48 FLORA. 



Potamogeton pusfllus polyph^llus Morong. Stem 7-14 cm. long, divaricately 

 branching from the base and very leafy throughout ; leaves very obtuse, 3-nerved. Plant 

 not known- to flower, but abundantly provided with propagating buds which are 

 thickened, hardened and closely invested with imbricated leaves. E. Mass. 



Potamogeton pusillus Sturrockii A. Bennett. A rare form with delicate bright green 

 pellucid leaves, 2-8 cm. long, obtuse or often apiculate at the apex, less than 2 mm. wide, 

 sometimes 5-nerved ; fruit much smaller than that of the type, short-beaked. E. Mass. 

 Also in Europe. 



28. Potamogeton gemmiparus (Robbins) Morong. CAPILLARY PONDWEED. 

 (I. F. f. 169.) Stems filiform, terete, branching, 0.1-1.3 m - l n g- Leaves capil- 

 lary, sometimes not as wide as the stem, often with no perceptible midrib, taper- 

 ing to the finest tip, 2-8 cm. long, 2 -glandular at the base; stipules 1-2.5 cm. long, 

 mostly deciduous; spikes interrupted, 3-6-flowered; peduncles filiform, or some- 

 times slightly thickened, 1-5 cm. long; fruit seldom formed, similar to that of P. 

 pusillus, except that it is flatter and somewhat impressed on the sides. In ponds, 

 E. Mass, and R. I. It is commonly propagated by its abundant buds; the leaves 

 and stems are often alike in thickness, so that the plant seems to consist of threads. 

 Aug. -Sept. 



29. Potamogeton diversifolius Raf. RAFINESQUE'S PONDWEED. (I. F. f. 

 170.) Stems flattened or sometimes terete, much branched. Floating leaves coria- 

 ceous, the largest 2.5 cm. long by 1.2 cm. wide, oval or elliptic and obtuse, or lan- 

 ceolate-oblong and acute; petioles filiform or dilated; submerged leaves setaceous, 

 seldom over 0.5 mm. wide, 2-8 cm. long; stipules obtuse or truncate, 6-10 mm. 

 long, those of the floating leaves free, those of the submerged leaves sometimes 

 adnate; emersed peduncles 6-14 mm. long; submerged peduncles 4-6 mm. long, 

 clavate, as long as the spikes; emersed spikes 6-io mm. long, occasionally inter- 

 rupted; fruit cochleate, rarely over I mm. long, 3-keeled, the middle keel narrowly 

 winged and usually with 7 or 8 knob-like teeth on the margin, the lateral keels 

 sharp or rounded; embryo coiled l^ times. In still water, Me. to Fla., west to 

 Neb. and Tex. June -Sept. 



Pomategon diversifblius multidenticul&tus Morong. Differs from the type in the 

 numerous teeth of the fruit, as many as 12 being sometimes found on the middle keel, 

 and each lateral keel with 6-8 more, the teeth often bristle-like and sometimes 2-pronged. 

 Conn, to E. Penn. and Del. 



Potamogeton diversifblius trichoph^llus Morong. Plant about 15 cm. long, with- 

 out floating leaves, the submerged leaves as fine as floss silk and entirely nerveless. 

 Lake Marcia, N. J. 



30. Potamogeton Spirillus Tuckerm. SPIRAL PONDWEED. (I. F. f. 171.) 



Stems compressed, branched, 15-50 cm. long, the branches often short and re- 

 curved. Floating leaves oval or elliptic, obtuse, the largest about 2.5 cm. long and 

 1.2 cm. wide, with 5-13 nerves deeply impressed beneath, their petioles often 2.5 cm. 

 long; submerged leaves linear, 34 mm. long, about I mm. wide, mostly 5-nerved; 

 stipules of the upper floating leaves free; those of the submerged leaves adnate to 

 the blade or petiole; spikes above water 6-10 mm. long, continuous, the lower 

 mostly sessile, capitate and i-io-fruited; fruit cochleate, roundish, less than 2 mm. 

 long, flat and deeply impressed on the sides, 3-keeled on the back, the middle keel 

 winged and sometimes 4-5 -toothed ; style deciduous ; embryo spiral, about \\ 

 turns. In ponds and ditches, N. S. and Ont. to Minn., south to Va., Mo., and 

 Neb. June-Aug. 



31. Potamogeton filiformis Pers. FILIFORM PONDWEED. (I. F. f. 172.) 

 Stems from a running rootstock, slender, 17 m. long, filiform above, stout and 

 thick toward the base. Leaves numerous, 5-30 cm. long, 0.5-1 mm. wide, 

 i-nerved with a few cross veins; sheaths about 2 mm. long and the free part of the 

 stipule 12 mm. long, scarious on the edges ; flowers on long, often recurved 

 peduncles, 2-12 in each whorl; fruit 2-3 mm. long, slightly less than 2 mm. wide, 

 the sides even, the back not keeled, the face nearly straight or obtusely angled 

 near the top; stigma nearly or quite sessile, remaining on the fruit as a broad 

 truncate projection. In ponds and lakes, Anticosti to W. N. Y. and Mich. August. 



