NOTES ON PONDWEEDS. 277 



Perhaps the strongest argument against hybridity in the plant 

 in question is to be found in its uniformity of character over widely 

 separated localities. At present in England it is absolutely without 

 a variety, the plant of Sussex cannot be distinguished from the plant 

 of Huntingdonshire! Of course it would be quite possible for a 

 vigorous hybrid form of this genus to be become distributed over 

 very wide areas indeed by offsets from the original plant, but the 

 peculiar distribution of P. fluitans in the Fens, strongly points to its 

 being distributed by seed rather than by division ; hence I confidently 



expect to obtain ripe seed from our plant some day. 



One other suggested reason for its hybrid origin remains to be 

 examined : — its being " intermediate " in character between P. 

 nutans and P. lucens. From the above given description, it will be 

 seen that I have been quite unable to detect any real resemblance 

 to P. nutans whatever, while on the other hand I have pointed out 

 numerous close resemblances to P. lucens. For the rest, if a Pota- 

 mogeton being intermediate in facies between two other allied 

 forms is a proof of hybridity, I am afraid nearly all our British 

 species must be called hybrids ! 



On present knowledge, therefore, I think it will be safest to assume 

 that our P. fluitans is a good species, and that it is identical with the 

 Continental plant so named ; of this latter proposition my friend, 

 Mr. Arthur Bennett, has given sufficient proofs. 



Perhaps a glance at the characters which distinguish P. fluitans 

 from its nearest (or supposed nearest) congeners, will enable the 

 student to form some opinion of its true position in the genus. 

 From P. natans, it is separated by its short phyllodes always 

 submerged, by its membranous submerged secondary leaves, and by 



If 



of the petiole. From 



P. polygonifolius, by the translucent nerves of the full-grown upper 

 coriaceous leaves, by its much stouter peduncles and larger flower - 

 spikes, and by its much longer -stalked, narrowly -lanceolate submerged 



leaves. From forms of P. Zizii, with the floating leaves well 

 developed, it is sufficiently distinguished by its elongate-lanceolate 

 long-stalked secondary leaves. From any known form of typical P. 

 lucens the floating coriaceous upper leaves at once form a wide ground 

 of separation. P. fluitans is, however, most closely allied to P. 

 lonchites ; and with that plant, and possibly with the Irish P. spar- 

 gunifolius, it would, perhaps, be most naturally placed in that section 

 of the group of which P. heterophyl I us and P. lucens are the extremes. 

 The first certain record of this plant was from Bamsey, 

 Huntingdonshire, June 29th, 1884 ; afterwards it was found in 

 Cambridgeshire, in two localities in 1886, and in a third in 1887 ; 

 all these stations being near Chatteris. In Mr. Beeby's herbarium 

 I found a specimen collected by him in West Sussex, in June, 1880; 

 &ad the examples from Surrey, collected by Mr. Beeby and Mr. 

 Bennett in 1886, have been already referred to. But since I began 

 "Us note, Mr. Beeby has again collected very characteristic 

 specimens in quite a new Surrey locality, and also in the original 

 Sussex station. No doubt P. fluitans will be found in many of our 

 southern counties, where it has likely been overlooked from its 



