|Bulletins, Circulars, Progress Reports|
Alabama Agricultural Experiment Station
R. Dennis Rouse, Director
Figure in Wood
An Illustrated Review1
TABLE OF CONTENTS
EFFECT OF VARIOUS INFLUENCES ON FIGURE
Color, luster, texture, grain, and figure are the major gross characteristics that aid in wood identification and provide a basis for decorative qualities. High values of most prized woods may be traced to unusual or rare features that involve one or more of these characteristics. Figured wood has been esteemed for its beauty and universal appeal for centuries. Certain types of figured wood are primary materials for numerous small but important industries throughout the world. Although comparatively little is known concerning figured wood, the subject has received more attention in recent years. Available literature is scattered widely in many journals, both foreign and domestic, and contradictory statements abound. An annotated bibliography of figure in wood that included abstracts of articles not found in other bibliographies was published in 1973 (9).
Probably figure is the most desirable, the least understood, and certainly the most complex gross characteristic of wood. Any design, pattern, or distinctive marking that appears either consistently or intermittenly on longitudinal surfaces of wood may be described as figure. A restricted definition would include only decorative qualities desired for furniture, paneling, gunstocks, or musical instruments.
Figure in wood results from combinations of color, luster, texture, and grain. Color and luster have ordinarily accepted meanings (63). Texture depends on size, distribution, and proportional volumes of cellular elements composing wood. Depending on relative sizes and distribution of cellular elements, texture may be fine or coarse, even or uneven. Individual elements in fine-textured wood are indistinguishable with aid of a hand lens; in coarse-textured woods, they are usually distinguishable with magnification. Grain of wood commonly is used with a variety of meanings, generally depending on the modifier and often (inaccurately) in place of texture (fine grain). Meaning of grain here is confined to direction of wood fibers relative to the longitudinal axis of the bole and to one another (straight grain).
Figure may be defined as the pattern produced on a wood surface by annual growth layers, rays, and knots; by irregular coloration; and by deviations from straight, regular grain. Three broad types of figure in wood are recognized.
(1) Normal figure, which results from textural variation, depends largely on the plane of cutting. Tangential cutting (plain sawing or rotary cutting) usually results in nested V's or U's when the wood has visible growth layers. Radial cuts (quarter sawn) reveal growth layers in relatively straight, vertical lines. All gradations between tangential and radial surfaces occur. Sections of rays exposed by quarter sawing are prominent in many species as ray-fleck. Knots mayor may not be present. Decorative knotty paneling is mainly plain sawn to expose circular knots. Wood with no more than normal figure paradoxically is called unfigured in the lumber and veneer trade.
(2) Pigment figure, which results from infiltration of coloring materials in regular or irregular patterns, may be local or generalized and is influenced occasionally by the plane of cutting.
(3) Specific figure, which results from non-vertical alignment of longitudinal fibers, may be hidden or enhanced by cutting methods. Specific figure is the main subject of this treatise. Except where specified as general or pigment figure and in brief, labelled sections, the unmodified term means specific figure.
This publication contains a general presentation of figure in wood that includes many facets on the subject ranging from basic to highly specific. The objective is to present subject matter in a fashion to enhance knowledge and understanding of figure in wood. The first two broad types of figure as listed above are considered GENERAL figure and will be reviewed and illustrated only briefly. The last figure type is considered SPECIFIC figure and will be reviewed and illustrated in considerable detail.
|FIGURE IN LIVING TREES||
Most published work concerning figured trees has been based upon observations of logs or from lumber or veneer cut from such logs (2, 6, 23). Few studies have been made involving figure as it occurs in living trees.
Figure occurs in living trees primarily as variations or distortions in the vertical alignment of wood elements (grain) in either radial or tangential directions (or combinations of both) that result in common figure types known as stripe, blister, curl, wavy, and several variations that are described later in this report.
Detection of figure in living trees, either located in a stand or singly, is a difficult process and is considered by many to be an art developed only after many years of experience. There apparently is no reliable indicator of figure that can be used to recognize figured trees, individually or in stands.
