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



»foliis lineari-lanceolatis». The note of the label is evidently directed to Prof. E. 

 Fries, who on a separate label autographically has added: »Potatnogeton salicifolius 

 WoLFG. ex Fr. S. V. Sc. ! Angermannia L^estadius. ' Afterwards Hartm., Skand. 

 Fl., has recorded, after Fries, Kengis as the single station of P. salicifolius, which 

 according to both Hartman's and Fries' earlier (cf. Fr. Nov. 2. 41) views has 

 been looked upon as P. prc^longus. With this »P. salicifolius >> Hartman later on 

 united a »p lanceolotus'>, comprising partly forms of P. gramineus, partly also of the 

 hybrid P. m'^ens (see above!). — Lapland, Lap. pit., 23, L^.st. (hb. Stockholm.), »P. 

 salicifolius Fr. S. V. Sc.», »P. prcelongus p graminifolius Hartm. »; Arjeploug, 24, 

 L^ST. (hb. Uppsal.), hb. Hartman, by L^st. named »P. gramineus v. lanceolaius-^ , 

 to which Hartman has added the following parenthesis »(v. boreale L. V. Ac. H. 

 1825)», narrow-leaved (stem-leaves 15 mm broad); Lp tornense, Dr. Deutsch, hb. 

 Z:DT. (hb. Lund.), Karesuando, L^st. (hb. Stockholm., Uppsak). 



According to Scheutz, PI. vase. Jeniseens., this species is gathered by H. W. 

 Arnell in the Nikandrovskij island situated in the Gulf of Yenesei 70° 20' N. L., 

 which is its most northern habitat. From this northern limit it descends to the 

 south and is met with in the Faroe Islands, Shetland Islands, British Isles, Den- 

 mark etc. through Europe to the Jura Mountains, Switzerland (Lac de Failleres, 

 Godet, hb. Uppsal.) and the Alps, and through Asia, Japan (Moraran, Ezo, 42° 10' 

 N. L,, Coll. Pere U. Faurie) to the year-isotherm of about + 12° C. (inner Asia 

 probably 10° or 5°) and in North America the southern boundary seems to be the 

 same (cf. Britton and Brown, 111. Fl. etc., 1896, I, 71!). 



Subsectio 25. Perfoliati. (Graebner) Hagstr. — P. perfoliatus-group 



Raunki^r. 



Caulis ut in prsecedente. Folia omnia submersa membranacea sessilia amplexi- 

 caulia vel infima basi rotundata, apice ± canaliculata serrulata; ligulse breves eco- 

 statae valde caducee vel in fibrillas cito scissse. Pistillum ut in prajcedente. Fructus 

 magnitudine media, vivus dorso rotundatus. — Anatomia caulis: 0-endodermis, fasci- 

 culi libriformes vascularesque corticales typice desunt. Fasciculi median! tubi cen- 

 tralis ut in Fig. 1 G dispositi. — Prsefoliatio convoluta. Turiones rhizomatici obvii. 



This group includes a few nearly allied species united formerly into one spe- 

 cies, P. perfoliatus, but lately, by P. A. Rydberg and M. L. Fbrnald detached 

 from the genuine P. perfoliatus and established as separate species. Of those P. 

 Richardsonii is a comparatively better marked form than P. buplewoides, which 

 perhaps rather might be put as a subspecies under P. perfoliatus L. 



As to the stem-anatomy they are all quite like, thus behaving almost as the 

 species of the group Polygonifolii, and you will have no help from the inner struc- 

 ture of the stem in distinguishing the species from each other. They are all non- 

 sclerenchymatous plants in contradistinction to the preceding group. It is noticeable 

 that P. Richardsonii with its strong ligular fibers nevertheless is devoid of ligular 



