DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 339 
Urtica gracilis, Ait. This is reduced to dioica, var. e, by "Wcddcll. 
Betula. I am quite unable to disentangle the species, forms, and varieties of this 
genus, or to harmonize the views of Fries, Spach, Itegel, 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. Hegel'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., j3. Carpatica; Kegel (Monog. Betulac. p. 21) to alba 8. glutinosa. 
B. intermedia, Wahl., is alba /3 of Ledebour, an Arctic Russian plant ; it is the humilis 
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 Kegel, 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 ; Kegel says it is narrow or almost absent. 
B. glandnlosa, Mich. This, according to Asa Gray, is the pumila, 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 Kegel, who keeps pumila, L., as a distinct species ; 
he apparently has not consulted Asa Gray's ' Botany of the N. U. States.' 
B. alpestris, Fr., is the humilis, Hartm., fid. Fries, and is so like British specimens of 
nana as to be scarcely distinguishable. I think it may well be included under fruticosa, 
Pall. ; Kuprecht, however, refers humilis, Hartm. (non Schrank), to intermedia {alba, var. 
intermedia, WahL). Kegel makes of it nana 2. alpestris, and possibly rightly. 
Alnus barbata, C. A. M. Fries keeps this distinct, and gives as a habitat Lapland, 
where glutinosa does not grow. It is the glutinosa y. barbata of Ledebour, and (3. pubescens 
of Kegel. 
A. viridis, DC. Ledebour distinguishes the plant of Chamisso, from Arctic America, 
from DeCandolle's ; but to me they seem identical. 
A.fruticosa, Kich. This, in the list, p. 301, is a misprint for glutinosa, Richardson 
(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 Kegel'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 
Enure (maxime septentrionem versus!), in terra Samojedorum m Kamchatka 
infra circulum polarem. In America sub forma Ucida ad Fort Franklin et Mackenzie 
River. Ibi itaque non ad floram arcticam pertinet. 
S. lanata, L. In omnibus regionibus arcticis vulgaris. 
& Bichardsoni, H., est S. lanata forma Americana : cf. And. I. c. p. J 3. 
S. speciosa, H. et A. Species elegantissima, America decus ! 
VOL. XXIII. 
