NAIADEJC. 783 



Ovaries either of 2 or 4 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, or 4 seed-like nuts, each with one seed, 

 without albumen. 



An Order not numerous in species, but abundantly diffused over all 

 parts of the world, in the sea as well as in fresh waters. 



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. Zosteba. 



Stems floating. Flowers axillary. 



Ovaries simple, with 1 style and 2 or 3 stigmas. Leaves 



opposite or whorled, and often toothed .... 2. Naiad. 

 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. Carpels 

 stalked, pear-shaped. Leaves alternate, very 



slender 4. EurriA. 



Flowers in pedunculate spikes or heads. Carpels 



sessile. Leaves alternate or rarely opposite . . 5. Pondweed. 



I. ZOSTERA. ZOSTEEA. 



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 two 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 into 2 valves, which fold 

 over a long, curved, linear radicle. 



A genus hitherto limited to the two British species. 



Leaves seldom a foot long. Eipe seeds smooth 2. Dwarf Z. 



Leaves usually more than a foot long. Eipe seeds furrowed . 1. Common Z. 



1. Common Zostera. Zostera marina, Linn. (Fig. 942.) 



(Eng. Bot. t. 467. Grass-ivrach.) 



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, 



