402 



THALLOPHYTES 



disease on the leaves and fruit. Upon the Apple tree, the aecidia 



stage is produced, and the aecidiospores are able to attack the 



Cedar and form new galls, thus completing the life cycle as shown 



in Figure 361. 



Pine Tree Blister-rust (Cronartium ribicola) . As its name 



suggests this Rust attacks Pine trees. It was introduced from 



Europe about ten years ago 



and has now become a seri- 

 ous disease in this country. 

 It has its aecidial stage on 

 Pines with five leaves in a 

 fascicle, such as the White 

 Pine and Sugar Pine, and 

 has species of Ribes (Goose- 

 berries and Currants) as the 

 other host. In this Rust the 

 aecidial stage is the most de- 

 structive. The mycelium of 

 the aecidial stage kills the 

 cambium and inner bark of 

 Pines, thus causing the 

 death of branches and some- 

 times of the entire tree. 

 FIG. 360. A Cedar Apple which has 



developed the gelatinous branches con- 

 taining numerous teleutospores. The 



teleutospores produce sporidia or basidio- 



spores that attack the Apple tree. These 



gelatinous branches develop in the spring 



after a rain and while the leaves and 



shoots of the Apple are young and easily 



attacked. After Bulletin 257, Wisconsin 



Agr. Exp. Sta. 



Both uredospores and teleu- 

 tospores are produced on 

 the infected Currant and 

 Gooseberry bushes, which 

 are apparently very little 

 injured thereby. Pines are 

 infected through the basid- 

 iospores. The chief means 



of checking the spread of 

 the disease is through the destruction of the wild Currant and 

 Gooseberry bushes. 



The damage done to Pine trees is serious and since our 

 Pine forests are valued at many millions of dollars, it is 

 not surprising that our government has put restrictions 

 upon the importation of Pines from Europe and has appro- 

 priated large sums of money to be expended in checking 

 this disease. 



