482 NAIADACEJ5. (PONDWEED FAMILY.) 



last; inflorescence simple; lower fertile heads usually supra-axillary, sessile or 

 peduncled; stigma linear, about the length of the style; fruit smaller, short- 

 stiped, contracted in the middle. (S. angustifolium, Miclix. S. affine, Schnitz- 

 lein; said to be the true S. natans of Linnfeus.) — Mountain lakes and slow 

 streams, New York, New England, and northward. — Heads 5" -7" wide. 

 Dwarf states, growing nearly out of water, have shorter erect leaves. (Eu.) 

 * * * Usually floating f with very slender stems and delicate altvays flat and narrow 

 leaves ; inflorescence simple, of fen) small lieads : stigma oval, about as long as 

 the short style, scarcely surpassing the oval or obovate denticulate scales : nuts oval, 

 loith a very short stipe and short point. 

 3. S. minimum, Bauhin, Fries. Fertile heads solitary or usually 2, ax- 

 illary, sessile or the lower one peduncled, fruit heads 4" -5" in diameter; nuts 

 somewhat triangular, the lower third usually contracted ; stems when out of 

 water only 5' - 6' high ; when submersed longer. (S. natans, of older authors, 

 but not of Linnaeus, according to Pries. S. angustifolium, Ed. 2.) — Northern 

 New England to Wisconsin and northward. (Eu.) 



Okder 110. NAIADACEa;. (Pondweed Family.) 



Immersed aquatic plants, with jointed stems and sheathing stipules within 

 the petioles, or with sheathing bases to the leaves, inconspicuous flowers, which 

 are naked or with a free merely scale-like calyx; the ovaries solitary or 2-4 

 and distinct, l-celled, 1-ovuled. Seed without albumen, filled by the large 

 embryo, often curved or hooked. Flowers usually bursting from a spathe, 

 sometimes on a spadix. 



# Flowers moncecious or dioecious, axillary, naked, monandrous. 



1. IVaias. Pistils solitary and naked. Srigma.s2or4 



2. Zaniiichellla. Pistils about 4 from a eup-shaped involucre or sheath. 



3. Zostera. Pistils and anthers alternately sessile in two rows OD one side of a linear spadix 



enclosed in a leaf. Stigmas 2. 



* * Flowers perfect, spiked or clustered. 



4. Rnppia. Flowers naked (no perianth), each of 4 large anther-cells, and 4 ovaries. 



5. Potamogeton. Flowers with sepals, stamens, and sessile ovaries each 4. 



1. NAIAS, L. Naiad. 



Flowers dioecious or monoecious, axillary, solitary and sessile ; the sterile con- 

 sisting of a single stamen enclosed in a httle membranous spathe : anther at 

 first nearly sessile, the filament at length elongated. Fertile flowers consisting 

 of a single ovary tapering into a short style: stigmas 2-4, awl-shaped: ovule 

 erect, anatropous. Fruit a little seed-like nutlet, enclosed in a loose and separa- 

 ble membranous epicarp. Embryo straight, the radicular end downwards. — 

 Slender branching herbs, growing under water, with opposite and linear leaves, 

 somewhat crowded into whorls, spinulose-toothed, sessile and dilated at the base. 

 Flowers very small, solitary, but often clustered with the branch-leaves in the 

 axils; in summer. (Nai'as, water-nymph; an ill-chosen name for these insig- 

 nificant water-weeds.) 



