24 FOREST TREE DISEASES. 



All the injurious agencies mentioned can combine. 

 The same tree might suffer at the same time from 

 needle miners, needle disease, mistletoes, root diseases, 

 bark beetles, drought, etc. Different diseases will also 

 attack the same tree at different stages of its life. 



FUNGI. 

 NATURE AND DEVELOPMENT. 



Most of the diseases of our forest trees are due to 

 fungi. A fungus is a very simple plant without green 

 pigment, and as such is unable to assimilate carbon 

 dioxide. It is unable to live on simple food and to build 

 up more complex chemical matter. A fungus lives on 

 highly composite matter produced by green plants and 

 decomposes it into simple matter, which again becomes 

 available for green plants. The fungi share this func- 

 tion with the bacteria and animals, and therefore play 

 a very important part in nature's economy. A great 

 number of fungi live in the soil on dead, decomposing 

 vegetable and animal matter; others attack living 

 plants, and in so far as they injure or destroy these by 

 living on and in their tissues are called parasites. 



Not all wood-destroying fungi can live indiscrimi- 

 nately in all trees; some are confined to one species, 

 others have a predilection for certain groups of trees. 

 They are just as dependent upon certain definite kinds 

 of food as are other plants and animals. Few attack 

 any trees within their reach. Different fungi not only 

 have a distinct predilection for certain species of trees, 



