or painted, and if conditions of exposure permit the use of sapwood. (See fig. 20.)

Considerable work has been done to determine the effect of the blue-stain fungi upon the mechanical properties of the wood they discolor. A variety of results were secured by the various workers. Rudeloff 25 found that the compressive strength of wood infected with a blue-stain organism did not differ from unstained wood, but it appears he took no account of the variation in moisture content of the test pieces, and the results are therefore not as reliable as in tests where this factor is considered. Von Schrenk 26 gives a series of tests made with stained and unstained pieces stating that for all practical purposes the stained wood is as strong as the unstained. He further notes that the higher results secured for the stained wood in tests for compression parallel and perpendicular to the grain are probably due to the difference in moisture content between the stained and unstained pieces. He observed a greater resistance to splitting

FIGURE 20.-A, Threads of a blue-stain fungus in the wood cells of scrub pine. Note the penetration of the walls but no evidence of marked decomposition. Most of the sap-stain fungi do not bore through the walls as this one does. Enlarged about five hundred times. B, The threads (a, c) of a wood-rotting fungus, Lentinus lepideus, in jack pine, Pinus banksiana. Note the numerous penetrations of the cell walls by the threads through large bore holes. The breaking down of the cell is plainly shown in the upper right-hand corner. Enlarged about five hundred times

along a tangential plane (flat grain) in the blued wood than in the unaffected wood. Münch,27 testing pine wood infected for six months with the blue-stain fungus, C. pini Münch, found the specific gravity less than normal and the resistance to compression slightly weakened. These effects he attributes to the presence of other fungi in the test pieces. Weiss and Barnum,28 testing stained and unstained pieces of longleaf (P. palustris) and shortleaf pine (P. echinata), conclude that for all practical purposes the blued wood is as strong as the unstained wood.

25 Rudeloff, M., Untersuchungen uber den Einfluss des Blauwerdens auf die Festigkeit von Kiefernholz. Theil I-II. Mitt. K. Tech. Versuchsanst. 15 (1897); 1-46, 55 figs., 17 (1899); 209-239, 9 figs., 1899.

28 Von Schrenk, H., The Blueing and the Red Rot of the Western Yellow Pine, with Special Reference to the Black Hills Forest Reserve: U. S. Dept. of Agri. B. P. I. Bul 36, 40 pp., 14 pl. (4 col.); 1903.

Münch, E., Die Blaufaule des Nadelholzes: Naturwiss. Zeitschr. Forst-u. Landw. 5:531-573, 1907; 6: 32-47, 297-323, illus., 1908.

28 Weiss, H. F., and Barnum, C. T., The Prevention of Sap Stain in Lumber: U. S. Dept. of Agri. For. Service Cir. 192: 1-19; 1911.

The heavily sap-stained shortleaf pine was practically as high as the unstained in bending strength and in stiffness but was slightly lower in toughness and in surface hardness. The longleaf pine was only slightly sap stained, and the tests indicate that the stain had no effect on bending strength, stiffness, or toughness, and little or no effect on hardness. The St. Louis tests 29 on stained and unstained western yellow pine (P. ponderosa) give higher results for the stained wood in compression parallel to grain and in static bending than the unstained wood. Weiss and Barnum 30 state this result is probably due to the fact that the stained wood was drier than the normal wood with which it was compared.

A review of the strength tests which have been made indicate a slight weakening effect due to the blue stain. For all practical purposes involving the use of structural timber where large factors of safety are employed and where slight weakening would be of no consequence, the stained wood is apparently as strong as the unstained. The slight weakening, however, such as the lowering of toughness and hardness, might seriously affect the usefulness of sapstained stock for purposes in which these properties are particularly important.

RESISTANCE TO THE PENETRATION OF PRESERVATIVES

The common statement, often heard, that the presence of sap stain or blue stain in the stock undergoing treatment materially retards the penetration of creosotes and other preservatives into wood seems to have no foundation in fact. Experimental work on a scale large enough to be conclusive has not been done on this project. There is much observational evidence that the high moisture content of the sapwood plays an important part in preventing the penetration of preservatives. Some claim that a hardening of the outer layers of sapwood due to rapid drying is responsible. Again it may be the thin inner layer of bark cells left on the surface of the sapwood after the removal of the bark that retards the penetration of preservatives. In certain species of wood used for poles and posts a perforator is employed to open up the wood before treatment.

