A Large CottonwoodFig. 14. A Large Cottonwood. One of the Associates of Red Gum.
Fig. 14. A Large Cottonwood. One of the Associates of Red Gum.
94. Black Cottonwood(Populus trichocarpavar.heterophylla) (Swamp Cottonwood, Downy Poplar). The largest deciduous tree of Washington. Very common.Heartwood dull brown, sapwood lighter brown. Wood soft, close-grained. Is now manufactured into lumber in the West and South, and used in interior finish of buildings. Northern Rocky Mountains and Pacific region.
95. Poplar(Populus grandidentata) (Large-Toothed Aspen). Medium-sized tree. Heartwood light brown, sapwood nearly white. Wood soft and close-grained, neither strong nor durable. Chiefly used for wood pulp. Maine to Minnesota and southward along the Alleghanies.
96. White Poplar(Populus alba) (Abele-Tree). Small to medium-sized tree. Wood in its quality and uses similar to the preceding. Found principally along banks of streams, never forming forests. Widely distributed in the United States.
97. Lombardy Poplar(Populus nigra italica). Medium- to large-sized tree. This species is the first ornamental tree introduced into the United States, and originated in Afghanistan. Does not enter into the markets. Widely planted in the United States.
98. Balsam(Populus balsamifera) (Balm of Gilead, Tacmahac). Medium- to large-sized tree. Heartwood light brown, sapwood nearly white. Wood light, soft, not strong, close-grained. Used extensively in the manufacture of paper pulp. Common all along the northern boundary of the United States.
99. Aspen(Populus tremuloides) (Quaking Aspen). Small to medium-sized tree, often forming extensive forests, and covering burned areas. Heartwood light brown, sapwood nearly white. Wood light, soft, close-grained, neither strong nor durable. Chiefly used for woodenware, cooperage, and paper pulp. Maine to Washington and northward, and south in the western mountains to California and New Mexico.
100. Sassafras(Sassafras sassafras). Medium-sized tree, largest in the lower Mississippi Valley. Wood light, soft, not strong, brittle, of coarse texture, durable in contact with the soil. The sapwood yellow, the heartwood orange brown. Used to some extent in slack cooperage, for skiff- and boatbuilding, fencing, posts, sills, etc. Occurs from New England to Texas and from Michigan to Florida.
101. Sourwood(Oxydendrum arboreum) (Sorrel-Tree). A slender tree, reaching the maximum height of 60 feet. Heartwood reddish brown, sapwood lighter color. Wood heavy, hard, strong, close-grained, and takes a fine polish. Ranges from Pennsylvania, along the Alleghanies, to Florida and Alabama, westward through Ohio to southern Indiana and southward through Arkansas and Louisiana to the Coast.
102. Sycamore(Platanus occidentalis) (Buttonwood, Button-Ball Tree, Plane Tree, Water Beech). A large-sized tree, of rapid growth. One of the largest deciduous trees of the United States, sometimes attaining a height of 100 feet. It produces a timber that is moderately heavy, quite hard, stiff, strong, and tough, usually cross-grained; of coarse texture, difficult to split and work, shrinks moderately, but warps and checks considerably in seasoning, but stands well, and is not considered durable for outside work, or in contact with the soil. It has broad medullary rays, and much of the timber has a beautiful figure. It is used in slack cooperage, and quite extensively fordrawers, backs, and bottoms, etc., in furniture work. It is also used for cabinet work, for tobacco boxes, crates, desks, flooring, furniture, ox-yokes, butcher blocks, and also for finishing lumber, where it has too long been underrated. Common and largest in the Ohio and Mississippi Valleys, at home in nearly all parts of the eastern United States.
103. Sycamore(Platanus racemosa). The California species, resembling in its wood the Eastern form. Not used to any great extent.
