INJURIES INDUCED BY PLANTS 213 



the case, however, that the diseased portion of a tree which is 

 easily recognized as, for instance, owing to brownness, &c. is 

 cut off till the saw-cut appears to the naked eye to be perfectly 

 sound. The apparently sound portion of the tree is afterwards 

 disposed of, say as a log. Now, it may easily happen that the 

 parasite has already penetrated into the portion of the tree that 

 was regarded as free from attack, and consequently an infected 

 piece of timber is sold as sound. Should such wood retain a 

 portion of its moisture for a considerable period, the parasite 

 will continue to grow until it destroys not only the wood that 

 contained the filamentous mycelium at the time the tree was 

 felled, but frequently also very considerable portions of the 

 timber that was primarily sound. 



Polyporus vapor arius, which occurs on spruces and pines even 

 when alive, and which I have described at page 198, is the 

 commonest and most destructive of these fungi. Frequently 

 when investigating the destructive effects of " dry-rot " I have 

 found the cause to be not Merulius lacrymans but P. vaporarius^ 

 whose mycelium forms snow-white sheets on beams and deals, 

 and produces stiff strands several yards in length. Should 

 timber which is infested by this parasite be applied to structural 

 purposes, and should it not dry quickly enough, the fungus 

 develops more or less luxuriantly, and in a short time com- 

 pletely destroys all the wood-work. This fungus is apt to be 

 specially prevalent in cellars, and in the wooden floors of the 

 ground flat of houses that are unprovided with cellars. 



Perfectly sound timber may, however, also be infected during 

 the time it is lying in the forest. The danger is greatest in 

 the case of peeled timber that is in immediate contact with 

 the ground. Various wood-fungi, and amongst them Merulius 

 lacrymans, may induce disease in felled timber when it is stored 

 for a considerable time on the ground in the forest. At the time 

 of issuing my publication on Merulius lacrymans, I stated that 

 it was doubtful whether this fungus occurs in the forest at the 

 present day. Since that time I have received genuine speci- 

 mens of M. lacrymans, from Herr W. Krieger, Konigstein, 

 Saxony. Peeled timber that is exposed to air-currents by being 

 piled upon supports is much better protected, because the 

 surface layers soon dry, and render the entrance of the fungus 



