UNDER THE APPLE-TREES 
cannot repeat the genesis of living matter without 
the aid of other living matter. The cows in the pas- 
ture crop off the tender shoots of the young red- 
thorn and apple-trees, and thus increase the strug- 
gle of the sapling to become a tree. They do not 
eliminate it; they retard its growth and add to its 
toughness. 
All these considerations illustrate how living 
things struggle with and against one another and 
survive. All the grasses and the herbs of the field 
struggle in the same way. If they are exterminated, 
it is usually by fire or by flood, or by protracted 
drought, or other elemental agencies. But not al- 
ways. The chestnut blight which has lately attacked 
our chestnut-trees threatens to exterminate the 
whole race; the potato-beetle would doubtless, if left 
alone, exterminate the potato; the currant-worm, 
exterminate the currant; but these pests would 
not be factors in developing new species. There 
would be no survival of the fittest; all would go. 
With the myriad forms of life that have become 
extinct during the geologic ages, doubtless similar 
agents were at work; enemies or unfavorable con- 
ditions, or some mysterious failure in the springs 
of life, have led to their disappearance. Natural 
selection has played no part. Adaptation implies 
adaptability — something fluid and mobile — which 
is characteristic of life. Osborn says that certain 
characters are adaptive from their first appear- 
286 