104. Tulip Tree(Liriodendron tulipifera) (Yellow Poplar, Tulip Wood, White Wood, Canary Wood, Poplar, Blue Poplar, White Poplar, Hickory Poplar). A medium- to large-sized tree, does not form forests, but is quite common, especially in the Ohio basin. Wood usually light, but varies in weight, it is soft, tough, but not strong, of fine texture, and yellowish color. The wood shrinks considerably, but seasons without much injury, and works and stands extremely well. Heartwood light yellow or greenish brown, the sapwood is thin, nearly white, and decays rapidly. The heartwood is fairly durable when exposed to the weather or in contact with the soil. It bends readily when steamed, and takes stain and paint well. The mature forest-grown tree has a long, straight, cylindrical bole, clear of branches for at least two thirds of its length, surmounted by a short, open, irregular crown. When growing in the open, the tree maintains a straight stem, but the crown extends almost to the ground, and is of conical shape. Yellow poplar, or tulip wood, ordinarily grows to a height of from 100 to 125 feet, with a diameter of from 3 to 6 feet, and a clear length of about 70 feet. Trees have been found 190 feet high and ten feet in diameter. Used in cooperage, for siding, for panelling and finishing lumber in houses, car- and shipbuilding, for sideboards, panels of wagons and carriages, for aeroplanes,for automobiles, also in the manufacture of furniture farm implements, machinery, for pump logs, and almost every kind of common woodenware, boxes shelving, drawers, etc., etc. Also in the manufacture of toys, culinary woodenware, and backing for veneer. It is in great demand throughout the vehicle and implement trade, and also makes a fair grade of wood pulp. In fact the tulip tree is one of the most useful of woods throughout the woodworking industry of this country. Occurs from New England to Missouri and southward to Florida.
105. Waahoo(Evonymus atropurpureus). (Burning Bush, Spindle Tree). A small-sized tree. Wood white, tinged with orange; heavy, hard, tough, and close-grained, works well and stands well. Used principally for arrows and spindles. Widely distributed. Usually a shrub six to ten feet high, becoming a tree only in southern Arkansas and Oklahoma.
106. Black Walnut(Juglans nigra) (Walnut). A large, beautiful, and quickly-growing tree, about 60 feet and upwards in height. Wood heavy, hard, strong, of coarse texture, very durable in contact with the soil. The narrow sapwood whitish, the heartwood dark, rich, chocolate brown, sometimes almost black; aged trees of fine quality bring fancy prices. The wood shrinks moderately in seasoning, works well and stands well, and takes a fine polish. It is quite handsome, and has been for a long time the favorite wood for cabinet and furniture making. It is used for gun-stocks, fixtures, interior decoration, veneer, panelling, stair newells, and all classes of work demanding a high priced grade of wood. Black walnut is a large tree with stout trunk, of rapid growth, andwas formerly quite abundant throughout the Alleghany region. Occurs from New England to Texas, and from Michigan to Florida. Not common.
107. White Willow(Salix albavar.vitellina) (Willow, Yellow Willow, Blue Willow). The wood is very soft, light, flexible, and fairly strong, is fairly durable in contact with the soil, works well and stands well when seasoned. Medium-sized tree, characterized by a short, thick trunk, and a large, rather irregular crown composed of many branches. The size of the tree at maturity varies with the locality. In the region where it occurs naturally, a height of 70 to 80 feet, and a diameter of three to four feet are often attained. When planted in the Middle West, a height of from 50 to 60 feet, and a diameter of one and one-half to two feet are all that may be expected. When closely planted on moist soil, the tree forms a tall, slender stem, well cleared branches. Is widely naturalized in the United States. It is used in cooperage, for woodenware, for cricket and baseball bats, for basket work, etc. Charcoal made from the wood is used in the manufacture of gunpowder. It has been generally used for fence posts on the Northwestern plains, because of scarcity of better material. Well seasoned posts will last from four to seven years. Widely distributed throughout the United States.
108. Black Willow(Salix nigra). Small-sized tree. Heartwood light reddish brown, sapwood nearly white. Wood soft, light, not strong, close-grained, and very flexible. Used in basket making, etc. Ranges from New York to Rocky Mountains and southward to Mexico.
109. Shining Willow(Salix lucida). A small-sized tree. Wood in its quality and uses similiar to the preceding. Ranges from Newfoundland to Rocky Mountains and southward to Pennsylvania and Nebraska.
110. Perch Willow(Salix amygdaloides) (Almond-leaf Willow). Small to medium-sized tree. Heartwood light brown, sapwood lighter color. Wood light, soft, flexible, not strong, close-grained. Uses similiar to the preceding. Follows the water courses and ranges across the continent; less abundant in New England than elsewhere. Common in the West.
