10 NOTES ON PONDWEEDS. 



coriacei notatum mense Martio a. 1822, cum Cel. Profesaore 

 Mertens commuuicavi. Post inserta est Mertens et Koch, Flor, 

 Germ, i., p. 850." 



Fries, * Novitiae Florae Suecicfe,' ed. 2, 1828, p. 84 :— "P. lucens 

 y. amphibius, anomalus, foliis natantibus chartaceis ovalibus 



brevissime petiolatis Scaniae lectus." Fries quotes Mertens 



and Koch, ' Deutschlands Flora,' and his description well agrees 

 ■with Nolte's plant. 



Reichenbach, • Icones,' vol. vii. p. 23, 1845, gives an excellent 

 account of this plant under "P. Incem var. ^. coriaceus Nolte," and 

 a very good figure on tab. 37. Following Nolte, he quotes Thore's 

 lucens-lacustre as a synonym. 



Dr. H. Trimen, in his admirable paper on P. Zizii (' Journal of 

 Botany,' Oct. 1879), amongst the synonyms of that species, doubt- 

 fully quotes Nolte's coriaceus, and says : — " Reichenbach has given 

 an excellent figure in the * Icones,' t. 37, drawn from an authentic 

 specimen, and well agreeing with one in the Museum herbarium, 



gathered by Nolte in 1821, at Schalisch, in Lauenberg It 



is, I think, rightly referred to luceiis in a wide sense, but is not 

 quite Zizii ; nor does it agree completely with the lucem with 

 floating leaves from Kinghorn Loch, Fife, collected by Mr. Bos well 

 (Syme). Some British botanists would certainly call it heterophyllus.'' 



In July, 1885, I found P. coriaceus at Welches' Dam, near 

 Chatteris, and, seeing it did not well agree with any local form of P. 

 Zizii, I sent a specimen to Mr. Arthur Bennett, who subsequently 

 published a short note on it in the 'Journal of Botany' for 1886. 

 In this note Mr. Bennett agrees with me in considering P. Zizii to 

 be its nearest ally. This was the first publication of the plant as a 

 British species. 



The species which have already been separated from the old 

 Linnean P. lucens are so crowded with varieties that I think most 

 workers at the genus will welcome an attempt to lessen the number 

 by further specific segregation. P. coriaceus certainly does not 

 come nearer to P. Zizii than that species does to P. lucens, so that 

 in proposing its specific segregation I am merely following a 

 generally- accepted precedent. We have here, as in Zizii, a form 

 that in its typical state is recognisable at a glance, and to which 

 Dr. Trimen's observations on that species may well apply: — 

 '• Probably the arrangement most in accordance with Nature, how- 

 ever, is that followed by Chamisso and Schlechtendal in their 

 monograph of the genus published in 1827 (' Linnaea,' ii., p. 201), 

 where P. Zizii is accorded equal rank with P. lucens and P. hetero- 

 phyllus, all being regarded as sub-species of one super-species, P. 

 Froteus C. & S." At present, however, I prefer to class all such 

 forms as species, leaving the final settlement of their rank to the 

 time when the whole genus shall be better known. 



Probably P. coriaceus will be found widely spread over the 

 British Isles, although I have seen no specimens that I can refer 

 with certainty to it, besides those I gathered in 1885, and more 

 abundantly in the present season. 



