24 J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOOETONS. 



by the colour of the ]eaves, their fragility and apexes (in general), the colour and 

 structure of the sheaths and their quality of being connate when young, and the 

 mode of branching with only one branch in each axil. Finally the pollengrains, 

 style and stigma belong to P. fUiformis, to which may be added that the fruit 

 when developed is intermediate or often hardly larger than in a macrocarp P. fili- 

 formis. The central cylinder of the stem is rather slightly differed from that of the 

 just mentioned species. 



Distribution. Denmark, Ju ti and, Kongeaa, 96, Baagöe (hb. Stockholm.). — 

 Tirolia sept. in rivö Giessen, Hellweger (hb. Lund.), Zimmeter et Zarntheim (hb. 

 Lund.), Innsbruck in Giessen, 83, Tiselius (hb. Stockholm, et Uppsal.). In lacu 

 >Pillersee» ad St. Ulrich 834 m s. m., 10, Keller (hb. Stockholm.). 



P. filiforillis Pers. x vaginatus Turcz. — P. vaginaius x fUiformis ex Fontell, 

 Von ein. Potam. Hybriden 1902, 2. — P. fUiformis X vaginatus ex Fontell, Beitr. 

 Anatom. Bau Pot.-Art. 1909, 30. — P. fennicus Hagstr. 



This bastard has a greyish tone of colour that points to P. vaginatus as the 

 one of the parents. This parentage is confirmed by the richer ramification, thus 

 differing from x P. suecicus, in which the evolution of branches more agrees with 

 P. fUiformis and the colour moreover inclines to brown or green. It differs from 

 P. pectinalus X vaginatus, the more slender forms of which it bears strong resemblance 

 to, through the slender, only at the base somewhat thicker stem, the usually shorter 

 weaker basal sheaths, the always obtuse, narrow and often longer, upwards less 

 tapering leav r es and a less number of cortical strands in the stem, commonly 6 — 8 

 in one circle at the middle internodes. For the rest the sheaths are intermediate, 

 but even when very young open as in P. vaginatus; ligules as in P. fUiformis, but 

 more persistent and of stronger structure, leaves elongated and narrowly linear, pe- 

 duncles thin and more elongated, spikes of four verticils or more. A cross-section 

 of the stem shows a central cylinder with four lysigene channels, an endodermis of 

 typical w-cells and usually a few narrower air-cells among the wider in the attermost 

 circle. The leaf-structure is more like that of P. vaginatus than of P. fUiformis, and 

 the marginal nerves retire more or less from the börder just as in that. In the 

 peduncle the four central vascular bundles appear conspicuously, and in the wholo 

 the hybrid in its hitherto known forms approaclies more the P. vaginatus than the 

 /\ fUiformis. The slendcrness, the thin elongate peduncle and intermediate mode of 

 branching makes it at the first glance rather easily recognizable. 



Distribution. Sweden, West-Bothnia, Löfånger, 1870, L. Andersson (hb. 

 .1. O. HAGSTRÖM). — Finland, Ostrob. bor., Karlö, 84, Sandman (hb. Uppsal.). The 

 third locality is Pedersöre, Ostrob. med., coll. C. W. Fontell 1901. 



A plant from Canada. Winipeg Walley, 1859, E. BouRGEAU (hb. Stockholm), 

 labelled »Pallisérs Brit. N. Am. Expl. Expedition. P. pectinatus var.- I as \\HI 

 refer to this hybrid. According to A. O. Kim. man (in Bfeddel. Soc. Fauna et Fl. 

 fenn. 1888, 113) P. vaginatus is said to have been collectcd by Bourgeau, on the 

 Expedition of PäLLISBB in 18f>8 in Naskatsohavan and communicated as P. 'pectinalus 



