10 



A DISEASE OF THE WHITE ASH. 



GEOGRAPHICAL DISTRIBUTIOX. 



The distribution of this fungus is very interesting when considered 

 with reference to its host. The white ash. as indicated on the accom- 

 panying map (fig. 1), is found throughout the entire eastern United 

 States, growing as far westward as eastern Kansas and Nebraska. 

 Judging from the very meager data now at hand, it seems that Poly- 

 porus fraxinophilus is most common near the western limit of the 

 distribution of the white ash. It is very common in parts of Missouri, 

 Kansas, Indian Territory, and Iowa. In the eastern United States, so 

 far as the writer was able to ascertain, it is comparativeh^ rare. 



Near its western limit Fraxlmus americana is at best a tree of medium 

 size and development. On the dry limestone hills west of the Missis- 



FiG. 1. — Map showing distribution of Fraxinus americana L. 



sippi it grows slowly, as is evident from the sections shown on PI. I, 

 which are three-fourths natural size. In this region Polyporus frax- 

 inophilus will be found on 90 per cent of the standing trees. The dis- 

 eased trees were counted in two circumscribed localities, in neither of 

 which was a tree more than .5 inches in diameter found to be sound. 



The fact that in a given locality' so high a percentage of the indi- 

 viduals of a species are diseased at a relatively early age ma}-^ be 

 explained by the greater virulence of the disease-causing- factor or by 

 the greater susceptibility of the indiA'idual: in this case, probabh" the 

 latter. That this disease does not directly affect the living parts of the 

 tree has no weight, for in the long run it affects it indirectly by under- 

 mining its support. 