Ecological factors, such as site, and morphological features of form, bark characteristics, foliage, or position in the stand often suggest the presence or absence of figure in trees; these indicators generally are used with caution even by experienced producers of figured wood. Intensive studies made in Europe on correlation of bark types with figured wood in birch have shown that certain bark characteristics are indicative of the presence but not necessarily any particular type or quality of figure (26, 27, 47, 54, 55, 56, 57, 58, 76, 78). Figured wood occasionally may be found in almost any tree species near roots or branches but is usually so limited in quantity and generally of such poor quality that it is considered a defect. In general, trees with figure concentrated in the butt or throughout lower portions appear no different from other trees in surrounding areas. Figured wood frequently may be present in poorly formed, damaged, or diseased trees but seldom in commercial quality. The figure known as birdseyefor many years was thought to be associated with suppression or with some type of mechanical damage (1, 3, 34, 35, 66,69). However, veneer manufacturers report that growth rate apparently has little effect on quantity or quality of the figure observed.
Although tree size sometimes is associated with figure, it is difficult to make valid size comparisions because of minimum size requirements for commercial veneer logs. However, commercially valuable figure is seldom found in trees less than 10 inches in diameter. Once initiated, figure becomes increasingly pronounced in subsequent growth rings. It usually diminishes with increasing stem height and almost always disappears above the first large limb. Figure frequently is concentrated in one or more stem quadrants; it is rare to find heavily figured wood throughout the entire bole circumference. Since blister and quilted figures in Oregon maple may develop at various heights in the bole, such trees may be overlooked for figured veneer logs when sampled only near the butt (10). These figures often occur in
leaning trees. Although bark abnormalities are used by trained observers as indicators of figure, attempted use of bark characteristics to detect figured trees is most times unsuccessful (51).
Tropical woods often contain a stripe figure traceable to interlocked grain that sometimes is so common as to be considered a normal feature of certain species.
Techniques for detection of figured trees within forest stands usually consist of some type of axe-chip analysis to detect variations of fiber alignment on tangential surfaces (47, 67). This method has been used for centuries in search of tone woods for use in musical instrument manufacture. Axe-chip analysis normally is extended to include splitting small chip samples to determine straightness of grain in addition to figure depth and quality (Figure 1). Since wounding can induce stain, decay, insect damage, and other defects, these techniques should be used only on trees that will be harvested within a short time period.
|GENERAL FIGURE IN WOOD||
Figure is a term that describes certain well-defined patterns in wood from many tree species. Patterns that occur on wide surfaces of lumber or veneer are results of variations in texture, grain, and color, as well as methods of cutting.
Common methods of processing logs into lumber or veneer produce two pattern types based on the wide surface exposed, tangential or radial (Figure 2). These pattern types result from planes of section passing through the radially symmetrical woody cylinder at different positions. Tangential surfaces exposed in flat (or plain) sawing typically exhibit growth rings in a pattern of nested, V-shaped lines. Radial surfaces exposed in quarter-sawn (or edge-grain) lumber show growth rings as a series of parallel lines. True transverse (or cross) sections, which are perpendicular to the tangential and radial planes, rarely contribute to figure. Patterns exhibited by transverse surfaces are concentric circles or arcs.
Brochures from various trade organizations such as the Fine Hardwoods Association, Mahogany Association, American Walnut Manufacturing Association, and others contain general descriptions of various figure types with respect to portions of trees where different figures occur and the development of figure by different methods of veneer cutting. These discussions merely acquaint readers with various figure types and explain which figures are most common in particular species.
Publications of a more general or popular nature have appeared in recent years. Examples are papers describing burl formation in several species (53) and the curly (blister) figure occasionally found in southern pine (29). Others describe either figure in general and its use in furniture (64) or technical aspects of converting curly grained wood into veneer (22).
One of the best available general discussions concerning figure in wood is presented in the Textbook of Wood Technology, Vol. I (63); a more thorough treatment, however, occurred in an earlier edition that is out of print. Similar presentations concerning figured material may be found in trade circulars from Australia (2, 80).
