DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 339 



Urtica gracilis, Ait. Tliis is reduced to dioica, var. e, by Weddell. 



Betula. I am quite unable to disentangle the species, forms, and varieties of this 

 genus, or to harmonize the views of Fries, Spach, Regel, and other botanists. The 

 Northern species are clearly most difficult of discrimination, as a reference to Fries's 

 notes (Summa, pp. 211 and 556) will show. Kegel's recent ' Monograph ' seems carefully 

 and judiciously executed. 



B. glutinosa, Wallr., is now by Fries and others considered one with alba. Koch refers 

 it to.pubescens, Ehr., /3. Carpatica ; Kegel (Monog. Betulac. p. 21) to alba S. glutinosa. 



B. intermedia, Wahl., is alba [3 of Ledebour, an Arctic Russian plant ; it is the Immilis 

 of Hartm. and Rupr. (non Schrank). Ledebour observes that it approaches to nana very 

 closely. 



B. papyracea, Ait., is reduced to a var. of alba by Spach and Regel, and possibly rightly ; 

 but the American botanists, who know both, keep them distinct. 



B. nana, L., is, according to Asa Gray, distinguished by a narrowly winged fruit; but 

 the wing of Scotch specimens is very broad, and Ledebour remarks that this is a variable 

 character ; Regel says it is narrow or almost absent. 



B. glandidosa, Mich. This, according to Asa Gray, is the pmnila, L., distinguished 

 by its cylindric catkins and broad-winged fruit. I have seen no Greenland specimens 

 of it. It is the nana ■y. intermedia of Regel, who keeps ptmiila, L., as a distinct species ; 

 he apparently has not consulted Asa Gray's ' Botany of the N. U. States.' 



B. alpestris, Fr., is the Immilis, Hartm., fid. Fries, and is so like British specimens of 

 nana as to be scarcely distinguishable. I think it may well be included under /r?/iicos«. 

 Pall. ; Ruprecht, however, refers Immilis, Hartm. (non Schrank), to intermedia {alba, var. 

 intermedia, Walil.) . Regel makes of it nana S. alpestris, and possibly rightly. 



Alntjs barbata, C. A. M. Fries keeps this distinct, and gives as a hal3itat Lapland, 

 where glutinosa does not grow. H is the glutinosa 7. barbata of Ledebour, and ^.pubescens 

 of Regel. 



A. viridis, DC. Ledebom' distinguishes the plant of Chamisso, from Arctic America, 

 from DeCandolle's ; but to me they seem identical. 



A.fruticosa, Rich. This, in the list, p. 301, is a misprint for glutinosa, Hiclmvdson 

 (non Willd., &c.), which has been referred to viridis in 'Flor. Bor.-Am.,' and rightly. 



A. repens, Vahl. The specimens I have examined of this appear identical with Richard- 

 son's glutinosa, and with A. viridis, DC. It is omitted in Regel's Monograph. 



Salix. I am indebted to Dr. Andersson of Stockholm for the Arctic List of this genus, 

 who has further kindly supplied the following observations. 



Salix pentandra. In Lapponia et Siberia certissime occurrit, in Lapponia ad locum 

 Enare (maxime septentrionem versus !), in terra Samojedorum, in Kamschatka 

 infra circulum polarem. In America sub forma lucida ad Fort Franklin ct Mackenzie 

 River. Ibi itaque non ad floram arcticam pertinet. 



>S'. lanata, L. In omnibus regionibus arcticis vulgaris, 



S. mdiardsoni, H., est S. lana tee {orraa Americana: cf. And. I. c. p. 3 3. 



S. speciosa, H. et A. Species elegantissima, Americce decus ! 



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