naiadEjE. 491 



1. Common Zannicliellia. Zannicliellia palustris, Linn. 

 (Eng. Bot. t. 1844. Honied Ponchveed.) 



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 vpithin 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 1^ 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. Fl. the whole summer. 



IV. RUPPIA. EUPPIA. 



A single species, distinguished as a genus from Zanniohellia by the 

 alternate leaves, 2 sessile anthers, and the carpels in fruit aU stalked and 

 pear-shaped. 



1. Sea Ruppia. Ruppia maritima, Linn. 

 (Eng. Bot. t. 136. R. rostellata, Bab. Man.) 



A slender, branched, floating plant, much resembling in appearance the 

 Fennel Pondweed. Leaves almost capillary, with a dilated, sheathing base. 

 Peduncles axillary, at first very short, bearing 1 or 2 flowers, each consisting 

 of 2 almost sessile anthers, with 2 distinct cells, and 4 carpels, at first nearly 

 BessUe. As the fruit ripens, the carpels become httle, ovoid or pear-shaped, 

 obliquely-pointed nuts, 1 to \\ lines long, raised on pedicels, varying from 

 2 or 3 Unes to an inch in length, the common peduncle also lengthening 

 considerably. 



In salt-marshes, lagoons, and shallow creeks and bays, dispersed over 

 nearly the whole globe, exceptmg perhaps South America. Common round 

 the British Isles. Fl. summer and autumn. 



V. PONDV/'ESD. POTAMOGETON. 



Aquatic herbs, with a perennial rootstock, long, floating, usually forked 

 stems, and alternate or rarely opposite leaves, either dilated and sheathmg 

 at the base, or having all or some of them a sheathing, scarious stipule in 

 their axil. Flowers small, sessile in a spike or head, on an axillary pedun- 

 cle rising above the water. Perianth of 4 scale-Uke segments. Stamens 4, 

 opposite the segments ; the anthers sessUe and 2-celled. Carpels 4, each 

 with a very short style or a sessile stigma. Nuts small and seed-like, sessile, 

 usually laterally compressed. 



A considerable genus, most of the species spread over the greater part of 

 the globe, chiefly in fresh-water, but some accommodating themselves also to 

 Bait-water, and many of them veiy variable in foUage. In the species with 

 axillary stipules, these are sometimes only to be seen under the peduncles or 

 vmder the branches of the stem. 



