482 NAIADACEiE. (POXDWEED 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, Michx. S. affiue, Schnitz- 

 lein; said to be the true S. natans of Linnaeus.) — 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, ivith very slender stems and delicate always flat and narrow 

 leaves : inflorescence simple, of few small heads : stigma oval, about as long as 

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

 with a very short stipe and short point. 

 3. S. minimum, Ba&hin, 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 Linnams, according to Fries. S. angustifolium, Ed. 2.) — Northern 

 New England to Wisconsin and northward. (Eu.) 



Order 110. NAIADACE2E. (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, 1-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 monoecious or dioecious, axillary, naked, monandrous. 



1. Nnias. Pistils solitary and naked. Stigmas 2 or 4 



2. Zannichellia. Pistils about 4 from a cup-shaped involucre or sheath. 



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



enclosed in a leaf. Stigmas 2. 



* # Flowers perfect, spiked or clustered. 



4. Ruppla. 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 little 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-shapcd : 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 liasc. 

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

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

 nificant water-weeds.) 



