64 LUTHER BURBANK 



a little farther, until in 1920 there were very few 

 chestnut trees unscathed within fifty or sixty 

 miles of the original center of contagion. 



The cause of the disease is a fungus that is 

 perpetuated by minute spores that are presum- 

 ably carried through the air and that, when 

 they find lodgment, develop in such a way as to 

 destroy the cambium layer of the bark, pres- 

 ently causing the death of the tree. The small 

 twigs of a single branch will often first show the 

 influence of the fungus and the leaves may die 

 and become brown and shriveled on one or two 

 large limbs of the tree when no other part of it 

 is affected. But in the ensuing season the dis- 

 ease is sure to spread, and the tree seldom sur- 

 vives beyond the third year. 



As yet no way of combating the pest has been 

 suggested, except the heroic measure of cutting 

 down trees immediately they are attacked, and 

 burning every portion of their bark. In this 

 way it is hoped to limit somewhat the spread of 

 the disease, but it is by no means sure that the 

 method will be effective. There appears to be 

 danger that the pest will spread until it has dec- 

 imated the ranks of the chestnut throughout the 

 eastern United States ; and of course there is no 

 certainty that it may not find its way to the Pa- 

 cific Coast, although the lack of chestnut trees 



