Saturday, March 28, 2009

Softwood Key



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Hardwood Key



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Meristems

Cormophytes produce new cells throughout their life and form new organs at regular intervals (some tallophytes do the same). All cells of an embryo display the same activity of division, but as soon as a certain state of differentiation and thus a certain size has been reached, the production of new cells is restricted to special tissues, the meristems.

Typical meristems are found at the tips of all stems and roots. They are called apical meristems. Those of the shoot are usually protected by involucral leaves and the whole complex forms a bud.

Scanning Electron Micropgraph: Longitudinal section through an inflorescence apex - Snapdragon (Antirrhinum majus))

Scanning Electron Micrograph: Immature Flower Bud - Snapdragon (Antirrhinum majus)

The apical meristems are the cause of tip growth that is one of the most striking features of vegetative growth. This contrasts with animal growth, that is an allometric process, i.e. all parts of the body grow in a weay that maintains the body's overall proportions. As soon as an animal has reached its final size, growth ceases. This, however, does not mean that no more cell divisions are taking place. Cell divisions occur all the time, especially in epithelia and in blood stem cells. But this division activity has always the function of replacing old or damaged cells. No such repair occurs in plants. If a leaf or flower or any other part is damaged, it is neither replaced nor repaired. Instead, new organs grow, and this again does not happen in animals.

The cells of a meristem have a potentially unlimited ability to divide. But division is controlled. Many plants, for example, follow the principle of apical dominance, where the activity of the lateral meristems is suppressed while the tip is growing. In this case, information is exchanged between the two tissues in question. If the tip of the main axis is cut off, suppression is abolished and the lateral buds start to sprout.

Many plants like gymnosperms and dicots have extensive lateral meristems (the cambium, the vascular cambium, and the cork cambium) that give rise to growth in girth, also called secondary growth. Their activity may fluctuate in the course of the year and is reflected by annual rings.

Other plants, like monocots, have intercalary meristems. They are actively growing meristems that differ clearly from apical meristems and are located between more or less differentiated tissues usually at the base of each internode. The formation of secondary meristems shows that differentiated cells can reverse their state and go back to a meristematic existence. Their ability to divide is thus not lost, though it is not used unless an adjustment to changed circumstances requires it. The ability of indeterminate growth is widely exploited by the use of cuttings in horticulture. It is also displayed in the formation of roots at the cutting sites of begonia leaves, for example.

But what exactly is a meristem ? The following three examples will help to answer this question.

The marine brown alga Dictyota dichotoma consists of a flat thallus with a thickness of three cell layers. The large cell at its apical tip divides periclinal, while the subapical progenitor cells divide in an anticlinal manner. The progenitor cells themselves display alternating peri- and anticlinal cell division. The thallus enlarges thus both in length and in width. At regular intervalls, the apical cell divides in an anticlinal manner, too, resulting in two apical cells and a subsequent forking of the thallus. Although this example explains the way a division scheme works, it does not explain where the meristematic cells end and where the differentiated ones begin. The classical scheme of a cormophyte given by SACHS says that no clear demarcation exists. Instead, there is a gradient between meristematic and differentiated cells. The meristematic properties are thus not lost during one division, but they decline gradually.

The second example shows how division takes place in some liverworts, in simple cryptogams like horsetail and in many ferns. Contrary to that of many algae, their cormus normally resembles a three-dimensional body with a single tetraedical initial cell at the tip of the axis. It produces progenitor cells by regularly alternating the planes of division. These progenitor cells are given off towards the base. The progenitor cells may again divide in both anti- and periclinal manners.

The tip of phanerogams, my third example, is formed by a whole group of cells. They are not specialized and therefore called vegetation zone (see illustrations of Acacia, Oxypolis, Wheat). The apical meristem is organized into several cell layers. In angiosperms and in some gymnosperms, it has to be distinguished between the outer tunica and the central corpus (A. SCHMIDT, 1924; F. A. L. CLOWES, 1924; A. FÖRSTER, 1943). The meristematic cells divide mostly in an anticlinal manner, while those of the corpus display both planes of division: anti- and periclinal. Some parts of the corpus are dominated by a certain plane of division, thereby determining the first step of differentiation. Usually, the outer layer of the tunica produces the epidermis. The inner tissues of the plant stem from the corpus, the tunica or both.

These schemes are useful guidelines for the understanding of the plant's morphogenesis, since they point out the importance of the information that is contained in the cell's position within the tissue. A cell will only develop into a certain direction, if its position within the tissue is "right". If a cell is transferred to a new position, it will adopt new functions and thus dedifferentiate. At the beginning of the 20th century, G. HABERLAND (Universität Graz, later Berlin) put forward the sentence of the totipotency of plant cells. It states, that each cell of a plant keeps the ability to develop a complete plant. This is true for most, but not all plant cells. And still: growth through division is in fact characteristic for the meristematic state of a cell, but it is by no means restricted to it. A meristem does not only include the initial cells and their immediate progenitors, but also some parts of the shoot.