Preliminary tests on Pondosa pine and southern yellow pine sapwood using a 5 per cent zinc chloride solution indicate that when clear and blued pieces are both brought to the oven-dry condition and then treated the blued pieces show a much deeper penetration than the clear pieces.

It is said that in Germany and other European countries railroad ties and other wood products showing heavy sap stain are culled from the loads prepared for preservative treatments on account of the resistance offered to the penetration of the chemicals. The blued stock is usually used, however, in an untreated condition. Such statements are difficult to substantiate, and when sifted down it may be found that blued wood is as easily treated as clear wood when good treating conditions are used.

Von Schrenk. H., The Blueing and Red Rot of the Western Yellow Pine. U. S. Dept. of Agri. B. P. I. Bul. 36. 40 pp., 14 pls. (4 col.): 1903.

30 Weiss, H. F., and Barnum, C. T., The Prevention of Sap Stain in Lumber: U. S. Dept. of Agri, For. Service Cir. 192: 1-19; 1911.

BLEACHING OF BLUED WOOD

Attempts are often made to bleach out the blue-gray color in heavily blued wood products. Several bleaching methods have been suggested for this purpose, but so far none have been successful in producing anything but a superficial bleaching. In preliminary tests made with a solution of calcium hypochlorite on pieces of blued pine wood the blue color was bleached out to a depth of one-sixteenth to one-eighth inch. During the bleaching, however, the outer layers of cells become considerably altered and show signs of brittleness. The commercial bleaching of blued wood has not become a successful practice with the one exception of the bleaching of blued fibers in wood pulp for paper making. Where large amounts of blued wood are used in the making of wood pulp, more bleaching liquid is re

FIGURE 21. An old fungus thread (darkly shaded) of the blue-stain
fungus which has revived and produced three new growing
branches. These threads in the wood of eastern white pine were
air dry and dormant for some time, but revived when sufficient
moisture was applied. Enlarged about eight hundred times.

quired than for wood pulp containing no blued stock. Pulp pre-
pared experimentally from spruce chips was found to require an
average of 10.6 per cent bleach powder. That made from selected
sound (unblued) chips required only 8.6 per cent, while that made
from badly stained chips required 15.7 per cent, based on the air-dry
pulp weight.31

The blue-stain threads, dormant for a considerable time in wood. stored in the dry atmosphere of a room, are capable of reviving and sending forth new threads on the return of favorable growth conditions. (Fig. 21.) In one case the blue-strain fungus remained

Sutermeister, E.. The Use of Rotten and Stained Wood for Making Sulphite Pulp: Pulp and Paper Magazine, Canada, 20: 513-514; 1922.

dormant for a period of seven years in the sap zone of a piece of structural timber, and when cultured at the end of this period it grew vigorously on the artificial food. The above fact has an important bearing on the piling of lumber for air-seasoning or for storage and on the shipment of lumber and other wood products in closed box cars or in the holds of vessels. In stock which has not been sterilized by heat or other means it is important to reduce the moisture content below 20 per cent as soon as possible. It is equally important to keep the material dry once it has been properly seasoned, for the fungus may revive and continue to spread as long as sufficient moisture is present for its growth.

The results of experiments on the effect of heat upon sap-stain fungi within the wood have a direct application in the kiln-drying and steaming of lumber. The killing of sap-stain and decay organisms present in the green wood may prevent considerable spread and development of these organisms during air-seasoning, storage, or in

transit.

