NAIADACE^. 33 



SPECIES (?) VX-POTAMOGETON LONCHITIS. Tuclc 



Plate MCCCCIV. 



Bekli. Ic. n. Germ, et Relv. Vol. VII. Tab. XXXI. Fig. 55. 



Graij, Man. Bot. of tho N. U. S. ed. v. p. 486. 



P. salicifolins, Wolfgang ; Fries, Samm. Veg. Scand. pp. 68 (67) and 215 (?). Earim. 



Skand. Fl. ed. ix. p. 243 (?). 

 P. lanceolatus, Eoich. I.e. p. 19 (?) (non Smith). 

 P. sparganiifolius {ex parte), Bah. Man. Brit. Bot. ed. vi. p. 363. 



Stem wiry, much branched; the lower branches barren. Leaves 

 mostly alternate, submerged, sessile and semi-amplexicaul, not recurved, 

 rather long, strapshaped or oblong-strapshaped, rather abruptly attenu- 

 ated at each end, slightly undulated, not denticulate, translucent, with 

 7 or 9 longitudinal ribs connected by rather numerous transverse veins, 

 and with several rows oi' greatly elongated cancellate areolations along 

 the midrib ; upper leaves opposite, sometimes floating, longly stalked, 

 elliptical or oblong-elliptical, rounded or abruptly attenuated into the 

 very long petiole at the base, subcoriaceous, of the same texture as 

 the petiole, with the numerous ribs and cross veins conspicuous if the 

 dried leaf be held against the light, when also rather large areolation 

 is very distinctly perceptible all over the leaf between the ribs : often 

 the upper leaves are submerged, pellucid, and similar to the lower ones 

 in shape and texture. Stipules rather long, subacute, not winged on 

 the back, scarious, with few fibres. Peduncles (always ?) axillary, 

 rather long and slender, very slightly thickened towards the apex. 

 Spike cylindrical, rather short. Fruit (of the British plant) unknown. 

 Plant with the submerged leaves turning olive when dry ; floating 

 leaves green. 



In the river Boyne, below Navan, Dr. D. Moore. 



Ireland. Perennial. Summer, Autumn. 



Stem more slender than in any of the preceding species, resembling 

 that of P. hetcropliyllus. Leaves 2 to 5 inches long by f to f inch 

 l)r(jad, clasping about one-fourth of the stem; floating leaves 2 inches 

 or more long, resembling those of P. heterophyllus, but thinner in 

 texture. Stipules l to 1 inch long, similar to those of P. hetei'ophyllus. 



This plant comes very near P. heterophyllus, but the leaves are more 

 parallel-sided, less attenuated towards the base, and straighter, less un- 

 dulated, and more flaccid ; the fl(xating ones thinner and with much 

 larger and more conspicuous areolation, and with the margins at the 

 base involute until they are nearly full grown as in P. polygonifolius, 

 P. natans, and P. plantagineus, while in P. heterophyllus they be- 

 come flat long before they have attained their full size ; the upper 



VOL. IX. F 