The situation is similar in root meristems, although their anatomy is different. The shoot apex is protected by the involucral leaves. In roots, this function is exerted by the root cap. Its cells are produced by a specialized root cap meristem and are progressively replaced towards the tip. These cells have to have a high turn-over, since the outmost cell layer is easily damaged by soil particles as a result of the growth movement of the root.



Procambium and Lateral Meristems

It is normally distinguished between primary and secondary growth of the shoot. The first is the phase of plant development that gives rise to new organs and to the basic plant form, the latter brings about growth in girth and the formation of new vascular tissues (A. de BARY, 1877).

The procambium is the meristematic tissue that produces the primary vascular tissues: xylem and phloem. It develops directly beneath the growing tip next to new leaf primordia. The development of new leaves is thus tightly connected with that of new vascular tissues. The vascular tissues of leaves are also called leaf veins. The cells of the procambium are generally combined in cords. They form an extension of the vascular tissues into the growing tip and do thus provide the connection of the newly developed organ with the conductive systems of the plant. The cells of the procambium are elongated and become even more so in the course of their development. The volume of their vacuoles increases considerably, lending them a lighter and more transparent appearance than their neighboring cells. This is decisive for their differentiation into xylem or phloem cells.


Growth processes within the first two millimetres of a radical apex of Allium cepa (onion). The following data was collected to characterize the growth occurring at the given stages. On the left: number of cells within a 100 µm thick cross-section. On the right: area of cross-section; length and surface of the cells at different distances from the radical apex (according to W. A. JENSEN and M. ASHTON, 1960).



Some of the meristematic cells in plants with secondary growth keep their meristematic state and become cells of the cambium.

What are the causes for the development of the procambium? Two models exist:

  1. They are to be found in the cell-cell interactions that take place between the cells of the bud, that determine the pattern of the leaf positions and the positions of xylem and phloem.

  2. Induction is achieved by fully differentiated tissues. The necessary information is conducted to the bud via already differentiated cells of the procambium.

The first model was confirmed experimentally, since formation and further development of the procambium are undisturbed in isolated bud meristems. The determination of cells takes place before any morphological change can be seen. Differentiation describes the (usually irreversible) changes of structures and functions that result in a certain specialization, while determination means the (usually irreversible) triggering of processes that lead to these changes.

The cambium is the prototype of a lateral meristem. It is mono- or multilayered depending on its origin and forms normally a continuous cell layer of tubular shape that is located at the periphery of the shoot or root. It separates xylem from phloem, if present. The cambium develops from the procambium next to the vessels, ensuring a continuity of the meristematic state.

The cambium between the vessels derived from already differentiated, parenchymatous cells. The first type is also called fascicular (within the vascular bundle) cambium, while the latter one is termed interfascicular (between the vascular bundles). The interfascicular cambium is a secondary meristem. A few monocots (Dracaena, Yucca, Aloe and others) have again another type of cambium, the extrafascicular cambium.

The cells of the cambium are often termed initials, since they initiate the formation of specialized progenitor cells after division. Two cell types occur within the cambium:

  1. Fusiform initials. They are the mother cells of all xylem and phloem elements, as well as of all other cells that are oriented parallel to the organ's axis. They are flat, elongated with pointed ends and highly vacuolate. It is their spindle-like shape that caused their name.

  2. Ray initials are nearly isodiametric, small cells that occur often in groups. They develop from fusiform initials or their progenitors. They produce the radially orientated rays in wooden plants (transversal elements).

I. W. BAILEY, who did the basic work on the organization of the cambium in the 20th of this century, gained the following data when comparing a one year old and a sixty years old stem of Pinus strobus (Weymouths Pine).


Differences in cambium girth and in number of initials between a one year old and a sixty years old stem of Pinus strobus

Age
1 year
60 years

radius of the tube

2 mm
20 cm

girth of the cambium

12,56 mm
1,25 m

average length of fusiform initials

870 µm
4000 µm

number of fusiform initials in
cross-section of stem

724
23,100

number of ray initials
in cross-section of stem

70
8796
I. W. BAILEY, 1923


His data show that both length and number of fusiform initials increases with the age of the stem. The increase in number and the widening (dilatation) of the cambium tube is caused by the widening of the central xylem cylinder, that is produced by the cambium itself.

Secondary vascular elements are given off into opposite directions by periclinal (tangential) division of fusiform cells. The developing xylem elements grow towards the inner cylinder, that of the phloem towards the outer of the cylinder. The progenitors of the initials are organized in radial rows that make it easy to trace back their descent. The increase in girth is compensated by the anticlinal divisions occurring at regular intervals. The activity of the cambium is temperature-dependent: it causes the annual rings. Their thickness, i.e. the activity of the cambium, is determined by extern factors like temperature, day length, soil humidity, temperature and others. Besides its function in the production of vascular tissues, the cambium has an additional capacity for the healing of wounds.

The cork cambium (or phellogen) is a secondary lateral meristem that serves to produce the secondary outer surface, the bark, that replaces the epidermis. It is without exception given off towards the outward direction. Often, though not always, the cork cambium produces cells towards the inner of the stem, that form the phelloderm.

