74 A MILL SCALE STUDY OP WESTERN YELLOW PINE. 



Number 2 Shop, and in some cases Number 1 Shop. The knots are 

 larger and farther apart than in any of the logs located farther down, 

 and it is this type of material that can be graded as Shop lumber, since 

 boards free from small knots and containing large ones will usually 

 pass the qualifications of these grades. The center of the log will pro- 

 duce lumber containing many knots of various sizes, and the quality 

 will compare favorably with that of the center of logs nearer the stump. 

 The strength will probably be greater, since the wood was formed after 

 the tree had a good start in life. The grain will be coarser than will be 

 found in the center of the lower logs, but the wood in general will not 

 be as brittle. Timbers cut from this part of the tree will manifest more 

 strength, if the knots are sound, than ones cut from the butt and second 

 logs, which contain wood at the center apt to be brittle, due to the fact 

 that it was laid on before the tree had become vigorous. 



All logs above the fourth from the stump will contain large knots 

 extending through the bark in the form of snags and live limbs. The 

 largest knots are generally ones formed by the presence of living 

 branches. The center of these logs will usually grade as Number 3 Shop, 

 Number 3 Common, and Box. The last log in a mature tree has an 

 enormous taper, and the knots are very large. They produce a low 

 grade of lumber, such as Box and Number 3 Common. 



The quality of material once formed in a tree, with the exception of 

 the gradual change from sap-wood to heart-wood, remains unchanged 

 by the process of growth. The new layers of wood formed from year to 

 year increase the quality of the tree as a whole, and small and inter- 

 mediate sized knots are covered by successive layers until clear, straight 

 grained lumber results in the lower portion of the bole near the barked 

 surface in sufficient quantities to be manufactured into boards of various 

 dimensions. 



A tree contains all wood formed by the process of growth from its 

 beginning up to the time it is milled, and each layer is unaffected by 

 the formation and accumulation of other layers which follow. The 

 same knots are present in the same location in the tree, and the grain of 

 the wood once formed remains unchanged. 



