402 



THALLOPHYTES 



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

 stage is produced, and the aeciospores 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 aecial 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 aecial stage is the most 

 destructive. The mycelium 

 of the aecial stage kills the 

 cambium and inner bark of 

 Pines, thus causing the 

 death of branches and some- 

 times of the entire tree. 

 Both urediniosporos and 

 teleospores 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. 



Fig. 360 — A Cedar Apple which has 

 developed the gelatinous branches con- 

 taining numerous teleospores. The 

 teleospores 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. 



