29], NAIAD ACE.E. Ruppia. 



ovoid, very shortly beaked, on elongated slender stipes. Lard and drupe-like. Seed 

 with membranous testa. Embryo ovoid, with a short cotyledon and short lateral 

 plumule. — Very slender branching herbs, growing in salt or brackish water, with 

 hliform or capillary alternate leaves, broadly sheathing at base. A single variable 

 species. 



1. R. maritima, Linn. Stems elongated, fJiform, a foot or two long or more, 

 leafy : leaves i^ to 4 inches long, with usually broadly dilated bases : flowers 2 to G 

 or 8 in a sluirt close spike : fruiting peduncles mostly very long (3 to 6 inches) and 

 contorted : fruit H lines long, the stipes 1 or 2 lines or often G to 12 lines long. — 

 Nees, Gen. iii, t. 47 ; lieichenb. Icon. Fl. Germ. vii. 10, t. 17. 



Near Santa Barbara {Mrs. Elwood Cooper) ; in Clear Lake {Bolander) ; Prussian River (Itattan) ; 

 Oregon and Wasliington Territory, on the Atlantic Coast, and in all (Quarters of the globe, ex- 

 cepting perhaps South America. 



7. POTAMOGETON, Tourn.* Pondweed. 

 Flowere perfect, in peduncled axillary spikes, with herbaceous perianth of 4 

 rounded valvate segments, 4 stamens opposite to the segments, and usually 4 sessile 

 ovaries. Anthers 2-celled, nearly sessile. Ovaries with oblique depressed nearly 

 sessile stigmas, and solitary ascending campylotropous ovules. Fruit somewhat com- 

 pressed, ovate, drupedike, with a crustaceous nutlet within. Seed with mem- 

 branous testa and strongly curved or spiral embryo. — Slender jointed and branching 

 submerged perennial acjiuatics, of fresh or brackish water, with mostly alternate linear 

 or dilated (often dimorphous) leaves, and scarious stipules, free and axillary or united 

 to the base of the leaf. Spikes enclosed in the bud, at length long-exserted. 



The largest genus of the order, of about 40 species, many of them widely distributed around the 

 globe. Of the 24 North American species one-half are jjeculiar to the continent. Mature fruit is 

 in most cases necessary for their positive determination. 



Floating leaves thick, dilated : stipules free : spikes dense. 

 Submerged leaves mostly narrowly grass-like or filiform. 



Floating leaves subcordate, mostly shorter than the petioles, the sub- 

 merged very narrow and elongated : stipules long and con- 

 spicuous : spike long : embryo nearly circular. 1. P. natans. 

 Floating leaves attenuate at base, on short petioles, the submerged 

 linear : stipules short, deciduous : sjiike 1 inch long or less : 

 embryo spiral. 2. P. Claytoxi. 

 Submerged leaves lanceolate, rarelj' oval or linear. 



Floating leaves 10 - 20-nerved ; the submerged narrow. 



Floating leaves attenuate to a very short petiole ; the submerged 



narrowly oblong-lanceolate, sessile : fruit beaked. 3. P. KFFESCEXS. 



Floating leaves abruptly narrowed to a long petiole ; submerged 

 linear-lanceolate, often elongated, the lower sessile : fruit 

 acute. 4. P. LONcmTES. 



Floating leaves small, rounded or cuneate at base, on slender 

 petioles ; submerged linear-lanceolate, short, attenuate to a 

 sessile base : fruit small. 5. P. gra.mineus. 



Floating leaves 30-50-nerved ; the submerged large, falcate, undu- 

 late, petiolate : fruit large. 6. P. AMrLiFOLius. 

 Leaves all .submerged, numerous, lanceolate to oval, mostly sessile : 

 spikes dense, on .stout peduncles. 

 Leaves oblong-lanceolate, acute or acuminate, attenuate to a very short 



petiole : fruit rounded, acute. 7. P. lucexs. 



♦ The determinations of the Californian species, and to some extent the following descriptions, 

 are from the notes of the late Du. J. W. RonniNs, who carefully .studied most of the material that 

 has been collected and at the time of his death had done much toward a revision of the western 

 species. 



