NAIADACEyE. 43 



England, Scotland, Ireland. Perennial. Sunmicr, 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 beuig 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 ^vith 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 re])resents P. nigre- 

 scens. Fries* 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 perfolie. German, Durchwachsenes Samkraut 



SPECIES XIV.-POTAMOGETON CRISPUS. Linn. 

 Plate MCCCCXin. 

 Bekh. Ic. Fl. Germ, et Helv. Vol. VH. 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, spreadhig-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 yoimg 

 shoots strapshaped, flat, and 3-nerved. Stipules small, subobtuse; the 



* This plant (which appears in want of a name) is in M. Gray's herbarium from 

 between Falaise and Vire, collected by M. Lenormand, and named "P. prselongus " 

 (^Breltssonl). But the collector informs me that il. Brubisson now considers it to be 

 P. nitcu.s, of which it may be an elongated abnormal form. 



