naiadEjE. 493 



3. Shining Pond^reed. Potamogeton lucens, Linn. 

 (Eng. Bot. t. 376. P. longifolms, Eng. Bot. Suppl. t. 2847.) 



A large species, the leaves usually all thin and under water, sessile or 

 nearly so, tapering at both ends or scarcely obtuse, 2 or 3 to near 6 inches 

 long, seldom above half an inch broad, marked with 2 or 3 well-defined 

 longitudinal nerves on each side of the midrib, besides several intermediate 

 fainter ones, and a few transverse reticulations. Flowers as in the broad P. 



In ponds and rivers, usually rather deep, generally distributed over the 

 globe, except the extreme north. Not uncommon in Britain. Fl. summer. 

 A variety with the upper leaves floating on the surface and shortly stalked, 

 either lanceolate or oblong, has been distinguished under the name of P. 

 riifescens (P. Jluitayis, Eng. Bot. t. 1286). The lanceolate P. (P. Ian- 

 ceolatus, Eng. Bot. t. 1985) appears to be a smaller state of the same 

 species, which is always to be distinguished from the broad P. and the 

 various-leaved P. by the sessile, many-nerved lower leaves. 



4. Iiong Pond-^eed. Potamogeton prselongus, Wulf. 

 (Eng. Bot. Suppl. t. 2858.) 



A large species, with the leaves all submerged and thin, with numerous 

 longitudinal veins, and a few transverse reticulations, like the shining P., but 

 the leaves are broader, all closely sessile, and half-clasping the stem by their 

 rounded base, usually 3 or 4 inches long, obtuse at the tip, and concave, so 

 as to split in drying. Stipid.es very prominent. Peduncles long and stout, 

 with the flowers and fruits usually larger than in the broad P., in a rather 

 close spike. 



In pools and rivers, generally distributed over the globe, except the ex- 

 treme north. In Britain, not so common as the shining P. Fl. summer. 



5. Perfoliate Pondvtreed. Potamogeton perfoliatus, Linn. 

 (Eng. Bot. t. 168.) 



Leaves all submerged, thin and many-nerved as in the long P. and the 

 shining P., but much shorter, usually ovate, obtuse, completely clasping 

 the stem; the auricles often united on the opposite side, so that the leaf 

 appears to be pierced through; from 1 to IJ inches long by fidl an inch 

 broad. Stipules as in the preceding species, but soon disappearing. Spike 

 of flowers seldom above 6 or 8 lines long. 



In rivers and ponds, aU over the nortliem hemisphere, and in Australia. 

 Generally distributed in Britain. Fl. summer. 



6. Curly Pond'weed. Potamogeton crispus, Linn. 

 (Eng. Bot. t. 1012, the leaves too much lobed.) 



One of the most marked of the alternate-leaved species. Leaves all sub- 

 merged and thin, narrow-oblong or broadly linear, obtuse, shortly tapering at 

 the base, 1 to 2 inches long, 3 to 5 hues broad, always waved and siuuated 

 on their edges, and marked by 1 strong midrib and 2 parallel slender nerves 

 at some distance from it, but connected with it by a few transverse vems. 

 Spikes small, consisting of about 3 to 6 flowers, at some distance fi-om each 

 other. 



In ponds, streams, and ditches, throughout Europe and central and 

 Russian Asia, except the extreme north. Common in Britam. Fl. summer. 



2T7 



