Evening star., 1938-05-28

means Of such minute clues he Is able to
construct tentative maps of the ice ages.
A notable example, he points out, is a
little yellow violet found in Alaska. 1t
also in found in Colorado. None ever
has been found in the vast region lying
between. This is almost indisputable
evidence, DR.. Hulten believes. of the
extent of one of the ice sheets. Once
the little violet probably grew generally
over the whole area. Under the stress
of extreme climatic conditions it be-
came so genetically frozen that when the
country was opened up again it could
spread neither northward nor south
ward by insect pollenation of closely re-
lated species. 1t could progress only
extremely slowly, so that any advances
are hardly yet discernible, although
much of the intervening territory has
been opened up for more than 10000
years.
This is an extreme illustrative case.
The genetic freezing progressed to vari-
GUS degrees with different varieties.
Some were able to spread out of the
Alaskan haven, and also northward from
the southern limits of the icecaps, at a
discernable rate. Some progressed very
rapidly so that they now cover good
deal of the Northern Hemisphere. In
any event the Alaskan area served as
the principal refuge of plant life during
the long winters of the ages, from which
the northern regions of the earth,
scraped bare of all life for thousands of
years, have been replenished again and
again. From this plant evidence DR..
Hulten is able to deduce the extent and
durations of the various glaciations and
the intervals between them.
The distribution of species shows, also
confirming geological evidence, that the
glaciers left curious little islands of life
in unexpected places. Some plants are
found only in Alaska and in Quebec S
Gaspe Peninsula. In the distribution of
a few others there is great jump from
the Yukon to Norway. The Kamchatka
Peninsula, he finds, also was an unglaci-
ated life reservoir during these periods
from which, when the ice retreated,
Northern Asia and Europe could be re-
planted.
Although geographically SO close to-
gether, DR.. Hulten finds, Kamchatka, the
Aleutians and Alaska have three very
distinct floras as a result of the glacial
OCSSCLOo. llC OlUCl1dl1 CIlAlouAd LIDO
forested regions with rich variety of
plants and shrubs. Then the long chain
Of the Aleutians shows very stunted
vegetation, with no trees and brambles of
low shrubs, until the islands nearest
Asia are reached. Then full-sized trees
appear again. The stunted vegetation OF
the Aleutians usually has been attributed
to the severe climate and the high winds.
This is undoubtedly one element in the
phenomenon, but, DR.. Hulten points out,
the climate does not change with the
vegetation on the westernmost isles.
Alaska, in turn, has a vegetation super
flcially similar to that of Kamchatka,
but with many distinct species.
The rational explanation, DR.. Hulten
says, is that repeatedly during the glacial
periods great rivers of Ice blotted out
all life on the Aleutians, separated the
Alaskan and Kamchatka gardens. Only
the western islands were left compare
lively free. The inhospitable climate
has tendency to act as deterrent to
the free spread of vegetation from either
direction. There is also substrata OF
flora common to all three regions, con-
sisting OF the more adaptable plants
which have been able to spread and
which survived in both Alaska ana
Kamchatka.