44 FLORA. 



at the apex, narrowed at the base, often strikingly like those of P. spatlmlaeformis, 

 5-9 cm. long, 15-25 mm. wide, I3~i7-nerved, petioled; submerged leaves oblong- 

 lanceolate, acute or sometimes obtuse, 7-13 cm. long, 1-25 cm. wide, 5~i3-nerved, 

 often with an irregular areolation on each side of the midrib; petioles 1.22.5 cm. 

 in length; peduncles slightly thicker than the stem; spikes dense, 2-5 cm. long; 

 fruit not collected. Little Otter Creek and Lake Champlain, Ferrisburg, Vt. 



?. Potamogeton heterophyllus Schreb. VARIOUS-LEAVED PONDWEED. 

 '. f. 150.) Stems slender, compressed, much branched, sometimes 4 m. long. 

 Floating leaves pointed at the apex, mostly rounded or subcordate at the base, 1.5 

 lo cm. long, 8-30 mm. wide, lo-l8-nerved, on petioles 2-10 cm. long ; submerged 

 leaves pellucid, sessile, linear-lanceolate, acuminate, cuspidate, rather stiff, 2-15 

 cm. long, 2-16 mm. wide, 3~9-nerved, the uppermost often petioled ; peduncles 

 often thickened upward, sometimes clustered; stipules spreading, obtuse 1.5-2.5 

 cm. long; spikes 1.825 cm. long; fruit roundish or obliquely obovoid, 23 mm. 

 long, 1-2 mm. thick, indistinctly 3-keeled ; style short, obtuse, apical ; apex of the 

 embryo nearly touching the base, pointing slightly inside of it. A very variable 

 species, occurring in different forms throughout almost all N. Am. except the extreme 

 north. Also in Europe. July-Sept. 



Potamogeton heterophyllus graminifolius (Fries) Morong. Submerged leaves deli- 

 cate, flaccid, linear, 4-12 cm. long, 2-6 mm. wide With the type. 



Potamogeton heterophyllus myriophyllus (Robbins) Morong. Stems dichotomously 

 branching, very leafy ; submerged leaves delicate, about 2.5 cm. long and 4 mm. wide, 3-5- 

 nerved, linear or the upper oblanceolate ; floating leaves elliptic or lanceolate-oblong ; 

 rootstock tuberous. Mass., R. I. and Conn. 



Potamogeton heterophyllus minimus Morong. Stems long and almost capillary, 

 the internodes 7-10 cm. long, densely clustered on short lateral branches, 1-2.5 cm - l n g> 

 scarcely 0.5 mm. wide, acuminate, i-nerved ; floating leaves 1-3.5 cm - l n &i 6-18 mm. 

 wide, lanceolate, oval or ovate, usually clustered at the summit of the stem. Mass, and 

 N. H. 



10. Potamogeton spathulaeformis (Robbins) Morong. SPATULATE-LEAVED 

 PONDWEED. (I. F. f. 151.) Stems many, branched, 0.6-1 m. long. Floating leaves 

 obovate or elliptic, abruptly acute at the apex, rather thin, 13-23-nerved, 2-6 cm. long, 

 1.52.5 cm. wide, borne on slender petioles; submerged leaves pellucid, spatulate- 

 oblong or linear-lanceolate, 5~* cm - l n g> 6 i8mm. wide, 5 13-nerved, cuspidate or 

 spinescent, sessile or subsessile, often reduced to phyllodes with a very narrow blade 

 and a long acumination at the base and apex; peduncles often thickening upward, 

 2-5 cm. long ; stipules obtuse, faintly keeled, the apex slightly hooded ; spikes 

 large ; fruit about 2 mm. long, roundish or obliquely ovoid, obscurely 3-keeled, with 

 a curved or slightly angled face ; embryo with the apex pointing slightly inside of 

 the base. In Mystic Pond, Medford, Mass. Also in Europe. Summer. 



xi. Potamogeton Illinoensis Morong. ILLINOIS PONDWEED. (I. F. f. 

 152.) Stem stout, much branched above. Floating leaves opposite, numerous, 

 thick, 10-14 cm. long, 5-9 cm. wide, many-nerved' oval or broadly elliptic, short- 

 pointed, petioled ; submerged leaves numerous, 10-20 cm. long, 2-5 cm. wide, 

 13-19-nerved, acuminate or the uppermost acute, mostly tapering at the base into a 

 short, broad, flat petiole, rarely reduced to phyllodes ; stipules 5^8 cm. long, obtuse, 

 strongly 2-carinate ; peduncles 5-10 cm. long ; spikes 2-5 cm. long ; fruit roundish 

 or obovoid, 3-4 mm. long, 2-3 mm. thick, dorsally 3-keeled ; style short, blunt. In 

 ponds, 111. to la. and Minn. Aug. 



12. Potamogeton Zizii Roth. Ziz's PONDWEED. (I. F. f. 153.) Stems 

 slender, branching. Floating leaves elliptic, 4-10 cm. long, 1-2.5 cm - wide, many- 

 nerved ; petioles mostly short ; submerged leaves mostly lanceolate or oblanceolate, 

 thin, acute or cuspidate, 5-15 cm. long, 6-30 mm. wide, 7-17-nerved ; stipules 

 obtuse, 2-keeled ; peduncles thicker than the stem, 6-15 cm. long ; spikes 2-5 cm. 

 long ; fruit obliquely obovoid, 2.5-4 mm. long, about 2 mm. thick, the face dorsally 

 3-keeled ; style short, blunt, facial ; apex of the embryo pointing directly to the 

 base. In lakes and streams, Que. to Mont., Fla. and Wyo. Also in Europe. 

 July-Aug. 



Potamogeton Zizii Methy^nsis (A. Benn.) Morong. Middle leaves narrow ; upper 

 leaves oval ; stipules long ; fruit small. Methy Lake, Can. 



