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considerable number of the outer sapwood rings are involved in the yields of gum obtained is evident from the discussion on pages 9 and 10 and from Plate III, figure 2.28 It would therefore appear that the proportion of the sapwood which it is desirable to expose in chipping probably varies somewhat according to circumstances, and that the range of depth should be more exactly determined by further experiments on different types of longleaf and slash pine timber, especially on young timber, since this is of great future significance.

Crop C, the narrow chipping, did not have as narrow streaks as those cut at Columbia, Miss. Although it was intended that the streaks should be about one-fourth inch in height, it is stated that "in spite of continued urging and the closest supervision, the chippers invariably made the cut wider than was desired. Neverthe

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less in spite of the failure to reduce the width of the cut as much as desired, a considerable decrease was made." The height of the faces at the end of 4 years on crop A (standard) was 64.3 inches, and on C, 50 inches, or an average height of chip of about 0.4 inch. Under the narrowed chipping this crop showed an increase over the standard which was greater than that secured by the shallow chipping of crop B. Furthermore, less dry-face and dead trees resulted, and about one year of chipping surface (14.3 inches) was gained. These facts, therefore, furnish another instance of successful narrow chipping. How far the streak can further be narrowed with advantage beyond this 0.40 inch and the 0.34 inch obtained at Columbia, Miss., and sometimes obtained in commercial "pulling," is a subject for further experiment.

Crop D, the light cupping at Walkill, Fla., where fewer faces were cut per tree and no tree under 10 inches was cupped, but where the standard streak was cut, gave the highest yield of all the crops and the least loss from dry-facing or death of trees. It should be borne in mind that on the other crops trees with a diameter as small as 6 inches were cupped, and two faces were permitted per tree on timber with a diameter of 13 inches and over. (See Table 7.) As has been recently shown, it is unprofitable from the point of view of the growth in length and diameter of the timber, as well as from that of the yield of gum, to turpentine too small trees by the methods generally practiced in the United States.29 (See Table 8.)

It was demonstrated clearly both in the Walkill experiment and in Cary's observations (Table 8) that it was of fundamental importance to maintain the vitality and responsive power of the tree. Too large

28 This fact was not recognized at the time that the conclusion in regard to shallow chipping was expressed in Forest Service Bulletin 90.

29 Cary, Austin, "A look ahead" in Naval Stores, published by the Weekly Naval Stores Review, and in "Money is actually lost in working small trees for turpentine and rosin." Naval Stores Review and Trade-Journal. Vol. XXX, Jan. 22, 1921, p. 14, and Nov. 19, Dec. 3, 10, 24, and 31, 1921, and Jan. 7 and 14, and Feb. 4, 1922,

and too numerous faces, which unduly reduce the relative percentage of uncut bark, are unquestionably harmful and unprofitable. The questions of depth and height of streak are intimately connected with the number of faces and the returns obtained, but further work is needed, as has been shown, to fix within narrower limits the range of the most successful depth and height of chipping. It is stated by careful operators that, at the very least, one-third of the bark should remain uncut, and undoubtedly a larger proportion is desirable. The area D at Walkill was so turpentined that it would be possible to work it for a second period (back cup) some time later.

TABLE 8.-Yield at first dipping from trees of different diameters.

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TABLE 9.-Gain obtained by light cupping as compared with Standard chipping at Walkill, Fla.a

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a For. Serv. Bul. 90, p. 20.

b This increase was chiefly due to the fact that in 1905 there were 31 streaks and in 1906, 35 streaks cut.

Because of the gains secured in the first three years of the Walkill experiments, a different experiment was instituted on two crops during the fourth year (1908), which combined both the shallow and the narrow chipping features. "Yearling" or second-year crops were used, and the yields of gum were compared with those from a similar adjacent crop chipped by the standard method. An increased production of about 35 to 38 per cent was secured in this experiment. The "dip" from these shallow and narrow-chipped

trees was also considerably richer in turpentine than the ordinary dip, and fewer dry faces and dead trees were found on these crops. In conclusion, therefore, it may be said that these early Forest Service experiments clearly showed the advantages of certain conservative turpentining methods, which as was at that time felt, were only an indication of what might be accomplished in this direction.

CHIPPING IN THE LIGHTWOOD.