111. Long-Leaf Willow(Salix fluviatilis) (Sand Bar Willow). A small-sized tree. Ranges from the Arctic Circle to Northern Mexico.
112. Bebb Willow(Salix bebbianavar.rostrata). A small-sized tree. More abundant in British America than in the United States, where it ranges southward to Pennsylvania and westward to Minnesota.
113. Glaucous Willow(Salix discolor) (Pussy Willow). A small-sized tree. Common along the banks of streams, and ranges from Nova Scotia to Manitoba, and south to Delaware; west to Indiana and northwestern Missouri.
114. Crack Willow(Salix fragilis). A medium to large-sized tree. Wood is very soft, light, very flexible and fairly strong, is fairly durable in contact with the soil, works well and stands well. Used principally for basket making, hoops, etc., and to produce charcoal for gunpowder. Very common, and widely distributed in the United States.
115. Weeping Willow(Salix babylonica). Medium- to large-sized tree. Wood similiar toSalix nigra, but not so valuable. Mostly an ornamental tree. Originally came from China. Widely planted in the United States.
116. Yellow Wood(Cladrastis lutea) (Virgilia). A small to medium-sized tree. Wood yellow to pale brown, heavy, hard, close-grained and strong. Not used to much extent in manufacturing. Not common. Found principally on the limestone cliffs of Kentucky, Tennessee, and North Carolina.
Theterms "fine-grained," "coarse-grained," "straight-grained," and "cross-grained" are frequently applied in the trade. In common usage, wood is coarse-grained if its annual rings are wide; fine-grained if they are narrow. In the finer wood industries a fine-grained wood is capable of high polish, while a coarse-grained wood is not, so that in this latter case the distinction depends chiefly on hardness, and in the former on an accidental case of slow or rapid growth. Generally if the direction of the wood fibres is parallel to the axis of the stem or limb in which they occur, the wood is straight-grained; but in many cases the course of the fibres is spiral or twisted around the tree (as shown inFig. 15), and sometimes commonly in the butts of gum and cypress, the fibres of several layers are oblique in one direction, and those of the next series of layers are oblique in the opposite direction. (As shown inFig. 16the wood is cross or twisted grain.) Wavy-grain in a tangential plane as seen on the radial section is illustrated inFig. 17, which represents an extreme case observed in beech. This same form also occurs on the radial plane, causing the tangential section to appear wavy or in transverse folds.
When wavy grain is fine (i.e., the folds or ridges small but numerous) it gives rise to the "curly" structure frequently seen in maple. Ordinarily, neither wavy, spiral, nor alternate grain is visible on the cross-section; its existence often escapes the eye even on smooth, longitudinal faces in the sawed material, so that the onlyguide to their discovery lies in splitting the wood in two, in the two normal plains.
Spiral Grain
Fig. 15. Spiral Grain. Season checks, after removal of bark, indicate the direction of the fibres or grain of the wood.
Alternating Spiral Grain in CypressFig. 16. Alternating Spiral Grain in Cypress. Side and end view of same piece. When the bark was ato, the grain of this piece was straight. From that time, each year it grew more oblique in one direction, reaching a climax ata, and then turned back in the opposite direction. These alternations were repeated periodically, the bark sharing in these changes.
Fig. 16. Alternating Spiral Grain in Cypress. Side and end view of same piece. When the bark was ato, the grain of this piece was straight. From that time, each year it grew more oblique in one direction, reaching a climax ata, and then turned back in the opposite direction. These alternations were repeated periodically, the bark sharing in these changes.
Generally the surface of the wood under the bark, and therefore also that of any layer in the interior, is not uniform and smooth, but is channelled and pitted by numerous depressions, which differ greatly in size and form. Usually, any one depression or elevation is restricted to one or few annual layers (i.e., seen only in one or few rings) and is then lost, being compensated (the surface at the particular spot evened up) by growth. In some woods, however, any depression or elevation once attained grows from year to year and reaches a maximum size, which is maintained for many years, sometimes throughout life. In maple, where this tendency to preserve any particular contour is very great, the depressions and elevations areusually small (commonly less than one-eighth inch) but very numerous.
