﻿POTAMOGETON POLYGONIFOLIUS v. PSEUDO-FLUITANS. 



(Plate 342.) 



By the courtesy of Professor I. Bayley Balfour I have been 

 able to examine the British Potamogetons of the Edinburgh 

 Herbarium, and to make a leisurely comparison of many of the 

 more interesting forms with those in my own collection; I am 

 further indebted to him for allowing me to figure and describe 

 the specimens regarded by Dr. Boswell Syme as types of his 

 variety pseudo-fluitans. 



These specimens are of unusual interest to students of the 

 genus Potamogeton, because the variety seems to be unrepresented 

 in Dr. Syme's own herbarium (now in the possession of Mr. Han- 

 bury), and because it has been regarded as depending on them 

 rather than on the sufficiently clear description in English Botany, 

 written before they were selected as types ; probably before they 

 were known to the author of the proposed variety. 



The specimens are mounted on two sheets, each of which is 

 labelled " Potamogeton fluitans, Eiver Leven, Loch Lomond, 1824." 

 On each sheet Dr Syme afterwards wrote " P. polygonifolius var. 

 pseudo-fluitans? J. B. S„" evidently then in doubt as to the correct- 

 ness of his reference of them to the form previously described in 

 English Botany in 1869. Subsequently he wrote in the Exchange 

 Club Report for 1876 :— " The most characteristic specimens of var. 

 pseudo-fluitans that I have seen are in the Edinburgh Herbarium, 

 from the Eiver Leven, but the name of the collector was not given : 

 J. T. Boswell." 



This state of P. polygonifolius has often been mistaken by 

 botanists for P. fluitans, to which it bears a superficial resemblance, 

 and it is probable that Dr. Syme at first hesitated as to which 

 species the River Leven form should be referred. A glance at 

 Plate 342 will show how like the two species are in general facies ; 

 but the following description will explain the wide difference in 

 specific character, and show that the River Leven plant is really a 

 form of P. polygonifolius: — Rootstock with slender stolons. Stem 

 simple, terete, slender, fiexuous with long internodes. Leaves all 

 stalked : lower leaves submerged, alternate, elongate, strap-shaped, 

 narrowly attenuate towards each end, membranous, 6-rib] 

 elongate cancellations on each side of the midrib, cross reticula- 

 tions coarse, ascending, continuous, apex elongately acuminate, 

 5-8 in. long by £-£ in. wide; upper leaves opposite, floating, 

 coriaceous or subcoriaceous, or membranous, long-stalked, narrowly 

 elliptical or elliptical-lanceolate, attenuate towards the petiole, 

 lamina not decurrent, apex slightly or longly acuminate, 13-ribbed, 

 ivith all the ribs prominent on the under side. Petiole 4 in. long ; 

 lamina 3^ in. long by \ in. wide; all nerves opaque. Flower-spike 

 much shorter than the suht, ieiin : i .■ peduncle rather stout, equal, 



1 in. long ; spike cylindrical, | in. long, jertiU. Stipules scarious, 



Joubhal of Botany.— Vol. 32. [April, 1894.] u 



