Last Updated on April 8, 2020 by Naeem Javid Muhammad Hassani
- Softwoods are those which are derived from gymnosperms such as pines. These are evergreen, having needle-like leaves, and their seeds are in cones.
- Softwoods are designated as nonporous woods due to the absence of vessels.
- In softwoods, conduction takes place through tracheids. They need not so much water translocation as the rate of transpiration is less due to the presence of needle-like leaves as compared to hardwoods with broad leaves.
- In softwoods, longitudinal tracheids are somewhat rounded or polygonal are regularly arranged in radial rows b/w the wood rays.
- Hardwoods are those derived from angiosperms such as oak, poplar, and mulberry, with broad leaves, seeds enclosed and bearing flowers.
- Hardwoods are designated as porous woods due to the presence of vessels.
- Pores often visible to the naked eye in hardwoods. Conduction of water and food material takes place through vessels.
- In hardwoods, radial alignment of longitudinal elements on the transverse surface is either lost entirely or is more or less obscure (dim).
- These differ by the size of rays and anatomical complexity of wood due to the presence of more wood element than softwoods.
- Wood portion responsible for the sap conduction is called sapwood.
- The portion in wood: the outer portion
- Function: sap conduction
- Color : light / lustrous
- Durability: Less due to food preserve
- Permeability: more
- Strength: less
- Fungal attack: more
- Tissue: live tissue
- Cell size: large
- Density: less dense
- Content: high cellulose content
- Conductor: allow electricity to pass
- Portion: generally commercial logs contain 25% – 30% sapwood.
- Use :
- If the sapwood portion is more than wood can be used for pulp and paper eg Eucalyptus camaldulensis, poplar spp.
- The wood portion which is in the center which is darker, older and harder is heartwood
- The main function is the mechanical support
- The portion in wood: the inner portion
- Function: mechanical support
- Color: dark, dull
- Durability: more because of dead cells and toxic material
- Strength: more
- Permeability: less
- Tissue: dead tissues
- Cell size: smaller
- Density: more
- Cell content: more lignin content
- Insulator: don’t allow the electricity to pass
- If heartwood portion is more than wood can be used for construction purposes.
A series of cells to form an articulated (connected to a joint) tube-like structure of intermediate length, each segment is called vessel member.
Purpose of Vessels:
Conduction of water in hardwoods
Vessels may be of various shapes, drum-shaped, ring-shaped, oblong, barrel-shaped, etc. in cross-section vessels are also of various shapes like oval, circular, angular.
Vessels also vary in diameters, smallest 20 microns (one-millionth of a meter) and largest 300 microns.
Opening from one vessel segment to other is called perforation plate. Perforation plates are of following types:
Simple Perforation Plate:
The open end of vessel member is called simple perforation plate eg populus.
With the multiple elongated and parallel perforation eg Betula.
With small and large parallel perforation eg Virola.
Pits occurring in longitudinal walls vary in size and shape but smaller than in softwood tracheids.
The arrangement of Pores:
When the secondary wall is laid down by protoplast, gaps are left to interchange the material b/w the cells. These gaps are known as Pits.
Pits rarely occur solitarily. A complementary pit is formed already opposite on the other side of the middle lamella in the contiguous (adjoining) cells and a pit pair is formed. In this way communication b/w the cells are greatly facilitated.
Parts of Pits:
The gap in the secondary wall is the pit cavity. The depth of the pit cavity is varied according to the thickness of the secondary wall.
Membrane closing the pit is the pit membrane. It is composed of intercellular substances holding the two cells.
Inner pit aperture:
The opening of the pit into the lumen of the cell is called the inner pit aperture.
Outer pit aperture:
The opening from the lumen into the chamber of the pit is called out pit aperture.
Sometimes the margin of the pit membrane becomes thickened. This thickened portion is known as pit annulus.
When the central portion of the pit membrane is thickened, the pit is said to be a tours. When torus is present bordered pit appears to be consisting of tree circle in surface view.
Unthickened portion ground the torus is called closing membrane.
Kinds of Pits:
When the pit cavity progresses from the pit membrane to cell lumen remain constant in width. Generally found in parenchyma cells. (see above fig)
Pit with an overhanging margin ie pit in which the cavity becomes abruptly constricted during the thickening of the secondary wall (see above fig). Bordered pits are of further following types:
- Half bordered pit
- Scalariform pit
- Vesturated pit
A pit without a complimentary pit in an adjacent cell called blind pit.
A cell in the trachea of conifers and other gymnosperm plants, with bands of lignin thickening the cell walls and adding structural support. Tracheid is a wood cell without end perforation as in the vessel, conducting and to some extent mechanical functions are performed by tracheid.
Tracheids are polygonal, rectangular, hexagonal, etc in cross section. Tracheid is extremely liner cell 75 to 200 times as long as wide, taper to a blunt end. The long axis is directed along the grains.
Tracheid varies in length, thickness, and breadth according to its position and spp:
Thickness … radial direction
Breadth ……Tangential direction
According to the position, tracheids are to two types:
- Earlywood or springwood tracheids
- Latewood or summer wood tracheids.
Types of Tracheids:
A tracheid resembling in form and position a small vessel member but without end perforation.
A short irregularly formed tracheid in the immediate proximity of a vessel member.
Typically as a fibrous cell, thick-walled with tapering ends and small bordered pits.
A storied or tired arrangement of wood rays or other wood elements like a vessel, parenchyma cells or fibers, produce on the tangential surface fine horizontal lines or band across the grain are called as ripple marks.
An elongated cell with pointed ends and a thick or not infrequently a thin-walled included gelatinous fiber and libriform fiber. It is only formed in hardwood only.
