NAIADACEX. 55 
SPECIES XXTUI—POTAMOGETON FILIFORMIS. Nolte. 
Prare MCCCCXXIYV. 
Reich. Ic. Fl. Germ. et Helv. Vol. VII. Tab. XVIII. Fig. 27. 
P, marinus, “ Linn.” Fries, Noy. Fl. Suec, p. 54, and Summ. Veg. Scand. p. 69 (68) 
and 216. 
Stem cylindrical or subcompressed, slender, filiform, sparingly 
dichotomous or trichotomous at the base, simple above. Leaves all 
similar and subtranslucent, with sheathing petioles, setaceous, acute, 
with only one longitudinal rib, most of the leaves without branches in 
their axils. Stipules rather long and narrow, subscarious, united to 
the sheathing petiole of the leaf, with only the apex free. Peduncles 
terminal, longer than the spike, generally three to five times as long, 
filiform, not thickened upwards. Sepals with their lamina obovate. 
Fruiting-spike very long, greatly interrupted, few-flowered, with all 
the whorls of flowers distant from each other. Fruit rather small, 
‘olive, compressed, half-oblanceolate on the upper surface, semicircular 
and yery bluntly 3-keeled on the back, with a very short nearly 
central beak. Plant grass green, turning nearly black in drying. 
In ditches, ponds, and slow streams. Apparently rare. I have 
specimens from Berwick-on-Tweed, and the Loch of Balgavies, Forfar; 
and have myself collected it in Loch Gelly, Fife, near Tarbetness, 
Cromarty; and in ditches at Swanbister, on the mainland of Orkney. 
Lough Cullen and Lough Conn, co. Mayo. 
Scotland, Ireland. Perennial. Summer, 
Very similar to P. pectinatus, but much smaller, the stems more 
slender, shorter and less branched, the leaves longer, tougher, and yel- 
lowish green, formed of 2 interrupted tubes as in that plant. Peduncles 
3 to 8 inches long, exclusive of the spike. Spike 2 to 5 inches long, of 
3 to 5 whorls of flowers, with usually two flowers in each whorl, the 
whorls separated by much more than their own diameter, especially 
towards the base of the spike. Nut more compressed, } inch long, 
and consequently much smaller than that of P. pectinatus, and of a 
paler olive, not tinged with orange-brown, the upper side much more 
convex towards the apex, and the lower more equally curved. 
The fruit of P. filiformis is too dissimilar to that of P. pectinatus 
to admit of its being considered a subspecies of that plant. 
This plant is the P. marinus of the Linnean Herbarium. 
Slender-leaved Pondweed. 
German, Meer-Samkraut, 