On tangent boards of such wood, the sections, pits, and prominences appear as circlets, and give rise to the beautiful "bird's eye" or "landscape" structure. Similiar structures in the burls of black ash, maple, etc., are frequently due to the presence of dormant buds, which cause the surface of all the layers through which they pass to be covered by small conical elevations, whose cross-sections on the sawed board appear as irregular circlets or islets, each with a dark speck, the section of the pith or "trace" of the dormant bud in the center.
Wavy Grain in BeechFig. 17. Wavy Grain in Beech (after Nordlinger).
Fig. 17. Wavy Grain in Beech (after Nordlinger).
Section of Wood
In the wood of many broad-leaved trees the wood fibres are much longer when full grown than when they are first formed in the cambium or growing zone. This causes the tips of each fibre to crowd in between the fibres above and below, and leads to an irregular interlacement of these fibres, which adds to the toughness, but reduces the cleavability of the wood. At the juncture of the limb and stem the fibres on the upper and lower sides of the limb behavedifferently. On the lower side they run from the stem into the limb, forming an uninterrupted strand or tissue and a perfect union. On the upper side the fibres bend aside, are not continuous into the limb, and hence the connection is not perfect (seeFig. 18). Owing to this arrangement of the fibres, the cleft made in splitting never runs into the knot if started on the side above the limb, but is apt to enter the knot if started below, a fact well understood in woodcraft. When limbs die, decay, and break off, the remaining stubs are surrounded, and may finally be covered by the growth of the trunk and thus give rise to the annoying "dead" or "loose" knots.
Fig. 18. Section of Wood showing Position of the Grain at Base of a Limb. P, pith of both stem and limb; 1-7, seven yearly layers of wood;a,b, knot or basal part of a limb which lived for four years, then died and broke off near the stem, leaving the part to the left ofa,b, a "sound" knot, the part to the right a "dead" knot, which would soon be entirely covered by the growing stem.
Color, like structure, lends beauty to the wood, aids in its identification, and is of great value in the determination of its quality. If we consider only the heartwood, the black color of the persimmon, the dark brown of the walnut, the light brown of the white oaks, the reddish brown of the red oaks, the yellowish white of the tulip and poplars, the brownish red of the redwood and cedars, the yellow of the papaw and sumac, are all reliable marks of distinction and color. Together with luster and weight, they are only too often the only features depended upon in practice. Newly formed wood, like that of the outer few rings, has but little color. The sapwood generally is light,and the wood of trees which form no heartwood changes but little, except when stained by forerunners of disease.
The different tints of colors, whether the brown of oak, the orange brown of pine, the blackish tint of walnut, or the reddish cast of cedar, are due to pigments, while the deeper shade of the summer-wood bands in pine, cedar, oak, or walnut is due to the fact that the wood being denser, more of the colored wood substance occurs on a given space,i.e., there is more colored matter per square inch. Wood is translucent, a thin disk of pine permitting light to pass through quite freely. This translucency affects the luster and brightness of lumber.
When lumber is attacked by fungi, it becomes more opaque, loses its brightness, and in practice is designated "dead," in distinction to "live" or bright timber. Exposure to air darkens all wood; direct sunlight and occasional moistening hasten this change, and cause it to penetrate deeper. Prolonged immersion has the same effect, pine wood becoming a dark gray, while oak changes to a blackish brown.
Odor, like color, depends on chemical compounds, forming no part of the wood substance itself. Exposure to weather reduces and often changes the odor, but a piece of long-leaf pine, cedar, or camphor wood exhales apparently as much odor as ever when a new surface is exposed. Heartwood is more odoriferous than sapwood. Many kinds of wood are distinguished by strong and peculiar odors. This is especially the case with camphor, cedar, pine, oak, and mahogany, and the list would comprise every kind of wood in use were our sense of smell developed in keeping with its importance.
Decomposition is usually accompanied by pronounced odors. Decaying poplar emits a disagreeable odor, while red oak often becomes fragrant, its smell resembling that of heliotrope.
