. Mass., and Mich. July- 

 Sept. Perhaps a variety of no. 25. 



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

 branching; leaves narrow-linear, acute or subacute, 2-6 cm. long, 0.5-1.5 mm. 

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

 ter-buds occasional ; stipules at first obtuse, soon deciduous ; spikes interrupted 

 or capitate, 2-10-flowered, on rather long (0.5-3 cm.) peduncles ; fruit obliquely 

 ellipsoid, scarcely keeled, 1.5-2 mm. long; apex of embryo incurved and directed 

 obliquely downward. Pools, ditches, and ponds, generally distr. July-Sept. 

 (Eurasia, Trop. Am.) Passing freely to the following varieties. 



Var. tenuissimus Mertens & Koch. Leaves setaceous, 0.2-0.5 mm. wide, 1- 

 3-nerved. Range of species. 



Var. polyphyllus Morong. A dwarf bushy-branched sterile plant, bearing 

 very abundant winter-buds. Ponds, Me. and Mass. 



Var. capitatus Benn. Internodes very long, mostly much exceeding the 

 leaves; peduncles elongate, mostly 3-6 cm. long. P. E. I. and N. S. to Sask., 

 B. C., and Ore. 



Var. Sturr6ckii Benn. Leaves obtuse, pellucid and bright green, 0.8-2 mm. 

 broad ; fruit smaller than in the species. Gasp^ Co., Que., to Ct. 



26. P. lateralis Morong. Plants of two sorts, only the fruiting producing 

 floating leaves ; stem filiform, branching ; floating leaves elliptical (0.8-1.2 cm. 

 long, 2-4 mm. wide), with 5-7 nerves deeply impressed beneath, tapering into a 

 somewhat dilated petiole; submersed leaves linear, acute (2.5-7 cm. long, 0.2- 

 0.9 mm. wide), 1-3-nerved, the midnerve with fine veins or cellular reticula- 

 tions on each side, bi-glandular at base ; stipules short, deciduous ; peduncles 

 widely spreading at maturity, sometimes even recurved, often thicker than the 

 stem ; spikes often interrupted (2-4-flowered) ; fruit obliquely obovoid (hardly 

 2 mm. long), the back much curved, with two fine grooves upon it ; embryo 

 oval in its curve, the apex nearly touching the base. Mass, and Ct. to 

 Mich. ; rare. July, Aug. Undeveloped specimens resemble no. 25. Propagated 

 by winter-buds on short lateral branches. 



27. P. Vaseyi Bobbins. Similar ; very delicate ; stem almost capillary ; 

 floating leaves obovate (0.7-1.4 cm. long, 3-6.5 mm. wide), the length of their 

 filiform petioles, with 5-9 nerves deeply impressed beneath, cross-veins distinct ; 

 submersed leaves filiform-linear, very attenuate (2.5-5 cm. long, 0.1-0.5 mm. 

 wide) and acute ; stipules scarious, long, acute ; spikes all emersed, few, in- 

 terrupted-cylindric, 3-5-flowered, on a thickish peduncle ; fruit oblique, round- 

 obovoid, compressed, slightly sharp-margined, tipped with a distinct recurved 

 style, the sides impressed and face acute ; upper portion of the embryo cir- 

 cularly incurved, its apex transverse to the fruit. Me. to Ont., s. to Ct., N. Y., 

 O., 111., and Minn., local. June-Aug. The fruiting form, with floating leaves, 

 rare ; the submerged form, bearing winter-buds, apparently much more abun- 

 dant. 



28. P. gemmiparus Robbins. Stem filiform, branching, terete, varying 

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

 with no apparent midrib, tapering to the finest point (1.5-8 cm. long), bi-glan- 

 dular at base; stipules 1.2-2.5 cm. long, obtuse, early deciduous ; spikes few (3- 

 6-flowered), interrupted, on long filiform peduncles; winter-buds very numer- 

 ous; fruit like that of P. pusillus, but flattened and impressed on the sides, very 

 rare. Slow-moving streams and still water, centr. Me. to R. I., local. Aug., 

 Sept. 



29. P. rutilus Wolfgang. Stems very slender, simple or slightly branching 

 at base ; winter-buds usually wanting ; leaves erect, narrowly linear, attenuate, 



