and Old World Birches. 169 
vegetation and are rapidly spread by means of their thin- 
winged or hairy fruit. In fact, this relation of the Alaskan 
willows to those of the Old World is brought out by Mr. F. V 
Coville in his scholarly monograph on the Willows of Alaska,* 
in which he recognizes 23 species, 2 of them cireumpolar in dis- 
tribution, and 9 others occurring in Siberia. That is, of the 
23 willows recognized by Mr. Coville in Alaska, only 12, or 
scarcely more than one-half, are endemic North American 
species. A similar detailed study of northeastern Salices will, 
it seems to the writer, likewise show a closer relationship be- 
tween certain other American and Old World forms than has 
been generally recognized. 
e examination of the birches by the writer has led to the 
uniting of some well-known American and Old World trees 
and shrubs. The conclusions reached in his studies, and cer- 
tain details of the studies themselves, may best be presented 
by discussing separately the species which have been specially 
examined. 
§$Albze. Trees or shrubs: the wing two or three times as 
wide as the achene ; rarely only a little broader. 
BetTuna ALBA. 
The original Betula alba of Linneeust seems to have em- 
braced both the common white birches of northern and central 
ramis ereetis strictis” : ; and “ Betula pendula. B. foliis ovato- 
acuminatis inciso-serratis glabris, ramis flaccidis pendulis.”’+ 
This separation of the two trees by Roth has been very g gen: 
Fe ignored by recent European authors, nevertheless, “and 
the species with pubescent (“scabrous ”) leaves and upright 
aus es, the true Betula alba as interpreted by Roth, is uni- 
ersally known abroad as B. pubescens, Ehrh.,§ while t 
Hears Sa species with pendulous branches, the Bevdle 
pendula, Roth., is ordinarily known by its later name, B. ver- 
PUCOSA, rh. 
By some authors, as Prantl| and Guerke,{ these two white 
birches are treated as distinct species, while by others the 
entire group is regarded as a polymor hous species with many 
subspecies and varieties. Rehder, in Bailey’s Cyclopedia of 
American Horticulture, disposes "of the forms in this way, 
* Proc. Wash. Acad. Sci., iii, ne ete + Sp., ii, 982 (1758). 
[Pran Fl. Germ., i, 404, 405 (17 "2 Beite., v, 160, vi, 98 (1700-91). 
Prantl in Engler & Prantl, Nat. yee iii, pt. 
‘| Pl. Eur., ii , 47, 48. 