A small cross-section of wood (as inFig. 19) dropped into water sinks, showing that the substance of which wood fibre or wood is built up is heavier than water. By immersing the wood successively in heavier liquids, until we find a liquid in which it does not sink, and comparing the weight of the same with water, we find that wood substance is about 1.6 times as heavy as water, and that this is as true of poplar as of oak or pine.
Cross-section of a Group of Wood FibresFig. 19. Cross-section of a Group of Wood Fibres (Highly Magnified.)
Fig. 19. Cross-section of a Group of Wood Fibres (Highly Magnified.)
Isolated Fibres of WoodFig. 20. Isolated Fibres of Wood.
Fig. 20. Isolated Fibres of Wood.
Separating a single cell (as shown inFig. 20,a), drying and then dropping it into water, it floats. The air-filled cell cavity or interior reduces its weight, and, like an empty corked bottle, it weighs less than the water. Soon, however, water soaks into the cell, when it fills up and sinks. Many such cells grown together, as in a block of wood, when all or most of them are filled with water, will float as long as the majority of them are empty or only partially filled. This is why a green, sappy pine pole soon sinks in "driving" (floating down stream). Its cells are largely filled before it is thrown in, and but little additional water suffices to make its weight greater than that of the water. In a good-sized white pine log, composed chiefly of empty cells (heartwood), the water requires a very long time to fill up the cells (five years would not suffice to fill them all), and therefore the log may float for many months. When the wall of the wood fibre is very thick (five eighths or more of the volume, as inFig. 20,b), the fibre sinks whether empty or filled. This applies to most of the fibres of the dark summer-wood bands in pines, and to the compact fibres of oak or hickory, and many, especially tropical woods,have such thick-walled cells and so little empty or air space that they never float.
Here, then, are the two main factors of weight in wood; the amount of cell wall or wood substance constant for any given piece, and the amount of water contained in the wood, variable even in the standing tree, and only in part eliminated in drying.
The weight of the green wood of any species varies chiefly as a second factor, and is entirely misleading, if the relative weight of different kinds is sought. Thus some green sticks of the otherwise lighter cypress and gum sink more readily than fresh oak.
The weight of sapwood or the sappy, peripheral part of our common lumber woods is always great, whether cut in winter or summer. It rarely falls much below forty-five pounds, and commonly exceeds fifty-five pounds to the cubic foot, even in our lighter wooded species. It follows that the green wood of a sapling is heavier than that of an old tree, the fresh wood from a disk of the upper part of a tree is often heavier than that of the lower part, and the wood near the bark heavier than that nearer the pith; and also that the advantage of drying the wood before shipping is most important in sappy and light kinds.
When kiln-dried, the misleading moisture factor of weight is uniformly reduced, and a fair comparison possible. For the sake of convenience in comparison, the weight of wood is expressed either as the weight per cubic foot, or, what is still more convenient, as specific weight or density. If an old long-leaf pine is cut up (as shown inFig. 21) the wood of disk No. 1 is heavier than that of disk No. 2, the latter heavier than that of disk No. 3, and the wood of the top disk is found to be only about three fourths as heavy as that of disk No. 1. Similiarly, if disk No. 2 is cut up, as in the figure, the specific weight of the different parts is:
showing that in this disk at least the wood formed duringthe many years' growth, represented in piecea, is much lighter than that of former years. It also shows that the best wood is the middle part, with its large proportion of dark summer bands.
Orientation of Wood SamplesFig. 21. Orientation of Wood Samples.
Fig. 21. Orientation of Wood Samples.
Cutting up all disks in the same way, it will be found that the pieceaof the first disk is heavier than the pieceaof the fifth, and that piececof the first disk excels the piececof all the other disks. This shows that the wood grown during the same number of years is lighter in the upper parts of the stem; and if the disks are smoothed on the radial surfaces and set up one on top of the other in their regular order, for the sake of comparison, this decrease in weight will be seen to be accompanied by a decrease in the amount of summer-wood. The color effect of the upper disks is conspicuously lighter. If our old pine had been cut one hundred and fifty years ago, before the outer, lighter wood was laid on, it is evident that the weight of the wood of any one disk would have been found to increase from the center outward, and no subsequent decrease could have been observed.
