ON THE QUICK GROWING WALNUT 
may be natural methods of elimination that will 
single out a species and destroy it as expeditiously 
and as certainly as man could accomplish that 
end. 
A case in point is furnished by the chestnut, 
which, as we have seen in a recent chapter, has 
been singled out in certain regions of the Eastern 
United States by a fungoid blight that leaves no 
chestnut alive in the regions over which it spreads. 
Yet this blight seems powerless to effect any other 
species. 
Here, then, we have an example of a destructive 
agency of an unpredicted kind that gives an ex- 
ample of the rapid destruction of a_ species, 
through natural selection, because that species 
could not rapidly enough adapt itself to a new 
condition. 
Given time, the chestnut would doubtless de- 
velop immunity to the fungoid pest. But time was 
not given it, and hence it was destroyed. 
This present-day illustration perhaps gives as 
vivid an impression of one of the more tangible 
ways of the operation of natural selection as could 
be desired. But we must suppose that such drastic 
measures as this are rather exceptional and that 
in general the processes through which species are 
eliminated are more subtle in their operation, 
although their ultimate results are no less striking. 
[209] 
