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 stabihty 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 li^'ing parts are concerned, in full health. Just as wild 

 animals are said to die mosth' 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 arri\-e, 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. 