Texture, Grain, and FigureTexture is a term used to classify relative size of wood elements. Woods are considered fine-textured when individual elements are so small that they cannot be distinguished individually with a hand lens. Coarse textured woods have large individual elements that often can be observed without magnification. Texture often is confused with grain. Coarse-textured woods are described as open-grained; they, therefore, require a filler in finishing. Such woods properly should be called coarse textured. Fine grained woods, similarly, should be called fine textured.
Texture also is often used to describe workability of wood with tools. Such terms as harsh or smooth texture and even or uneven texture are used frequently in describing wood qualities (50).
Grain is a term used to describe the alignment of wood elements in relation to the longitudinal axis. Wood is considered to have straight grain when elements are parallel to the longitudinal axis. When ele-ments are sloped, wood is described as spiral grained. In many tropical woods and a few native species, spiral grain reverses at periodic intervals and produces a condition called interlocked grain. Undulations in wood elements are responsible for wavy or curly grain.
Grain also is used to describe arrangement of wood elements. When transition from springwood to summerwood is uniform and there is little difference between the two, wood is described as even-grained. When the transition is abrupt or the difference between springwood and summerwood is pronounced, wood is described as uneven-grained. Examples of uneven-grained wood are southern pine, hemlock, and oak. Examples of even-grained wood are maple, basswood, and white pine. Uneven grain frequently is associated with fast growth and occurs in wood near the pith.
Figure is a term applied to certain patterns formed naturally in wood; it may be enhanced by specialized cutting techniques that accentuate normal markings (28,40,44,45,46,68). Many types of figure are described as optical illusions normally perceived by viewers. Figure also may be caused by uneven coloration resulting from pigmentation in wood.
In general, figure is not considered to be produced by normal methods of cutting lumber or veneer, i.e., nested V-shaped lines on tangential faces produced by flat sawing or series of parallel lines on radial faces produced by quarter sawing (Figure 2). However, when figure caused by grain orientation is present, method of cutting becomes of great importance in development of a particular figure.
Figure Caused by Pigmentation
There are a few woods in which a well defined pattern, or figure, is developed because of uneven pigmentation (63). Color patterns appear as uneven streaks in figured red gum (21). Strongly contrasting colors may be concentrated in growth increments of a few tropical species such as zebra wood. Several other tropical woods belonging to the rosewood group exhibit variegated pigmentation, ranging in color from reddish brown to black, which produces figure patterns. Figure types caused by pigmentation lack the luster of figures caused by grain variations (23).
Figure Types Caused by Variations in Grain Orientation
normal orientation of longitudinal cellular elements in wood is parallel
to the longitudinal axis of the woody cylinder. Various deviations from
the parallel develop a number of well-defined figure patterns.
Longwood The bole or stem (from stump to first limb or fork) produces the majority of wood. It normally is available up to 16 feet (4.88m) in length and may or may not exhibit patterns different from typical patterns found in flat or quarter-sawn lumber. This type of wood is used primarily for architectural installations and wall paneling. It may exhibit any or all common figure types in some areas, but generally shows little figure development (Figure 4).
Crotch Crotch figures are characterized by feather-like patterns that are obtained by cutting through forks where main boles branch. They normally are obtained from walnut or mahogany and were used extensively in furniture during the 18th and 19th centuries. They seldom are seen today except in high grade gun stocks. Excessive end grain exposure and random orientations frequently cause crotch-figured wood to check severely. This type wood must be reinforced with backing to prevent such checking (Figure 5).
Stumpwood As the name implies, this particular figure type is obtained from stumps. It seldom is seen except in walnut and is characterized by wrinkles and blotches of color variations. It is a very attractive figure that may be observed occasionally in furniture and gunstocks (Figure 6).
