182 MANUAL OF TREE DISEASES 



spores from the blisters infect the leaves of species of blue- 

 berry. On this host plant are formed small yellowish spots 

 on the imder sides of the leaves. Later light brown spots 

 appear in the same areas. The spores produced the following 

 spring from the brown spots cause the infection of the young 

 hemlock leaves. 



Control. 



By keeping rhododendrons and blueberry bushes away from 

 hemlock trees, these blister-rusts can be prevented. The 

 heaviest infection of the hemlock occurs when one of these 

 alternate host plants stands within a few feet. 



Reference 



Spaulding, P. Diseases of the eastern hemlock. Proe. Soe. Amer. Poiv 

 esters 9 : 245-256. 1914. (Bibliography given.) 



Leaf-, Cone- and Twig-Rusts 



Caused by Melampsora ahietis-canadensis (Pari.) Ludwig, and Necium 

 Farlowii Arthur 



In addition to the two blister-rusts of hemlock (page 180) 

 two other rust-diseases occtu* on these trees. In Nova Scotia 

 instances have been noted in which the leaves and twigs of 

 the entire top of the tree were killed by the later fungus. 



Symptoms. 



The first species, M. abietis-canadensis, causes a rust on the 

 leaves, cones and twigs similar in appearance to the blister- 

 rusts. This fungus was known on the hemlock previously 

 as CcBoma abietis-canadensis on the leaves and as Peri- 

 dermium friictigemim on the cones. The spores from the 

 pustules produced in early summer on the affected parts 

 of the hemlock cause the infection of the leaves of the large- 

 tooth aspen. On this second host small orange or brown- 



