Seasoning of Wood by Joseph Bernard Wagner (bill gates best books txt) π
Keeping especially in mind the arrangement and direction of the fibres of wood, it is clear at once why knots and "cross-grain" interfere with the strength of timber. It is due to the structural peculiarities that "honeycombing" occurs in rapid seasoning, that checks or cracks extend radially and follow pith rays, that tangent or "bastard" cut stock shrinks and warps more than that which is quarter-sawn. These same pecu
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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 classes 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 BorersFig. 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 class 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 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.
Flat-headed BorersThe 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.
Timber WormsFig. 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 class 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.
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.
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 BorersThe character of the work of this class 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.
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 InjuryβCrude ProductsβRound Timber with Bark onNewly 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.
The sapwood of pine, spruce, fir, cedar, cypress, and the like softwoods is especially liable to injury by ambrosia beetles, while the heartwood is sometimes ruined by a class of round-headed borers, known as "sawyers." Yellow poplar, oak, chestnut, gum, hickory, and most other hardwoods are as a rule attacked by species of ambrosia beetles, sawyers, and timber worms, different from those infesting the pines, there being but very few species which attack both.
Mahogany and other rare and valuable woods imported from the tropics to this country in the form of round logs, with or without bark on, are commonly damaged more or less seriously by ambrosia beetles and timber worms.
It would appear from the writer's investigations of logs received at the mills in this country, that the principal damage is done during a limited periodβfrom the time the trees are felled until they are placed in fresh or salt water for transportation to the shipping points. If, however, the logs are loaded on a vessel direct from the shore, or if not left in the water long enough to kill the insects, the latter will continue their destructive work during transportation to other countries and after they arrive, and until cold weather ensues or the logs are converted into lumber.
It was also found that a thorough soaking in sea-water, while it usually killed the insects at the time, did not prevent subsequent attacks by both foreign and native ambrosia beetles; also, that the removal of the bark from such logs previous to immersion did not render them entirely immune. Those with the bark off were attacked more than those with it on, owing to a greater amount of saline moisture retained by the bark.
How to Prevent InjuryFrom the foregoing it will be seen that some requisites for preventing these insect injuries to round timber are:
1. To provide for as little delay as possible between the felling of the tree and its manufacture into rough products. This is especially necessary with trees felled from April to September, in the region north of the Gulf States, and from March to November in the latter, while the late fall
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