Burls Burls are irregular, spherical growths that occasionally occur on trees near ground level (24,53). They occur primarily on elm, walnut, maple, and redwood. Rarely do they occur commercially in other trees. Many of the most prized possessions of early emperors and kings were made from burlwood (53). Utilization of elm burls for furniture in the U.S. during the 1920's probably led to introduction of Dutch elm disease into this country. Ceratocystis ulmi (causal fungus of Dutch elm disease) probably was introduced into this country within elm-burl material imported from France for use as veneer and subsequently in furniture manufacture. Burls are usually small and characterized by eye-like markings surrounded by swirls and distorted tissues. Burl tissue is soft and velvet-like to the touch (Figure 7).
Figure Caused by Ray Structure
occasionally results from cutting wood so that rays are parallel to the
wide face where a series of shiny, light-reflecting surfaces are formed
(63). These are known as ray flecks. In such woods as the oaks (Quercus)
or sycamore (Platanus), ray flecks are very pronounced and exhibit
typical patterns (Figures 8 and
|SPECIFIC FIGURE IN WOOD||
Specific figure in wood can be divided into three categories based upon the type of growth within trees that initiates the figure:
(1) Figure related to spiral growth;
(2) Figure related to undulating growth; and
(3) Figure related to indented growth rings.
Figure Related to Spiral Growth
Spiral Grain As mentioned before, normal orientation of longitudinal cellular elements is parallel to the longitudinal axis (Figure 10). However, slight undetectable spiraling is a rule rather than an exception in most trees. In certain trees, elements are sloped or spiraled circumferentially to an extent sufficient to be detected. When wood with this characteristic is split, exposed surfaces will not be parallel to the longitudinal axis as in straight-grained material (Figure 11). Spiral grain occurs quite commonly in certain species and is considered a defect in many cases (60, 85). Spiral grain in simple form does not cause figure since the surface reflects light rays at approximately the same angle at which the rays strike. However, figure initiated by other causes may be enhanced by spiral grain.
Grain Interlocked grain is a variation of spiral grain that is
exhibited almost universally in tropical woods and in a few native hardwoods
such as elms, gums, and sycamore (6). Interlocked grain is the cause of
a particular figure type commonly called ribbon stripe or stripe figure.
Figure Related to Undulating Growth
contrast to previous examples of spiral and interlocked grain, there are
a number of figure types that are formed by grain which is straight in
a sense that it is parallel to the longitudinal axis in whole perspective
but undulating or wavy when viewed closely. Some of these are wavy in
the radial plane while others are wavy in the tangential plane (22). Together
they collectively are called wavy or curly grain, irrespective of the
plane in which they occur.
Radial SurfaceCurly and Fiddleback Figure
When the radial surface
of wood exhibits wavy growth or grain, the tangential face is smooth and
the wavy or undulating grain can be observed, but is not evident to the
touch (Figure 16). When a wood section with
curly grain is split, it separates along the rays and along the wavy grain
and is exhibited as a corrugated surface that can be seen and felt on
the radial surface (figures 17 and 18).
Tangential SurfaceBlister and Quilted Figure
Curly or wavy grain occasionally
affects the tangential surface instead of the radial surface (8). When
this occurs, the effect rarely may be indicated by a series of irregular
annual bark bulges. External evidence of figure, however ,usually is not
visible through the bark. Birch (Betula) exhibits this figure occasionally,
and debarked logs may resemble a corrugated drainage pipe (58). A similar
figure in some species of pine (29) is observed but rarely (figures 25
and 26). Tangential surfaces (circumference)
exhibit a series of bumps and flat areas occurring in an irregular pattern.
Bumps may enlarge and coalesce; then the junction between adjacent bulges
is reduced to a line (figures 27 and 28).
Rounded figures are designated blister(Figure
27); rectangular figures, which usually result from coalescense, are
designated quilted (Figure 28).
Figure Related to Indented Growth Rings
third type of figure that is recognized originates from indented growth
rings. In this class fall such figures as dimple, birdseye, and indented
ring or bear scratches.
For unknown causes certain specimens of Douglas fir, lodgepole pine, sugar
maple, Sitka spruce, birch, and mahogany exhibit reduced growth in localized
circular or lenticular areas that, continued year after year in the same
location, results in circular or lenticular depressions in the wood (figures
30 and 31).
