NAIADACE.T5. 55 



SPECIES XXm— POTAMOGETON PILIFORMIS. Nolte. 



Plate MCCCCXXIV. 



Fr!ch. Ic. Fl. Germ, et Helv. Vol. VII. Tab. XVIH. Fig. 27. 



P. marinus, " Linn." Fries, Nov. Fl. Succ. p. 54, and Suinm. Vcg. Scand. p. 69 (C8) 

 and 216. 



Stem cylindrical or subcompressed, slender, filiform, sparingly 

 dichotomous or tricliotomous 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, feAV-flowered, with all 

 the whorls of flowers distant from each other. Fruit rather small, 

 olive, compressed, half-oblanceolate on the upper surface, semicircular 

 and veiy 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 Balga^des, Forfar ; 

 and have myself collected it in Loch Gelly, Fife, near Tarbetness, 

 Cromarty; and in ditches at Swanbister, on the mainland of Orkney. 

 Lough CuUen and Lough Conn, co. Mayo. 



Scotland, Ireland. Perennial. Summer. 



Yery 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. Xut 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 Linnajan Herbarium. 



Sleiider-leaved Pondiceed. 



Gei-man, Meer-Sanikmnt. 



