The San Francisco call., 1904-02-09
Plants of Ice Age.


BY FREDERICK WRIGHT. A. NJ. Ii. d.
Author OF The Age of Ice in North America
Man and tie Glacial Period" etc
Copyright. 1904. by Joseph B. Bowles)
Before the glacial period the plants
which now flourish in the latitude Of
Virginia and North Carolina were
growing in happy family IN Spitzber-
gen, Northern Greenland and on the
Arctic shores OF North America. Arctic
expeditions have repeatedly brought
back from the midle tertiary deposits
north Of Disco Island the embedded
leaves and fruit OF magnolias, sasafras,
hickories, NAPLES, pOplars, birches, lin
dens, southern cypress and several spe-
cies Of sequoias, including the gigantic
forms now found only in California,
and three kinds OF ginko trees now
peculiar TO Japan. The evidence Of
these fossil plants is conclusive that
just before the glacial period there was
n warm climate all around the north
pole.
Until the theory of the origin of
species by natural selection was ac-
cepted and the facts about the glacial
period brought TO light this distribution
II trees and plants was a profound
mystery. For the solution Of the prob
lem we are largely indebted to the late
professor Asa Gray who in 1859 read a
paper before the American Academy Of
Arts and Sciences on the fora of Japan
which attracted the attention Of the
scientific world and opened the way to
the full exposition Of his theory, which
was set forth in an address before the
American Association for the Advance
rrent Of Science at Dubuque. Iowa, in
1872. The way had been prepared for
this work by the fact that the large
collection Of japanese plants gathered
by Commodore Perry's expedition in
1857. which opened Japan to the world.
was placed in his hands for eXamina-
ton. The result was that il appeared
that there was a striking similarity be-
tween the plants Of Japan and those
Of the Altai Mountains, Of the Hima-
layas and the eastern portion Of North
America, and a striking dissimilarity
between the plants of these regions and
those of the Pacific slope Of North
America, while the most remarkable re-
semblance was between the plants Of
Japan and those Of Eastern United
States.
The Pacific coast Of the United
states is rich in coniferous trees like
cedars sequoias and redwOOds,' but is
conspicu0usly lacking in most Of the
trees familiar on the Atlantic slope.
For example there are not half as
many naples. or ashes, or poplars, or
walnuts or birches, or oaks on the
Pacific slope as on the Atlantic slope,
and those are Of such inferior quality
that il is said "a passable wagon wheel
cannot be made Of California wood,
nor a really good one in oregon" The
Atlantic slope has four times as many
species OF non-cOniferous trees as the
Pacific slope, but only a little more
than half as many coniferous species.
The first step in the solution of this
problem is found in the relation Of the
land continents in the northern hemis
phere to each other. Whereas, the
southern ends Of the continents project
far out into deep seas so that they
are widely separated from each other,
At the north they all approach each
other and are separated by shallow
seas. The water in Bering Strait is
only $50 feet deep, and that in the sea
only a few hundred feet. so that a
slight elevation Of the bottom Of the
ocean there would join Asia to Amer
lea. and permit the migration of plants
and animals from one continent TO an
other That these continents have been
recently Joined by such a change in
lard level is proved by the fact that
bones of the mammoth have been found
on both sides Of Bering Strait, and even
on the Pribyloff Islands, far out in
Bering Sea. A similar belt Of shoal
water extends from Greenland by way
o. Iceland 10 Norway. II is therefore
easy 10 suppose a continuous land con-
nection clear around the north pole
enabling plants and animals to migrate
freely. On the other hand, the gen.
eral resemblance Of species both Of
plants and animals in the lands sur
rounCing the 18th pole is proof that
there has been such opportunity for
migration Whereas there is this great
similarity in species in the northern
hemisphere, there is a total dissimilar-
ity betA. cen the species occupying the
southern extremities Of the continents
ln the southern hemisphere.
But with the coming on OF the
glacial period this happy family OF
species around the north pole was
rudely disturbed by the new condi-
tions. The lowering of temperature
and the slow accumulation Of glacial
ice made il impossible for trees OF a
temperate climate 10 maintain their
existence on those inhospitable shores.
il they were TO exist any longer they
must emigrate to milder climes. But
how shall a tree which is fixed in the
soil remove to better its fortune? OF
course, A single tree is helpless in such
situation. But, as Professor Gray
wittily says. when a tree is driven to
IN extrerSity IL can take TO the
woods" and the forest can begin a
majestic movement toward better
chmes.
As the conditions favoring the for
est became severe along its northern
belt they would become favorable oyer
= corresponding belt stretching TO the