Dimple Indentations in growth rings that create numerous localized, conical depressions that are small and shallow (usually less than one growth ring), are termed dimples (17). Tangential surfaces of wood from lodgepole pine (Pinus contorta) characteristically exhibit dimples (Figure 32), which are useful in identification.
Indentations that create less numerous localized, conical depressions
that are larger and deeper (usually one or more growth rings), are termed
birdseyes. Birdseye of sugar maple (Acer saccharum) is the best
known of indented ring figures (Figure 33).
Birdseye figure has been reported in a number of other species including
ash, walnut, and birch; in Cuban mahogany (Sweitenia mahogani),
it takes the form of a giant birdseye (59).
Bear Scratches Indented growth rings in the form of elongated or lenticular depressions are termed bear scratches. Bear scratches occur most commonly in Sitka spruce (Picea sitchensis) and Douglas fir (Pseudotsuga menziesii). The term is derived from the appearance of lighter colored tissues that form longitudinal streaks on the tangential face. For many years, such streaks were thought to be caused by animal claw injury.
|INITIATION OF FIGURE||
Since the development and anatomy of unfigured wood are outside the scope of this publication, interested readers are referred to the Textbook of Wood Technology, Vol. 1(63). Phases of figure formation that differ from normal development are described.
Spiral Growth Spiral growth apparently originates from a modified anticlinal division of cambial initials that develops an organized intrusive growth, which results in a helical orientation (either right or left) of the cambial initials and in subsequent woody tissues. Helical or spiral orientation of elements in mature woody stems causes a twisted appearance. Certain tree species characteristically have elements that spiral to the right; others, to the left. Still other species exhibit regular alternation of spiral direction in successive growth increments to form interlocked grain. The variations appear to be largely hereditary within species. Many tropical woods exhibit interlocked grain so regularly that straight grain is considered unusual.
Undulating Growth After initiation by cambial
division, cells enlarge first by elongation and reach final size after
differentiation. Elongation of individual cells initiated at the same
time is sometimes delayed, resulting in some that are longer than others.
Cells that are somewhat slower in elongation are restricted in available
space, particularly when the ends are held rigidly in place. As cell elongation
continues, central portions are pushed to either side resulting in a sinuous
grain orientation. A certain amount of intrusive growth occurs where enlongating
tips of adjacent cells force their way between cells lying above and below,
particularly between ray cells (figures 34
and 35). This penetration evidently takes
place while the intruding cell is relatively undifferentiated. After intrusive
growth has occurred, the cell may become a vessel, fiber, or other element
and continues to enlarge normally (figures 36
and 37). Such enlargement may result in lateral
displacement of tissues, which appears to be the primary method by which
the radial plane is affected. Lateral displacement also may affect the
tangential plane (figures 38 and 39).
The ultimate cause of figure in living trees is largely unknown.
It has been suggested that stresses of various types ranging from lean
forces (forces produced in leaning trees) to unfavorable climatic conditions,
disease, suppression, and several other factors contribute to figure formation
Abnormal Tissues Associated with Figure
As a general rule, abnormal tissues such as compression wood
and tension wood are not associated with figure types that affect the
radial plane. It often has been observed, however, that types of figure
that occur near branches or tree bases and on undersides of leaning trees
may be accompanied by reaction wood. In well-formed figured wood where
the pattern is regular, little reaction wood normally is encountered.
The most easily recognized external expression of figure in
trees is an overgrowth commonly referred to as a burl. Burls are relatively
large, abnormal bulges that sometimes form on trunks and limbs of almost
any tree species (Figure 40). Burl surfaces
may be corrugated or smooth, but usually are somewhat gnarled. Conifer
burls generally are corrugated. Fiber alignment within burls, which is
extremely irregular, produces a striking figure that is highly prized
for veneer and turned articles. Burls for commercial use are obtained
from Oregon myrtle (Umbellularia californica), elm, maple, walnut,
and redwood (Sequoia sempervirens).
