NOTES ON PONDWEEDS. 9 



the size of the plant ; inner margin nearly straight, terminated by 

 the short beak ; outer margin semicircular, with an acute, almost 

 winged keel, from which the lateral ridges are rather distant, 

 projecting at right angles from the base of the fruit. Colour of the 

 whole plant bright green, or brownish green, usually drying darker. 



P. curiaceiis is closely allied to P. Zizii, from which, however, 

 it is readily separable in its typical state by the densely-coriaceous 

 floating leaves, which resemble those of P. heterupJujIlus in texture, 

 and which are obovate, oblun/j, or orbicular, not elliptical, as in 

 Zizii. The whole of the foliage, too, is usually flatter, and the 

 lower leaves have no denticulations, and are rarely crenulate when 

 dry ; they are also more coarsely reticulate, resembling in this 

 respect those of P. lucens. The fruit is more acutely keeled, and 

 with the sides much flatter than that of P. Zizii. From P. lucens 

 the coriaceous floating leaves sufiQciently distinguish it ; I think we 

 may now safely assume that lucens never produces coriaceous leaves ; 

 the specimens distributed by Dr. Bos well from Kinghorn Loch, 

 Fife, certainly are a form of P. Zizii, and it is highly probable 

 that some such form has in all instances furnished the reputed 

 " /i/c^-^zs with coriaceous leaves." P. coriaceus in some states may 

 be mistaken for P. heterophyllus, but it differs in the lamina of the 

 coriaceous leaves always greatly exceeding the petiole in length, by 

 the much larger lower leaves, and by the great mass of the foliage 

 rising to the surface of the water ; although, as in P. Zizii, some of 

 the lower branches always remain submerged. 



P. coriaceus seems almost equally allied to Zizii, lucens, and 

 heterophyllus, states of all three of which it at times closely 

 resembles ; another remarkable resemblance — remarkable because 

 there is no alliance — remains to be noticed : when growing in very 

 shallow water, or exposed to the air on mud, it so closely simulates 

 the "land form" of P. itlayitafjineus as to be barely distinguishable. 



As it is here sought for the first time to establish P. coriaceus as 

 a species, the following synonymy is given : — 



Potamoqeton lucens var. lacustre Thore, * Cliloris des Landes,' 

 p. 46, 1803 (or 1798?). 



Mr. Bennett tells me that Nolte, in his herbarium, quotes the 

 above synonym for his P. lucens var. coriaceus, and so I repeat it 

 here ; but, from There's description, " Feuilles parfaiteinent ellip- 

 tiques'' and "nerveures tres-saillantes,'" I do not think it represents 

 our plant, but very well agrees with Dr. Boswell's ''lucens with 

 floating leaves,'' which I am unable, on the evidence of the poor 

 specimens I have seen, to place under coriaceus. 



P. lucens ^. coriaceus Nolte, in Kohling's * Deutschlands Flora,' 

 p. 850, 1823. — This is the first pubhcation of Nolte's plant, who 

 sent named specimens, gathered in 1821, to the editors, Merteus 

 and Koch. 



Subsequently Nolte himself published his plant in his 'NoviticTB 

 Florae Holsaticae,' 1828, p. 21, footnote (a copy of which, by the 

 kindness of my ever-helpful friend, Mr. Bennett, I am able to 

 give): — " Hanc quoque speciem florescentem cum coriaceis foliis 

 natantibus sestate a. 1821 reperi, nomincque Potamogeton lucentis 



