ECONOMIC IMPORTANCE OF FUNGI 301 



1892, is common in the plant houses of commerical 

 florists. 



287. Pine Tree Blister-rust. — Among the more im- 

 portant plant diseases recently appearing in the United 

 States is the pine tree blister-rust, introduced from 

 Europe about 1909. One species is Cronartium pyri- 

 forme, which is the tehal stage of Peridermium pyriforme. 

 The secial stage {Peridermium) appears on the pine, 

 while the alternating host is the "false toad-flax" {Com- 

 andra umbellata and C. pallida).^ This fungus attacks 

 species of pine that have less than five leaves to the fascicle, 

 such sis Pinus contorta, P. ponderosa, and jP. rigida. 



Another species {Cronartium rihicola) passes its secial 

 stage on five-leaved pines, where it is commonly known 

 as Peridermium Strobi;^ the telial stage, as its name in- 

 dicates, is passed on species of Ribes (gooseberries and 

 currants) (Fig. 222). 



The importance of such a disease as this may be inferred 

 when we consider that the value of the white pine grow- 

 ing in the New England states is estimated at $75,000,000. 

 that of the Lake states at $96,000,000, of the Western 

 states at .$60,000,000, and of other National forests at 

 $30,000,000, a total of $261,000,000. The western sugar 

 pine {Pinus Lambertiana) has a total value estimated at 

 $150,000,000. Thus, timber to the value of $411,000,000 

 is threatened with destruction by this one parasitic dis- 

 ease. In order to reduce the danger of infection from the 

 blister-rust, and also from the pine-shoot moth {Evetria 



' The Comandra is itself a parasite on the roots of various species of 

 blueberry {Vaccinium), and other woody plants. 



* From Strobus, the specific name of the common white pine [Pinus 

 Strobtis). 