Internal ExpressionFigure that exists in rough logs often cannot be detected by visual inspection. Factors that indicate possible existence of figure are not normally visible until the log is debarked (figures 42 and 43). Even when presence of figure is indicated, quality and quantity often cannot be appraised.
Probably the surest method of checking extent and quality of figure is splitting a small section of the wood along the radial or tangential plane where the appropriate figure is exposed to best advantage (figures 44 and 45). There is no other method of determining interlocked grain, which is of periodic origin. The same test is useful in separating imperfectly formed figure types (some commonly called ghost figures) from well-developed figure.
Split blocks that expose figure also illustrate how grain distortion forms the figures that are exhibited in veneer or lumber (Figure 46). Figure that is formed by gradual change in grain direction may not be readily apparent. Sawn surfaces frequently conceal any figure that might be present, or saw marks may give a false impression of figure when none is present. The split-block method is useful to ensure that figure is present and to indicate the cutting surfaces that will yield the most beautiful and interesting figure patterns (figures 47 and 48).
All four stem quadrants are generally sampled near the tree base to determine extent and penetration of figure and its quality. Additional samples are removed from various bole heights to determine longitudinal extent.
|OPTICAL ILLUSIONS IN FIGURE||
Optical illusions play an important part in formation of figure in wood (43). The fine, parallel, wavy lines produced in cutting tubular wood elements form the basis for a typical optical illusion (figures 16, 19, and 28).
Figure caused by undulating grain in wood is similar to striations formed in certain gemstones (particularly tigereye quartz and cats-eye) and various star figures found in sapphire, ruby, and quartz. Figure in these minerals is characterized by a moving light either in the form of a broad or narrow band or in the form of a "star." This phenomenon in gemstones is called chatoyancy, referring to the eye of a cat. It is formed by the presence of tiny, parallel or divergent, tubular inclusions within gem crystals. When gemstones are cut en cabonchon (i.e. with a rounded top) a band of light appears to move as the stone is tilted. The figure is best observed, as in wood, when viewed with unilateral lighting or in sunlight.
Tigereye quartz exhibits figure most similar to that in wood because it is a pseudomorph of a wavy form of chrysotile (asbestos), a fibrous mineral. The undulating fibrous structure is reformed in chalcedony (quartz), where it becomes translucent. When fibers are cut at or near the peaks or valleys of undulations, differential refraction and absorption of light produce apparently moving, alternating bands. This produces stripes that change in color and intensity as the position of viewing is shifted from one side to the other and are similar to fiddleback figure of wood.
Figure also is a result, in part, of an interference pattern produced by light rays striking the fine, undulating fibrous elements contained within figured wood. This effect, as previously mentioned, can be observed in many materials of fibrous origin (including certain types of fabrics as well as in some minerals and gemstones). The effect often is produced deliberately in many man-made materials and in op art illusions by varying the distance between parallel lines or by varying the depth of striae. Figures in wood caused by wavy grain are enhanced by an optical interference effect (figure 49). The interference pattern takes the form of a narrow band that appears brighter than surrounding tissues and appears to move as the specimen or light direction is changed. This is caused partly by the contrast-brightness effect observed in many optical illusions of similar origin. The contrast-brightness effect is prominent in well-developed fiddleback, where it forms the bright band characteristic of this figure, and in birdseye figure, where it forms the pupil of the eye (Figure 33).
These bands are augmented by light rays striking essentially parallel elements at peaks and valleys of the undulating grain. Elements at peaks are convex while those located in valleys are concave. As direction of viewing is changed or the position of the light angle is shifted laterally, the bright band also is shifted vertically. Some light rays become partially absorbed in the cut end-grain of steeply sloping ele-ments and are partially refracted and reflected along the shallow walls of the more or less tubular elements that are exposed along their longitudinal axes.
