Old Age 31 
through the dead twigs as well as through the larger branches, 
broken off by the winds; the danger of damage from wind, 
snow, and ice pressure increasing with the growth in length 
which adds to the leverage. Rot, riddling the bole (which 
is really dead matter) and eating out the heart of the giant, 
does not really kill, but after years of work the stability of 
the bole is undermined and eventually the tree succumbs 
to a windstorm; broken, it may be, in full leaf and, as far as 
the living parts are concerned, in full health. Just as wild 
animals are said to die mostly from violence, so trees in 
nature break down under the violence of windstorms rather 
more often than they succumb to natural death or disease. 
When this time of insufficiency of water-supply and hence 
endangered old age will arrive, depends on a variety of con- 
ditions. Difference in wood structure and hence in conduc- 
tivity for water may make long-lived and short-lived species; 
deep soil and ready water-supply for the roots and favorable 
climatic conditions, increase height growth, and may also 
possibly lengthen, or, as may be, shorten the life of the 
individual. 
Again, some species, or some varieties or even some 
individuals of a given species may be found to resist damage 
more readily than others, or else be more predisposed and 
liable to disease. Some are more adaptive to a change in 
the environment, while others quickly resent such changes, 
especially as regards water-supply at the roots or transpira- 
tion at the foliage. 
Diseases in trees are usually more or less localized, spread- 
ing gradually, and in the absence of a nervous system, sec- 
ondary complications in other organs, as they occur in the 
animal body, are not generally observable. One portion 
of the tree may remain perfectly normal and healthy while 
another portion may be diseased or even dead. 
