47o 



THE POPULAR SCIENCE MONTHLY 



Fig. 1. 



and 



ilarty, serious American plant dis- 

 eases such as potato blight, grape 

 black rot, grape downy mildew and 

 powdery mildew have made the 

 European tour or even the world 

 tour "personally conducted" under 

 some unwitting guides. 



The chestnut bark disease (Fig. 

 3) illustrates well the rapid and 

 destructive invasion that is pos- 

 sible in case of new diseases. First 

 noted in 1904 by Murrill in New 

 York, and now well known in New 

 York, New Jersey, Delaware, Con- 

 necticut, Rhode Island, Maryland 

 and Virginia, it is rapidly spread- 

 ing in every direction (Fig. 4). In 

 Brooklyn 16,695 trees Avere killed 

 on 350 acres, and the loss in and 

 about New York city is placed at 

 five to ten million dollars. The 

 chinquepin and chestnut alone are 

 susceptible. The attack is made 

 upon the bark through wounds, but 

 twigs and leaves are not directly affected. From the point of attack the 

 disease spreads in all directions until the diseased parts meet on the 

 opposite side of the branch, thus girdling the twig and killing it. 

 Sometimes it happens that a newly introduced disease causes much 



loss in its first years and later sinks to com- 

 parative insignificance. Such was the his- 

 tory of the carnation rust which about 1892 

 caused the loss of entire houses of plants, 

 but which in a few years spent its force 

 until it is now regarded as a disease of no 

 unusual menace. In other instances im- 

 ported diseases continually remain serious, 

 as have the numerous grape diseases intro- 

 duced into Europe from America and from 

 Europe into America. . 



The diseases mentioned in Diagram I. 

 are nearly all of great destructiveness. The 

 potato blight is that which caused the 

 famous potato famine in Ireland in 1845, 

 in which year it swept Great Britain as well 

 as much of Europe and America with a 



Tear Blight, healthy 

 diseased twigs. 







«K 







* * 



v^P^V 





Fig. 2. A Potato half De- 

 stroyed by " Wart Disease " ; 

 the large " warty " outgrowth is 

 soft and rapidly decaying. 



