NA1ADACEAE. 45 



13. Potamogeton lucens L. Shining Pondweed. (I. F. f. 154.) Stem thick, 

 branching below and often with masses of short leafy branches at the summit. Leaves 

 all submerged, elliptic, lanceolate or the uppermost oval, shining, sessile or short- 

 petioled, 6-20 cm. long, 1.5-4 cm. wide, the tips oiten serrulate ; stipules 2-carinate, 

 sometimes very broad ; peduncles 7- 15 cm. long ; spikes 5-6 cm. long, very thick ; 

 fruit about 3 mm. long and 2.5 mm. thick, roundish, the face usually with a slight 

 inward curve at the base ; apex of the embryo pointing transversely inward. In 

 ponds, N. S. to Fla., west to Cal. and Mex. Local. Also in Europe. Sept. -Oct. 



Potamogeton lucens Connecticut(5nsis Robbins. Stems flexuous ; leaves acuminate ; 

 fruit larger than that of the type (about 4 mm. long), distinctly 3-carinate and with a 

 facial style. Saltonstall's Pond, Conn., and White Plains, N. Y. 



14. Potamogeton praelongus Wulf. White-stemmed Pondweed. (I. F. f. 

 155.) Stems white, flexuous, flattened, much branched, growing in deep water, 

 sometimes 2.6 m. long. Leaves all submerged, oblong or oblong-lanceolate, semi- 

 amplexicaul, bright green, 1— 3.5 cm. long, 5-30 cm. wide, with 3-5 main nerves; 

 stipules white, scarious, obtuse and commonly closely embracing the stem ; 

 peduncles 7-50 cm. long, erect, straight, about as thick as the stem; spikes 2-5 

 cm. long, thick, cylindric; fruit dark green, obliquely obovoid, 4-5 mm. long, 3-4 

 mm. thick, the back much rounded, often with the upper curve nearly as high as 

 the style; the middle keel sharp ; style short, obtuse, facial. N. S. to Br. Col., 

 N. J., Minn, and Cal. Also in Europe. June-July. 



15. Potamogeton perfoliatus L. Clasping-leaved Pondweed. (I. F. f. 

 156.) Stems slender, much branched. Leaves all submerged, orbicular or ovate, 

 sometimes lanceolate, usually obtuse and minutely serrulate at the apex, cordate- 

 perfoliate at the base, 3-5 cm. long, 0.5-2.5 cm. wide; peduncles 3.5 cm. long, 

 usually erect or slightly spreading; spikes 1.5-2.5 cm. long; fruit obliquely 

 obovoid, 2.5-3 mm. long, 2 mm. thick, obscurely 3-carinate on the back, the face 

 slightly curved outwardly toward the top, the sides with a shallow indentation 

 which runs into the face; style nearly facial; embryo slightly incurved or with its 

 apex pointing directly toward the base. In ponds and streams, Newf. to Br. Col., 

 Fla., and Cal. Also in Europe and Asia. July-Sept. 



Potamogeton perfoliatus Richards5nii A. Bennett. Leaves 2-12 cm. long, 8-16 

 mm. wide at the broadened amplexicaul base, often curving inward at the apex, 13-23- 

 nerved. Fruit somewhat larger than that of the type, about 4 mm. long and 2.5 mm. 

 thick. N. N. E. to Or., Del., Neb., and Cal. 



16. Potamogeton M^sticus Morong. Mystic Pond Pondweed. (I. F. f. 

 157.) Whole plant very slender and delicate, stems irregularly branching above, 

 nearly filiform, terete, 0.3-3.3 m - l° n g« Leaves all submerged, scattered oblong- 

 linear, 2-4 cm. long, 2-6 mm. wide, 5-7-nerved, obtuse and rarely with minute 

 serrulations near the apex, abruptly narrowed at the base and sessile or partly 

 clasping; stipules obtuse, about 12 mm. long, hyaline and with many fine nerves, 

 mostly deciduous, but sometimes persistent and closely sheathing the stem; spikes 

 few, capitate, 4-6-fiowered, borne on erect peduncles 2-5 cm. long; immature fruit 

 obovoid, less than 2 mm. long, about I mm. wide, obscurely 3 -keeled on the back, 

 slightly beaked by the slender, recurved style. Mystic Pond, Medford, and 

 Miacount Pond, Nantucket, Mass. Aug. -Sept. 



17. Potamogeton confervoides Reichb. Alga-like Pondweed. (I. F. f. 

 158.) Stems slender, terete, 15-45 cm. long, the upper branches repeatedly 

 forking. Leaves very delicate, flat, setaceous, 2-6 cm. long, the broadest scarcely 

 0.5 mm. wide, tapering to a long hair-like point, 1-3-nerved and often with a few 

 cross-veins; stipules delicate, obtuse, 4-6 mm. long; peduncles 5-20 cm. long, erect, 

 somewhat thickened upward; spikes 6-8 mm. long; fruit roundish -obovoid, 2-3 mm. 

 long and about as thick, the back sometimes a little angular or sinuate, 3-keeled, 

 the middle keel sharp, the face notched near the base, the sides impressed with a 

 shallow indentation which runs into the notch of the face ; apex of the embryo 

 nearly touching the base a little to one side. In cold or mountain ponds, Me. and 

 >". II. to N, J. and Penn. Also in Europe. Aug.-Sept. {P. Tuckermani Robbins.) 