The cork cambium has a rather simple structure, if compared to the cambium. In cross-section, the cells have a right-angled shape, they are flat in radial and tangential sections. Their plasma is highly vacuolated and may contain chloroplasts and tannic acids.

The cork cambium stems from epidermal cells or/and from cells of the underlying parenchyma. It is distinguished between primary and secondary cork cambium taking into account the fact that it can be assembled within the stem several times during a plant's life. The cork cambium is monolayered during the first year in some species and becomes multilayered later on. It may be active for several years, sometimes even for the whole life or for just one year. Its activity is, just as that of the cambium, influenced by extern factors.

Xylem

The Xylem


The xylem is the principal water-conducting tissue of vascular plants. It consists of tracheary elements, tracheids and wood vessels and of additional xylem fibres. All of them are elongated cells with secondary cell walls that lack protoplasts at maturity. Bordered pits are typical for tracheids, while wood vessels are marked by perforated or completely dissolved final walls.


The xylem takes also part in food storage, support and the conduction of minerals. Xylem and phloem together form a continuous system of vascular tissue extending throughout the plant. The principal conductive cells of the xylem are tracheary elements, of which there are two types, tracheids and wood vessels. Both are elongated cells with secondary cell walls that lack protoplasts at maturity. They are completed by the xylem fibres and parenchyma cells. Much speaks on behalf of the origin of xylem fibres and wood vessels from the tracheids.

Since 1851, the isolation and depiction of lignified cells is done according to the maceration procedure of SCHULZE. Small pieces of wood are covered with a mixture of potassium perchlorate and concentrated nitric acid. The complete volume should not be larger than 1/10 of the reaction container, because a lot of gas develops very quickly at cautious heating. The surfaces of the wooden pieces are strongly attacked. The single cells can be scraped off after washing of the preparation and examined under the microscope.

Let us start with a portrait of the different cell types.:Tracheids are the chief water-conducting elements in gymnosperms and seedless vascular plants. They can also be found in angiosperms. Tracheids are elongated cells, closed at both ends. They are 1 mm on average. Tracheids are regarded as the prototype of prosenchymatic cells, since the cell's ends are pointed and true final walls are missing. Tracheids look often square in cross-section, the lignified secondary wall is relatively thin. Their entire cell surface is evenly coated. The walls are opened by numerous pits that are, depending on their origin, either round, oval, gap- or groove-shaped. They occur solitarily, statistically scattered, arranged in turns around the middle axis or grouped together. Such groups can often be found at the cell's ends. If gap-like pits lay on top of one another, a ladder- or stair-like perforation may be the result. It is commonly called scalariform. We will meet this structure again, when talking about vessel elements. The pits are often surrounded by a halo and are then called bordered pits. Bordered pits are especially common in the tracheids of some gymnosperms. Their structure can be discerned best in a cross-section through neighbouring cells. The middle lamina between the cells is preserved within the pits. Their centre is made up by a disc of primary cell wall material, called torus. No secondary walls exists in the pit's structure. The area between torus and wall (the former middle lamina) is called margo and is very porous, allowing the movement of water and ions from tracheid to tracheid. Bordered pits exist only in cells with secondary walls.

Botanists think of wood vessels (tracheae) as the water-filled tubes of the xylem. M. MALPIGHI, who thought that he had found an important common element in the anatomy of animals and plants introduced the term trachea in the 17th century. Wood vessels are the chief water-conducting elements of angiosperms.

In contrast to the tracheids the final walls of the single vessels are perforated or, much more so, completely resolved. Wood vessels are therefore generally thought to be more efficient water conductors than tracheids. The length of the single tube (composed of numerous cells) makes it difficult to isolate a vessel as a whole. It can be as long as several meters. It is commonly assumed that at least in some species the wood vessels are as long as the whole shoot.

During ontogenesis the wood vessels increase strongly in width.They are usually round in cross-section and have a larger diameter than the tracheids, a feature that enhances their capacity for water-conduct. Exceptionally wide-lumened elements can be seen with deciduous trees, that are known to lose particularly large amounts of water due to transpiration. The water-loss of a fully developed birch tree with an estimated number of 200 000 leaves can be up to 400 litres per day. Even wider are the vessel elements of many lianas. But the oldest living trees, the redwoods and other sequoias at the pacific coast of California have without exception tracheids with very narrow lumina. Vessels are marked by characteristically structured secondary wall coatings (lignin) at the inner surface of the primary walls. Deposits in the form of screws, rings or nets exist. These strengthenings make it possible for tracheary elements to be stretched or extended, although the cells are frequently destroyed during the overall elongation of the organ.

Beside this vessels with pits or scalariform openings exist, whose walls are nearly completely lined with secondary wall material that is only opened by round or gap-like pits. Many transitions between the two pit types can be found. Often some or even all of the types are members of the same vascular bundle. But there are species, that lack one or the other type. Wood vessels develop -just like tracheids- during primary growth from the cells of the procambium. Where secondary growth occurs wood vessels are produced by the cells of the cambium.

