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



him described and determined as »P. lucens L. psilostachyum Tin. » The label bears 

 the note »Tineo scrips. !» See fig. 103, CI 



The hybrid also spreads eastward following the parent-species, but few localities 

 are hitherto known. 



N. America. True specimens are seen from Fresh Pond in Massachusetts, 

 MoRONG (hb. Stockholm, and Kristiania) f. fulcherrimus Hagstk.; Pine Plains, N. Y., 

 HoYSRADT (hb. Stockholm.), labelled »P. gram. L. var. maximus Morong*, »Ex hb. 

 MoRONG»; Lake Champlain ad Alburgh, Vt., 85, Morong (hb. Stockholm.), f. pulcJier- 

 rimus Hagstr. — Ar. Bennett has established four special North American varie- 

 ties (see Graebner, Potamog. 1907, 83), but many Zizii-like North American plants 

 are not at all this hybrid, but of another origin, and great carefulness is necessary 

 when considering these difficult forms. 



^& 



P. gramineus L. x lucens L. x nataiis L. 



(P. crassifoUus Fryer, On a new hybrid Potamogeton, in The Journal of 

 Botany, 1890, 321—322, t. 299). 



Fryer has displayed an abundant and splendid collection of plants from Eng- 

 land which are said to represent this hybrid, signed by the author as »P. Zizii X 

 natans». The specimens from Cambridgeshire, Co. 29, Distr. 7, Westmoor, Dodding- 

 ton (P. crassif. i. verruttis Fryer) gathered in 1890 under no. 1668 (hb. Stockh.) 

 must be considered to have the greatest probability for this descent. Also nos. 422 

 and 423 from Doddington, 1887 (hb. Stockholm.), seem to be this double hybrid. 

 They have longer and narrower petioles than the »crassifolhis»-ioTm.s from the two 

 other localities, thereby showing their relation to P. gramineus, of which the ligules 

 also remind. Towards P. lucens point the apexes of the floating leaves by being some- 

 what elongated, and their comparatively short petioles (not longer than the blades). 

 P. nutans appears especially in the structure of the submersed leaves and in the 

 ligules. Its occurrence in a place where P. Zizii was growing together with P. nu- 

 tans confirms also the supposition made by Fryer. The stem-anatomy, however, 

 cannot give any positive conclusion in the case. Respecting the rest of the spe- 

 cimens, see under P. lucens X natansi 



P. gramineus L. x luceus L. x perfoliatus L. 



(P. Torssandri (Tis.). — P. decipieus [5 Torssandri Tiselius, Potamog. suec. 

 exsicc, II, 1895 no. 75. — (P. gramineus X lucens) X perfoliatus ex Hagstrom in 

 Neuman, Sveriges Fl. 1901, 796). 



I have formerly considered the plants belonging hereto to be a mule between 

 P. Zizii and perfoliatus, but must now leave open whether we have to think this 

 combination or possibly P. lucens X nitens, or decipiens X gramineus. I still, however, 

 consider the three species written above to have partaken in producing the plants 

 concerned. P. perfoliatus evidently appears in the rounded leaf-bases, especially those 



