TABLE 5.-Seasoning of chestnut poles at Pisgah, N. C., based on 600 poles.

The average volume of 30-foot poles was 21.12 cubic feet, and of 25-foot poles 14.70 cubic feet.

Table 6 is based upon original weight and does not consider the air-dry condition of the timber. Like Table 2, it is mainly valuable to the shipper in showing what reduction in weight may be looked for by holding poles cut in any season.

It will be understood that this table does not serve as a basis for comparison of poles cut at different seasons, since in this case the practical consideration is not the percentage of the original weight lost, but the actual weight reached, which was shown in Tables 3, 4, and 5.

TABLE 6.-Loss of first weight of chestnut poles cut at three seasoning stations.

SPECIFIC GRAVITY OF WOOD.

While there is but little, if any, difference in the specific gravity of pure wood substance or cellulose, regardless of the kind of tree, the specific gravity of wood as found in the tree varies considerably. Density, or the closeness with which the fibers are compacted in growth, affects specific gravity. The amount of water contained affects it greatly, and similarly its content of minerals, resin, or oils. These all affect specific gravity directly. Other things operating through these exert an indirect influence. Age influences the moisture content. Season varies the moisture content and perhaps also the content of albuminous matter. Soil and climate influence both the density of wood and the substances it contains.

For the reasons just set forth, there may be considerable variation in the specific gravity of timber cut in any particular locality. For instance, young, thriftily grown timber cut in summer might easily have a greater specific gravity than old timber cut in winter; but in timber of approximately the same age and growth, that cut in winter would usually be heaviest, that in spring and summer of about the same weight, with the difference, if any, in favor of the summer cut, and that cut in autumn lightest.

The following figures were obtained from the green chestnut poles cut at the three stations at different seasons:

Trees normally contain the greatest amount of water during that period when the roots are active and the leaves not yet out. In climates like those in which these experiments were made root activity commonly begins in January, February, or March, the exact time varying with the kind of timber and the local atmospheric conditions. The results also indicate that green wood becomes lighter in late spring or early summer, when transpiration through the foliage is most rapid. The weight at any season, however, is doubtless much influenced by the amount of moisture in the soil.

The results are in accordance with those obtained by Robert Hartig in his investigations of the specific gravity of wood cut at different times of the year. From a careful study of 30 different species of trees practically all of the same age (16 years), which he grouped into three classes, he found, by eliminating as far as possible all variables other than the one under investigation, that the specific gravity varied materially with the season, as is shown in Table 7.a

• Russian Forests, Vol. II, pt. 2, p. 4, Th. K. Arnold, St. Petersburg, 1899.

TABLE 7.-Percentage of moisture contained in wood cut at different times of

The water in green wood is contained in the cell cavities, in intercellular spaces, and in the cell walls. When green wood is exposed to the air, the water it contains begins to evaporate. The amount and rapidity of evaporation depend upon the length of time the timber is exposed, the amount of water in the wood, and the heat and dryness of the surrounding air. By far the greater part of the water evaporated during air seasoning is that from the cell cavities and intercellular spaces. Since the water contained in the cell walls is not greatly reduced, the shrinkage during air seasoning is very little. As soon, however, as wood begins to lose water from its cell walls, shrinkage commences, and continues as long as the amount of such water is reduced.

Shrinkage in wood may be distinguished as longitudinal, radial, and tangential. Longitudinal shrinkage (in the direction of the length of the fibers) is practically inappreciable; radial shrinkage (in the direction of the radius) is from 4 to 6 per cent; and tangential shrinkage (in the direction of the circumference) is about double the radial. In round timbers, such as telephone poles, shrinkage can best be determined by measuring the circumference.

From thousands of measurements made on telephone poles during this experiment, it was found that shrinkage was so slight as to be almost negligible.

Table 8 gives the circumference at the 6-foot and 30-foot points for all the chestnut poles, and also the per cent of shrinkage at the end of twelve months. From this table it is evident that the maximum shrinkage was less than 1 per cent, and that the average was but about 0.5 per cent for the butt and 0.6 per cent for the top. TABLE 8.-Shrinkage of chestnut poles.

CHECKING.

All wood when undergoing a seasoning process, either natural (by air) or mechanical (by steam, kiln-drying, etc.), checks or splits more or less. This is due to the uneven drying out of the wood and the consequent strains exerted in opposite directions by the wood fibers. in shrinking. There is more checking in the wood of broadleaf trees than in that of coniferous trees, more in sapwood than in heartwood, and more in summer wood than in spring wood. Inasmuch as under normal conditions of weather water evaporates less rapidly during early seasoning in winter," wood cut in autumn and early winter is considered less subject to checking than that cut in spring and summer. Rapid seasoning, except after wood is soaked or steamed, almost invariably results in more or less serious checking.

The worst checking during seasoning experiments occurred at the Pisgah, N. C., station, where the poles were cut from comparatively young, rapid-growing trees. The trees were felled with axes and the chopping was carelessly done, so that in many cases the butts and tops were somewhat ragged and at times split. During seasoning, especially in summer, many of these poles checked and split badly at the butt and top, and in some cases pieces of wood of a width of several inches and of a depth of three to six annual rings curled up from the ends of the poles for a distance of several feet. Such pieces or slabs separated along an annual ring from the remainder of the pole, the point of separation being between the summer wood of one year's ring and the spring wood of the next. Had these poles been more carefully chopped or sawed the checking would probably have been slight.

PRACTICAL ADVANTAGES OF WINTER CUTTING.

Winter cutting of poles has long been the general rule, since conditions continue to make it the best and cheapest season for the logger. Moreover, sap contains fewer nitrogenous substances in winter than at other seasons, and since fungi obtain much of their food from these substances winter-cut timber is least liable to attack from this source. Nor does the harder and denser wood found in summer and early autumn afford fungi as good a chance to lodge and develop as the undeveloped wood, immediately under the bark, which forms in spring and early summer. Again, winter-cut poles season more gradually, and at that time of the year the wood fibers shrink more uniformly, and checking is less serious.

Winter at the experiment stations where chestnut was cut is usu

The experiments on white cedar poles were conducted at Wilmington, N. C., where little winter weather is experienced. This accounts for the relatively greater evaporation of water from poles at this point during the winter months.

ORGANIZATION OF THE FOREST SERVICE.

GIFFORD PINCHOT, Forester.

OVERTON W. PRICE, Associate Forester.

P. P. WELLS, Law Officer.

HERBERT A. SMITH, Editor.

GEORGE B. SUDWORTH, Dendrologist.

Grazing-ALBERT F. POTTER, Assistant Forester, in Charge.

Operation-JAMES B. ADAMS, Assistant Forester, in Charge.
Maintenance-HERMON C. METCALF, Chief.

Accounts GEORGE E. KING, Chief.
Organization-C. S. CHAPMAN, Chief.

CLYDE LEAVITT, Assistant Chief.

Engineering-W. E. HERRING, Chief.

Lands-GEORGE F. POLLOCK, Chief.

Silviculture--WILLIAM T. Cox, Assistant Forester, in Charge.

Extension-SAMUEL N. SPRING, Chief.

Silvics-RAPHAEL ZON, Chief.

Management-E. E. CARTER, Chief.

W. G. WEIGLE, Assistant Chief.

Products-WILLIAM L. HALL, Assistant Forester, in Charge.

[Cir. 104]

Wood Utilization-R. S. KELLOGG, Chief.

Wood Preservation--CARL G. CRAWFORD, Chief.
Publication-FINDLEY BURNS, Chief.

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