I2 
By a glance at a map of the northern hemisphere, we may at 
once compare the regions inhabited by each of these trees and see 
their geographical relationships; as we have already shown, they 
are all either North American or Asiatic. The question at once 
arises why is there no European member of the genus? In reply, 
it may be said that there almost certainly has been a hemlock 
spruce in northern Europe, now extinct, for the study of fossil 
plant remains of the Miocene epoch, collected on the island of 
Spitzbergen, indicate that such a tree grew in Tertiary geologic 
times in the region now occupied by that island, and perhaps 
elsewhere in northern Scandinavia and Russia. 
We now know that plants and animals of such close affinity as 
to be grouped in the same genus, have in most cases, at least, had 
a common ancestry; that is to say, all these slightly different 
hemlock spruces have descended from an ancient hemlock spruce 
almost certainly as different from any of them as they are dif- 
ferent from each other. We also know that the climate of high 
northern regions was far milder during part of the Tertiary era 
than it now is, and also that there was complete, or essentially 
complete, land connection in the Arctic regions between Europe, 
Asia and North America. Following this warm period there 
came on very gradually, a long time of intense cold in the northern 
part of the northern hemisphere, which culminated in the glacial 
period, when immensely thick sheets of ice and snow covered 
the continent as far south as Perth Amboy, doubtless forcing all 
vegetation that was not obliterated to the south. The next great 
climatical change was a relatively warm wave of great duration, 
extending, indeed, into our own times, during which the plants 
and animals not éxterminated slowly reoccupied part of their ol 
territory, but the period of time taken by these two migrations 
was so great that evident changes took place in most of them; 
thus, instead of the tertiary parent hemlock spruce of Arctic lands, 
we now have the several different existing ones as its offspring 
in the north temperate zone. 
As to the more distant relatives of the hemlock spruce, we may 
say that the true spruces, of which there are many kinds, differ in 
having four-sided leaves spreading in all directions from the twig, 
and that the firs, also numerous, differ in having their cones erect 
on the branches instead of drooping. All are natives of the 
northern hemisphere only, and we have but to go far enough back 
in geologic times to discover the common ancestry of the whole 
tribe. 