In a thrifty young pine, then, the wood is heavier from the center outward, and lighter from below upward; only the wood laid on in old age falls in weight below the average. The number of brownish bands of summer-wood are a direct indication of these differences. If an old oak is cut up in the same manner, the butt cut is also found heaviest and the top lightest, but, unlike the disk of pine, the disk of oak has its firmest wood at the center, and each successive piece from the center outward is lighter than its neighbor.
Examining the pieces, this difference is not as readily explained by the appearance of each piece as in the case of pine wood. Nevertheless, one conspicuous point appears at once. The pores, so very distinct in oak, are very minute in the wood near the center, and thus the wood is far less porous.
Studying different trees, it is found that in the pines, wood with narrow rings is just as heavy as and often heavier than the wood with wider rings; but if the rings are unusually narrow in any part of the disk, the wood has a lighter color; that is, there is less summer-wood and therefore less weight.
In oak, ash, or elm trees of thrifty growth, the rings, fairly wide (not less than one-twelfth inch), always form the heaviest wood, while any piece with very narrow rings is light. On the other hand, the weight of a piece of hard maple or birch is quite independent of the width of its rings.
The bases of limbs (knots) are usually heavy, very heavy in conifers, and also the wood which surrounds them, but generally the wood of the limbs is lighter than that of the stem, and the wood of the roots is the lightest.
In general, it may be said that none of the native woods in common use in this country are when dry as heavy as water,i.e., sixty-two pounds to the cubic foot. Few exceed fifty pounds, while most of them fall below forty pounds, and much of the pine and other coniferous wood weigh less than thirty pounds per cubic foot. The weight of the wood is in itself an important quality. Weightassists in distinguishing maple from poplar. Lightness coupled with great strength and stiffness recommends wood for a thousand different uses. To a large extent weight predicates the strength of the wood, at least in the same species, so that a heavy piece of oak will exceed in strength a light piece of the same species, and in pine it appears probable that, weight for weight, the strength of the wood of various pines is nearly equal.
Weight of Kiln-dried Wood of Different Species
Many theories have been propounded as to the cause of "figure" in timber; while it is true that all timber possesses "figure" in some degree, which is more noticeable if it be cut in certain ways, yet there are some woods in which it is more conspicuous than in others, and which for cabinet or furniture work are much appreciated, as it adds to the value of the work produced.
The characteristic "figure" of oak is due to the broad and deep medullary rays so conspicuous in this timber, and the same applies to honeysuckle. Figure due to the same cause is found in sycamore and beech, but is not so pronounced. The beautiful figure in "bird's eye maple" is supposed to be due to the boring action of insects in the early growth of the tree, causing pits or grooves, which in time become filled up by being overlain by fresh layers of wood growth; these peculiar and unique markings are found only in the older and inner portion of the tree.
Pitch pine has sometimes a very beautiful "figure," but it generally does not go deep into the timber; walnut has quite a variety of "figures," and so has the elm. It is in mahogany, however, that we find the greatest variety of "figure," and as this timber is only used for furniture and fancy work, a good "figure" greatly enhances its value, as firmly figured logs bring fancy prices.
Mahogany, unlike the oak, never draws its "figure" from its small and almost unnoticeable medullary rays, but from the twisted condition of its fibres; the natural growth of mahogany produces a straight wood; what is called "figured" is unnatural and exceptional, and thus adds to its value as an ornamental wood. These peculiarities are rarely found in the earlier portion of the tree that is near the center, being in this respect quite different from maple; they appear when the tree is more fully developed, and consist of bundles of woody fibres which, instead of being laid in straight lines, behave in an erratic manner and are deposited in a twisted form; sometimes it may be caused by the intersection of branches, or possibly by the crackling of the bark pressing on the wood, and thusmoving it out of its natural straight course, causing a wavy line which in time becomes accentuated.
It will have been observed by most people that the outer portion of a tree is often indented by the bark, and the outer rings often follow a sinuous course which corresponds to this indention, but in most trees, after a few years, this is evened up and the annual rings assume their nearly circular form; it is supposed by some that in the case of mahogany this is not the case, and that the indentations are even accentuated.