Friday, March 27, 2009

Wood growth and structure

Wood growth and structure



Wood is a complex, natural product. Between different tree species, its density, stability, durability, strength, burning properties, electrical resistance, reaction during drying, impact resistance, bending properties, acoustic properties, pulping qualities, workability and appearance varies markedly.

Hardwoods and softwoods

Trees are classified into two groups: hardwoods and softwoods. This can be confusing because not all hardwoods are hard and not all softwoods are soft. Balsa wood, for example, is a hardwood, while some of Australia's hardest timbers—for example, Callitris pine, are softwoods. The difference is in the cellular structure of the wood.

Hardwood timbers are made up of four cell types. Small wood fibres make up the bulk of the wood. Large cells, called vessels, function as pipes that move sap up the tree through the mass of fibres. Other cells are largely used to store food. With some experience it is possible to distinguish different hardwood timbers based on the number, size and location of the vessels.

Softwoods do not have vessels. Softwoods have a simpler fibrous structure based on only two cell types.

The easiest way to distinguish between the two tree groups is to remember that flowering trees are all hardwoods while cone-bearing trees are softwoods. Hardwoods include eucalypts, wattles and oaks while pines and cypresses are softwoods.




Growth rings and the pith

As the tree trunk and branches thicken, a series of concentric layers of wood cells are laid down around a central core called the pith. These appear as growth rings. The pith is the remnant of the growing shoot that gives the tree its height. Because the pith has a cell structure different to the rest of the tree, it is often easily seen as a corky pipe in the log’s centre.

Growth rings often, but not always, represent annual growth. In temperate areas, tree growth during spring is represented by the presence of large cells with thin walls that appear lighter in colour. The darkness is due to the presence of smaller, thick-walled cells that are laid down towards the end of the growing season. In some hardwoods, the vessels form a ring in the early wood (ring-porous species) making the rings easier to see.




Sapwood and heartwood

The living tree’s stem is composed of different layers, illustrated in the cross-section diagram above. The cambium is a very thin layer of cells that divide to produce the bark cells (which protect the tree) and the wood cells. Sugars produced in the leaves travel down the inner bark, or phloem, feeding the cambium and, ultimately, the roots.

Only a very small proportion of the wood cells produced by the cambium are actually alive. Most of the newly formed wood cells hollow out to form the sapwood through which water and dissolved minerals travel from the roots to the leaves. Other cells are used to store food provided by photosynthesis, including starch. The sapwood is almost always creamy white or yellow in colour and is usually two to five centimetres thick.

In most tree species the sapwood band can be easily distinguished from the inner heartwood. The heartwood supports the tree’s stem but doesn't otherwise contribute to its growth. Heartwood’s colour comes from resins, minerals and other compounds being deposited in the cells as they are decommissioned from their role as sapwood. These deposits, and the lack of food, add durability, colour and strength to the timber

Xylem

Multiple cross sections of a stem showing xylem and companion cells
Multiple cross sections of a stem showing xylem and companion cells[1]

In vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek ξυλον (xylon), "wood", and indeed the best known xylem tissue is wood, though it is found throughout the plant. Its basic function is to transport water.

The xylem transports water from the root up the plant. The xylem is mainly responsible for the transportation of water and mineral nutrients throughout the plant. Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. This transport is not powered by energy spent by the tracheary elements themselves, which are dead at maturity and no longer have living contents. Two phenomena cause xylem sap to flow:

  • Transpirational pull: the most important cause of xylem sap flow, is caused by the evaporation of water from the surface mesophyll cells to the atmosphere. This transpiration causes millions of minute menisci to form in the cell wall of the mesophyll. The resulting surface tension causes a negative pressure in the xylem that pulls the water from the roots and soil.
  • Root pressure: If the water potential of the root cells is more negative than the soil, usually due to high concentrations of solute, water can move by osmosis into the root. This may cause a positive pressure that will force sap up the xylem towards the leaves. In extreme circumstances the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is most common in the morning before the stomata open and cause transpiration to begin. Different plant species can have different root pressures even in a similar environment; examples include up to 145 kPa in Vitis riparia but around zero in Celastrus orbiculatus[2].

Xylem can be found:

  • in vascular bundles, present in non-woody plants and non-woody plant parts
  • in secondary xylem, laid down by a meristem called the vascular cambium
  • as part of a stelar arrangement not divided into bundles, as in many ferns.

Note that, in transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only.

The most distinctive cells found in xylem are the tracheary elements: tracheids and vessel elements. However, the xylem is a complex tissue of plants, which means that it includes more than one type of cell. In fact, xylem contains other kinds of cells, such as parenchyma, in addition to those that serve to transport water.

Primary xylem is the xylem that is formed during primary growth from procambium. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. It is distinguished by wider vessels and tracheids.

