affected slash and the rapid handling of infected logs are believed to be of value. GRAYISH-BLACK STAIN OF ASH Dark-tan to grayish-black streaks in white ash (Fraxinus americana), pinkish-colored areas in yellow poplar (Liriodendron tulipifera), dark-colored streaks in red gum and basswood, and brownishblack areas in eastern hemlock (Tsuga canadensis) have been found to contain a fungus (Torula ligniperda) which is decidedly different from most stain-producing organisms.is This fungus is commonly found in the heartwood and is a common cause of blemish in white ash. Tests made to correlate the color with the toughness strength 19 20 indicate that visual inspection can not be relied upon to separate the infected from the uninfected stock. Toughness tests and specific-gravity determinations are considered of value in determining the value of the stock for commercial use. The threads of this fungus in the wood are small and colorless, usually following the hollow of the cells but occasionally penetrating the cell walls. A characteristic spore formation consisting of dark ovoid spores borne in chains is often found within the wood cells. The wood structure is apparently little affected by the presence of this fungus, and such wall penetrations as were noted were few and difficult to determine. In hemlock the fungus is usually found associated with a brown cubical rot of the heartwood, the Torula infected area bordering the outer limits of the early decay. "MINERAL STREAK" OF MAPLE A greenish to olive discoloration is frequently noted in maple stock cut in the hardwood region. This stain is known locally as "mineral streak" or "mineral stain" and is supposed to be caused by the absorption of iron or copper salts through the roots of the living tree. (Fig. 16.) It is a troublesome defect and is found causing depreciation in a variety of wood products. In thick stock, kilndried for automobile construction, the greenish areas almost invariably develop "honeycomb" while the surrounding uncolored areas remain unchanged. (Fig. 16.) Again, in veneer stock cut for butter baskets and other products the green streaks are found to check readily and so cause a high percentage of "rejects." Millmen all agree that the greenish areas are harder than normal wood and that the edges of tools are prematurely dulled when cutting this kind of stock. Very often the saw will "heat up" when it begins cutting its way through the discolored areas. This fact lends color to the belief that an infiltration of "mineral" is responsible for the defect. Microscopical examinations of the discolored areas have disclosed minute colorless threads of a wood-inhabiting fungus within the wood cells. Cultural tests using fragments taken from air-dried stock have shown a fungus developing from the greenish pieces of 18 Siggers, P. V., Torula Ligniperda (Willk) Sacc. A Hyphomycete Occurring in Wood Tissue Phytopath. 12:369-374; August, 1922. 1 Colley, R. H., The Relation Between Color and Toughness Strength in Commercial White Ash: Prog. Rept. pp. 1-5; 1924. 20 Luxford, R. F., Effect of Decay on Strength of Commercial White Ash: Office report, Forest Products Laboratory; 1922. Note FIGURE 16.-Honeycomb in the "mineral streak" areas of kiln-dried maple. that no checking appears in the areas beyond the discolored portions, and that in the transverse section the checks are placed radially and are confined to the spring wood of the annual ring. The transverse section at left shows typical zone line and incipient discoloration characteristic of early stages of decay. wood. The discoloration is apparently an early stage of some common heart rot of maple. The following key is submitted as an aid in roughly determining the causes of given discolorations in wood other than the brownish discolorations of wood and those produced by the early stages of wood-rot organisms: KEY FOR THE IDENTIFICATION, BY COLOR, OF WOOD STAINS CAUSED BY FUNGI A. Stains found in sapwood__ A-1. Blue to bluish black_. A-2. Brown to olivaceous black. A-4. Rer, or shades of red____ A-1; A-2; A-3; A-4; or A-5. A-1-a or A-1-b. A-2-a; A-2-b; A-2-c; A-2-d; A-2-e. A-4-a or A-4-b. A-5. Yellow, or shades of yellow----- A–5–a. A-1-a. Bluish gray or bluish black in softwoods and hardwoods -BLUE STAIN. (Ceratostomella spp.). A-1-b. Bluish black to grayish black (Graphium spp.)------BLUE STAIN. A-2-a. Reddish brown to dark brown, in softwoods, sometimes associated with blue stain in sapwood (Sclerotiopsis 21 BROWN SAP STAIN. spp.) (Torula -BLACK STREAK. A-2-c. Brownish black to black (Hormiscium gelatinosum) _ BLACK STAIN. A-2-d. Olivaceous black, principally in hardwoods (Lasiosphaeria pezizula) --- -_GRAY-OLIVE STAIN. --BLACK STAIN. A-2-e. Intense black in irregular patches, in pines and hard- ----GREEN STAIN. A-3-b. Bright verdigris green, in softwoods (Chlorosplenium A-4-a. Orange to red, in scattered spots, on softwoods (Penicil- --ORANGE-RED STAIN. A-4-b. Pink, red to violet blotches, in pines (Fusarium roseum 21 PINK STAIN. A-5-a. Bright yellow color, in streaks or patches, in hardwoods B-1-a. Reddish brown to dark brown, in softwoods, often associated with blue stain in sapwood (Sclerotiopsis spp.)__BROWN SAP STAIN B-1-b. Grayish black streaks or patches, in ash, cottonwood, aspen, birch, maple, pine, and hemlock (Torula ligniperda) ----BLACK STREAK B-1-c. Olivaceous black, in hardwoods (Lasiosphaeria pezizula) GRAY-OLIVE STAIN B-2-a. Bright verdigris green, in hardwoods (Chlorosplenium aeruginascens"). -GREEN STAIN B-3-a. Pink to carmine red, in box elder (Fusarium negundi) RED STAIN B-4-a. Light lemon yellow, in streaks or patches, in oak, birch, chestnut, Fungi-producing coloring matter which stains the wood cell walls. The other fungi discolor the wood mainly through the presence in the wood tissues of colored hyphæ. Certain blue-stain fungi have the ability to stain the cell walls to a certain extent. INTERIOR BLUE STAIN Casehardening, or a "setting" of the outer layers of wood during seasoning, has often been confused with unequal drying as a direct factor in producing certain stain and decay defects in lumber, developing in the central core of the wood. Both interior dote (figs. 17, A and 17, B) and interior stain (figs. 18 and 19) may be found in casehardened lumber.22 In rare cases where casehardening is present