In fabrics, related figures classified as moire (watered) are formed by means of parallel lines producing wavy patterns of interference. Moire patterns also are characterized by moving bands of light, although less prominent than those in gemstones. Similar figures also can be observed in cut-pile fabrics such as velvet or velour; they also occur in suede leather. All of these are similar to some of the figures that appear in wood.
|EFFECT OF VARIOUS INFLUENCES ON FIGURE||
Effect of Species
Figured wood occurs in almost every species that produces
wood of commercial importance and in many non-commercial species. Most
current information concerning figure in wood has been derived from species
that supply the majority of figured woods of commerce.
Effect of Climate, Soil, and Location
No particular climate, soil, or geographical location appears
to be essential to formation of figure in trees. Certain climates, soils,
and geographical locations, however, can be cited as being conducive to
formation of certain figure types in some species. For example, figured
wood of several species currently is produced in the Pacific Northwest
to a far greater extent than in other areas. One explanation for this
fact may be that exploitation of hardwood species is relatively recent
in the Pacific Northwest.
Effect of Growth Rate
Rate of growth apparently has some effect on the type or strength
of figure produced. It often has been stated that growth retardation is
a definite factor in figure formation and that the best development occurs
only in slowly grown trees. Equal strength of figure, however, has been
observed in rapidly grown specimens as in those grown slowly. Fast-grown
wood is considered undesirable for certain products, which may prejudice
the selection of figure in fast-grown wood.
Effect of Tree Size
Tree size apparently has little effect on figure; small and
large trees have been observed to exhibit equally well developed curly
and blister figures. However, there is some effect of tree size on the
strength of figure because figure normally increases in intensity toward
the bark. This results in the best developed figure occurring in the outer
areas of tree stems. There is usually a sterile, juvenile zone surrounding
the pith that is devoid of figure and frequently contains reaction wood.
Effect of Disease
Some tree disease organisms characteristically cause their
hosts or host parts to grow abnormally. This abnormal growth can be expressed
either as undergrowth (hypotrophy) or overgrowth (hypertrophy). Either
type might result in abnormal woody tissues. However, there also could
be specific situations where the abnormality could be expressed only as
a misalignment of cells and/or tissues.
|ARTIFICAIL PRODUCTION OF FIGURE||
Since the supply of figured wood always has been limited and its occurrence appears to be mostly a matter of chance, it is desirable to reproduce figured trees by vegetative propagation or to induce figure in normally unfigured trees (52). Few successful attempts of figure production by artificial means have been recorded. Near Kyoto, Japan, however, considerable success has been achieved in producing a blister figure referred to as shibo (crinkle figure) that occurs in Japanese cedar (Cryptomeria japonica) (61, 62). Shibo apparently occurs with several variations in size and shape of crinkles. Figured trees sometimes are propagated from cuttings taken from trees with figure of high quality. Crinkles develop in wood by the time cuttings are about 10 years of age, when the presence of figure can be recognized externally from their deeply fissured bark and a characteristic secretion of resin from the fissures. Japanese cedar with natural figure usually grows in a poor, stony soil in association with kumassa (Sasa alba-marginata), a broad-leaved pygmy bamboo.
Artifically produced crinkles sometimes are made mechanically in unfigured trees (61). First a 10-foot section of bole is smoothed and wound spirally with an elastic cord. A number of small bamboo sticks inserted between cord and bole are then tied firmly into place (Figure 52). The elastic cord is removed after the sticks are secured. Crinkle figure becomes evident after 2 or 3 years, when ties and sticks are removed. Blisters attain a rounded appearance approximating natural figure after the removal. When the figure has reached a desired state, the tree is cut, log sections are debarked, and figured surfaces are polished for use as alcove posts. Since the trees are not converted into lumber, this method apparently is practical only for products used in the round (62, 83). It was noted, however, that artificially produced figure often lacks the luster displayed by naturally figured trees.
Other attempts to induce figure mechanically are described in a detailed report made almost 30 years ago (5). Some of the trees described in this report still exist, but information concerning figure development is meager. These trees were examined several years following the mechanical treatment (along with some grafted trees) but no figured wood was detected; unusual bark characteristics were the only effect noted (79). The only natural mechanically produced figure of any value yet described is drape figure in mahogany, which is caused by complex actions of the strangler fig described previously (40).
