538 



SPECIAL PLANT PATHOLOGY 



has been considered to be of such great importance, that strict quaran- 

 tine regulations were established in order to keep it out of the country, 

 but the result of a thorough exploration of the New England States 

 during the summer of 1916 has shown its general distribution through- 

 out them and even as far west as Minnesota. It appears to have been 



Fig. 193. — White pine blister-rust, Cronarliutn ribicola. A, Diseased tree with 

 aecial blisters broken open from which spores are blown to currant or gooseberry- 

 leaves; B, D, teliosori on under leaf surface of currant, Ribes. {From Gager, after 

 Perley Spaidding.) 



introduced into America on nursery stock from Holland, and all the 

 trees in these advanced posts of infection have been destroyed. In 

 igo6, there was an outbreak on currants at Geneva and measures were 

 taken to destroy the fungus in that vicinity. The aicidial stage, known 

 as Peridermium sirobi, appears on the pine tree and the uredinia and the 