Secondary xylem is the xylem that is formed during secondary growth from vascular cambium. Secondary xylem is also found in members of the "gymnosperm" groups Gnetophyta and Ginkgophyta and to a lesser extent in members of the Cycadophyta. The two main groups in which secondary xylem can be found are:

  1. conifers (Coniferae): there are some six hundred species of conifers. All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is marketed as softwood.
  2. angiosperms (Angiospermae): there are some quarter of a million to four hundred thousand species of angiosperms. Within this group secondary xylem has not been found in the monocots. In the remainder of the angiosperms this secondary xylem may or may not be present, this may vary even within a species, depending on growing circumstances. In view of the size of this group it will be no surprise that no absolutes apply to the structure of secondary xylem within the angiosperms. Many non-monocot angiosperms become trees, and the secondary xylem of these is marketed as hardwood.

Photos showing xylem elements in the shoot of a fig tree (Ficus alba): crushed in hydrochloric acid, between slides and cover slips.
Photos showing xylem elements in the shoot of a fig tree (Ficus alba): crushed in hydrochloric acid, between slides and cover slips.

Xylem appeared early in the history of terrestrial plant life. Fossil plants with anatomically preserved xylem are known from the Silurian (more than 400 million years ago), and trace fossils resembling individual xylem cells may be found in earlier Ordovician rocks. The earliest true and recognizable xylem consists of tracheids with a helical-annular reinforcing layer added to the cell wall. This is the only type of xylem found in the earliest vascular plants, and this type of cell continues to be found in the protoxylem (first-formed xylem) of all living groups of plants. Several groups of plants later developed pitted tracheid cells, apparently through convergent evolution. In living plants, pitted tracheids do not appear in development until the maturation of the metaxylem (following the protoxylem).

In most plants, pitted tracheids function as the primary transport cells. The other type of tracheary element, besides the tracheid, is the vessel element. Vessel elements are joined by perforations into vessels. In vessels, water travels by bulk flow, like in a pipe, rather than by diffusion through cell membranes. The presence of vessels in xylem has been considered to be one of the key innovations that led to the success of the angiosperms[3]. However, the occurrence of vessel elements is not restricted to angiosperms, and they are absent in some archaic or "basal" lineages of the angiosperms: (e.g., Amborellaceae, Tetracentraceae, Trochodendraceae, and Winteraceae), and their secondary xylem is described by Arthur Cronquist as "primitively vesselless". Cronquist considered the vessels of Gnetum to be convergent with those of angiosperms[4]. Whether the absence of vessels in basal angiosperms is a primitive condition is contested, the alternative hypothesis being that vessel elements originated in a precursor to the angiosperms and were subsequently lost.

Wood ID: Species Characteristics

Wood ID: Species Characteristics

Ring-porous hardwoods

American Elm
Ulmus Americana
Average specific gravity: 0.50 Heartwood color: Light brown to brown or
reddish brown Pore distribution: Ring-porous Earlywood: Pores large, in continuous row Latewood: Pores in wavy bands Tyloses: Present in earlywood, but usually sparse Rays: Not distinct without lens; homogeneous 1-7
(mostly 4-6) seriate.

Ash Fraxinus spp.
Average specific gravity: 0.60Heartwood color: Light brown or grayish brown.Sapwood color: Creamy white (may be very wide)Pore distribution: Ring-porousEarlywood: 2-4 pores wide; pores moderately large,
surrounded by lighter tissue
Latewood: Pores solitary and in radial multiples of 2-3, surrounded by vasicentric parenchyma or connected by confluent parenchyma in outer latewood. Thick-walled.
Tyloses: Fairly abundant (some vessels open) Rays: Not distinct to eye, but clearly visible with lens; 1-3 seriate

Black Locust
Robinia pseudoacacia
Average specific gravity: 0.69 Heartwood color: Olive or yellow-brown to dark
yellow-brown; dark russet brown with exposure Fluorescence: Bright yellow Sapwood: Never more than 3 growth rings wide Pore distribution: Ring-porous Earlywood: 2-3 pores wide; pores large. Latewood: Pores in nest-like groups, which merge
into interrupted or somewhat continuous bands in outer latewood; latewood fiber mass appears dense and dark in contrast to yellowish; tyloses filled pores and rays.
Tyloses: Extremely abundant with yellowish cast and sparkle, solidly packing vessels and making adjacent pores indistinct.
Rays: 1-7 (mostly 3-5) seriate

Hickory
Carya spp.
Average specific gravity: 0.72 Heartwood color: Light to medium brown or
reddish brown Pore distribution: Ring-porous Earlywood: Mostly an intermittent single row or
thick-walled pores with fiber mass where inter-rupted Latewood: Pores not numerous, solitary and in radial
multiples of 2-5. Thick-walled. Tyloses: Moderately abundant Rays: 1-4 seriate Parenchyma: Banded parenchyma and rays form a
reticulate pattern distinctly visible against the background fiber mass with a hand lens (but banded parenchyma absent from earlywood zone)

