36 BULLETIN 1064, U. S. DEPARTMENT OF AGRICULTURE. 



DEPTH OF THE WOUND. 



The width of the sapwood appears to be very intimately con- 

 nected with the distance that it is advantageous to cut (radially) 

 into the tree (cf. p. 28). At the present time it can only be stated 

 that a considerable portion of the moist sapwood should be left be- 

 hind the face. Instances undoubtedly occur in which a very con- 

 siderable yield of gum may be obtained by making relatively deep 

 cuts, 3/4 inch to 1 inch into sapwood which is as much as 3 inches 

 wide; for a notable yield has been found to come from the resin 

 passages of a number of the outer sapwood rings (PI. Ill, fig. 2), 

 not merely from those formed after turpentining. Before chipping 

 more than one-half inch in depth, however, the width of the sapwood 

 should be determined. Some operators judge the amount of sap- 

 wood and the yielding capacity of the tree by the roughness or 

 loose, scaly appearance of the bark, as contrasted with the rela- 

 tively smooth bark found on some trees. No consistently dependable 

 characteristic, however, is known for predicting the productivity 

 of a given tree, for individuals are found to show wide variations. 



HEIGHT OF CHIPPING. 



The amount of wood removed vertically with the grain at each 

 chipping has been very fully discussed in the preceding pages. It 

 is evident that weekly chipping less than one-half inch in height has 

 been found successful both as to yield and with reference to main- 

 taining the productivity of the trees by not unduly reducing their 

 vitality. The lower limit for the height of chipping has not yet 

 been determined, but in the narrow chipping at Columbia, Miss., an 

 average height of 0.34 inch was actually obtained. 



ADVANCE STREAK. 



The practice of cutting one streak some weeks before regular chip- 

 ping begins appears to be advantageous (cf. pp. 10 to 12). Regular 

 winter chipping, however, is considered unprofitable. The advance 

 streak is used in India. 



JUMP STREAK. 



On many operations, when the cups are raised, a section of uncut 

 bark is left (PI. VII, fig. 3) so that in driving in the aprons the sap- 

 wood layer or conductive tissue will not be completely severed. As 

 a consequence, some chipping surface is lost, but this is reduced to a 

 minimum by changing, as the end of the season approaches, the "set" 

 of the peak, or the angle made by the two streaks at the middle of 

 the face, so that the angle is obtuse. 



