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. Weight a.s.sists 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 -----------------------------------------+---------------------------- | Approximate |----------+----------------- | | Weight of | |---------+------- Species | Specific | 1 | 1,000 | Weight | Cubic | Feet | | Foot | Lumber -----------------------------------------+----------+---------+------- (_a_) Very Heavy Woods: | | | Hickory, Oak, Persimmon, Osage Orange, | | | Black Locust, Hackberry, Blue Beech, | | | best of Elm and Ash |0.70-0.80 | 42-48 | 3,700 (_b_) Heavy Woods | | | Ash, Elm, Cherry, Birch, Maple, Beech, | | | Walnut, Sour Gum, Coffee Tree, Honey | | | Locust, best of Southern Pine and | | | Tamarack |0.60-0.70 | 36-42 | 3,200 (_c_) Woods of Medium Weight: | | | Southern Pine, Pitch Pine, Tamarack, | | | Douglas Spruce, Western Hemlock, | | | Sweet Gum, Soft Maple, Sycamore, | | | Sa.s.safras, Mulberry, light grades of | | | Birch and Cherry |0.50-0.60 | 30-36 | 2,700 (_d_) Light Woods: | | | Norway and Bull Pine, Red Cedar, | | | Cypress, Hemlock, the Heavier Spruces | | | and Firs, Redwood, Ba.s.swood, Chestnut, | | | b.u.t.ternut, Tulip, Catalpa, Buckeye, | | | heavier grades of Poplar |0.40-0.50 | 24-30 | 2,200 (_e_) Very Light Woods: | | | White Pine, Spruce, Fir, White Cedar, | | | Poplar |0.30-0.40 | 18-24 | 1,800 -----------------------------------------+----------+---------+-------
"FIGURE" IN WOOD
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 p.r.o.nounced. 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 thus moving 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 a.s.sume 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.
SECTION V
ENEMIES OF WOOD
From the 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 cla.s.s 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 ill.u.s.trations 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.
Ambrosia or Timber Beetles
[Ill.u.s.tration: Fig. 22. Work of Ambrosia Beetles in Tulip or Yellow Poplar Wood. _a_, work of _Xyleborus affinis_ and _Xyleborus inermis_; _b_, _Xyleborus obesus_ and work; _c_, bark; _d_, sapwood; _e_, heartwood.]
[Ill.u.s.tration: Fig. 23. Work of Ambrosia Beetles in Oak. _a_, _Monarthrum mali_ and work; _b_, _Platypus compositus_ and work; _c_, bark; _d_, sapwood; _e_, heartwood; _f_, character of work in wood from injured log.]
The characteristic work of this cla.s.s of wood-boring beetles is shown in Figs. 22 and 23. 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 unseasoned lumber, 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 are dependent 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 cla.s.ses of these galleries: one in which the broods develop together in the main burrows (see Fig. 22), the other in which the individuals develop in short, separate side chambers, extending at right angles from the primary galleries (see Fig. 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 (see Figs. 22, _a_, and 23, _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.
Round-headed Borers
[Ill.u.s.tration: Fig. 24. Work of Round-headed and Flat-headed Borers in Pine. _a_, work of round-headed borer, "sawyer,"
_Monohammus spiculatus_, natural size _b_, _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 cla.s.s of wood- and bark-boring grubs is shown in Fig. 24. The injuries consist of irregular flattened or nearly round wormhole defects in the wood, which sometimes result in the destruction of 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 cla.s.s 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.
Flat-headed Borers
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 cla.s.s of products, but they are of much less importance. The adult forms are flattened, metallic-colored beetles, and represent many species, of various sizes.
Timber Worms
[Ill.u.s.tration: Fig. 25. Work of Timber Worms in Oak. _a_, work of oak timber worm, _Eupsalis minuta_; _b_, barked surface; _c_, bark; _d_, sapwood timber worm, _Hylocoetus lugubris_, and work; _e_, sapwood.]
