482 NAIADACE^.. (PONDWEED FAMILY.) 



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

 pedundctl ; stiiinia line:ir, about the length of the style; fruit smaller, short- 

 stipcd, contracted in the middle. (IS. anLjustii'olium, Mic/tx. S. affiiie, Schnitz- 

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

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

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

 • * * Usually flouting, with venj slender stems and delicate alwaj/sflat and narrow 

 leaves: inflortscence simple, of flto small heads: stifjma oval, about as long as 

 the short style, scared y surpassing the oval or olmvate denticulate scah s : nuts oval, 

 loith a very short stipe and short jwint. 

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

 illary, sessile or the lower one pedunded, 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 Linnieus, according to Fries. S. angustifolium, Ed. 2.) — Northern 

 New England to Wisconsin and iiortiiward. (Eu.) 



OrDF.U 110. NAIADACE.I:. (PONDWEI^D FaMII.Y.) 



Immersed aquatic plants, u-ilh Jointed stems and sheathing stipules within 

 ' the petioles, or with sheathing bases to the leaves, inconspicuous flowers, tohich 

 are naked or with a free merely scale-like calyx: (he ovaries solitary or 2-4 

 and distinct, 1-celled, 1-ovuled. Seed -withGut albumen, filled by the large 

 embryo, often curved or hooked. Flowei-s usually bursting from a spatbe, 

 sometimes on a spadix. 



* Flowers monoecious or dioecious, iixillary, naked, nionandrous. 



1. Nnias. Pistils solitary and n.aked. Siigaias2or4 



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



3. Zoslcro. Pistils and anthers alternately sessile in two rows on one side of a lincarspadis 



enclo.sed 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. 

 6. Potamogetoii. Flowers with sepals, stamens, and sessile ovaries each 4. 



1. NAIAS, L. Naiad. 



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

 tisting 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 sejjara- 

 blc membranous cpicarp. Embryo straight, the radicular end downwards. — 

 Slender branching herbs, growing under water, with o])j)osite 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. (Naids, water-nymph; au ill-chosca uame for these insig- 

 nificant water- weeds.) 



