io TIMBER AND SOME OF ITS DISEASES. [CHAP. 



delicate walls, each cell having the form of a rect- 

 angular prism with its ends sharpened off like the 

 cutting edge of a carpenter's chisel : this prism is 



FIG. . A small block of wood from a spruce-fir, supposed to be magnified about 100 

 times, showing elevation and sectional views of the tracheides of the autumn (to 

 the right) and spring wood, and medullary rays (; ) running radially between 

 the tracheides. (After Hartig.) 



broader in the direction coinciding with the plane of 

 the sheet of cambium i.e. in the tangential direction, 

 with reference to the trunk of the tree than in the 



