232 



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



Habitat: Siveden, Smoland, Alem, Stromsrum in fluvio Alsteran, 96, H. Rappe 

 et H. TiSELius; Tveta in rivo Eman, 1862, Johansson (hb. Uppsal.). 



Another form is found in Scania with more gramineus-like lower 

 leaves : 



P subcuspidatus n. f. Folia submersa inferiora sessilia ut in P. gra- 

 mineo apice subcuspidata, superiora petiolata summa coriacea basi ssepe 

 subcordata; ligulse caducae; spica major ut in P. gramineo. 



The colour of this form is lilie that of P. polygonifolius. Both forms 

 accord with each other as to the ligules, the non-serrulate leaf-margins and 

 the nervation, non-incrassate peduncles, and in the complete sterility. The 

 stem-anatomy also corresponds very nearly: P. gramineus generally pre- 

 dominates in the periphery, polygonifolius again in the central cylinder. 

 Consequently we always find cortical and subepidermal bundles as in the 

 former, but two median xylem canals and more or less free lateral bun- 

 dles in the stele as in the latter. Endodermis of ?t-cells, intermediate. 



Habitat: Sweden, Scania, Pinnea, 1911, L. M. Neuman. 



The plants described above do not coincide with a plant from Bor- 

 Icum preserved in the Berlin Museum, gathered by O. v. Seemen and la- 

 belled iP. polygonijolins X gramineus. P. Seemenii.» »P. Graebnbr det. » 

 »Herb. P. Ascherson.» The hybrid nature of this plant is not quite cer- 

 tain, as all its pollen is fresh and fertile. At any rate it extremely ap- 

 proaches to P. gramineus: Leaf-margin serrulate (ca. 10 teeth a cm), apex 

 acute, branch-leaves — like the lower stem-leaves — sessile, style and anatomy 

 of the stem like those of P. gramin. On the other hand the upper nar- 

 row leaf-bases and the narrow peduncle are really a little strange to P. 

 gram,ineus; but the specimen is also a late flowering autumnal shoot 

 (gathered 23. VIII, with fresh pollen!), from which no certain conclusions 

 can be drawn. Be this as it may, the name P. Seemenii must stand for 

 the hybrid P. gram. X polygonif. {polygonif. X gram., ex Graebn.). 



A dubious plant from Scotland, gathered by F. Coles is also pos- 

 Fig. 109. p. gibiy this hybrid. No other localities are hitherto known. 



(jrtoiiineus X 

 polij()onifQliHs 

 {P. Seemenii A.. 

 & Gr.). a, i. 

 ianceolatifo- 

 ;i»s(Tls.)HAO- 

 stu., Submer- 

 sed leaf,-}. B, 

 f. tiithciispida- 



Topofayomfg in Hartm., Haiidb. Skand. FL, ed. 12, 1889 p. 49, P. Lundii Right., PI. 

 leatr'""^ Eur. I, 1890, 13, qui est P. gramin. X ferjol. (P. niiens Web.) v subinter- 

 medius Hagstr. f. mmlarensis Tis., vide supra, p. 226.) 



Habitu et colore P. prcelongo similis. Folia ramea superiora parva, basi lan- 

 ceolata vel brevissime lateque petiolata; omnia margine integerrima apice navi- 

 cularia. 



In 1889 S. Almqxjist {I. c.) relates of a Potamogeion from »0. Sm., Vimmerby, 



P. gramineus L. x prseloiigus Wulf. 

 (P. navicularis n. hybr., non P. gramin. x prcelongus ex Almquist 



