NAIADACE. 43 
England, Scotland, Ireland. Perennial. Summer, Autumn. 
A well-marked species, with tender, diaphanous leaves cordate at the 
base, 1 to 3 inches long, and with the stipules either entirely absent 
or mostly decayed before the plant flowers, their place being indicated 
only by a few fibres, except at the places where the leaves are opposite, 
or where peduncles are produced. 
In deep water, as in the Kyle of Sutherland, the Lossie, and other 
places, a form occurs with the leaves much narrower than usual, less 
amplexicaul, darker in colour, and turning black and dim in drying. 
Allied to this elongate form is the plant which represents P. nigre- 
scens, /ries,* in his Herbarium Normale at Kew, but the specimen is 
very imperfect, and may readily have got mixed with the true P. nigre- 
scens, of which the description corresponds well with the P. lanceo- 
latus, Smith. 
P. perfoliatus is, in some states, liable to be confounded with 
_P. nitens, but the latter has much firmer and less amplexicaul leaves, 
not cordate at the base; there is no tendency to dichotomous ramifi- 
cation; the peduncles are stouter, and more or less evidently thickened 
upwards. In P. nitens the stipules are of much thicker texture, and 
consequently do not so soon decay. 
Perfoliate Pondweed. 
French, Potamot perfolié. German, Durehwachsenes Samkraut. 
SPECIES XIV—POTAMOGETON CRISPUS. Lim. 
Prats MCCCCXIII. 
Reich. Ic. Fl. Germ. et Helv, Vol. VII. Tabs. XXIX. and XXX. Figs. 50 to 52. 
Stems slender, sparingly branched, the lower branches barren, the 
upper branching more or less dichotomous. Leaves all similar, the 
lower ones alternate, the upper ones and those at the base of the forks 
opposite, submerged, sessile, semi-amplexicaul, spreading-ascending, 
usually strongly undulated or crisped, oblong or strapshaped-oblong, 
rounded at the base, obtuse or subobtuse, not apiculate nor cuspidate 
nor hooded at the apex, serrulate, with 3 strong ribs and usually a 
fainter rib on each side near the margin, connected by rather distant 
ascending veins, and with a narrow band of very elongate cancellate 
areolation along the sides of the midrib only; leaves of the young 
shoots strapshaped, flat, and 3-nerved. Stipules small, subobtuse; the 
* This plant (which appears in want of a name) is in M. Gay’s herbarium from 
between Falaise and Vire, collected by M. Lenormand, and named “ P. prelongus” 
(Brébisson!). But the collector informs me that M. Brébisson now considers it to be 
P. nitens, of which it may be an elongated abnormal form. 
G2 
