66 NOTES ON PONDWEEDS. 



P. nitens reveal something antagonistic, I do not truly see how your 

 plant is to be separated therefrom, further than as a var. or sub- 

 species Your plant may quite likely be distinct, and if you 



can really show that it is as distinct from jiitens as it is from hetero- 

 plnjUus (always speaking of our ordinary British forms), then, to 

 my ideas, it should take equal rank with those two forms — but at 

 present it seems to me too near nitens; this is, I think, the point to 

 be worked out" (W. H. Beeby, in litt., Jan. 1, 1888; see footnote 

 at end). 



To this point, then, I address myself: I may as well say plainly 

 in the outset that I cannot place P.fakatus under nitens, because I 

 regard the latter plant, as presented in the ordinary British and 

 continental forms, as a barren hybrid. I have never seen a fruiting 

 specimen, and I do not know any botanist who has. It is remark- 

 able that, although all authors describe the fruit of P. nitens, I have 

 never been able to meet with a single fertile spike in any herbarium 

 which I have looked through. Surely the absence of fruiting 

 specimens from such collections as those of Mr. Arthur Bennett, 

 and Mr. Charles Bailey, and from the British part of the National 

 Herbarium at the British Museum, and from the fine collection of 

 British Potamogetous in Prof. Babington's herbarium, is somewhat 

 significant ! Mr. Beeby, too, failed to procure a single fruiting 

 spike of P. nitens from the Surrey stations he so carefully examined 

 throughout the past summer. From a great quantity of fresh 

 specimens he furnished me with from time to time I formed the 

 opinion that, although the drupelets of P. nitens grow up to a 

 certain size, like those of P. decipiens, they are all abortive, and 

 decay as the season advances. This is but negative evidence I 

 admit, but it is of a very strong nature. The leaf-characters of the 

 two plants afi'ord more direct evidence of specific distinctness : in 

 P. nitens the leaves are usually longitudinally folded and recurved, 

 and 12-ribbed ; in P.falcatus they are 6-ribbed, flat, and ascending. 

 The coriaceous floating leaves are more frequently produced in the 

 latter species, and resemble those of P. heteropJujUus rather than 

 those of P. nitens; and, above all, they essentially belong to the barren 

 state of the plant, although sometimes present on the flowering 

 branches. In P. nitens, as far as I have seen, these coriaceous 

 leaves belong to the flowering branches, and are rarely present on 

 those which produce no flower-spikes. P. falcatus never produces 

 the broad perfoliate leaves so commonly present in luxuriant states 

 of P. nitens (var. lati/olius of Tiselius), and the stipules differ con- 

 siderably, approaching those of heterophyllus. Finally, the peduncles 

 are more equal, being very slightly swollen upwards. 



Turning to other allied forms: — P.falcatus is sufficiently dis- 

 tinguished from P. heterophytliis by its amplexicaul leaves ; from 

 /'. Zizii by the same character, and by the opaque ribs of the 

 coriaceous tioating leaves, those of Zizii being translucent. The 

 entire leaves without denticulations at once show that the 

 resemblance to P. crispns is only superficial, although when 

 growing and in the young state the two plants are not readily 

 distinguished at a glance, even by the most accustomed eye. 



