454 NAIADACEJE. (PONDWEED FAMILY.) 
4. RUPPIA, L. Ditch-grass. 
Flowers perfect, 2 or more approximated on a slender spadix, 
which is at first inclosed in the sheathing spathe-like base of a 
leaf, naked (entirely destitute of floral envelopes), consisting of 2 
sessile stamens each with 2 large and separate anther-cells, and 4 
small sessile ovaries, with a single campylotropous suspended 
ovule : stigma sessile, depressed. Fruit of little obliquely-ovate 
pointed drupes, each raised on a slender stalk which appears after 
flowering ; the spadix itself also then raised on an elongated 
thread-form peduncle. Embryo ovoid, with a short and pointed 
plumule from the upper end, by the side of the short cotyledon.— 
Marine herbs, growing under water, with thread-like forking 
stems, long and almost capillary alternate leaves with a dilated 
sheathing base or adherent stipule. Flowers brought to the sur¬ 
face at the time of expansion. (Dedicated to Ruppius, a German 
botanical author, early in the 18th century.) 
!• R* marftima, L. Leaves linear-capillary ; nut ovate, ob¬ 
liquely erect; fruiting peduncles capillary (^ - 1/ long). — Shallow 
bays, along the whole coast: chiefly a narrowly leaved var. with 
strongly pointed fruit, approaching R. rostellata, Koch. June-Aug. 
5, POTAMOGETON, Tourn. Pondweed. 
Flowers perfect, spiked. Sepals 4, rounded, valvate in the bud. 
Stamens 4, nearly sessile, opposite the sepals : anthers 2-celled. 
Ovaries 4, with an ascending campylotropous ovule: stigma ses¬ 
sile or nearly so. Fruit 4 sessile nutlets, or drupes when fresh, 
compressed or angled on the inner side. Seed hook-shaped ; the 
radicular end of the embryo thickened and pointing downwards. — 
Herbs of fresh or barely brackish ponds and streams, with jointed 
creeping and rooting stems, and 2-ranked pellucid leaves, which 
are usually alternate, the upper sometimes dilated and floating- 
Stipules membranous, united and sheathing. Spikes sheathed by 
the stipules in the bud, raised on a peduncle to the surface of the 
water. (An ancient name, composed of irorapos, a river , and *y fl 
tcov, a neighbour , from their place of growth.) 
§ 1. Stipules free from the petiole: upper haves floating on the sar 
face, alternate , or the uppermost opposite , different in figure and m 
their firmer (herbaceous or coriaceous ) texture from the thin and mem 
branaceous immersed ones. 
