160 



J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



3 



been set up but witliout argumentation. Fry er has also first of all pointed ont 

 the near relationship between P. lanceolatus and P. rivularis. 



The stem of this plant is te re te and capillarv without the compression charac- 

 teristic to the body of the pusilloids. This being the case, there can be thought of 

 only three linear-leaved species which possibl)- may havc produced P. lanceolatus and 

 P. rivularis, viz. P. pusittus, panormitanus, and trichoides. The last mentioned is 

 excluded partly on account of the short peduncles of the hybrid, partly for its livch 

 green colour, partly for the weak nervation and obtuse broad apex of the submersed 

 leaves, and finally for the very faint subepidermal strands in its stem-anatomy. 

 The nervation and leaf-apexes taken together with the beliaviour of the stem-prolonga- 

 tiou are against P. panormitanus also, which, besides, usually has longer peduncles. 

 The ligules, however, are decisive to my opinion. They are always o pen 

 and convolute and as to the nervation intermediate between the above two species 

 by being 4 — 6-nerved in the front-field. 



If we proceed from the leaves, \ve must as the one of the 

 parents think of a species with floating leaves and many-nerved 

 submersed leaves, thus P. gramineus, alpinus, polygonifolius or 

 coloratus. The first mentioned is excluded partly on account of 

 the smooth margin of the submersed leaves, partly and absolutely 

 for the obtuse leaf-apexes with their peculiar nervation, as fche 

 side-nerves do not bend out into the point but end with a curve 

 in the midrib. P. gramineus X pusiUus and still more P. groin. X 

 m a c ronatus must necessarily have cuspidate submersed leaves since 

 this character is essential to both these species. Other circum- 

 stances also are against P. gramineus, for instance the form of the 

 pedunele, the O-endodermis of the stem, the absence of eortieal 

 interlacunar bundlcs in the stem, the feeble ligules, etc. The sessile submersed 

 leaves exclude also undoubtedly the suggestion of P. polygonifolius and coloratus. 

 uhereas everything points in the direetion of P. alpinas, the stem-anatomy also by 

 the epidermis consisting of large-roomed cells without hypodermatic laver and the 

 endodermis of O-cells. Cf. under P. variifolius! Above all it is the nervation of 

 the submersed leaves together with their blunt points, the form of the floating Leaves 

 and their stalks (always shorter than the blades) and the feeble ligules without rid- 

 ges that favour the supposition t hat /'. alpinus has been active in this case. 

 The stem' s mode of prolonging itself corresponda entirely to that of /'. pusiUus 

 and /'. alpinus. — Turios are not seen by me and are not hitherto deSClibed l'\ 

 any author. 



The central cylinder of the stem is the same as in /'. pusillus, which holdfi 

 good for both the Knglish and 1'Yench forms. ( 'oncerning t lic deseript ion and 1'igui vs 

 of the former I rclcr to Au. BBNNBTT, /'. lanceolatus Sm., in the JouiU. of Hot., 

 1881, t. 217. 



Distribution. Englund. Anuclsea. N. Wales. ISOS, DAVIES (hl). l'|)|)sal.), 



Potamogeton sp. nov. ftev. II ron Davibs to Smith 1808 Ironi North Wales-; is;{(). 



68. /'. lanceolatus 



i i op of b Bobmeraed 



iiowing the ii('i \ a t ion, 



\. B, Floatmg leaf, \. C, 



Pistil, Bide-i iew, ',"■ 



