WEST VIRGINIA GEOLOGICAL SURVEY. 



67 



SO that they seldom reach maturity unscarred. Other species 

 are less frequently attacked and may attain maturity in com- 

 parative perfect health. The extent to which trees are infected 

 frequently varies with their age. Those that are young and 

 vigorous are in little danger from fungi and insects that usually 

 enter through broken limbs or wounded bark. The diseases 

 which work upon the surface, however, sometimes find the most 

 favorable ' conditions for their rapid growth in the tender 

 foliage and twigs of seedlings. There comes a time in the life 

 of every tree when growth practically ceases. It is then, when 

 its vitality is low and its power to heal greatly reduced, that 

 the tree is most powerless against disease; and it is after that 

 time in most cases, that the increase in wood of timber trees is 

 not sufficient to counterbalance the loss from various causes. 

 Trees reach the inactive, mature stage at various ages according 

 to the species and in spite of unfavorable climatic conditions or 

 other adverse influences. Hence^ it must not be concluded from 

 a study of the natual enemies of the different kinds of trees 

 that the variation in their length of life is caused entirely by 

 the presence or absence of disease ; for those with approximately 

 the same susceptibility, in similar situations, and under the same 

 environment, will react in case of infection in an entirely differ- 

 ent manner, and with entirely different results. A white oak 

 and a beech standing close together may be equally diseased but 

 the former will probably outlive the latter by many years. 

 The giant redwood of the Pacific coast having certain inherent 

 powers of resistance to its enemies and by nature extremely 

 long-lived, is able to stand at the end of three or four thousand 

 years in a state of vigorous and healthy maturity. On the other 

 hand, such trees as our cottonwoods, willows, and the wild red 

 cherry, with fewer disease-resisting properties and with shorter 

 natural life, are old and ready to die at a hundred years. 



Some Dangers Surrounding Trees Enumerated. 



The health and life of trees are endangered almost con- 

 stantly. J^rst, there are the unfavorable natural conditions 

 often surrounding them^ including excessive or meager water 



