i86 TIMBER AND SOME OF ITS DISEASES. [ch\k 



decrease in weight to the same extent during the 

 progress of the disease. There is an excellent 

 opportunity for further research here however, since 

 one observer maintains that in one case at any rate 

 {Pz?ms sylvastris) the timber felled at the end of 

 April suffered from the disease, whereas that felled 

 in winter resisted the attacks of the fungus : internal 

 evidence in the published account supports the 

 suspicion that some error occurred here. The 

 wood which succumbed was found to contain much 

 larger quantities of potassium and phosphorus (two 

 important ingredients for the fungus), and Poleck 

 suggests that this difference in chemical constitution 

 explains the ease with which his April specimens 

 were infected. 



It appears probable from later researches and 

 criticism that Poleck did not choose the same parts of 

 the two stems selected for his experiments, for (in the 

 case of Ptnus sylvestris) the heart-wood is attacked 

 much less energetically than the sap-wood — a circum- 

 stance which certainly may explain the questionable 

 results if the chemist paid no attention to it, but 

 analyzed the sap-wood of one and the heart-wood of 

 the other piece of timber, as he seems to have done. 



The best knowledge to hand seems to be that no 

 difference is observable in the susceptibility to dry-rot 