Northern Red Oak
Quercus rubra
Average specific gravity: 0.63 Heartwood Color: Light brown, usually with flesh or
pinkish-colored cast. Pore Distribution: Ring-porous Earlywood: Up to 4 or 5 rows or large solitary pores. Latewood: Pores solitary in radial lines, few and
distinct ("countable"), vessels thickwalled Tyloses: Absent or sparse in earlywood Rays: Largest rays conspicuous; tallest less than 1 in.
(tangential surface). Narrow raysuniseriate (one cell wide) or in part bisariate

White Oak
Quercus alba
Average specific gravity: 0.68 Heartwood color: Light to dark brown to grayish
brown. Pore Distribution: Ring-porous Earlywood: Up to 4 rows of large pores Latewood: Pores small, solitary or in multiples, in
spreading radial arrangement, numerous and indistinct ("uncountable"), grading to invisibly small with lens. Vessels thin-walled.
Tyloses: Abundant Rays: Largest rays conspicuous; tallest greater than 11/4 in. Narrow rays uniseriate or in part biseriate.

Semi-Ring-Porous Hardwoods

Black Walnut
Juglans nigra
Average specific gravity: 0.55 Heartwood color: medium brown to deep
chocolate brown Pore distribution: semi-ring-porous Pores: earlywood pores fairly large, decreasing
gradually to quite small in outer latewood; pores
solitary or in radial multiples of 2 to several Tyloses: Moderately abundant Rays: fine, visible but not conspicuous with hand
lens, 1-5 seriate, cells appear round in tangential view Crystals: Occur sporadically in longitudinal paren-chyma cells

Diffuse-Porous Hardwoods

American Basswood
Tilia americana
Average specific gravity: 0.37 Heartwood color: Creamy white to pale brown Odor: Faint but characteristic musty odor Pore distribution: Diffuse-porous; growth rings
indistinct or faintly delineated by marginal parynchyma, sometimes with blurry whitish spots along the growth ring boundary
Pores: Small, mostly in irregular multiples and clusters
Rays: Distinct but not conspicuous on transverse surface with lens. 1-6 seriate; ray cells appear laterally compressed in tangential view; rays have bright yellow cast

American Beech
Fagus grandifolia
Average specific gravity: 0.64 Heartwood color: Creamy white with reddish tinge to medium reddish-brown Pore distribution: Diffuse porous; growth rings distinct.
Pores: Small, solitary and in irregular multiples and clusters, numerous and evenly distributed through-out most of the ring; narrow but distinct latewood in each ring due to fewer, smaller pores
Rays: Largest rays conspicuous on all surfaces; darker ray fleck against lighter background on radial surfaces. Largest rays 15-25 seriate; uniseriate rays common

Black Cherry
Prunus serotina
Average specific gravity: 0.50
Heartwood color: Light to dark cinnamon or reddish-brown
Pore distribution: Diffuse-porous; growth rings sometimes distinct because of narrow zone or row of numerous slightly larger pores along initial earlywood.
Pores: Pores through growth ring solitary and in radial or irregular multiples and small clusters
Gum Defects: Common
Rays: Not visible on tangential surface; conspicuous light ray fleck on radial surfaces; distinct bright lines across transverse surface, conspicuous with lens. 1-6 (mostly 3-4) seriate.

Black Gum
Nyssa sylvatica
Average Specific Gravity: 0.50 Heartwood Color: Medium grey or grey with green
or brown cast (wood usually has interlocked grain)
Pore Distribution: Diffuse-porous
Pores: Very small, numerous, solitary and in mul-tiples and small clusters
Rays: Barely visible even with hand lens; 1-4 seriate

Eastern Cottonwood
Populus deltoides
Average specific gravity: 0.40
Heartwood color: Grayish to light grayish-brown. Occationally olive.
Pore distribution: Diffuse porous or semi-diffuse-porus. Usually an apparent size graduation from earlywood to latewood
Pores: Small to medium small; Solitary and in radial multiples of 2 to several
Rays: Very fine, not easily seen with hand lens

Sycamore
Platanus occidentalis
Average specific gravity: 0.49
Heartwood color: Light to dark brown, usually with a reddish cast
Pore distribution: Diffuse-porous; growth rings distinct due to unusual lighter color of latewood (thinner band and clearer than beech)
Pores: Small, solitary and in irregular multiples and clusters, numerous and evenly distributed through-out most of the growth ring; latewood zone evident by fewer, smaller pores
Rays: Easily visible without hand lens on all sur-faces, appearing uniform in size and evenly spaced on transverse and tangential surfaces, producing conspicuous dark ray fleck on radial surfaces. Largest rays up to 14 seriate; uniseriate rays not common.

Sugar Maple
Acer saccharum
Average specific gravity: 0.63
Heartwood color: Creamy white to light reddish-brown
Pore distribution: Diffuse-porous; growth rings distinct due to darker brown, narrow latewood line
Pores: Small, with largest approximately equal to maximum ray width in cross section; solitary or in radial multiples; very evenly distributed
Rays: Visible to eye on tangential surface as very fine, even-sized, evenly distributed lines; on radial surfaces, ray fleck usually conspicuous. Rays: Two distinct sizes: largest 7-8 seriate; uniseriate rays numerous.

