CHAPTER III 
DISEASE AND DEATH OF TREES—GENERALI- 
TIES 
Sq] OR normal development trees require, as we have 
p seen, light, heat, water, air, and nutritive ele- 
ments in certain amounts. If any of these 
conditions or elements are temporarily deficient 
(or sometimes when in excess) the normal functions are 
interfered with, and the tree may be ailing, although not 
necessarily sick, for it may recover its normal condition as 
soon as the deficiency is corrected. 
We speak of disease only when live parts fail to perform 
their normal functions and begin to die before their time, 
that is to say, when buds, rootlets, or cambium die at any 
time, and leaves change color, become dry, and fall before 
the end of the season. 
Since, as we have seen, the living parts of the tree lying 
on its periphery rejuvenate themselves every year by the 
formation of new shoots, buds, cambium and rootlets, there 
can be actually no natural death from old age in the same 
sense as in animals. Even death from internal causes as a 
direct result of disease, at least sudden death, is rare. 
Trees die mostly as a result of unfavorable external con- 
ditions, which interfere with their nutrition, and which are 
generally capable of control. As a rule, they succumb so 
gradually that they actually die by inches; it may take many 
years before all life is gone, and hence there is time for 
recuperative measures. 
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