81 



(qi) The Blister Rust of White Pine and Currant 



( Cronartiuni ribicola ) . This very serious rust of the white pine 

 has been introduced from Europe and has established itself at Gen- 

 eva, N. Y. It has also been introduced into Canada with im- 

 ported nursery stock. Attempts have been made to eradicate it 

 in Canada but with what success the writer is not aware. The spring 

 spore stage attacks the bark of the w^hite pine. The bark swells and for 

 a time the mycelium develops. Eventually the spring spores are produced 

 in yellow pustules on the bark. The fungus frequently attacks the stems 

 of young trees and soon kills them. The life cycle of the fungus is 

 completed on some species of the genus Ribes which include the wild 

 and cultivated currants and gooseberries. The uredospore and teleuto- 

 spore stages are quite conspicuous on the under side of the leaves. 

 Professor Stewart of the Geneva Experimental Station believes that 

 the only way to control the disease in North America is the 

 destruction of the cultivated black currant which he believes to be the 

 chief factor in the spread of the disease in North America. Com.pared 

 with the white pine the black currant is of little importance. In time, if 

 it has not done so already, the disease will reach Canada and it is im.- 

 portant that measures be taken to hold it in check. The spread of this 

 disease in the white pine forests of Canada w^ould be serious. 



( r ) Rust of the^Hemlock. ( Necium Farlowii. ) This is an ex- 

 ample of a one host or autoecious rust. Only one spore form, the win- 

 ter spore, is present in the life cycle and this attacks the cones and 

 twigs of the hemlock. The writer found it locally abundant but not wide 

 spread in the Maritime Provinces. Many of the young hemlocks were 

 stunted fromi the death of the tw^igs. 



Measures for Control of the Rusts. The destruction of 



one of the hosts in the case of heteroecious rusts will usually cause the 

 rust to disappear. For example, in the case of the rust that attacks the 

 spruces and the L/abrador tea, the destruction of the latter which is of no 

 economic importance would lead to the disappearance of this rust. In 

 species with perennial myceliuim the fungus might persist in spite of the 

 destruction of one host. Another means of control is the destruction of 

 the parts that bear the winter spores, such as the leaves. These may be 

 gathered and burned. Usually only a knowledge of tlie life history of 

 each species will alone suggest some means of holding it in check. 



GILL AND PORE FUNGI. 



( a ) Root Rots. One of the most common and destructive root 

 rots of trees in Canada is tjhat caused by one of the gill fungi or mush- 

 rooms, the honey ag^aric ( Armillaria mellea ) . The mycelium of this fun- 

 gus enters the roots, grows into the cambium and attacks the living 

 cells; finally the tree is encircled by the fungus and eventually dies. The 

 fungus keeps on grow^ing in the dead root system and produces its fruit 

 bodies abundantly. It also spreads by strands of mycelium to the roots 

 of neighbouring trees. The fungus is v^ery common, especially in groves 

 of trees surrounded by open fields. 