Red Maple
Acer rubrum
Average specific gravity: 0.54 Heartwood color: Creamy white to light reddish-
brown, commonly with grayish cast or streaks.
Pore distribution: Diffuse-porous
Pores: Small, solitary and in radial multiples, very evenly distributed; largest as large or slightly larger than widest rays on cross section.
Rays: May be visible on tangential surface as very fine, even-sized and evenly spaced lines; on radial surface, ray fleck usually conspicuous. 1-5 seriate.

Yellow Birch
Betula alleghaniensis
Average specific gravity: 0.62Heartwood color: Light brown to dark brown,
reddish-brown.
Pore distribution: Diffuse porous
Pores: Small to medium, solitary and in radial multiples of two to several pores
Rays: Rays smaller than pore diameters. Some pores may appear to be filled with a substance; 1-5 seriate.

Yellow Poplar
Liriodendron tulipifera
Average specific gravity: 0.42 Heartwood color: Green, or yellow to tan with
greenish cast Sapwood color: creamy white (often wide) Pore distribution: Diffuse-porous; growth rings
delineated by distinct light cream or yellowish line of marginal parenchyma. Pores: Small, solitary, but mostly in radial or irregu-lar multiples and small clusters
Rays: Distinct on cross section with lens; produce conspicuous fine light ray fleck on radial surfaces. 1-5 (mostly 2-3) seriate

Softwood Identification

Eastern White Pine
Pinus strobus
Average specific gravity: 0.35 Odor: Pleasant, piney Heartwood: Distinct, darkening with age Grain appearance: Fairly even Earlywood / Latewood transition: Gradual Resin Canals: large, numerous, mostly solitary,
evenly distributed

Southern Yellow Pine
Pinus spp.
Average specific gravity: 0.51 to 0.61 Odor: “pitchy” pine odor Heartwood: Distinct Grain appearance: Uneven Earlywood / Latewood transition: abrupt Resin Canals: Large, numerous, mostly solitary,
evenly distributed

Red Spruce
Picea rubens
Average specific gravity: 0.40 Odor: None Heartwood: Light in color; indistinct from sapwood Grain appearance: Fairly even to moderately even Earlywood / Latewood transition: Gradual Resin Canals: Small, relatively few; solitary or
several in tangential groups, variably distributed

Hemlock
Tsuga Canadensis
Average specific gravity: 0.40 Odor: None Heartwood: Indistinct, light in color Grain appearance: Fairly uneven Earlywood / Latewood transition: Fairly abrupt
to gradual Texture: Medium to medium-coarse

Balsam Fir
Abies balsamea
Average specific gravity: 0.36 Odor: None Heartwood: Indistinct, light in color
Grain appearance: moderately uneven to
moderately even Earlywood / Latewood transition: Very gradual Texture: Medium

Eastern Red Cedar
Juniperus virginiana
Average specific gravity: 0.47 Odor: “cedar-chest” odor, very distinct Heartwood: Distinct, deep purplish red, aging to
reddish-brown Grain appearance: Moderately uneven to fairly
even; latewood narrow Earlywood / Latewood transition: Gradual Texture: Very fine

Baldcypress
Taxodium distichum
Average specific gravity: 0.46 Odor: Faint to moderately rancid Heartwood: Usually distinct Grain appearance: Uneven Earlywood / Latewood transition: Abrupt; early-
wood medium yellow-brown; latewood amber to dark brown Texture: Coarse to very coarse


Reference:
Brian Bond, Assistant Professor, and Peter Hamner, Research AssociateDepartment of Forestry, Wildlife and FisheriesThe University of Tennessee

Wood Types and Techniques

Wood Types and Techniques

About the Different Woods:

Different woods are the palette of the furnituremaker. They provide color and texture, strength and beauty to handmade furniture.

Each type of wood has characteristics to be considered when building a piece of furniture. Some are very hard and durable; some are flexible and suitable for bending. "Hardwood" is a term applied to trees that lose their leaves in winter. "Softwood" describes evergreens such as fir, pine and redwood. The actual durability a wood is described in a range from very soft to very hard.

Every wood has a distinctive grain structure. Woods such as white and red oak, ash and walnut have "open-pores". These woods have small holes in their surface that give the piece a textural quality. When a stain is applied to this type of surface, the stain tends to collect in the "open-pores" and appears darker than the rest of the piece. Tight grained woods include maple, alder, and cherry. These woods are smooth to the touch and can take finish evenly.

Many woods have unique "figure" such as quilting, birdseye, fiddleback or spalting.


Quilted Pacific Maple

Fiddleback Pacific Maple

These naturally occurring characteristics can make a piece of furniture that reaches beyond the ordinary.

The following is a list of some of the woods used by Northern California woodworkers and their characteristics.

Find the type that most attracts you and consider using that wood for a special piece of furniture. The experienced craftworkers of Humboldt Woodworkers Guild can help find the right wood for your project.

