36 J. O. HAGSTRÖM, CRITICAL RESEÅRCHES ON THE POTAMOGETOXS. 



Tlie Canadian vaginatus constitutes a peculiar race: 



V. fjinadcnsis n. var. — Ligula paulo nervosior. Fruetus latior, 2, a 2,ö mm (in 

 statu sicco), margine ventrali recto. — Anatomia caulis: cellulse epidermidis elongata?. 



The ligule has the same form with subretuse apex and the same length as in 

 the main-form, but is endowed with stronger nerves, by which, after the ligule has 

 decayed, the upper margin of the sheath gets another appearance than in the pri- 

 mary form. 



This variety stånds to the main-form almost as the v. Macouni of P. jilijormis 

 to the main-form of this species. It is unlike inasmuch as the stem-anatomy also 

 deviates by its stretched epidermis-cells, and it may perhaps be necessary to sepa- 

 rate it as a distinct species P. canadensis, which I leave to future decision. 



The specimens examined are collected by Asa Gray, named P. pectinatus L., 

 mentioned in A. O. Kihlman, Pot. vag., in Medd. Soc. pro Fauna et Fl. fenn. 1888, 

 113, and by Macoun, near Banff in Alberta, Canada, 1891, named P. pectinatus L., 

 both preserved in the Univ. Mus., Christiania. Cypress Lake, Assiniboia, 95, Macoun 

 (hb. Haun.). 



Distribution. Sweden, West-Bothnia, Haparanda, 87, Hammaren (hb. Upp- 

 sal., Lund.), Skellefteå, Bäckfors, 75, Melander (hb. Stockholm., Uppsal.), Piteå, 

 Bredskär, 69, Lundberg (hb. Uppsal.), Piteå, Recknön, 66, Lundström (hb. Lund.), 

 Umeå, Tafle Skärgård, 89, Andersson (hb. Uppsal.), Bygdeå, Ratan, 68, Berg- 

 holm (hb. Stockh., Uppsal., Gotenb.), 1901, Fahlander (hb. Lund.). Anger- 

 mania, Nora, Grönvik, 56, Fristedt & L^estadius (hb. Stockholm.), Själevad, 96, 

 Blomqvist & Lundberg (hb. Stockh., Uppsal.), Hernösand, 99, Tisélius (hb. Uppsal.). 

 Medelpad, Tynderö, 88, Neuman (hb. Stockholm., Uppsal., Lund.), 91, Edvall 

 (hb. Uppsal., Lund., Gotenb.), 98, Lidholm (hb. Uppsal.). — Environs of Stockholm, 

 Stora Värtan, 46, J. E. W— m (hb. Stockh.), Värmdön, Rörsundsvik, 88 & 96, Ti- 

 sélius (hb. Uppsal., Lund., Got.), f. tenuior, Ulfsundasjön, 90, Östling (hb. Stockh.), 

 in fresh water. 



Rörsundsvik at Stockholm is the most southern station on the Swedish coast, 

 59° 19' N. Lat. In Finland this species does not descend along the coast southward 

 farther than to 63° 30'. No specimen having been found between Stockholm and 

 Tynderö, the former place is to be considered as outside the proper distribution- 

 area, which may be reckoned to extend from 62° 30' northward. Followiug tho ycar- 

 isotherm of this district of the Bothnian Gulf eastward, we arrive at the neighbour- 

 hood of Lake Baikal (Irkutsk — Selenginsk), see p. 33, abové, and at Kamtschatka 

 Aleutian Islands- South Canada. It is therefore probable that the Tunv.aninowian 

 habilat, Selenginsk, belongs to the south boundary line of the species, which may 

 fairly coincide with the year-isotherm for + 2°C. The particular distribution fcerri- 

 tory of P. vaginatus may hv the large river-district of North Asia or the väst forest 

 territorv of Siberia and northward up to the aretie regions (Tolstoi nos, Yenisei- 

 valley, 1876, Bkknnkr, hb. Stockholm). From there it has spread eastward and 

 we&tward as is gtated above. 



This Buppositioo is oonfirmed by the records of the vegetation of Yenisei-valley 



