1863.] POX OWE EDS. 467 



Note. This species or variety is very abundant in Ham ponds, 

 or rather ditches, Kent, near Sandwich. 



4. P. lucens, Linn. This species has a very stout (thick) cy- 

 lindrical, leafy stem. The leaves ai'e elliptical, tapering at both 

 ends, sessile or nearly sessile, ending in a small, short, sharp 

 point; they are somewhat wider than those of P. rvfescens, and 

 not quite so long ; their ribs, or nervation, or network, or frame, 

 is like that of the above-mentioned. The stipules are large and 

 winged. The peduncle increases upwards. 



The colour is greenish with a tinge of red. The spike of fruc- 

 tification is dense and the fruit like most of that of the broad- 

 leaved species. It is generally distributed over Europe. 



5. P. rufescens, Schrader, is in some respects an intermediate 

 species or form. It has a slenderer stem than P. natans, and a 

 shorter spike ; but it has not shining and pellucid leaves like P. 

 lucens. It may be known from the former, P. natans, by its 

 lanceolate leaves, which taper at both ends, and are either sessile 

 or on short stalks which gradually dilate ; the lateral iil)s are 

 connected by prominent tertiary, transverse (crossing) nerves : 

 their colour is greenish and purplish, and they do not float on 

 the surface like those of P. natans, but swim or are suspended 

 under water like P. lucens. They are all uniform, and the sti- 

 pules arc not conspicuous, excepting those which subtend the 

 peduncle. 



This species is pretty general in Europe, being distributed from 

 Norway to the Adriatic Sea. 



6. P. perfollaius, Linn. In several characters this species ap- 

 proaches P. lucens, viz. in having a round stem, pellucid leaves, 

 dense fructification, etc. Its prominent distinctions are its ovate, 

 sessile, clasping leaves, which are of a pale green colour and occa- 

 sionally tinged with olive. 



7. P. prcelongus, Wulf, approaches P. rufescens in the shape 

 and size, but not in the colour of the leaves, which are green, or 

 green tinged with olive, and not pellucid. The stem is very long, 

 being always (?) found in deep water. The peduncles and spike 

 are like those iii the foregoing, not always of the same dimen- 

 sions, but varying with the size of the fruit. 



8. P. heterophyllus, Schreber; P. gramineus, Linn.(?) Several 

 authors, — Nyman, for example, — enter A. gramineus, Linn., as 

 a synonym of P. heterophyllus, Schreber ; and consequently the 