The character of the work done by this cla.s.s is shown in Fig. 25. The injury consists of pinhole defects in the sapwood and heartwood of felled trees, sawlogs and like material which have been left in the woods or in piles in the open for several months during the warmer seasons. Stave and shingle bolts and closely piled oak lumber and square timbers also suffer from injury of this kind. These injuries are made by elongate, slender worms or larvae, which hatch from eggs deposited by the adult beetles in the outer bark, or, where there is no bark, just beneath the surface of the wood. At first the young larvae bore almost invisible holes for a long distance through the sapwood and heartwood, but as they increase in size the same holes are enlarged and extended until the larvae have attained their full growth. They then transform to adults, and emerge through the enlarged entrance burrows. The work of these timber worms is distinguished from that of the timber beetles by the greater variation in the size of holes in the same piece of wood, also by the fact that they are not branched from a single entrance or gallery, as are those made by the beetles.
[Ill.u.s.tration: Fig. 26. Work of Powder Post Beetle, _Sinoxylon basilare_, in Hickory Poles, showing Transverse Egg Galleries excavated by the Adult, _a_, entrance; _b_, gallery; _c_, adult.]
[Ill.u.s.tration: Fig. 27. Work of Powder Post Beetle, _Sinoxylon basilare_, in Hickory Pole. _a_, character of work by larvae; _b_, exit holes made by emerging broods.]
Powder Post Borers
The character of the work of this cla.s.s of insects is shown in Figs.
26, 27, and 28. The injury consists of closely placed burrows, packed with borings, or a completely destroyed or powdered condition of the wood of seasoned products, such as lumber, crude and finished handle and wagon stock, cooperage and wooden truss hoops, furniture, and inside finish woodwork, in old buildings, as well as in many other crude or finished and utilized woods. This is the work of both the adults and young stages of some species, or of the larval stage alone of others. In the former, the adult beetles deposit their eggs in burrows or galleries excavated for the purpose, as in Figs. 26 and 27, while in the latter (Fig. 28) the eggs are on or beneath the surface of the wood. The grubs complete the destruction by boring through the solid wood in all directions and packing their burrows with the powdered wood. When they are full grown they transform to the adult, and emerge from the injured material through holes in the surface.
Some of the species continue to work in the same wood until many generations have developed and emerged or until every particle of wood tissue has been destroyed and the available nutritive substance extracted.
[Ill.u.s.tration: Fig. 28. Work of Powder Post Beetles, _Lyctus striatus_, in Hickory Handles and Spokes. _a_, larva; _b_, pupa; _c_, adult; _d_, exit holes; _e_, entrance of larvae (vents for borings are exits of parasites); _f_, work of larvae; _g_, wood, completely destroyed; _h_, sapwood; _i_, heartwood.]
Conditions Favorable for Insect Injury--Crude Products--Round Timber with Bark on
Newly felled trees, sawlogs, stave and heading bolts, telegraph poles, posts, and the like material, cut in the fall and winter, and left on the ground or in close piles during a few weeks or months in the spring or summer, causing them to heat and sweat, are especially liable to injury by ambrosia beetles (Figs. 22 and 23), round and flat-headed borers (Fig. 24), and timber worms (Fig. 25), as are also trees felled in the warm season, and left for a time before working up into lumber.
The proper degree of moisture found in freshly cut living or dying wood, and the period when the insects are flying, are the conditions most favorable for attack. This period of danger varies with the time of the year the timber is felled and with the different kinds of trees. Those felled in late fall and winter will generally remain attractive to ambrosia beetles, and to the adults of round- and flat-headed borers during March, April, and May. Those felled in April to September may be attacked in a few days after they are felled, and the period of danger may not extend over more than a few weeks.
Certain kinds of trees felled during certain months and seasons are never attacked, because the danger period prevails only when the insects are flying; on the other hand, if the same kinds of trees are felled at a different time, the conditions may be most attractive when the insects are active, and they will be thickly infested and ruined.
The presence of bark is absolutely necessary for infestation by most of the wood-boring grubs, since the eggs and young stages must occupy the outer and inner portions before they can enter the wood. Some ambrosia and timber worms will, however, attack barked logs, especially those in close piles, and others shaded and protected from rapid drying.