NAIADACEAB 303 



1. Z. palusl ris, L. Fruit somewhat compressed, sometimes 

 pedicellate ; style half the length of the fruit. 

 MARSH ZANNICHELLIA. 



Stem 6 to 15 inches long, floating. Leaves 1 to 2 or 3 inches in length. Flowers 

 green ; antfier tawny. Fruit blackish, rugged or dentate on the back. 

 Hah. Pools, and slow streams : rare. Fl. July. Fr. 



Obs. This aquatic was detected in White Clay Creek, near Avon- 

 dale, in the S. Western part of the County, in 1849, by my friend 

 EZRA MICHENER, M. D. whose attainments in Zoology, and success- 

 ful researches in Cryptogamy, and other difficult branches of Botany, 

 have placed him in the front rank of our Chester County Natural- 

 ists. 



2. Flowers perfect, on pedunculate spikes; stamens 4, opposite as many sepals. 



411. POTAflfOGE^TOtf, Tournef. 

 [Gr. Potamos, a river, and Gfiton, a neighbor; from its place of growth.] 

 Sepals rounded, valvate in the bud. Anthers subsessile, 2-celled. 

 Ovaries 4, free ; ovule ascending ; stigma subsessile. Fruit consist- 

 ing of 5 sessile fleshy or coriaceous nutlets ; seed hook-shaped. P6- 

 rennials : stems jointed, often creeping or radicating ; leaves opposite, 

 or alternate, pellucid when immersed, the upper ones sometimes 

 floating on the surface^ opaque, and coriaceous ; spikes axillary and 

 terminal ; flowers dull green. 



f Upper leaves floating, often opposite, on long petioles. 



1. P. ii at a its, L. Immersed leaves lance-linear, often imperfect; 

 floating ones elliptic-oblong, sometimes rounded or cordate at base. 

 SWIMMING POTAMOGETON. Floating Pond-weed. 



Stem 9 to 18 inches long, usually simple. Floating leaves 2 to 3 inches long ; 

 petioles 3 to 6 inches in length. Immersed leaves 2 to 6 inches long, sometimes 

 abortive, or nothing more than a petiole. Spike emerged, about an inch long, on 

 an axillary peduncle 2 to 3 inches in length. 

 Hob. Pools, and sluggish streams: frequent. Fl. July. Fr. Sept. 



f f Leaves all immersed and similar, mostly alternate. 



. P. lilcens, L. Leaves varying from lance-linear to oblong- 

 and oval-lanceolate, acute, tapering to a petiole at base; spike 

 rather long. 

 SHINING POTAMOGETON. 



Stem 2 to 4 feet long, slender, somewhat branched. Leaves netted-nerved, mem- 

 branaceous and shining, the upper ones 3 or 4 inches long, on petioles about an 

 inch in length, the lower ones often imperfect. Spike 1 to 2 inches long, the 

 flowers somewhat distant, greenish-brown ; peduncle of the spike 2 or 3 to 6 inches 

 in length. 

 Hob. Flowing streams; Brandywine: frequent. Fl. Aug. Fr. Octo. 



3. P. perfolisttus, L. Leaves oblong-ovate, mostly obtuse, 

 sessile, and clasping by a cordate base ; spike short. 

 PERPOLIATE POTAMOGETON. 



-Stem 1 to 3 feet long, numerous from the root, branching somewhat dichotom- 

 ously. Leaves about an inch long, sometimes rather acute, obscurely 5-nervedj 



