250 J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETOKS. 



Subsectio 24. Praelongi. Hagstr. — P. prcelongus-group Raunkijer. 



Caulis teres ramosus. Folia omnia submersa membranacea sessilia margine 

 integerrima apice cucullata, basi cordata semiamplexicaulia vel intima lanceolata; li- 

 guke fibrosse ± persistentes ecostata?. Pistillum stylo conspicuc ± angusto. Frucius 

 magnus valde carinatus. — Anatomia caulis: H-endodermis, fasciculi librif. et vascu- 

 lares corticales numerosi. Fasciculi tubi centralis prototypice dispositi. — Piwfolia- 

 tio convoluta. Turiones rhizomatici desunt. 



On account of the peculiar cucullate form of the leaf-apex etc, see below, the 

 single hereto belonging species cannot be placed together with /'. perfolia&us, 

 though the pistils and stigmas of the two species are much the same. In his Ana- 

 tomical Potatnogeton-Studies (1903) C. Raunki^r therefore is correct in putting 

 them in separate groups after having classed them together in his earlier work, De 

 danske blomsterplanters naturhist. (1896, 108 — 109). In the Synopsis der mitteleur. 

 Fl. 1912, P. Grjebner still unites them into a common group Pcrjoliati. 



P. pneloiigus WULFEN. 



Plantarum nov. descriptiones, in Roemer, Archiv fur die Botanik. Ill, st. 3, 

 1805, 331. — P. flexuosus Wredow, Mecklenb. Fl. 1807, ex Schleicher, Cat. pl. 

 Helv. 1815, 23. — P. flexicaulis Detharding, in Strelitzcr Anzeig., 1809 no. 50. — 

 P. acuminatus Wahlenberg, Flora upsal., 1820, 58. — P. perjuVudus v. lacustris Wall- 

 man, in S. Liljeblad, Utkast till en Sv. flora, 1816, 706. — /\ gramineus a borea- 

 lis L^stauius, Beskrifning öfver några sällsyntare växter etc, in K. Sv. Vet. Ak. 

 Handl. 1824, 162. P. salicijolius Wolfg. ex Fries, Summa veg. scand. I, 1846, 

 213, et ex Hartman, Handb. Skand. Fl., 1879, 432. 1 Figs. 1, A, 116, 117, /'. 

 Ils, C. 



With regard to the styles and stigmas this species does not essentially differ 

 from /'. perfolialus; the pollengrains are also much the same, of middle size, spheric 

 or spheric-o\ oid in shape. Nor do the form and the nervation of the lenes present 

 any more considerable differences. The ligules are thicker and more })ersistent but 

 without the double ridges like 7*. perfdliatus and alpinus. What, nevertheless, necessi- 

 tates to put these habitually similar species into separate groups is above all the fruit- 

 form, the form of leaf-apex, the character of leaf-margin, and some anatomical proper- 

 feies. The lid of the putamen mostly quite rounded in /'. perfoliaius, is in /'. ]>nt- 

 longua sharply keeled, t lic fruil therefore, bolh in fresh and div state with a promi- 

 nent kcel cs|)cciallv upwards, while the Iruit of the former in fresh state is rounded 

 on the hack and increly in diy state sometimes endowed with a laint false keel. 

 The cells of the endocarp, on the contrary, in both groups comparatively thin-walled 



1 A fossil from Toppeladug&rd (Scania) described by me in Geol. Pören:s Förbandi, 1906 under the 

 oame "t Hohtia splendens haa låter proved to be /'. pralongus. 





