HEMLOCK DISEASES 181 



Symptoms. 



Although these two species of fungi differ sufficiently so 

 they can be recognized by their microscopical characters, the 

 general appearance of fruiting-structm-es and the effect on 

 the tree is very similar. The leaves of young trees or of 

 the lower limbs of older trees are much oftener affected than 

 the tops of older trees. Sometimes one-half of the cones 

 may be affected. The most conspicuous symptom of these 

 diseases is the production, on the leaves or cones of golden- 

 yellow or reddish colored blisters in June and July. These 

 blisters burst through the epidermis of the affected parts and 

 when abundant their color stands out prominently against the 

 dark green of the healthy foliage. The spores borne in the 

 blisters sift out as a fine powder and are blown away by the 

 wind. 



Caiise. 



Two species of the rust-fungi are known to cause the blister- 

 rust of the leaves and cones of hemlock. The life history 

 of these species varies slightly in that different kinds of 

 shrubs are required for their further development. 



The first species mentioned, Pucciniastrum minimum, occurs 

 on the leaves and cones. This fungus was known on 

 the hemlock previously as Peridermium Peckii Thiimen. 

 The spores from the blisters on the leaves cause the in- 

 fection of the leaves of species of Rhododendron. On 

 this host plant, very small yellowish spots are developed on 

 the under sides of the leaves. The spores produced in early 

 spring on the rhododendron leaves infect the newly developed 

 leaves and cones of the hemlock. 



The second species, Pucciniastrum myrtilli, is known to occur 

 only on the leaves. This fungus was also previously known as 

 Peridermium Peckii. The blisters on the hemlock leaves 

 are more reddish than those of the other species. The 



