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] 