in rapidly and unevenly seasoned stock of larger dimensions the rapid removal of moisture from the surface layers of wood favors the development of fungi in the interior areas by breaking the water column leading from the moisture-laden interior to the drier surface. Following the rapid drying and setting of the outer layers of wood the diffusion of moisture from the center outward is retarded. A somewhat different but perhaps more common condition in seasoned stock— but giving similar results-is to be found in the unequal moisture distribution in a piece of wood which leaves the outer layers of wood too dry for fungous development and which contains favorable moisture conditions in the central areas. The outer layer in wood showing interior development of fungi becomes too dry to favor fungous development, but in the central moist area the conditions remain favorable long enough for the blue-stain fungus to thoroughly stain the central area (figs. 18 and 19) or for the white-rot fungus in elm to completely rot the central portion (fig. 17). In samples showing interior stain the surfaces of the board appear bright except occasionally where crossers come in contact with the stock. Upon resawing such stock, however, the entire central areas are found to be heavily blued. Western yellow pine plank stock, when airseasoned, appears to be particularly susceptible to this type of defect. It is occasionally found in 8/4-inch and thicker sap gum stock which has been improperly steam treated. The question is frequently asked, "How does the fungus enter the plank?" Studies so far conducted have shown that the stain organisms may enter by way of the moist areas where the crossers or stickers rest upon the boards. Here the blue stain appears upon the surfaces and extends through the wood to the opposite face. Where the entire piece shows no signs of blue stain upon the surface another answer must be sought. Sections for microscopical examination, when cut from an area including both stained and unstained wood, very often show the unstained cells containing several small colorless threads of a fungus. The adjacent heavily blued cells show numerous brownish-colored threads of a larger diameter than the colorless ones. Both types of threads are recognized as those belonging to the blue-stain organism. Apparently the unstained outer areas when in the green condition favored the entrance of the fungus, but upon rapid drying the fungus growth was arrested. During the early development of certain blue-stain fungi the hyphæ remain colorless, and as they age they become brownish in color, thus imparting a bluish color to the wood. The young colorless hyphæ succeeded in reaching the more moist central region and there were able to continue their development. The rapid removal of moisture from the outer layers of wood, however, had prevented the further develop 22 See footnote 7. ment of threads to the point where they turned brown and discolored the wood. Hence the outer layers of wood remained clear of stain. The control of this defect is difficult, and only in the case of interior dote in elm has any control method been tested. For the prevention of interior dote in 6/4 and 8/4 inch elm a steaming treatment has been reported effective.23 It is believed that effective steaming methods for the control of interior stain are practicable and that avoidance of "setting" in the stock may also prove of value. The conditions for the rapid development of staining fungi are an abundant food supply, a comparatively high moisture content of the wood, and warm weather. Staining is always severe during rainy periods in the warmer seasons of the year, when the air is humid and the wood dries correspondingly slowly. Very heavy staining may occur in such circumstances, more particularly when lumber fresh from the saw is bulk-piled, or when green stock is improperly stored or shipped in closed cars or in the holds of vessels. It has been observed that the mold fungi grow best on substances which contain some acid, for which reason normal acid sap and the "sour" sap containing even more acid make a very favorable medium for the rapid development of the stain organisms. This fact is believed to explain in part why alkaline dips which neutralize the acidity of the sap are effective in the prevention of stain. 24 Some of the staining fungi appear to prefer certain species of wood. The exact nature of this affinity, whereby some species of wood seem to "blue" more readily than others, has not been determined. Perhaps the food or moisture conditions in the sapwood vary sufficiently among species to account for the selective action. Curiously enough, the heartwood seems to be unfavorable soil for the development of molds, and the blued areas frequently end where the heartwood begins. This peculiarity of behavior has often been discussed, and general opinion now inclines toward the theory that a favorable field for the development of the stain fungi is found in freshly killed sapwood which has lost some moisture and gained a little air. In a few rare cases blue-stain organisms have been found in the heartwood of certain woods. These woods are usually of the type that show little difference between sapwood and heartwood and in which the heartwood shows a fairly high moisture content. MOISTURE CONTENT IMPORTANT The amount of moisture in the wood thus appears to be a determining factor. Apparently the heartwood in many cases is not moist enough and the sapwood of the living tree perhaps too moist to favor the growth of blue-stain fungi. Since it is not feasible to keep lumber wet after manufacture, it is obvious that in the airseasoning, storing, and shipping of wood products the main effort in the prevention of stain lies in the opposite direction-rapid drying. Investigations here and abroad have demonstrated that the species of fungi causing blue stain react quite definitely to different moisture contents in wood. The writer has conducted tests by growing a particular fungus on several pieces of fresh sapwood, the pieces containing known amounts of water in a graduated series. It was Loughborough, W. C., and Hubert. E. E.. Problems in the Seasoning of Southern Hardwoods: So. Lumberman 117: 170-174; 1924. 24 Rumbold, C. T., Blue Stain on Lumber: In Science n. s. 34: 94-96; 1911. |