LUTHER BURBANK 
to-day along the same lines that have character- 
ized it in the past. 
To accept the doctrine of evolution at all re- 
quired the overturning of the most fundamental 
ideas. After the conception had been grasped that 
in the past there had been eras of change and 
development, it was a long time before even the 
most imaginative scientist fully grasped the notion 
that our age also is a time of change and transi- 
tion, and that the metamorphoses of plants and 
animals through which new forms have evolved 
in the past are being duplicated under our eyes 
in our own time. 
And in particular, as regards so massive and 
seemingly stable a structure as the tree, was it 
peculiarly difficult for botanists to conceive of 
flexibility and propensity to change, or to evolve, 
in the present time. 
It is true that no very keen eye was required 
to observe that trees differ among themselves 
within the same species, but it is also true that 
these divergencies always fall within certain lim- 
its and that on the whole they may be regarded as 
insignificant when weighed in the balance against 
numberless characteristics in regard to which the 
trees of a species seem practically identical. 
Take, for example, all the individuals that one 
could observe of, let us say, the common shagbark 
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