428 



DISEASES OF ECONOMIC PLANTS 



change, a word is due to it on account of its vast impor- 

 tance, involving, as it does, all structural wood. The fact 

 that the railroads use more than 110,000,000 ties annually, 

 and that the number of posts in use is approximately 





Fi(i. 180. — Drj rut fungus (Merulius lacrymans) ; on the right the mycelium is 

 visible as white strings. After Freeman. 



4,000,000,000, necessitating an annual replacement of 

 some 500,000,000 in the United States, indicates the enor- 

 mous money values involved. 



This kind of decay is brought about by agencies similar, 

 sometimes identical, with those causing rot in living trees, 



