700 



PROTECTION AGAINST DISEASES. 



Fig. 298. Oaks near a manufacturing town, the foliage damaged by acid fumes, 

 photographed August, 1882.* 



Fig. 299. Same oaks photographed July, 1888, several years' cumulative injury 

 having killed the trees.* 



* From Croonian Lecture by Marshall Ward (vide p. 671), 



