58 FOREST TREE DISEASES. 



and this, too, is often killed. This " top " mistletoe is 

 responsible for by far the greater number of spike tops 

 in white fir, though these are caused also by lightning 

 and the Tussock moth. Razoumofskya occidentalis, 

 which inhabits white fir of all ages, grows lower down 

 on twigs and branches and is also often found on limbs 

 and the trunk. As it can not penetrate old bark, the 

 infection must in the latter case have taken place when 

 the tree was young. This shows that the tree can live 

 for a long time after infection. The effect on the 

 trunk is the development of huge barrel-shaped swell- 

 ings, which later break and present a large open wound 

 or canker. Besides rendering this part of the tree 

 wholly unmerchantable, the swelling, made up of un- 

 healthy and abnormal tissue, weakens the tree very con- 

 siderably, while the open wound offers an easy entrance 

 to germinating spores of Echinodontium tinctorum, the 

 cause of the reddish-brown, stringy heartrot. White 

 fir snags, broken off in a storm either just below or 

 above the canker or in the swelling itself, are extremely 

 common. Almost all trees with canker are completely 

 worthless from decay. All white fir with this mistle- 

 toe should be cut and utilized as soon as possible. 



CONTROL OF DISEASE. 



It is impossible to grow sound, thrifty young trees 

 for future stands if conditions in the forest are such 

 that there is constant danger from insects and disease. 

 Every diseased or abnormal tree (leaning, forked, etc.) 

 in the forest, as well as every snag, in other words, 

 every individual that can not finally produce the great- 



