310 
are interested in the problem of the distribution of plants. In this 
connection the fact that the genus was of almost universal distribu- 
tion in the past, at least over the whole Northern hemisphere, 
until comparatively recent geologic times, is of the greatest interest 
and significafice, not only in regard to its present distribution, but ; 
also in regard to the evolution of the living species. We are no 
longer under the necessity of accepting the almost impossible the- 
ory that the plants have migrated in modern times from one con- 
tinent to another, but are irresistibly led to the rational conclu- 
sion that, inasmuch as the genus existed on both continents until 
very recent geologic times, the presence of the living species in 
their now isolated and widely separated ranges is merely due to 
the extinction of plants from former intermediate localities, prob- 
ably due to the vast climatic changes wrought by the advent of 
the Ice Age. We should also be within the bounds of reason if 
we supposed that the two living species may have been merged 
in one common ancestor at no very remote date, and that the 
specific differences which we now note as existing between them 
have resulted from differences in environment since their isolation 
from each other. 
We may also note, as of interest, that the leaves have com 
stantly increased in size up to the present time. The American 
cretaceous species, if we except V. arctica Heer, from Greenland, 
began with leaves little more than an inch in diameter. In 
tertiary times they had developed to a diameter of four or five 
inches, while at the present day they reacha size of two feet or 
more. 
Varieties of Solidago and Aster. 
SoLmpaGoO CANADENSIS GLABRATA N. var. 
_ Stems low, 2-3 ft. high, puberulent above; leaves numerov®, 
linear-lanceolate, upper ones entire, lower ones with a few sharp Sef 
ratures, smooth above, somewhat pubescent on the midrib and veins 
beneath; panicles small, with slender branches; heads small ; 
bracts of the involucre acute or acutish; rays short and few. : , 
Mt. Desert Island, Me., Rand and Redfield. At several poin's 
along the Susquehanna river, Pa. In some states it approaches 
S. rupestris Raf. | 
