32 



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



nical strands both on the upper and lower surface and in addition 1 — 2 over the 

 midrib (fig. 10, B). In this manner the leaves become a little striate. Counting 

 also these faint nerves, the leaves appear 7 — 9-ribbed. 



The verticils closely placed at regular intervals suggest in this species an ob- 

 vious affinity to P. vaginatus. The characteristic apex of the involucral leaves 

 resembling that of the Callitriche vernalis (possibly only a secondary formation) and 

 the bifurcate fruit make it easily distinguishable from all the other Coleogetons. 



Distribution. Siberia, Yenisei, Nikandrovskij -island, 1876, M. Breisiner (hb. 



Fig. 11. P. vaginatus Trncz. A, Top of a stem-leaf, cf. the next fig. E.', 'j'. B, and C, Tops of branch-leaves, 'j'. D, Leaf- 

 axil and ramification (natural size, but for better illustration somewhat schematized), a, main-shoot beneath the middle, 6, leaf 

 with sheath and ligale (c) clasping the basal parts of four evolved branches of Ist to 4th rank {1, 2, 3, 4) and a small bud 

 (5) of 5th rank, f, prophyllum, If scale-leaves, from which the branches 3, 3, 4, 5 grow out, the youngest ones therefore always 

 turning towards the leaf h. The internode next above the scale much elongated (i^ of the branch 1 and so on). The two inter- 

 nodes of each branch beneath it, on the contrary, extremely abbreviated, all taken together forming a sympodium of only a few 

 mm in length (much shorter, thus, than in the figure) included within the basal part of the sheath. E^ Hibernating tnrio, nat. 

 size; explanation, see the text and the explanation of the tnrio of P. fiUformis Pers., p. 1.5. 



Uppsal.), and Malo Briochovskij island, 1876, Sahlberg (hb. Stockh.). The latter 

 island is situated on 70° 50' N. L., and P. subretusus therefore seems to be the most 

 northern PotowJogron-species of the world (see under the following!). 



P. vaginatus Turczaninow. 



Flora Baicalensi-Dahurica, — in Bull. Soc. Imp. des naturalistes de Moscou 

 1854, T. XXVII. 2<J partie, p. 66. — Cfr Kihlman, Pot. vaginatus TuRCZ., ny for 

 Europas Flora, — in Meddelanden af Soc. Fauna et Fl. fenn. 14. 1888, 111—115. — 

 Fig. 11 and 12. 