It is unlikely that mechanical binding of stems or distortion will induce permanent figure in trees; even elastic ligatures are soon over-grown. While such constrictions create adjacent bulges, they rarely in-terrupt tissues sufficiently to cause definite figure (except as previously noted). It might be possible to induce blister-like figure in smooth-barked trees by means of reflective or absorbtive surfaces applied to tree trunks in desired patterns; this may cause differential growth of specific cambial areas. The two effects might be combined by applying patterns of black and reflective paints. Growth regulators applied in patterns might yield a similar result.
Success at reproducing figured trees by grafting has been inconsistent. Probably the most widely known grafted figured tree is the Lamb walnut, propagated in 1929 by J. F. Wilkinson of Rockport, Indiana (38). Specimens from grafted trees cut in 1951 showed figure in outer wood portions of 7- to 8-inch trees (81). Figure also was noted in branches of other grafted trees only 5 to 7 years of age (84). Aspects concerning growth of figured walnut trees were investigated (49). Several grafted plantings have been initiated in Europe (18, 19, 25).
Grafted specimens of birdseye-figured sugar maple apparently were planted in the early 1930s, but no records of any current living trees have been found (66). Grafted specimens of other figured trees have been produced but, again, records concerning their progress have not been published (42). Although European work with figured trees appears to exhibit more variation (73,74,75) intensive studies have been concentrated on maser figure in birch (Betula verrucosa), which is known to be quite variable (32, 36, 70, 71, 72). Several specimens of maserbirch have been reported in an arboretum near Poznan, Poland (12) and in the Horsholm Arboretum in Denmark (41). A small European birch tree in plantings established by Bailey near Norris, Tennessee, was examined by the senior author in 1968. This tree exhibited indications of well-developed maser figure.
Burls commonly contain numerous apparently aborted buds that (as many persons believe) arose as a result of injury. Frost, fire, insect, and mechanical injuries are possible causes. Formation of burl-like growths in boxwood was induced by placing close-fitting metal bands around stems (65). Adventitious buds that formed near these bands produced swellings. A common practice in Algeria during the seventeenth and eighteenth centuries was inducing burl-like excrescences on African thuja by repeated burnings of stem portions (65), which consumed any sprouts that developed around injured areas. As a result, trunk swellings formed on sides opposite the burn injuries. Burl-like growths also develop in some cases through irritation of the cambium by viruses, bacteria, and fungi (as well as by a few higher plants). Repeated pollarding (limbs cut back to the trunk) occasionally will cause burl-like tissues to form.
|GENETICS AND FIGURE||
Little information is available concerning genetic effects on figure. Only eight of more than 150 Canadian and foreign workers in forest genetics contacted in 1968 were involved in some aspect of figure (13).
Summarization of research in Scandanavian genetic studies concerning maserbirch (37) resulted in seven conclusions:
(1) Maser figure varies in intensity and pattern;
(2) Maser characteristics are transferred by grafting;
(3) Maser characteristics can be transferred by seed;
(4) The maser property is dominant or semi-dominant;
(5) The homozygous condition is sublethal;
(6) Maser formation is caused by gene-controlled disturbances in the cambium area; and
(7) The maser condition is associated with slow growth and deformed trees.
No work in the U.S. has been directed toward genetic investigations of figure in recent years; little apparently is planned for the future. A genetic study in Puerto Rico (59) concerns transmission of giant birdseye figure in Cuban mahogany (Sweitenia mahogani).
An interesting aspect of fiddleback figure found in manaki mango from Hawaii is a condition of polyembryony never reported for any other mango species or variety (86). This tree is propagated primarily by vegetative means, but the figure apparently can be seed transmitted (86).
Efforts to reproduce curly or blister figures in walnut and birdseye figure in maple have not been consistently successful. A number of grafted stems now approaching 40 years of age have developed figure in some ramets but not in others (81).