The tests so far conducted 32 show that a temperature of 140° F. maintained for three hours at saturated atmosphere (relative humidity, 100 per cent) kills the blue-stain fungus in Eastern white pine (P. strobus) and in Northern white cedar (Thuja occidentalis) in 1 and 2 inch stock containing blued sapwood. The fungi remained alive, however, in the central portions of the 4-inch stock. After treatment of the 1, 2, and 4 inch test pieces for six hours under the above conditions no revival of the fungi was observed. The tests also indicated that the sap-stain organisms and the molds in general were more resistant to heat than were many of the wood-destroying fungi. In some cases mold growth is found developing on boards in the dry kiln and thus obstructing the circulation. In general practice it has been found 33 that a preliminary steaming of the stock at 170 to 180° F. for a period not exceeding an hour stopped the surface growth of mold. This treatment heats the surface of the stock sufficiently to kill the mold, and at the same time too-rapid drying is prevented by the saturated air.

RELATION OF BARK BEETLES TO SAP STAIN

Several references may be found indicating the possible relation between the bark beetles and other insects inhabiting standing and felled trees and the sap stain that soon appears following the entrance of these insects. Observational data taken in the field would indicate that bark beetles are carriers of the sap-stain spores and thus serve to introduce these fungi into the moist sapwood. Areas of discolored sapwood are commonly found in close association with the areas under the bark where bark beetles have been activę. Similar areas of both blue stain and brown sap stain have repeatedly been observed spreading from the small shot-hole borings made in sapwood by the ambrosia beetles. This is a very common observation in logs stored in decks for periods of time.

The investigations on this subject carried out by the Bureau of Entomology and other Federal bureaus have not yet been published,

22 Hubert, E. E.. Effect of Kiln-Drying, Steaming, and Air-Seasoning on Certain Fungi in Wood: U. S. Dept. of Agri. Bul. 1262: 1–20; 1924.

33 Forest Products Laboratory Technical Note No. 136.

and detailed information on this interesting point will appear in time.

no doubt Some preliminary tests have been conducted by the writer during 1928. Adults of the bark beetle, Dendroctonus monticolae, were captured just prior to their entrance into the bark of the host tree. These beetles were placed, one to a tube, in culture tubes containing malt agar, the tubes and the agar having been previously sterilized. The tubes were set aside for incubation over a period of two to three months, at the end of which time they were examined. It was found that about 75 per cent of the tubes showed fungous growths which were brown to black in color, indicating the presence of dark-colored fungi. The isolation and identification of these fungi, which are numerous in these cultures are in progress in order to determine whether they are sap-stain organisms. The cultural characteristics of several of the organisms resemble closely a bluestain fungus found in lodgepole pine.

The tests indicate that bark beetles carry spores or fragments of fungous threads attached to their bodies and that these are viable and capable of producing new growths of the organisms they represent.

LOSS DUE TO SAP STAINS

LOSSES IN LOG HANDLING AND STORAGE

The principal losses in stored and improperly handled logs are caused by fungi and insects and by the damage due to checking. A great part of these losses occur in the more valuable hardwood species selected for particular utilization. (Figs. 22 and 23.) Due to seasonal logging and other causes, much of this raw material is accumulated and stored in quantities in order to insure an adequate supply. (Fig. 23.)

This storage of logs is practiced in many of the industries, and the piles may be erected in the woods, at shipping points, at the mill, or at the manufacturing plant. Very often the storage of logs in the woods, at shipping points, or along railroad spurs or main lines is carried on in a haphazard fashion, and the logs are bulked without skids on swampy or undrained ground. Here they are left for a considerable time before they are finally loaded and shipped to their destination. During this storage period stain and decay organisms enter the logs, heart rots may continue to develop (figs. 24 and 25), end checks make their appearance, and insects begin and continue their destructive activities. The data so far accumulated indicate that the loss due to decay in stored logs represents from 3 to as high as 50 per cent of the merchantable volume. We will assume that the lowest figure, or 3 per cent, is lost through decay in storage. This would give an annual loss of 310,000,000 cubic feet on the basis of the total production (1922 basis) of the various groups of forest products taken from industries which usually store quantities of logs for considerable lengths of time. The equivalent in lumber taken from these logs equals more than 1,000,000,000 board feet having an approximate money value of $42,250,000. This is the Nation's annual bill for waste in log storage and handling due to decay alone. The additional losses due to sap stain, end checks, and insects would 42717°-29