California Softwoods and Hardwoods

Alder, Pacific Maple, Black Oak, Madrone, Tan Oak, Redwood, Myrtlewood (pepperwood), Claro Walnut, Western Red Cedar, and Yew

Humboldt County woodworkers prize the unique woods of the Pacific Northwest for their beauty and durability. Local woodworkers use native woods alone and in combination with domestic and exotic species creating the furniture that is part of the distinctive designs of Northern California.



Alder


Warm brown color with a figure like cherry. Alder is a medium soft wood suitable for cabinetry and furniture with the appropriate sized joinery.


Pacific Maple


Golden yellow wood with a variety of figure available, can be found in the curly or fiddleback varieties. This is a medium hard wood suitable for all types of furniture.



Madrone


One of the harder California native woods, Madrone has a reddish pink color with streaks of color throughout. Madrone is used in furniture and turnings, and can be used in flooring and architectural woodwork.

Softwoods and Hardwoods

Ash, Basswood, Beech, Birch, Butternut, Tennessee Aromatic Cedar, Cherry, Fir, Hickory, Maple, Pine, Poplar, Red Oak, Walnut, White Oak.

Long a staple of the American furnituremaker, these mostly eastern hardwoods are most familiar to the public. Humboldt County woodworkers use these woods to make the finest handmade furniture.


Maple
Hard rock maple is one of the hardest of domestic woods. The "select white" grade of maple has a warm gold-ivory color when finished with a hand rubbed oil. Because of its hardness rock maple is suitable for all types of furniture and cabinetry.


Cherry


Furniture grade cherry is a moderately heavy, hard, strong, wood. Close grained, it can be polished to a deep and glowing red. Many of the finest early American table tops and interior panels were made of cherrywood. This wood is suitable for all furniture and cabinetry including chairs.


Walnut


North American walnut is one of the most prized hardwoods. It can range in color from deep rich brown to an almost purple brown. This is an open-pored wood that is relatively hard. Walnut is durable and finishes beautifully. The wood is useful in many furniture applications.

Exotic Woods

Andiroba, Bayo, Bloodwood, Bocote, Bubinga, Spanish Cedar, Chaktekok, Chechen, Chicozapote, Cocobolo, Ebony, Fishtail Oak, Granadillo, Ironbark, Ipe, Jabin, Jarrah, Jatoba, Katalox, Kingwood, Koa, Lacewood, Lignum Vitae, African Mahogany, Machiche, Narra, Obeche, Pau Ferro, African Paduak, Peruvian Walnut, Purpleheart, Brazilian Rosewood, Satinwood, Snakewood, Teak, Vesi Wenge, Zebrawood

With bright colors and expressive grain patterns these woods are often used as highlights in furnishing and turnings. Also, some of these exotic woods such as African mahogany and granadillo are excellent for building whole pieces of furniture, chairs and cabinetry.

Lacewood


A relatively soft wood grown widely in Australia, lacewood has an unusual grain structure that has the look of hammered copper when properly cut. It can be used as an accent wood or in veneered tabletops.


Granadillo


A beautiful, very hard wood from Southern Mexico with a tan-deep brown streaking. This close grained wood is a "Smart Wood" selectively harvested in cooperation with the indigenous people. This wood is suitable for all furniture applications.


African Mahogany


Here is traditional mahogany, deep rich, red and suitable for any furniture application. This wood is imported from Ghana, which has had a sustained yield forestry program in place since 1910.

About Techniques

The solid wood furniture of Humboldt Woodworkers Guild is built using time-honored joinery that gives the work beauty and durability.

All wood is made up of cells that continue to shrink and swell with changes in humidity. A 12-inch wide board will move on average about 1/8 of an inch over the course of a year.

If wood is not properly joined the boards will crack and break apart over the years. Antique furniture that has survived today was crafted with joints such as the mortise and tenon, dovetail, finger joint, floating panels and beautifully glued veneers. It's not that they didn't make bad furniture 100 years ago, it's just that only the good furniture has survived.

Mortise and Tenon - A mortise is the opening cut in wood, a tenon is the piece that is shaped to fit in it. This joint is used to join cross members, for example, connecting a rail to the leg of a chair.

Dovetail - The traditional joint used for drawers and to join casework work in fine cabinetry. The dovetail actually locks the wood in place in one direction.

Finger Joint - A simple joint that is similar in usage to the dovetail, the finger joint is stronger than the dovetail and compliments drawers and casework with a square patterned appearance.

Floating Panels- Frame and panels doors feature solid wood panels that fit into grooves in the wood of the frame. This construction allows the wood panel to "float" with the seasonal movement of wood.

Veneered woods - Another way to control the movement of wood to glue thinly sliced sheets of wood to a more moisture resistance substrate. Using this technique woodworkers can select unusually beautiful boards and carry the appearance of the wood grain throughout the piece.

Humboldt County woodworkers use both hand and machine tools to make fine furniture.

Chisels, hand planes and cabinet scrapers are still used in all shops along with tools as modern as a computer assisted router.