524 OXXXVIL NAIADACE^E. POTAMOGETON. 



more) ; filament slender, often elongated ; anther 4-valved, valves 

 spreading. 9 Perianth j style filiform ; stigma 2 3-fid ; capsule 

 1 -seeded. Fls. axillary. 



N. CANADENSIS. Michx. (Caulinia flexilis. Willd. Fluvialis flexilis. 

 Pers.) Water Nymph. St. filiform, coespitose, dichotomously branching ; 

 Ivs. opposite or fasciculate in 3s, 4s or 6s, at the nodes, linear, obscurely denticu- 

 late, spreading, 1-veined. A slender, flexible, rather erect, submersed aquatic 

 plant, Can. to N. J. and W. States, consisting of tufts of thread-like, knotted 

 stems 6 12' long. Leaves 1' long, i" wide, sessile and sheathing at base. 

 Flowers solitary, sessile, axillary, very small, the fertile ones consisting of an 

 oblong ovary tipped with a filiform style, with 2 3 stigmas at summit. Aug. 

 ft. (Caulinia fragilis. Willd.) St. arid Ivs. rather rigid, the latter mostly 

 opposite and recurved. 



3. ZANNICHELLIA. 



In honor of Zannichelli, an eminent botanist of Venice. 



Flowers c?. cT Stamen 1 ; filament elongated. 9 Calyx mono 

 phyllous 5 corolla j ovaries 4 or more, each with a single style and 

 stigma, and becoming in fruit an oblong, incurved, subsessile acheniuin. 



Z. PALUSTRIS. Horn Pond-weed. 



St. filiform, floating ; Ivs. opposite, linear ; a?ith.' 4-ce\\ed ; stig. entire ; ach. 

 toothed on the back. In pools and ditches, N. States. Stem found, smooth, 

 1 2f long, branching, leafy. Leaves grass-like, 2-^-3' long, sessile. Flowers 

 issuing from axillary bracts, small, 2 together, a sterile and fertile, the former 

 consisting of a single, naked, erect, yellowish-brown stamen, the latter of 4 G 

 ovaries which are free from the inflated, one-sided, 2 3-toothed calyx. Jl. Aug. 



4. RUPPIA. 



In honor of Ruppi, a German botanist. 



Flowers $ , 2 together on a spadix or spike arising from the sheath- 

 ing base of the leaves ; perianth ; stamens 4, sessile : ovaries 4, 

 pedicellate, becoming in fruit 4 dry drupes or achenia. Root TJ-. 



R. MARIT1MA. 



A grass-like plant, in salt marshes, Mass. Stems several feet long, fili- 

 form, branched, floating. Leaves 1 2f long, linear and setaceous, with inflated 

 sheaths at base, all immersed. The common peduncle is contorted and spiral, 

 and by winding and unwinding bears the naked, green flowers on the surface 

 of the water as it rises or falls. July. 



5. POTAMOGETON. 



Gr. Trorctyiof, a river, yetrcoj', near. 



Flowers $ , on a spadix or spike arising from a spathe ; calyx 4- 

 gepaled ; anthers 4, alternate with the sepals ; ovaries 4 ; achenia 

 4, sessile, flattened on one or two sides. Mostly Q, aquatic and sub- 

 mersed, only the flowers arising above the surface of the water. Spadix 

 (or spike) pedunculate, 3 IQ-flowered. Lvs. stipulate, parallel-veined, 

 lower alternate, the upper (mostly) opposite. Fls. small, greenish. 



1. Leaves of two forms, the upper floating. 



1. P. NATANS? (P. pulcher. Tuckerman.) Broad-leaved Pond-weed. 



Floating; los. coriaceous, oblong, or elliptic-ovate, acute or obtuse or cor- 

 date at base, on long petioles, submersed ones linear-lanceolate, membrana- 

 ceous, elongated, attenuated to petioles at base, lowest reduced to mere petioles, 

 all stipulate; spikes rather dense, shorter than the peduncles ; fr. somewhat 

 semi-globose, roughish, more or less carinate at the back. A very common 

 species, in slow waters or ponds, N. Eng. ! to Wise., Lapham! Stem slender, 



