Zostera.] LXXVIII. NAIADEJC. 423 



LXXVIII. NAIADES. THE NAIAD FAMILY. 

 Floating, or submerged or marsh plants ; the leaves either 

 sheathing at the base or accompanied by sheathing stipules, 

 alternate or sometimes opposite. Flowers axillary, incon- 

 spicuous, solitary or spiked, often proceeding from a sheathing 

 bract. Perianth none, or inferior and consisting of 4 or 6 

 small, scale-like segments. Stamens 1, 2, 4 or 6. Ovaries 

 either of 2, 4, or 6 distinct carpels, each with a single ovule 

 and a separate stigma, or single, with 1 ovule and 2 to 4 

 stigmas. Fruit consisting of 1, 2, 3, 4, or 6 seed-like nuts, 

 each with one seed, without albumen. 



An Order not numerous in species, but of very various habit, 

 abundantly diffused over all parts of the world, in the sea as well as 

 in fresh waters. 



Water-plants. Stems creeping In sand or mud under salt-water. 

 Leaves very long and linear. Flowers within the base of a 



long, linear bract, like the stem-leaves 1. ZOSTERA. 



Water-plants. Stems floating. Flowers axillary. 

 Ovaries simple, with 1 style and 2 or 8 stigmas. Leaves oppo- 

 site or whorled, and often toothed 2. NAIAS. 



Ovaries of 4 carpels, each with a separate stigma. 

 Flowers and carpels axillary and sessile. Leaves opposite, 



very slender 3. ZANNICHELLIA. 



Flowers usually 2, on an axillary peduncle. Carpel* 



stalked, pear-shaped. Leaves alternate, very slender . 4. RUPPIA. 

 Flowers in pedunculate spikes or heads. Carpels sessile. 



Leaves alternate or rarely opposite 6. POTAMOOBTON. 



Marsh-plants. Stems erect Leaves rush-like. Flowers In 

 spikes or racemes. 



Flowers bracteate. Anthers long 6. SCHEUCHZKRIA, 



Flowers ebracteate. Anthers short 7. TRIOLOCHIN. 



I. ZOSTERA. GRASS-WRACK. 



Marine herbs, the stem creeping and rooting in the sand or mud, 

 with long, grass-like, alternate leaves. Flowers enclosed in a sheath 

 near the base of leaves similar to the others, but usually smaller. 

 Within this sheath is an oblong or linear, thin, leaf-like peduncle, on 

 one side of which are arranged in 2 rows a few sessile anthers, with 

 3 or 4 sessile or nearly sessile ovaries, tapering into a deeply 2-cleft, 

 linear style. Embryo split longitudinally, with a deep groove forming 

 2 valves, which fold over the long, curved, linear cotyledonar end. 



A genus hitherto limited to the two British species. 



Leaves seldom a foot long. Ripe seeds smooth 8. Z. nana. 



Leaves usually more than a foot long. Ripe seeds furrowed . . 1. Z. marina. 



1. Z. marina, Linn. (fig. 951). Grass-wrack. Creeping stems or 

 rootstocks often very long and rather fleshy. Leaves varying from 

 near a foot to several feet in length, and from 2 to 3 or 4 lines in 

 breadth, with 3, 5, or even 7 more or less distinct parallel nerves. 

 Flowering sheath near the- base of the floral leaves, from 1 to 1 J or near 

 2 inches long. The flattened peduncle narrow-linear, and said to be 

 always without the horizontal appendages of Z. nana. Seeds oblong, 

 niarfced by longitudinal furrows. 



