254 
HAROLD’S DISCCJSSIOHS. 
and the numerous rodents which infest the region dig 
the very roots out of the ground. Thus tlie young 
tree shoots come up during the wet season, hut in the 
succeeding dry months they perish in the struggle 
with drought and animal life. 
Animals furnish equally striking examples. Some 
years ago, in California, the cottony cushion-scale, 
brought in from Australia, became so numerous that 
it threatened to destroy the entire orange-crop of the 
State in a few years. An entomologist discovered 
that in Australia this insect had a natural enemy in a 
ladybird beetle. Some of these beetles were brought 
to California, and as they increased the insect rapidly 
diminished. When the natural food of the beetles 
was exhausted they almost died out. Now, in order 
to preserve the balance between beetles and insects in 
California, man steps in and assists the scale in the 
struggle by protecting some colonies from destruction. 
It is quite probable that the beetle in its native home 
had other food than the insect. 
It has been computed that if no English sparrow 
perished except by a natural death, that species of 
bird would increase so rapidly that in twenty years, 
in the State of Indiana, there would be one sparrow 
to every square inch. Even a slow-breeding animal 
would, if allowed to live its natural life, in time cover 
the whole earth. But where one survives, a thousand 
perish in the struggle for existence. Mr. Thompson- 
Seton truthfully says that wild animals always come 
to a tragic end. 
The struggle for existence is naturally more 
