190 A. Gray—Forest Geography and Archeology. 
applicable even to such wide wanderings and such vast inter- 
vals of time. the specific essence has not changed, an 
even if it has suffered some change, genealogical connection is 
to be inferred in all such cases. 
hat is, in these days it is taken for granted that individuals 
of the same species, or with a certain likeness throughout, ha 
asingle birthplace, and are descended from the same stock, no 
matter how widely separated they may have been either in 
space or time, or both. The contrary supposition may be made, 
and was seriously entertained by some not very long ago. It 
is even supposable that plants and animals originated where 
they now are, or where their remains are found. But this is not 
science: in other words it is not conformable to what we now 
know, and is an assertion that scientific explanation is not to 
be sought. 
Furthermore, when species of the same genus are not found 
almost everywhere, they are usually grouped in one region, as 
are the Hickories in the Atlantic States, the Asters and Golden- 
rods in North America and prevailingly on the Atlantic side, 
the Heaths in Western Europe and Africa. From this we are 
because birds have carried seeds from the one to the other. 
I take it that the true explanation of the whole problem 
Ns, Sea ee 
