•2\t) J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETOXS. 



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

 the note »Tineo scrips.!> See fig. 103, C/ 



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

 are hitherto known. 



X. America. True specimens are seen from Fresh Pond in Massachusetts. 

 Morosg (hb. Stockholm, and Kristiania) f. jndcherrimus Hagstr.; Pine Plains, N. Y., 

 Hoysradt (hb. Stockholm.), labelled »P. gram. L. var. maximus Moroxg», »Ex hb. 

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

 H ni as Hagstr. — Ar. Bexxett has established four special North American varie- 

 ties (see Graebxer, Potamog. 1907, 83), but many Zizii-Yike North American planta 

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

 when considering these difficult forms. 



P. grammens L. lucens L. natans L. 



(P. crassifolius 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 

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

 ton (P. crassif. f. verrutus Fryer) gathered in 1890 under no. 1G68 (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 »crassifolius»-\orn\* from the two 

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

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

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

 /'. milans appears especially in the structure of the submersed leaves and in the 

 ligules. Its occurrence in a place Avhere P. Zizii was growing together with /'. na~ 

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

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

 cimens, see under /'. lucens x natans! 



I\ gramineus L. lucens i< perfoliatus L. 



(/'. Torssandri (Tis.). P. decipieus (3 Torssandri Tiselius, Potamog. sueo. 



exsicc, II, 1895 no. 75. (/'. gramineus lucens) perfoliatus ex Hagström in 



\i.i \i \\, Sveriges Fl. 1901, 790). 



I have toinicily considered Ihe plants belonging hereto lo be a nuile between 



/'. Zizii and perfoliatus, but must now leave open whether we Inne (o (hink this 

 eombination or possibly /'. lucens nitens, or decipiens gramineus. I Btill, however, 

 consider the three species written above (<> have partaken in produoing the plants 

 concerned. P. /" irfoliai us evidently appears in the rounded leaf-bases, especially those 



