DURABILITY OF WOODS 167 



structure was found to be most perfectly preserved in all its 

 details, showing no evidences of decay and a remarkable freedom 

 from fungus mycelia, from which we may conclude that the tree 

 was not only buried but practically hermetically sealed up- 

 possibly by the operation of an avalanche - - before an oppor- 

 tunity for the action of fungi and the operations of decay was 

 possible. 



The genus Picea is a widely distributed type in the Pleistocene 

 deposits, particularly in Canada. A large amount of material 

 has been obtained from the Pleistocene clays of the Don valley 

 at Toronto and elsewhere, and it affords an excellent index of 

 the durability of the wood under such conditions. All of the 

 material has been found to be devoid of silicification or other 

 mineralization, and it presents somewhat diversified aspects with 

 respect to conditions of preservation. P. alba, of the Scarbor- 

 ough period, although the wood is fairly well preserved as a 

 whole and readily admits of a determination of the species, shows 

 a great abundance of fungus mycelia. Wherever this is to be 

 found there is a marked alteration in the structure of the cell 

 wall, involving a breaking down of the secondary layer, as usu- 

 ally occurs under such circumstances, this disintegration being 

 always most marked in those regions where the mycelium is 

 most abundant. In this case the relation of the fungus to the 

 changes noted is very obvious. 



Picea nigra from the Don deposits is in some cases so well 

 preserved as to permit of a determination of the species with- 

 out difficulty, while in other cases the decay has progressed so 

 far as to render identification impossible. Fungus mycelia are 

 always present and they clearly constitute the active agents 

 of decay. The widely different conditions of preservation here 

 represented suggest the operation of specific causes wholly 

 apart from the inherent qualities of durability which the wood 

 naturally possesses. These are to be sought for in two direc- 

 tions, --either in local conditions of preservation, as varying 

 permeability of the soil, or in the conditions of decay established 

 prior to entombment. All of the material has been derived from 



