VII.] THE "DRY-ROT" OF TIMBER. 187 



of winter-wood and summer-wood of the same timber ; 

 i.e. Merulius lacrymans will attack both equally, if 

 other conditions are the same. 



But air-dry and thoroughly seasoned timber is much 

 less easily attacked than damp fresh cut wood of the 

 same kind, both being exposed to the same con- 

 ditions. 



Moreover, different timbers are attacked and 

 destroyed in different degrees. The heart-wood of 

 the pine is more resistant than any spruce timber. 

 Experimental observations are wanted on the com- 

 parative resistance of oak, beech; and other timbers, 

 and indeed the whole of this part of the question is 

 well worth further investigation. 



When the spore has germinated, and the fungus 

 hyphae have begun to grow and branch in the moist 

 timber, they proceed at once to destroy and feed upon 

 the contents of the medullary rays ; the cells 

 composing these contain starch and saccharine 

 matters, nitrogenous substances, and inorganic 

 elements, such as potassium, phosphorus, calcium, 

 &c. Unless there is any very new and young wood 

 present, this is the only considerable source of proteid 

 substances that the fungus has : no doubt a little may 

 be obtained from the resin-passages, but only the 

 younger ones. In accordance with this a curious fact 