Fibers may separate eg in many generals of Meliaceae family. The septa do not include the middle lamella. Protoplast divides after the formation of the secondary wall dividing the cell in a number of compartments. The septa or cross walls are thin and unpitted.
Gelatinous fibers are also present in certain woods having an unlignified inner wall with a gelatinous appearance. Fiber tracheids have greater dia than libriform fibers.
Having simple pits smaller in size than fiber tracheid, more mechanical in nature, narrower lumened and thick walled than fiber tracheid may be gelatinous as in Mulberry and septate like fiber tracheid.
Tissue consisting of short, relatively thin-walled cells with simple pits, convened with storage of food material and its distribution
Parenchyma occurring in xylem should be strictly called wood or xylem parenchyma and in phloem as phloem parenchyma.
Types of Parenchyma:
- Longitudinal or axial parenchyma: Directed along the grain.
- Transverse or ray parenchyma: Extended across the grain.
The arrangement of Parenchyma:
- Apo tracheal parenchyma: Not associated with pores
- Para-tracheal parenchyma: Associated with pores.
Ray is defined as the ribbon-like aggregate of parenchyma cells radiating from center to periphery. Ray initials and extends radially in the xylem and phloem.
Classification on the basis of Size:
- Very broad
- Extremely broad
Rays can be:
- Uniseriate: One cell wide
- Biseriate: Two cells wide
- Triseriate: Three cells wide
- Multiseriate: Many cells wide
Classification on the basis of types of cells:
- Homocellular ray: Ray composed of one type of cells.
- Heterocellular ray: A ray composed of cells of different types.
The arrangement of Rays:
- Storied: When rays are arranged in tiers or in echelon as seen in tangential section.
- Non-storied: When rays are arranged in an alternate position to each other as seen in tangential section.
A sac that forms in the water-conducting vessels of the older wood of a tree, often in response to drought or disease. Tylosis may cause blockage, and often filled with resins, gums, or pigments that may help to preserve, strengthen, or color the wood or provide a source of dyes.
The proliferation of the protoplast of a living cell through a pit pair into the cavity of a vessel segment is called tylosis. The cause of formation of tylosis is the difference in pressure existing b/w a turgid parenchyma cell with living contents and a dead vessel segment which was ceased or is about to cease function.
The membrane of the pit pair involves in the formation of a tylosis enlarged and arches into the cavity of the vessel segment: a portion of protoplast then passes into the cavity thus formed.
Sometimes many tyloses from as many pit pairs have met completely plugging the pore, and a secondary tylosis bud has formed.
Resin canals are sometimes confused with vessels. Resin canals are tubular intercellular spaces sheathed by secreting cells. Cavity and sheath cells both collectively called as Resin Canals.
Resin canal may occur vertically in the wood and horizontally in rays. Vertical canals may occur in tangential series or may be distributed in short tangential series throughout the wood or scattered singly throughout the wood.
Intercellular canals or gum ducts are produced as a result of wounding in many hardwoods and also softwoods. Such canals contain dark-colored more or less viscous gum-like deposits. In some spp traumatic canals (due to injuries) are frequently present eg deodar.
Resin canals are the common features of the wood of pine, spruce, etc. such cancels are known as normal resin canals and are larger in size ie visible to the naked eye eg chir. Whereas in kail resin canals can be seen with the hand lens in cross section. So size and type of resin canal is an important character and play role in the microscopic identification of wood. An odor of resin produced in resin canals is also helpful in identification.
The contents of canals of the Dipterocarpaceae usu consist of white or yellow solid deposits. But in Dipterocarpus spp the deposits are viscous oleo resins which tend to move over the sawn surface. This causes difficulties in painting and other finishing processes.
GRAIN, TEXTURE, AND FIGURE:
Refers to the direction of fibers or cells relative to the long axis of a tree.
Types of Grain:
- Straight grain: When fibers and other elements are parallel to the long axis.
- Irregular grain: When wood elements are at varying and irregular to the vertical axis.
- Diagonal grain: This is milling defect results from straight grained cut so that the fibers do not run parallel.
- Spiral grain: When fibers follow a spiral course in the living tree. The twist may be left or right handed.
- Interlocked grain: When fibers inclined in opposite direction producing ribbon or straight figures.
- Wavy grain: When the direction of fibers is constantly changing so that lines drawn parallel with them appear as wavy lines on the tangential surface.
Refers to the relative size and amount of variation in the size of the cells
Types of Texture:
- Uneven or coarse texture: Timbers in which some wood elements are large and some are small are said to be of a coarse texture
- Even or fine texture: When wood elements are of a generally equal size, the wood is said to be of fine texture.
Refers to the pattern produced on the longitudinal surface of the wood as a result of the arrangement of wood elements and nature of the grain
Types of Figure:
- Feedle back figures: Wavy types of grain give rise to a series of diagonal or more or less horizontal dark and light stripes on the longitudinal surface because of variation in the reflection of light from the surface of fibers. This is called Feedle back figure.
- Roe figure: When wavy and interlocked grains occur together, give rise to a bookend ripple on the quarter sawn surface called roe figure.
- Blister figure: Irregular grain give rise to blister figure.
- Ribbon or stripe figure: Interlocked grains produce ribbon or stripe figure.
- Bird eye figure: Depression in blister figure produce bird eye figure.
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NJMH is working as Deputy Conservator of Forests in Balochistan Forest & Wildlife Department (BFWD). He is the CEO of Tech Urdu (techurdu.net) Forestrypedia (forestrypedia.com), Majestic Pakistan (majesticpakistan.pk), All Pak Notifications (allpaknotifications.com), Essayspedia, etc & their YouTube Channels). He is an Environmentalist, Blogger, YouTuber, Developer & Vlogger.