142 PROPERTIES OF WOOD. 



2. Defects in the Physical Properties of Wood, 

 (a) Discolouration. 



Any abnormal discolouration of the sapwood or heartwood 

 usually denotes disease and the commencement of decay in 

 wood. Many fungi may be determined specifically by the 

 nature of these coloured stripes or specks in wood. Some 

 abnormal colours, however, do not denote any fungoidal 

 attack, as when pale zones resembling sapwood appear in 

 the heartwood of oaks, in the pale heartwood of suppressed 

 stems, in cold climates or in the rootstock of several species 

 of trees. 



[In oaks the pale heartwood forming a zone 1 to 1J inches 

 wide in the midst of the normal heartwood and termed 

 mondring, or lunure, on the Continent, may here be called 

 internal sapwood to distinguish it from wind- shake and cup- 

 shake, when the defect is confined to a part only of an annual 

 zone. It is termed ring-shake, when the central heartwood 

 is loose. Internal sapwood forms the subject of an important 

 paper by Emile Mer,* from which most of the following 

 paragraphs are taken. 



Severe winter-frost may kill the cambium of a tree, in 

 which case the tree dies. In other instances, it is found that, 

 the sapwood just inside the cambium is killed, but that the 

 cambium is not killed, and continues to produce wood 

 externally. In such specimens the central zones of wood 

 have no connection with the external zones, a dark ring 

 usually separating the dead and living wood. There is no 

 external evidence of this frost ring-shake, but when the tree 

 is felled the internal core of the wood separates at once from 

 the external wood. Specimens of frozen wood are in the 

 Oxford Forestry Museum and in that of the Forest of Dean, 

 where not only the main stem of an oak, but also its branches, 

 are in this condition, the internal wood being quite loose from 

 the external wood in which it rests like a metallic casting 

 in its mould. In this case no decay is discernible in either 

 the external or internal layers of the wood. 



It may, however, happen, as in the cases described by Mer, 



* Boppc et Mer, " La lunure." Kev. lies Eiiux et Forets. l!S ( J7. 



