.18 FOREST TREE DISEASES. 



No age is free from disease; but certain diseases an- 

 confined to definite ages. Some fungi, for instance, 

 only attack young reproduction or branches and twi<is 

 in the same youthful stage of development. Others are 

 confined to mature and overmature trees. 



Few implements are required for the examination of 

 diseased trees. A hatchet or an ax is sufficient for 

 opening up the bark or outer layers of wood. A pick 

 and shovel are needed when the seat of the disease 

 seems to be in the root system. Whenever parts of the 

 trunk, branches, or the root system are affected or 

 killed, it is important to find out the extent of the 

 disease and, if possible, to follow any abnormal signs 

 to their source. For the examination of the foliage an 

 ordinary magnifying glass will do in most cases. 



SYMPTOMS OF DISEASE. 



The foliage being the most sensitive visible organ, its 

 general aspect is a valuable index of the health of a 

 tree. When the foliage of a coniferous tree, for ex- 

 ample, appears to be diseased, and no other cause, such 

 as drought, girdling, smelter fumes, or recent fire, can 

 be found, the needles should be held to the light to see 

 whether they are hollowed out by needle miners, the 

 larvae or pupse of which may at certain times be found 

 inside them. Partial or total destruction of the needles 

 or leaves is due to browsing by mammals or to cater- 

 pillars and the larvrc of sawflies. We may also find the 

 fruiting stage of a fungus in the shape of small black 

 spots or narrow black lines on discolored parts of the 



