1891.] Botany. 149 
southeastward. The same_is true, less noticeably, of the smaller 
genera. Marked exceptions, however, will be noted in the genera 
Viola, Vaccinium, and Kalmia. These are all northern genera, and 
their anomalous distribution demands explanation. Of Viola it might 
be said with reason that many of the species have entered from the 
east rather than from the west. It is a cosmopolitan genus at the 
present day, and may have entered the continent by other paths than 
the ordinary passage across Bering Strait. In Europe, according to 
Nyman,! there are fifty-six species of Viola, while in the Russian Em- 
pire, according to Ledebour? there are but forty. This would indicate 
an eastern expansion in North America, corresponding with the west- 
ward expansion in the old world. At any rate, the present diffused 
condition of Viola species makes the problem of the general distribu- 
tion much more complicated than it might at first appear. The genus 
Viola, then, although probably northern in point of origin, has been 
= fedistributed from southern stations, ‘it may be, and the position of 
= Species over continental areas is due to a more complicated interaction 
i of Causes than the present writer is able to explain. With reference to 
Vaccinium and Kalmia, however, no such argument can be employed. 
Of Vaccinium there are but ten species in the Russian Empire and but 
three in Europe. The genus is seen, therefore, to center in North 
America. Kalmia is a North American genus, one species ranging to 
Cuba, but none found native in the Eastern Hemisphere. Both of these 
genera, then, are somewhat differently situated from Pyrola, which, al- 
though centering in British America, has five species in Europe and 
fve in the Russian Empire. Kalmia and Vaccinium, being typically 
ye American, may have originated far eastward on the continent, 
and this would give an explanation of the greater distribution south- 
: —e than southwestward. It is a fact that even the Canadian 
n Dore these two genera are principally in the eastern provinces. 
i ‘Ba Y one species and one variety of Kalmia range west of Hudson 
Tal 
ad 
<i yan fifteen of the twenty-two species and varieties of Vaccinium 
‘ ‘ ate the eastern provinces. A similar state of affairs on the west 
i ic. “sie the genera Arenaria and Peucedanum. Both of these 
Wa = < Upon me western plateau-regions of the continent. 
& up the column which shows the southeastern extension it 
up the t the total is just about half of that obtained by add- 
; R y column which shows the southwestward extension ; that is, 
2 eae peces of northern genera come south along the Rocky 
