ORDER 133. NAIADACE^E. 321 



2 N. Iiidica Cham., ft. srracilllma. Stems filiform, forking ; leaves opposite and iu 



3's, very narrowly linear, remotely epinulous-serrate. N. Y. and Pa. (Porter). 



3 N. flexilis Eostk. Leaves narrowly linear, in 3's, 4's, and 6's, minutely serrulate, as 



well as their abruptly-widened sheathing base, 3 12''. Ponds : common. 



2. ZANNICHELLIA, Micheli. HORN PONDWEED. Fls. .9 , both kinds 

 together in the same axil. $ Sta. 1, with a slender fil. ? Cal. of 1 sepal, 

 cor. 0. Ova. 4 or more, each with a style and stig. Fr. 4 or more oblique 

 achcnia. ? Submersed, with filiform branches, and linear, entire leaves. 



Z. paliistris L. Stems round, leafy, 1 2f ; leaves opposite, grass-like, 2 3' ; anther 

 4-celled ; achenia 46, toothed on the back. Pools and ditches : rare. 



3. ZOSTERA, L. SEA WRACK. Spadix linear, leaf-like, bearing the 8 

 fls. in 2 rows on one side. Perianth 0. 3 Anther ovoid, sessile, opening 

 lengthwise, with hair-like pollen. $ Ova. as long as the anther, style bifid. 

 Utricle 1-seeded. if. ? Stipules united into a sheath. Leaves grass-like. 

 Z. marina L. Rhizome creeping, sending up long simple stems ; Ivs. alternate, rib- 

 bon-like, 1 5f long ; spadix 2', in a spathe at base of a leaf. Grows in the sea, along 

 shore, Me. to Ga., and is washed up by the waves. 



4. RUPPIA, L. DITCH-GRASS. Fls. 9 , 2 together on a spadix arising 

 from the sheath of a leaf. Perianth 0. Anthers 2, large, sessile, 2-celled. 

 Ovaries 4, fruit 2 4 dry drupes on pedicels, if, x? A grass-like plant, all 

 submersed but the flowers. Flower-stalk at length very long. 



R. maritima L. Stems filiform, branched, 2 5f ; leaves linear-setaceous, 2 6', on 

 inflated sheaths ; flowers arising to the surface. Seas, and lakes (Hankeneon), E. 



5. FOTAMOGETON, Tourn. POND-WEED. Fls. $ on a spadix aris- 

 ing from a spathe. Cal. 4-sepalled. Anth. 4, alternate with sepals. Ova. 4. 

 Ach. 4, sessile, flattened on one or two sides. Seeds curved or coiled. , v 

 Mostly U , only the spadix with its 3 10 small green fls. arising to the sur- 

 face of the water. Lvs. stipulate, the upper often opposite. Fr. July, Aug. 



Leaves of two kinds, the floating oval-elliptical, coriaceous, petiolate ; 

 stipules free from the petiole, connate ; submersed leaves thin.. .(*) 



* Submersed leaves linear or reduced to mere petioles Nos. 1 4 



* Submersed leaves lanceolate, rarely lance-linear Nos. 5 8 



Leaves all similar, submersed, mostly thin and membranous., .(a) 



a Leaves lanceolate or lance-oblong, petiolate or merely sessile Nos. 9, 10 



a Leaves oval or oblong, broad and clasping at base Nos. 1113 



a Leaves linear or setaceous. x Stipules 0, or adnate to the leaf Nos. 14, 15 



x Stipules free. y Stems flat Nos. 16, 17 



y Stems filiform Nos. 1820 



1 P. uataiis L. Subsimplc ; floating Ivs. 23', lance-oblong, narrowly obtuse, on nlen- 



der (26') petioles ; stipules long, linear ; lower Ivs. few, linear, 26' ; spikes 12', 

 on thick peduncles much longer ; fruit turgid, 3-keeled. Ponds and ditches. 



2 !* Clayton! Tuckm. Simple; float ing leaves lance-oblong, about 15-veined, 1 1$', 



longer than their petioles, opposite ; lower Ivs. linear, 3- veined, 3 6'x 1", spikes and 

 their peduncles near 1' ; fruit orbicular, 3-keeled. Streams and ponds : common. 

 ft. htttroph(i\l\i*. Petioles and peduncles longer than me leaves (23'). Mass. 



3 f t liybritlus MX. Stems branching, filiform ; floating Ivs. oval, 5-7-veined, 7 10" 



their petioles shorter, subopposite ; spikes and their stalks 4 6''; lower Ive. linear- 

 setaceous, 1 3', many ; fruit minute, dentate. Common. 



21 



