unknown. A more intimate knowledge of the substances of the greatest significance in resin production-as, for instance, the effects of the constitution of the soil-might have a marked influence on future practice. This has been found to be the case with fruit culture, as a result of the work on the effects of the carbon-nitrogen ratio upon vegetative and reproductive responses. Indeed, as has been suggested by Dr. W. D. Bancroft, chairman of the division of chemistry and chemical technology of the National Research Council, who selected oleoresin production as an example of an important presentday problem, the understanding of this subject appears to involve cooperative work by a botanist, a microscopist, an organic chemist, and a colloid chemist. Much valuable information on oleoresin has already been collected by the Bureau of Chemistry and by different units of the Forest Service, and with the timber on the Florida National Forest available for experiment, the opportunities for carrying on further research are exceptionally good. That the future need in this direction is recognized and that plans (in the carrying out of which microscopically obtained data can unquestionably be of service) are being formulated, is indicated in the following statement of Col. W. G. Greeley, Forester: 41

One of the things which must be worked out as part of our general progress in forest conservation is a system of extracting gum turpentine which will make this industry and its valuable commercial products a permanent resource of the Southern States. We must develop a plan for tapping second-growth timber, somewhat along the lines used in France but adapted to commercial requirements in the United States, under which this can be a continuous forest industry, obtaining yields of gum from the same trees for 20 or 30 years, right up to the time when they are cut and converted into lumber. Without some method of this nature the gum turpentine industry will soon cease to exist. I am hopeful that the Forest Service can extend the instructive experiments in various methods of conservative chipping and cupping which you 42 have already initiated on the Florida National Forest in order to work out completely a plan of tapping second-growth timber without injury which can be adopted commercially by the owners of pine land throughout the South.

SUMMARY.

The results of this work and of the other earlier and current experiments of the Forest Service clearly demonstrate that those methods which conserve the vitality of the tree and its responsive power, under stimulation such as is given by turpentining, insure the greatest production of oleoresin. The process of turpentining is not merely a draining out of the gum already formed; it is a collection of the oleoresin constantly being manufactured by the tree.

40 Kraus, E. J., and H. R. Kraybill, Oregon Agric. College, Exper. Station. Bulletin 149, 1918.

41 For. Serv. Bul., Jan. 3, 1921,

42 That is, Florida National Forest organization.

This production of gum by the tree is greatly increased as a result of the stimulation of the wound or face cut.

The institution of cupping, in place of boxing, made it possible to eliminate the unnecessary injury to the tree caused by cutting the box, and hence was a marked advance in the direction of improved operation.

The proper placing of faces with reference to the size and conformation of the tree, and the maintenance of bark bars of sufficient width between faces, are matters of fundamental importance, which too often are neglected in practice. These matters if not cared for involve waste and loss throughout the operation.

The fact that it is unprofitable to turpentine too small trees, at least by present commercial methods, has been demonstrated beyond question.

The practice of cutting a streak in advance of the regular season's chipping on a virgin or first year operation appears to be productive of an increased early yield, which is of practical importance. This effect, as has been clearly shown, is not produced by the induced resin passages, formed at once as the immediate result of the streak, but presumably is due to the wound stimulus given to the resiniferous tissue already present.

The following effects of turpentining on the structure of the wood have been pointed out: 43

The structure of the annual rings of the wood formed before turpentining was not found to be visibly affected as a result of the turpentining, although the activities and responses of the living parenchyma cells in the outer layers of the sapwood already present in the immediate vicinity of the wound were undoubtedly stimulated by it. It was demonstrated that the resin passages of a considerable number of these outer sapwood rings contributed a very significant portion of the yield of oleoresin.

The structure of the wood produced after wounding was considerably modified, especially in the region immediately above the face. The effect in a tangential or circumferential direction was relatively slight, being hardly noticeable at a distance of 2 or 3 inches to the side of the wound. In all material the number of resin passages formed was greatly increased. The resin passages were formed earlier in the ring than normally. They varied from about the same diameter as that of the normal resin passages to rarely larger and frequently smaller diameters. The response to the wound stimulus, particularly in respect to the increased number of resin passages formed, was observed to be greatest within about 1 foot above the

43 See also Gerry, E., "Proper Methods of Turpentining," Sci. Am. Sup. 2176, Sept. 15, 1917; and Gerry, E., "Production of Crude Gum by the Pine Tree," Naval Stores, p. 147, 1921.

wound. It was also registered in the wood produced 6 to 9 feet vertically 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 intimately connected with these features is also of fundamental significance. Characteristic effects on the structure of wood, resulting 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 turpentining 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.