The best figured logs of timber are secured from trees which grow in firm rocky soil; those growing on low-lying or swampy ground are seldom figured. To the practical woodworker the figure in mahogany causes some difficulty in planing the wood to a smooth surface; some portions plane smooth, others are the "wrong way of the grain."
Figure in wood is effected by the way light is thrown upon it, showing light if seen from one direction, and dark if viewed from another, as may easily be observed by holding a piece of figured mahogany under artificial light and looking at it from opposite directions. The characteristic markings on mahogany are "mottle," which is also found in sycamore, and is conspicuous on the backs of fiddles and violins, and is not in itself valuable; it runs the transverse way of the fibres and is probably the effect of the wind upon the tree in its early stages of growth. "Roe," which is said to be caused by the contortion of the woody fibres, and takes a wavy line parallel to them, is also found in the hollow of bent stems and in the root structure, and when combined with "mottle" is very valuable. "Dapple" is an exaggerated form of mottle. "Thunder shake," "wind shake," or "tornado shake" is a rupture of the fibres across the grain, which in mahogany does not always break them; the tree swaying in the wind only strains its fibres, and thus produces mottle in the wood.
Fromthe writer's personal investigations of this subject in different sections of the country, the damage to forest products of various kinds from this cause seems to be far more extensive than is generally recognized. Allowing a loss of five per cent on the total value of the forest products of the country, which the writer believes to be a conservative estimate, it would amount to something over $30,000,000 annually. This loss differs from that resulting from insect damage to natural forest resources, in that it represents more directly a loss of money invested in material and labor. In dealing with the insects mentioned, as with forest insects in general, the methods which yield the best results are those which relate directly to preventing attack, as well as those which are unattractive or unfavorable. The insects have two objects in their attack: one is to obtain food, the other is to prepare for the development of their broods. Different species of insects have special periods during the season of activity (March to November), when the adults are on the wing in search of suitable material in which to deposit their eggs. Some species, which fly in April, will be attracted to the trunks of recently felled pine trees or to piles of pine sawlogs from trees felled the previous winter. They are not attracted to any other kind of timber, because they can live only in the bark or wood of pine, and only in that which is in the proper condition to favor the hatching of their eggs and the normal development of their young. As they fly only in April, they cannot injure the logs of trees felled during the remainder of the year.
There are also oak insects, which attack nothing but oak; hickory, cypress, and spruce insects, etc., which have different habits and different periods of flight, and require special conditions of the bark and wood for depositing their eggs or for subsequent development of their broods. Some of these insects have but one generation in a year, others have two or more, while some require more than one year for the complete development and transformation. Some species deposit their eggs in the bark or wood of trees soon after they are felled or before any perceptible change from the normal living tissue has taken place; other species are attracted only to dead bark and dead wood of trees which have been felled or girdled for several months; others are attracted to dry and seasoned wood; while another class will attack nothing but very old, dry bark or wood of special kinds and under special conditions. Thus it will be seen how important it is for the practical man to have knowledge of such of the foregoing facts as apply to his immediate interest in the manufacture or utilization of a given forest product, in order that he may with the least trouble and expense adjust his business methods to meet the requirements for preventing losses.
The work of different kinds of insects, as represented by special injuries to forest products, is the first thing to attract attention, and the distinctive character of this work is easily observed, while the insect responsible for it is seldom seen, or it is so difficult to determine by the general observer from descriptions or illustrations that the species is rarely recognized. Fortunately, the character of the work is often sufficient in itself to identify the cause and suggest a remedy, and in this section primary consideration is given to this phase of the subject.
Work of Ambrosia Beetles in Tulip or Yellow Poplar WoodFig. 22. Work of Ambrosia Beetles in Tulip or Yellow Poplar Wood.a, work ofXyleborus affinisandXyleborus inermis;b,Xyleborus obesusand work;c, bark;d, sapwood;e, heartwood.
Fig. 22. Work of Ambrosia Beetles in Tulip or Yellow Poplar Wood.a, work ofXyleborus affinisandXyleborus inermis;b,Xyleborus obesusand work;c, bark;d, sapwood;e, heartwood.
