386 DISEASES OF CULTIVATED PLANTS 



is no evidence that trees are infected above ground. When 

 the wood is infested with mycelium it turns yellow and 

 becomes brittle, and afterwards cracks due to shrinkage of 

 the wood. The cracking of the wood is said by Hartig to be 

 due to spiral cracks forming in the walls of the tracheids, due 

 to shrinkage of the substance of the wall. The mycelium 

 does not form white branching strands, but sometimes covers 

 the walls of the fissures with a white chalk-like coating. The 

 smell of the decayed wood is very strong, and somewhat 

 resembles turpentine without being identical. 



This parasite appears to confine its attention to conifers. 

 In Europe it has been recorded as parasitic upon the Scots 

 fir, the Weymouth pine, and the larch. In the United States 

 it attacks the white and red spruces, balsam fir, arbor vitae, 

 and the white pine {Pi mis strobus). 



Sporophore dark rusty brown, coarsely tomentose or hispid, 

 flesh thick, soft and fibrous, bright brown, tubes about i cm. 

 long, pores large, irregular, greenish-yellow, spores pale 

 yellow, 7-SX4 /*. Sometimes with a short, stout, central 

 stem ; when growing on a trunk often sessile and imbricated, 

 6-9 in. across. Schrenk says the hymenium is rose coloured 

 when fresh, turning dark red very quickly when bruised. 

 Are the European and United States fungi identical ? 



Von Schrenk, who has studied this species carefully in the 

 United States, considers that it spreads through the soil, 

 and only attacks a tree through the root system. He observed 

 that wherever one tree is affected, others similarly diseased 

 will usually be found close by. When infection occurs in the 

 root on one side of a tree only the heart wood of that branch 

 of the root will be destroyed, and the wood of the trunk 

 nearest that particular branch of the root becomes affected. 



badly diseased trees should be felled, as when the trunk is 

 once infected the mycelium continues to ascend higher and 

 higher, and destroys wood that might be utilised if cut down 

 earlier. The fruiting bodies of the fungus should be collected 

 and burned or buried. The trenching method, if practicable, 

 would check the spread of the mycelium in the ground from 

 extending from <1 1 to adjoining healthy trees. 



Hartig, Zersetzunger t p. 45 (there called Polyporus mollis). 

 Hartig and Somerville, Diseases of Tret s | Engl, ed.), p. 198 



(1894). 



Schrenk, H. von, U.S. Dept. A^r., Dir. Vet. Phys. and 



Path., Bull. No. 25 (1900). 



