2i8 DISEASES OF TREES 



give rise to vexatious litigation between the architect, builder, 

 carpenter, and timber-merchant. Nor are the distinctions be- 

 tween this form of dry-rot and that induced by Menilius 

 lacrymans sufficiently appreciated as a rule, although the ravages 

 of the latter may be easily recognized since the publication of 

 my work on the subject. 



As a rule the term " dry-rot " is applied to those forms of 

 decomposition in structural timber where the fungus that does 

 the damage is invisible to the naked eye. This want of 

 conspicuousness is accounted for by the fact that such fungi, 

 instead of covering the wood or of filling up cracks in the timber 

 or spaces between the woodwork and the walls with mycelial 

 growths, distribute their fine hyphae in the substance of the wood 

 itself. But in a series of fungi which destroy structural timber a 

 luxuriant mycelial growth is produced outside of the wood, and 

 it is to these that the term " House Fungus " is generally applied. 

 These fungi vary exceedingly as regards appearance and life- 

 history. Of them the most important and destructive is Merulius 

 lacrymans. Then we have also Polyporus vaporarins y which has 

 already been described, and a number of other fungi which I am 

 at present busily engaged in investigating. 



Space may also be found here for a few remarks on the 

 soundness and quality of timber furnished by conifers that have 

 been entirely defoliated by caterpillars, and especially by 

 Liparis monacha and Gastropacha pini. When spruces or pines 

 have been completely defoliated during spring or summer, the 

 leafless branches as well as the top of the tree die in the course 

 of the following autumn, winter, or spring, while the more 

 valuable parts of the stem remain perfectly sound till the middle 

 of the succeeding summer. As a rule it is not till the beginning 

 of July that the inner cortex, especially on the south-west side of 

 the tree, begins to show brown patches and die. During the 

 devastations committed by the nun moth in recent years, the older 

 classes of spruces were almost all dead by autumn that is to say, 

 the cortex was brown. Underneath the dead cortex the wood 

 of the alburnum became discoloured, and rapidly decomposed 

 under the influence of numerous fungi. The timber of all those 

 trees which were felled and immediately barked before the 

 beginning of July of the year in which the havoc was committed 



