482 NAIAD AC E^E. ( POND WE ED 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. 3. affiue, Schnitz- 

 lein; said to be the true S. natans of Linnasus.) — 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, with 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, Bauhin, Eries. 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 tisually contracted ; stems when out of 

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

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

 New England to Wisconsin and northward. (Eu.) 



Order 110. NAIADACE2E. (Pondv> t eed 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. Naias. Pistils solitary and naked. Stigmas 2 or 4 



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

 6. 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 

 listing 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-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. (Naias, water-nymph; an ill-chosen name for these insig- 

 nificant water-weeds.) 



