5 o6 



DISEASES OF CULTIVATED PLANTS 



LICHENES 



The majority of lichens are not parasites, and when growing 

 on the bark of trees, are simply saprophytes, deriving no 

 nourishment from the tree. On the other hand, when lichens 

 are present in abundance on the bark of cultivated trees 



FIG. 153. Usnea barbata axiARamalinafraxinea, lichens 

 growing on branch of apple-tree. Reduced. 



they prove injurious to the extent of preventing the bark 

 from performing its functions, and more especially in afford- 

 ing shelter to numerous forms of insect life which are 

 decidedly injurious to vegetation. Lichens and mosses are 

 killed by spraying with strong Bordeaux mixture or with a 