There is a belief current among practical turpentine operators that, to obtain the best yields from turpentining a substantial amount of wood, a high chip sould be cut away each week in order to "keep ahead of the lightwood." By lightwood is meant the region above the streak which is more or less saturated with oleoresin. The presence of lightwood is indicated by the difference in color between the surface of the freshly cut streak and that of a wound newly cut in round timber. It may be that the wood is only slightly impregnated with resin, so that the summer wood bands appear somewhat darker than normally, or, on the other hand, that a considerable amount of resin may have soaked into the wood, markedly darkening it, and often making the summer wood appear translucent, especially when the light is allowed to shine through a chip from such a region. An extreme example of this is shown in Plate III, figure 1, in which case the saturation probably occurred as a result of the undue drying out and dying of the overstimulated tree.

Narrow chipping, one-fourth inch to a strict one-half inch in height, will not keep ahead of all lightwood, especially during the midsummer season. For this reason many practical operators were convinced in advance that narrow chipping would fail. However, as has been shown, the results of reducing the height of the chipping speak for themselves in terms of increased yields and sustained vitality of the trees, as indicated, for instance, by the late autumn response shown in Plate III, figure 2, and by the recovery of the tree under turpentining, shown by the amount of wood formation in Plate V, figures 3 and 4.

The following interpretation of the observations made appears to be justified by the results obtained. When a tree is chipped or scarified the living cells in the wood are injured and a strong wound stimulus is given. Oleoresin 'exudes from the resiniferous parenchyma present. It tends to coat the surface and to cover it with a more or less complete seal, which materially assists in preventing the drying out of the exposed sapwood. Probably most of the parenchyma cells close to the surface of the wound, especially those actually cut, may die. The wound stimulus is undoubtedly greatest in the immediate vicinity of the wound. Its effect appears to be mani

fested in the increased yields obtained by using the "advance streak.” (See pp. 10 to 12.) The effect of the wound on the actively growing tissue is apparent in the tendency of the tree to heal or close the wound. More than the normal amount of parenchyma or resinyielding tissue is formed, often at the expense of ordinary wood formation. More resin passages or resiniferous parenchyma aggregates were generally produced in a definitely limited region, 8 to 12 inches above the wound, than further above it, as is indicated by the resin passage graphs in figures 1 to 6. Twenty or more inches above the original wound the number of resin passages is notably reduced, as is shown by the 1916 data as compared with those of 1917 in figures 1 to 6. Nevertheless, the wound response giving evidence of the extent to which the stimulus is transmitted, although less marked at a distance, was manifested as far as 7 to 10 feet above the wound. (Pl. VI, figs. 1, 2, 3, and 4.) Both increase in resiniferous tissue, most marked in the transition wood and in the summer wood in the specimens from the higher portion of the tree, and often some reduction in ring width or summer wood formation, occurred in the wood produced after turpentining. The chipping or freshening of the wound is designed to remove the dried and hardened surface of the streak and the unproductive parenchyma cells in order to permit the fresh exudation of the oleoresin, which forms and collects above this sealed surface during the period following the chipping. The chipping also serves to stimulate the living cells to further responses. It appears as if a very narrow chipping should successfully accomplish this purpose. It is obvious that a high chipping cuts away the most intensely stimulated and presumably the most responsive tissue, especially for gum production, in the tree. It is as if a whole organized battery of the tree's forces were wiped out at each stroke of the hack and a new organization had to be mustered afresh in the attempt to respond to the new condition. After a number of such responses, the results of which are cut away and wasted, the tree's resources tend to become more and more exhausted, and the yield of gum and the wood formation are reduced. Many trees under these circumstances become dry-faced-that is, physiologically speaking, their living cells cease production, and they frequently die (Pl. VII, fig. 3); at best the vitality of the timber is too severely taxed to assure the best returns possible.

In brief, then, chipping in the lightwood (progressing up the tree slowly less than one-half inch per week) is to be recommended because: (1) This is performed in the region of maximum stimulation, (2) it conserves chipping surface, (3) it tends to keep the surface from drying out because of the oleoresin saturating it to a greater or less extent, and (4) it has been found experimentally and practically to give sustained yields. Much "pulling" (see Pl. IV,

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