ECONOMIC IMPORTANCE OF FUNGI 301 



1892, is common in the plant houses of commercial 

 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 telial stage of Peridermium pyriforme. 

 The aerial stage (Peridermium) appears on the pine, 

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

 andra umbellata and C. pallida). 1 This fungus attacks 

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

 such SisPinus contorta, P. ponder osa, and P. rigida. 



Another species (Cronartium ribicola) passes its serial 

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

 as Peridermium Strobi; 2 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 



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

 blueberry (V actinium), and other woody plants. 



2 From Strobus, the specific name of the common white pine (Pinus 

 Strobus), 



