52 Forests and Trees 



the host, the fungus sends out certain bodies to the surface 

 which produce large numbers of spores, and from these 

 spores new plants may grow. These fruiting bodies take 

 various forms, but the shelf fungus so often seen project- 

 ing from a dead or dying tree is one of the most common. 



All the poplars are subject to fungous diseases, the aspen 

 particularly so. It is quite common to find the aspens 

 dying along the route of an old fire where there is a large 

 quantity of decaying timber, or in groves which have been 

 cleared of undergrowth and are used for park purposes. 

 Examination will show that these trees have fallen victims 

 to some fungus. 



The most dangerous disease of this kind which has to be 

 dealt with at the present time, 1919, is a form of rust, which 

 is attacking the white pine of eastern Canada and the eastern 

 States. The rusts are fungi which live on two hosts, pro- 

 ducing different spores on each host, the spores varying 

 greatly in appearance. The name rust comes from the 

 fact that in certain plants the spores of one kind are red 

 or yellow and discolor the hands or clothing much as iron 

 rust would. The rust of wheat is, perhaps, the best known 

 example of this. The disease which is attacking the pines 

 is known as the white pine blister rust, and its alternate 

 host is the black currant or any member of the genus ribes, 

 which include both currants and gooseberries. The spores 

 which are formed on the currant grow in the young tissue 

 of the pine and destroy the leaves, in the end killing the 

 tree. It is particularly injurious to young trees. 



This disease has practically destroyed all the white pines 



