Ruppia.| — LXXVIII. NAIADER. 425 
1, R. maritima, Linn. (fig. 955). Sea Ruppia.—A slender, branched, 
floating plant, much resembling Potamogeton pectinatus. Leaves almost 
capillary, with a 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 sessile. As the fruit ripens, 
the carpels become little, obliquely pointed nuts, 1 to 14 lines long, on 
pedicels from 2 or 3 lines to an inch in length, the common peduncle often 
becoming spirally coiled, and also lengthening. 
In salt marshes, lagoons, and shallow creeks and bays, dispersed over 
nearly the whole globe. Common round the British Isles.—/FV. summer 
and autumn. 
[ There are two British forms usually regarded as species. 
a. R. maritima proper. Sheaths inflated. Fruiting peduncles spiral. 
b, R. rostellata, Koch. Sheaths notinflated. Fruiting peduncles short, 
flexuous. Nut beaked, gibbous. | 
V. POTAMOGETON. PONDWEED. 
Aquatic herbs, with a perennial rootstock, long, floating, usually forked 
stems, and alternate or rarely opposite leaves, either dilated and sheathing 
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 
peduncle rising above the water. -Perianth of 4 scale-like segments. 
Stamens 4, opposite the segments ; the anthers sessile and 2-celled. Cap- 
sules 4, each with a very short style or a sessile stigma. Nuts small and 
seed-like, sessile, usually laterally compressed. Seed much curved or 
almost coiled round an obovoid projection of the endocarp. 
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 salt-water, and many of them very variable in foliage. In the species 
with axillary stipules, these are sometimes only to be seen under the 
peduncles or under the branches of the stem. 
Upper leaves on long stalks, floating on the surface of the 
water. 
Lower submerged leaves stalked or reduced to mere leaf- 
stalks . : » LP. natans. 
Lower submerged leaves sessile or nearly so. 
Lower submerged leaves linear, 1-nerved or shghtly 3- 
nerved . 2. P. heterophyllus. 
Lower submerged leaves lanceolate, with 6, ”, or more 
nerves. : A ‘ 3. P. lucens. 
All the leaves under water and sessile. 
Leaves allopposite . : 7. P. densus. 
Leaves alternate, except under the peduncles or forks. 
Leaves broadly ovate, clasping the stem all round 5. P. perfoliatus. 
Leaves ovate-lanceolate or oblong, broad at the base and 
clasping the stem 4. P. prelongus. 
Leaves lanceolate or linear, tapering at the pase, or not 
stem-clasping. 
Leaves broadly linear or lanceolate, flat and entire, with 
many nerves . ° : « 3. 2. daeens. 
Leaves broadly linear, waved, 1- or 3-nerved : : . 6. P. erispus. 
Leaves narrow-linear, not waved, 1- or 3-nerved. 
Leaves not dilated at the base, with a scarious stipule 
in most axils. 
Leaves 1 to 2lines broad. Nuts 13 lines long. 