44

Chipping should progress up the tree at the rate of not more than one-half inch a week. In experiments in which chips of an average height of 0.40 to 0.34 45 inch were actually cut, a higher sustained yield was produced than in comparable workings in which the chip averaged one-half inch high. In the case of the double chipping at Columbia, Miss., an average height of chip of 0.32 inch was obtained with a 00 hack in 1916, and an average 0.26-inch chip with a puller during 1917. During the second year these trees, under this treatment, showed a smaller relative reduction in yield of turpentine, when compared to the first year yield, than did the half-inch chipping (standard). Using such a narrow streak means chipping in the lightwood or region of maximum stimulation, at least for a part of the season. It is yet to be determined whether the height of the chip can be further reduced.

Sufficient experiments to determine the most advantageous depth of chipping have not been carried out. It appears probable that the significant factor in this case, however, is the width of the sapwood, since, as has been shown, a considerable yield is obtained from many of the outer sapwood rings. A layer of healthy moist sapwood should always be present behind each face to maintain at the maximum the vital activities of the sapwood layers exposed at the streak. With wide sapwood and deep chipping (about three-fourths inch) very high yields may be obtained.

The advantages to be gained by the practice of conservative narrow chipping were shown to be the following:

1. Higher yields (40 to 50 per cent) per inch of height of chipped surface.

2. Higher sustained yields—that is, less reduction in yield from year to year, approaching the optimum condition, confidently to be expected, when the yields of subsequent years will surpass that of the first year.

3. Total annual yield approximating or even surpassing the yield from heavier chipping.

4. Little reduction, on the average, below the wood formation of the round timber, either in amount or quality.

5. Very high production of resiniferous tissue. This, for a given year, was markedly greater about one foot above the early streaks made that year. Hence narrow chipping enables the operator to reap the full benefit from this region of maximum stimulation and response by the practice known as chipping in the lightwood instead of wasting the wood containing the greatest number of resin passages by cutting it away with high chipping.

44 Early Forest Service Experiments, page 27. 45 Narrow chipping, Columbia, Miss., page 21.

6. Low rate of death of trees from turpentining and the production of few dry faces, hence less degrade of lumber due to pitch saturation or to infection at the face area.

7. Responsive vigor not reduced, as is shown by (a) the early formation of wood and resiniferous tissue; (b) the increases in diameter growth found even under turpentining; (c) the formation of the summer wood, which also occurred earlier in the narrow than in the standard and double chipped timber at Columbia, Miss.; and (d) a relatively very high total production during the second year of operation, especially since this was sustained as is shown, for instance, late in the season even after a severe drought, when neighboring crops showed a comparatively poor exudation of gum. 8. Greater ease in operating, once the chipper becomes accustomed to the method, since less wood is removed and the chipping period can be prolonged and the pulling period deferred, because the amount of surface chipped yearly is less.

FREQUENCY OF CHIPPING.

From the results obtained with the double chipping at Columbia, Miss., it was concluded that the yield obtained did not show a sufficient increase to offset the additional cost in the case of turpentine operations lasting for a considerable number of years. For a very short operation, when it is planned to turpentine for a period of perhaps two years before cutting the timber, double chipping might possibly be practiced regularly, or perhaps with greatest advantage for a limited period during the height of the producing season. The microscopic study of the material from the double tract showed that this method exerted a decidedly detrimental influence on wood formation and on the general vitality of the timber; and that it used up chipping surface to the same extent as ordinary commercial practice.

STANDARDS FOR ESTIMATING THE EFFECTS PRODUCED BY DIFFERENT METHODS OF CHIPPING.

In estimating the responses of the timber turpentined by the various methods of operation used at Columbia, Miss., the wood formation, especially the width of ring and the amount of summer wood produced by unturpentined trees growing in the same locality under the same conditions, was determined as a basis for judging the effects of turpentining on the wood structure. The best diameter growth and summerwood formation for the three years 1915, 1916, and 1917, were found in the round timber in 1916. Hence marked decreases in the wood formation of the turpentined timber for that year could be attributed directly to the effect of the wounding. De