452 NAIADACEJE. (PONDWEED FAMILY.) 
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. 
Synopsis« 
* Flowers monoecious or dioecious, axillary, naked, monandrous. 
1. Naias. Pistils solitary: stigmas 2-4. 
2. Zannichellia. Pistils about 4 from a cup-shaped involucre. 
3. Zostera. Pistils and anthers alternately sessile in 2 rows on one 
side of a linear spadix, inclosed in a leaf. Stigmas 2. 
* * Flowers perfect. 
4. Ruppia. Flowers naked on a spadix: each of 4 large anther- 
cells, and 4 ovaries which are raised on long stalks in fruit. 
5. Potamogeton. Flowers and fruit spiked, 4-sepalled. Stamens 
4. Ovaries 4. 
i. rAias, l. Naiad. 
Flowers dioecious (or sometimes monoecious), axillary, solitary 
and sessile ; the sterile consisting of a single stamen inclosed in a 
little membranous spathe : anther at first nearly sessile, the fila¬ 
ment 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, inclosed 
in a loose and separable membranous epicarp. Embryo straight? 
the radicular end downwards. — Slender branching herbs, grow¬ 
ing entirely under water, with opposite and whorled-crowded 
linear leaves, sessile and dilated at the base. Flowers very small, 
solitary, but often clustered with the branch-leaves in the axils. 
(Naias-, water-nymph; a name inaptly applied to these humble 
water-weeds, from their place of growth.) 
1. flexilis, Rostk. Leaves membranaceous, spreading, nar¬ 
rowly linear, sparingly very minutely denticulate (under a lens) as 
well as the sheathing base; stigmas usually 3-4. (N. Canadensis, 
Michx. Caulinia flexilis, Willd.) — Ponds and slow streams, common. 
July-Sept. —Stem 6>-20' long, many times forked. Leaves less 
than 1" wide. 
N. minor (Caulinia fragilis, Willd .), with the more rigid and re¬ 
curved fragile leaves rather strongly toothed, I have not seen in this 
country. 