Work of Ambrosia Beetles in OakFig. 23. Work of Ambrosia Beetles in Oak.a,Monarthrum maliand work;b,Platypus compositusand work;c, bark;d, sapwood;e, heartwood;f, character of work in wood from injured log.
Fig. 23. Work of Ambrosia Beetles in Oak.a,Monarthrum maliand work;b,Platypus compositusand work;c, bark;d, sapwood;e, heartwood;f, character of work in wood from injured log.
The characteristic work of this class of wood-boring beetles is shown inFigs. 22and23. The injury consists of pinhole and stained-wood defects in the sapwood and heartwood of recently felled or girdled trees, sawlogs, pulpwood, stave and shingle bolts, green or unseasonedlumber, and staves and heads of barrels containing alcoholic liquids. The holes and galleries are made by the adult parent beetles, to serve as entrances and temporary houses or nurseries for the development of their broods of young, which feed on a fungus growing on the walls of the galleries.
The growth of this ambrosia-like fungus is induced and controlled by the parent beetles, and the young aredependent upon it for food. The wood must be in exactly the proper condition for the growth of the fungus in order to attract the beetles and induce them to excavate their galleries; it must have a certain degree of moisture and other favorable qualities, which usually prevail during the period involved in the change from living, or normal, to dead or dry wood; such a condition is found in recently felled trees, sawlogs, or like crude products.
There are two general types or classes of these galleries: one in which the broods develop together in the main burrows (seeFig. 22), the other in which the individuals develop in short, separate side chambers, extending at right angles from the primary galleries (seeFig. 23). The galleries of the latter type are usually accompanied by a distinct staining of the wood, while those of the former are not.
The beetles responsible for this work are cylindrical in form, apparently with a head (the prothorax) half as long as the remainder of the body (seeFigs. 22,a, and23,a).
North American species vary in size from less than one-tenth to slightly more than two-tenths of an inch, while some of the subtropical and tropical species attain a much larger size. The diameter of the holes made by each species corresponds closely to that of the body, and varies from about one-twentieth to one-sixteenth of an inch for the tropical species.
Work of Round-headed and Flat-headed Borers in PineFig. 24. Work of Round-headed and Flat-headed Borers in Pine.a, work of round-headed borer, "sawyer,"Monohammus spiculatus, natural sizeb,Ergates spiculatus;c, work of flat-headed borer,Buprestis, larva and adult;d, bark;e, sapwood;f, heartwood.
Fig. 24. Work of Round-headed and Flat-headed Borers in Pine.a, work of round-headed borer, "sawyer,"Monohammus spiculatus, natural sizeb,Ergates spiculatus;c, work of flat-headed borer,Buprestis, larva and adult;d, bark;e, sapwood;f, heartwood.
The character of the work of this class of wood- and bark-boring grubs is shown inFig. 24. The injuries consist of irregular flattened or nearly round wormhole defects in the wood, which sometimes result in the destructionof valuable parts of the wood or bark material. The sapwood and heartwood of recently felled trees, sawlogs, poles posts, mine props, pulpwood and cordwood, also lumber or square timber, with bark on the edges, and construction timber in new and old buildings, are injured by wormhole defects, while the valuable parts of stored oak and hemlock tanbark and certain kinds of wood are converted into worm-dust. These injuries are caused by the young or larvae of long-horned beetles. Those which infest the wood hatch from eggs deposited in the outer bark of logs and like material, and the minute grubs hatching therefrom bore into the inner bark, through which they extend their irregular burrows, for the purpose of obtaining food from the sap and other nutritive material found in the plant tissue. They continue to extend and enlarge their burrows as they increase in size, until they are nearly or quite full grown. They then enter the wood and continue their excavations deep into the sapwood or heartwood until they attain their normal size. They then excavate pupa cells in which to transform into adults,which emerge from the wood through exit holes in the surface. This class of borers is represented by a large number of species. The adults, however, are seldom seen by the general observer unless cut out of the wood before they have emerged.
The work of the flat-headed borers (Fig. 24) is only distinguished from that of the preceding by the broad, shallow burrows, and the much more oblong form of the exit holes. In general, the injuries are similiar, and effect the same class of products, but they are of much less importance. The adult forms are flattened, metallic-colored beetles, and represent many species, of various sizes.