424 THE NAIAD FAMILY. [Naias. 
inear, usually in whorls of 3, or sometimes opposite, often clustered in the 
axils, about 6 or 8 lines long; the teeth few and very minute, Stigmas 
usually 3, sometimes 4. Fruit oblong, about a line long. 
A common North American species, observed in a few scattered localities 
in Europe, and found in Perthshire, Skye, and Connemara in Ireland. 
Fl. summer. 
[2. N. marina, Linn. (fig. 952). Holly-leaved Naias.—Stems with here 
and there toothed wings. Leaves opposite and ternate, linear, strongly 
spinular-serrate. Fruit ellipsoid, + of an inch long. 
Common in the tropical and some temperate regions of the Old World. 
In Britain, found only in Hickling Broad, Norfolk. J. summer. 
3. NW. graminea, Del. (fig. 953). Grassy Naiad.—Leaves in clusters 
at the nodes, narrowly linear, less than an inch long, serrulate. Stigmas 
2. Fruit linear-oblong. 
A native of stagnant waters in the hotter regions of Asia, which has 
been introduced into Italy, Austria, and Lancashire. For an excellent 
account of it see ‘‘ Journal of Botany,” 1884, p. 307, by C. Bailey, F.L.S.] 
Ill. ZANNICHELLIA. ZANNICHELLIA. 
A genus limited to a single species; differing from the narrow-leaved 
Potamogetons by the moncecious flowers sessile in the axils and without 
perianth, from Ruppia in the usually opposite leaves, in the single stamen, 
and in the shape of the fruit. 
1. Z. palustris, Linn. (fig. 954). Common Zannichellia, Horned 
Pondweed.—Stems slender, branched and floating. . Leaves finely linear, 
bright green, 1 to 2 inches long, mostly opposite, with a small, sheathing, 
membranous stipule embracing the stem withinside. At the time of 
flowering there are usually about 4 ovaries together, almost sessile within 
the stipule, each with a short style and a broad, disk-shaped stigma, and a 
solitary stamen with a slender filament in the same or in a separate axil; 
the anthers 2- or 4-celled. When ripe the carpels are 1 to 13 lines long, 
sessile or shortly stalked, somewhat curved and flattened, tipped by the 
remains of the style; the ribs on the back often crenated, warted or 
slightly winged. 
In ponds, or lagoons of fresh, or brackish or even salt water; dispersed 
over a great part of the globe. Common in Britain. #1. the whole summer. 
[There are four well-marked forms of this. 
a. Z, palustris proper. Stamens long; anther 4-celled. Carpels 2-4, 
sessile, style half as long, stigma small. | 
b. Z. brachystemon, Gay. Stamens short; anther 2-celled. Carpels 
2-4, subsessile, their backs crenated ; stigma large. 
ce. Z. pedunculata, Reichb. Stamens short ; anther 2- celled. Carpels 
pedicelled, their backs muricate; stigma large. 
d. Z. polycarpa, Nolte. Stamens very short; anther 2-celled. Carpels 
4—6, subsessile, their backs smooth ; stigma large. ] 
IV. RUPPIA. RUPPIA. 
A single species, distinguished from Zannichellia by the alternate leaves, 
2 sessile anthers, and the ripe carpels all stalked and ovoid. 
