So 



ZANNICHELLIACEAE. 



Vol. I. 



14. Potamogeton praelongus Wulf. White-stemmed Pondweed. Fig. 187. 



Potamogeton praelongus Wulf. in Roem. Arch. 3 : 



331- 1805. 



Stems white, flexuous, flattened, much branched, 



growing in deep water, sometimes 8° long. Leaves 



all submerged, oblong or oblong-lanceolate, semi- 



amplexicaul, bright green, 2'-i2' long, i'-ii' wide, 



with 3-5 main nerves, stipules white, scarious, 



obtuse and commonly closely embracing the stem; 



peduncles 3-20' long, erect, straight, about as thick 



as the stem ; spikes i'-2' long, thick, cylindric ; 



fruit dark green, obliquely obovoid, 2"-2$" long, 



ll"-2" thick, the back much rounded, often with 



the upper curve nearly as high as the style; the 



middle keel sharp ; style short, obtuse, facial. 



Nova Scotia to British Columbia, south to New 

 Jersey, Minnesota and California. Also in Europe. 

 Fruits in June and July, and usually withdraws its 

 stems beneath the water as soon as the fruit is set. 



15. Potamogeton perfoliatus L. 



Potamogeton perfoliatus L. Sp. PI. 126. 1753- 

 Potamogeton perfoliatus lanceolatus Robbins in A. Gray, 



Man. Ed. 5, 488. 1867. Not Blytt 1861. 

 Potamogeton perfoliatus Richardsonii A. Bennett, Journ. 



Bot. 27 : 25. 1889. 

 Potamogeton Richardsonii Rydb. Bull. Torrey Club 32 : 



599. 1905. 

 Potamogeton bupleuroides Fernald, Rhodora 10 : 46. 1908. 



Stems slender, much branched. Leaves all sub- 

 merged, orbicular or ovate, sometimes lanceolate, 

 obtuse or acutish and minutely serrulate at the apex, 

 cordate-perfoliate at the base, s"-2o" long, 3"-i2" 

 wide; peduncles ii' long, usually erect or slightly 

 spreading; spikes 8"-i2" long, often flowering and 

 fruiting under water; fruit obliquely obovoid, ii"-2" 

 long, ii" 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, Newfoundland to British Co- 

 lumbia, south to Florida and California. Also in Europe and Asia. 



Clasping-leaved Pondweed. Fig. 188. 



July-Sept. 



16. Potamogeton mysticus Morong. Mystic Pond 

 Pondweed. Fig. 189. 



Potamogeton mysticus Morong, Coult. Bot. Gaz. 5 : 50. 1880. 



Whole plant very slender and delicate, stems irregularly 



branching above, nearly filiform, terete, i°-4° long. Leaves 



all submerged, scattered, oblong-linear, i'-ij' long, i"~z" 



wide, 5-7-nerved, obtuse and rarely with minute serrula- 



tions near the apex, abruptly narrowed at the base and 



sessile or partly clasping; stipules obtuse, about 6" long, 



hyaline and with many fine nerves, mostly deciduous, but 



sometimes persistent and closely sheathing the stem ; spikes 



few, capitate, 4-6-flowered, borne on erect peduncles i'-2' 



long; immature fruit obovoid, less than 1" long, about i" 



wide, obscurely 3-keeled on the back, slightly beaked by 



the slender, recurved style. 



Mystic Pond, Medford, and Miacount Pond, Nantucket, 

 Mass. Aug.-Sept. Apparently a depauperate form of the 

 preceding, and scarcely distinct from it. Perhaps a hybrid. 



