194 NAIADACI'LE. ii'^p/^m. 



ovoid, very sliortly beaked, on elongated slender stipes, liard and dru[)e-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 

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

 species. 



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

 leafy : leaves 2 to 4 inches long, with usually broadly dilated bases : llowers 2 to G 

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

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

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



Near Santa Baibaia {Mrs. Ehcood Cooper) ; in Clear Ijoka^Bolandcr) ; Russian Itiver (7?n/<«)t) ; 

 Oregon and Wasliington Tunitory, on the Atlantic Coast, and in ail (luartuis of llie globe, ex- 

 cepting perhaps South America. 



7. POTAMOGETON, Touvn.* Pondwekd. 

 Flowers 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 ovides. Fruit somewhat com- 

 pressed, ovate, drupe-like, witli a crustaceous nutlet within. Seed with mem- 

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

 submerged perennial aquatics, 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 s|)eeies, many of them wiilely distributed around the 

 globe. Of the "24 North Ameiican species one-half are peculiar to the continent. Mature fruit is 

 in most cases necessary for their positive determination. 



Floating leaves thick, dilated : stipules free : si)ikes dense. 

 Submerged leaves mostly narrowly grass-like or liliform. 



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 i)etioles, the submerged 

 linear : stipules short, deciduous : si>ike 1 inch long or less : 

 embryo sjjiral. 2. P. Ci.aytoni. 

 Submerged leaves lanceolate, rarely 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. khfescexh. 



Floating leaves abruptly narrowed to a long ])etiole ; submerged 

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

 acute. 4. P. LONcurrKs. 



Floating leaves small, ronndeil or cuneate at ba.se, on slender 

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

 .sessile base : fruit small. 5. P. oiiamineiis. 



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

 late, jtetiolate : fruit large. 6. P. AM1'I.IK0LIU.S. 

 Leaves all submerged, innnerous, lane<'olate to oval, mostly sessile : 

 spikes dense, on stout ])ednneles. 

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



]ietiole : fruit rounded, acute. 7. P. M'cENS. 



» The determinations of the Californian species, and to some extent the fcdlowing descriptions, 

 are from the notes of the late [)i;. ,1. "W. RoiuiiNs, 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. 



