12 



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 exterminated slowly reoccupied part of their old 

 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. 



