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



longus % eu-decipiens Asch. & Graebn., Synopsis, 1897, 331, Graebn. Potamog. 1007, 

 137, Syn. 1913, 505, but no character of P. prcelongus is here present; they are all 

 verv clear lucens X perfoliatus. »Tilsit in Memela, 1866, Heidenreich» (hb. Stock- 

 holm., Berolin.), /. memelanus, is P. Heidenreichii Asch. et Gr. The Berlin speci- 

 mens are labelled: »Flora Borussiae orien talis. Potamogeton longifolius Gay. Tilsit 

 in Memela fluvio Junio 1886 legit Dr. F. Heidenreich Tilsit» »Herbarium A. Eng- 

 lkr>. »Potamogeton lucens x gramineus (P. Heidenreichii) A. u. G. Syn. I. 327. 

 (1897). 1897. P. Graebner det.»: Leaf margin strongly serrulated, apex of dcci- 

 juens-type, see above! base, see fig. 113! Ligules 40—60 mm, thin, fugitive; ana- 

 tomy: subepidermal strands lacking or almost lacking (influence from perfol.), cen- 

 tral stele lucens-Yike. It is impossible to discover anything of P. gramineus in this 

 plant. — Switzerland, Geneva in Rhöne, Chavin (hb. Stockholm., Lund.). — Lithua- 

 nia in lacu Kromån ad Naliboki, 93, Dybowski (hb. Stockholm.), f. Uthuanicus; 

 »Im Flusse Vilia (Nevis Lithuanorum) bei Vilna. Prof. S. B. Gorski» (hb. Stock- 

 holm., Uppsal.), »P. Uthuanicus Gorski»! Only the upper portion of a stem witfa a 

 branch at the primary spike. No tendency of forming floating leaves; Leaves lan- 

 ceolate, sessile, serrulate; involucral leaves rounded at base, 100 X 12—15 mm; Li- 

 gules pretty durable, without ridges, 30 mm long; Anatomy: 2 cortical circles of 

 bundles and scattered subepidermal strands. On account of these poperties the 

 plant can neither be lucens X prcelongus (Gorski), nor ulpinus X lucens (Asch. & 

 Graebner, Ar. Bennet), nor gramineus X perfoliatus, but is an evident and beauti- 

 ful decipiens-form approaching to the Swedish form from the Fyris River at Jäsevad, 

 see above! 



This hybrid is not vet discovered in Å T . America. 



P. lucens L. x praBlongns Wulf. 



(P. Bahingtonii Ar. Bennett, Notes on Potamogetons in The Journ. of Bo- 

 tany, 1894, 204-205.) 



In its Danish forms this hybrid comes partly very near x P. dåöifrit ne, partly 

 /'. lurens, with which two it has also been mixed up. From the latter, howevcr, 

 it is easily distinguished by the sessile leaves with only rudimental, only in not 

 yet full-grown leaves microscopically percoivablc teeth. Leaf-base most f requentlv 

 narrower tlian in X P. decipiens, often stalk-likc; Ligules longer and more strongly 

 bicarinate. The verv fcip of the leaves is always a little broader and shorter than 

 in P. lucens, flat or somewhat bent upward by influence from /'. ptcelongus; in 

 the two just mentioned (/'. decip. and /'. lur.) t lic tip is somewhat canaliculate 

 and recurved. Peduncles also usually more elongated than in x P. decipiens, and 

 the spikea larger. The cortical bundles of the stem are present in serera] oircles be- 

 sido the Bubepidermal one. The bundles of this oirole have an molination to bending 

 inward, from the epidermis into the radial septums (influence from /'. pra- 

 longus) which never or at least extrcmely seldom may be met with in x P. decipitns. 



