424 THE NAIAD FAMILY. [Zostera. 



Common near the sandy or muddy edges of the sea, in temperate 

 regions of the world, usually at or below low-water mark, and often 

 thrown up in great quantities by the tide. Abundant round the British 

 Isles. Fl. summer, or, according to some, in spring only. 



2. Z. nana, Roth. (fig. 952). Dwarf O. Closely resembles the 

 smaller forms of Z. marina, of which it may be a variety. The leaves 

 are usually from a few inches to near a foot long, very narrow, with 

 only 1 or rarely 3 distinct nerves ; the flowering sheath about half an 

 inch long, and the flattened peduncle inside has to every ovary a little 

 transverse appendage or band. Seeds shorter than in Z. marina, per- 

 fectly smooth. 



On sandy shores, usually between high- and low-water marks, in 

 various parts of the world. Common in western Europe, and has been 

 found on several points of the British coasts. Fl. summer and autumn. 

 The seeds appear certainly distinct in the two species ; the constancy 

 of the other characters is doubtful I have examined only the dwaxf 

 species in a living flowering state. 



II. NAIAS. NAIAD. 



Slender, branching, submerged plants, with linear, opposite or ter- 

 nate, entire or toothed leaves, often crowded into whorls or clusters. 

 Flowers small and sessile, often clustered with the branch-leaves in the 

 axils, and dioscious or rarely monoecious; the males consisting of a 

 single, nearly sessile anther, enclosed in 2 bracts ; the females of a 

 single ovary, sessile in the sheathing base of the leaf, with 2 to 4 sub- 

 ulate stigmas. Fruit a small, seed-like drupe. Embryo straight. 



A genus of few species, widely spread over a great part of the globe. 



1. N. flexilis, Rostk. (fig. 953). Slender N. Leaves narrow-linear, 

 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 Eurqpe, and found in Perthshire, Skye, and Connemara 

 in Ireland. Fl. summer. 



[2. N. marina, Linn. (fig. 954). Holly-leaved N. 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. FL summer. 



3. N. graminea, Del. (fig. 955). Grassy N. 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.] 



IIL ZANNICHELLIA. HORNED PONDWEED. 

 A genus limited to a single species ; differing from the narrow-leaved 

 Potamoyctons by the monoecious flowers sessile in the axils and without 



