ORDER 133. NA1ADACE.E. 321 



2 N. Indlca Cham., 0. $-racillima. Stems filiform, forking ; leaves opposite and In 



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



3 N. Hex ill* Rostk. 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, Michcli. HORN PONDWEED. Fls. s , 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 

 aclicnia. z? Submersed, with filiform branches, and linear, entire leaves. 



Z. pailuHtrlw L. Stems round, leafy, 1 2f; leaves opposite, grass-like, 23' ; anther 

 4-celled ; achenia 4 6, 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. $ Anther ovoid, sessile, opening 

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

 Utricle 1-seeded. V ? 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. RUFPIA, L. DITCH-GRASS. Fls. 5 , 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. li? A grass-like plant, all 

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



1C. miiri liniii L. Stems filiform, branched, 2 5f ; leaves linear-setaceous, 2 6', on 

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



5. POTAMOGETON, Tourn. POND-WEED. Fls. 3 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. f 

 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 NOB. 9, 10 



a Leaves oval or oblong, broad and clasping at base Nos. 11 18 



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. liatans L. Subsimple ; floating Ivs. 2 3', lance-oblong, narrowly obtuse, on nlen- 



der (26') petioles ; stipules long, linear ; lower Ivs. few, linear. 2 6' ; spikes 1 2 / , 

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



2 P. flaytoni Tuckm. Simple; floating leaves lance-oblong, about 15-veined, 1 1}', 



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

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

 ft. hrtfrophf/llu*. Petioles and peduncles longer than tne leaves (23'). Mnsn. 



3 P. hybrid us MX. Stems branching, filiform ; floating Ivs. oval, 5-7-veined, 7 10" 



their petioles shorter, subopposite ; spikes and their stalks 46" ; lower Ivg. llneer 

 setaceone, 1 3', miiiiy ; fruit minute, dentate. Common. 



21 



