42 BULLETIN 1064, TJ. S. DEPARTMENT OE AGRICULTURE. 



wound. It was also registered in the wood produced 6 to 9 feet verti- 

 cally above the wound. At this point the resin passages were fewer 

 than near the streak, but, nevertheless, were more numerous than in 

 the round timber. The resin passages in the specimens studied were 

 observed in both the open and closed condition, as is shown in the 

 illustrations. Although this increased number of the resin passages, 

 formed after wounding, is an important factor in securing a high 

 yield, they are not, as has been shown, the only or possibly even the 

 chief source of the gum. 



Provided the size of the timber and the faces and their location 

 have been properly cared for, the method of chipping which is inti- 

 mately connected with these features is also of fundamental sig- 

 nificance. Characteristic effects on the structure of wood, result- 

 ing from different methods of chipping, were determined and fully 

 described in the discussion of the microscopic investigations made. 



HEAVY CHIPPING. 



Heavy chipping (more than one-half inch in height and more than 

 three-fourths inch in depth) or overcupping tends to produce the 

 following undesirable results in the wood formed after turpentining. 



1. Delay in the beginning of wood formation. 



2. Delay in the formation of resiniferous tissue. 



3. Reduction in width of annual rings. 



4. Reduction in amount and thickness of walls of the summer 

 wood. 



5. Tendency to develop resiniferous parenchyma at the expense 

 of other wood cells. ' 



6. Death of a relatively high percentage of trees and tendency to 

 produce dry-face. 



7. Markedly reduced yield from year to year. 



CONSERVATIVE NARROW CHIPPING. 



Conservative chipping, of which the narrow, as practiced at 

 Columbia, Miss., is an example, produced results in direct contrast 

 to those from heavy chipping. The optimum methods of turpen- 

 tining are still to be determined, but in the light of our present 

 knowledge, the application of the following specifications would 

 appear likely to produce the nearest approach to ideal operation that 

 has thus far been attained. 



No tree under 10 inches in diameter, breast high, should be 

 cupped. 



One-half, or at the very least one-third, of the total circumference 

 in the neighborhood of the faces should be covered with uncut 

 bark. Bark bars, at the minimum about 6 inches wide, should be 

 left between faces. 



