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Forestry 240

Lecture 5 – Hardwood Anatomy

Softwood vs. HardwoodStructure

• CONIFERS / SOFTWOODS– Conduction Longitudinal tracheid– Support Longitudinal tracheid– Storage Parenchyma (ray)

~10%– Rays always narrow

• DICOTYLEDONS / HARDWOODS– Conduction Vessel element– Support Fibers– Storage Parenchyma– Rays short & narrow to wide & tall,

varies by species

Hardwoods versus Softwoods• Hardwood ray widths vary within and between

species.

Hardwoods versus Softwoods• Straight radial rows of cells characterize softwoods,

but generally not hardwoods.• Softwood cells are aligned in straight radial rows in

parallel form, with straight spoke-like rays, each rowof cells is formed by a single fusiform initial in thecambium

• Hardwood rays are seldom aligned in straight radialrows. Deviations occur in the vicinity of large vesselelements.

• After formation, vessel elements may expand 2 to 50times their original diameter, pushing other cells outof radial alignment.

Hardwoods versus Softwoods Hardwoods versus Softwoods

• Hardwood fibers areshorter than softwoodtracheids.– Softwood tracheids are

preferred for paper, sincelonger fiber length isimportant for paperstrength.

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Hardwood versus Softwood

• The terms “hardwood” and “softwood” haveno relevance to the actual hardness of thewood produced.

• Many softwoods produce wood that is harderand denser than wood produced by somehardwood.

Hardwood Cell Types – Vessels(Pores)

• Vessel – articulated, tube-like structure of indeterminatelength in porous woods; formed through the fusion of thecells in a longitudinal row and perforation of commonwalls in a number of ways.

• Vessel Element – one of the cellular components of avessel.

• Vessel elements link end to end along the grain to formvessels.

• Vessels are not arranged in precise parallel and verticalalignment.

• This arrangement ensures that each branch of the crownreceives water from many different roots, providing asafety feature against crown damage from root damage.

Ring Porosity• Ring-Porous Wood –

porous wood in whichthe pores formed at thebeginning of the growingseason (in the earlywood) are much largerthan those farther out inthe ring, if the transitionfrom one to the othertype is abrupt.

Ring Porosity

• Diffuse-Porous Wood – ahardwood in which thepores exhibit little or novariation in size within agrowth ring, as viewed in across section.– The majority of hardwoods

are diffuse-porous.

Ring Porosity

• Semi-Ring-PorousWood – woodintermediate betweendiffuse-porous and ringporous wood.

Pore Arrangement• Solitary pore – a single pore that does not

touch any others.

Maple (Acer spp.)

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Pore Arrangement• Pore Multiple – two or more pores come in

contact with one another, typically, in radialalignment.

Jelutong (Dyera costulata)Cottonwood (Populus deltoides)

Pore Arrangement• Pore Chains – A distinct radial series or

alignment of several to many solitary pores orpore multiples.

Holly (Ilex spp.)

Pore Arrangement• Nested Pores (clusters) – Pore multiples

where larger numbers of pores contact oneanother both radially and tangentially.

Kentucky Coffeetree (Gymnocladus dioicus.)

Pore Arrangement• Wavy Bands (ulmiform) – Pores arranged in

undulating bands approximately parallel to thegrowth rings, characteristic of elm andhackberry.

American Elm (Ulmus alata)

End to End Vessel Connections• One of the primary functions of vessels are as

avenues of conduction• Common end walls of longitudinally linked vessel

elements are perforated by unrestricted holes.• These perforations form in the perforation plate near

the end of the cell maturation process, as certainenzymes dissolve portions of the perforation plate.

• These perforations vary in appearance:– Simple– Scalariform– Foraminate

Simple Perforation• A single and

usually large andmore or lessrounded openingin the perforationplate.

• Best viewed intangential section

American Basswood (Tiliaamericana)

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Scaliform Perforation Plate• A perforation

plate withmultiple elongatedand parallelperforations, withbar-like remnantsof the platebetween openings.

• Best viewed inradial section

Red Alder (Alnus Rubra)

Foraminate (Reticulate) PerforationPlate

• A multipleperforation plate,with netlikeappearance.

Sparkleberry (Vaccinium arboreum)

Intervessel pitting• Pitting between

adjacent vesselelements

• When vesselsare in multiples,there will bebordered pitsalong theircommon walls.

Populus spp.

Intervessel Pitting Arrangement• Alternate Pitting – pits that are crowded

together resulting in an irregular ordiagonal arrangement.

Aspen Yellow-Poplar Magnolia

Intervessel Pitting Arrangement• Opposite Pitting – short rectangular or

slightly rounded pits in distinct horizontalarrangement.

Aspen Yellow-Poplar Magnolia

Intervessel Pitting Arrangement

• Scaliform Pitting – Elongated bar-like pitsin parallel, ladder-like arrangement

Aspen Yellow-Poplar Magnolia

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Tyloses

• Saclike or cystlike structures that sometimes developin a vessel and rarely in a fiber through theproliferation of the protoplast of a parenchyma cellthrough a pit pair.

• They commonly form in hardwoods as a result ofwounding and effectively act to prevent water lossfrom the area around damaged tissues.

• They may also develop as a result of infection fromfungi or bacteria, again to prevent water loss.

Tyloses• Bubble-like

structures thatform in thevessel elementsof certainhardwoodspecies, usuallyin conjunctionwith heartwoodformation.

Black locust

Tyloses• Tyloses partially or

completely block thevessels in which theyoccur.– This makes species like

white oak preferred in themanufacture of barrels,casks, and tanks.

– This makes white oakdifficult to dry orimpregnate with decay-preventive or stabilizingchemical.

White Oak

Which one is White Oak?

A B

Vasicentric Tracheids

• Short, irregularly shaped fibrous cells withconspicuous bordered pits; vasicentrictracheids abound in the proximity of the largeearly-wood vessels of certain ring-poroushardwoods; they differ from vascular tracheidsnot only in shape but in arrangement (they arenot arranged in definite longitudinal rows likevascular tracheids).

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Vasicentric Tracheid• Forms a light colored tissue seen with hand

lens.

Fibers• An elongated cell

with pointed endsand a thick or notinfrequently thinwall, Includes:– Fiber tracheids with

bordered pits.– Libriform fibers with

simple pits.

Fibers• Hardwood fibers are similar to softwood

tracheids with these differences:– Hardwood fibers are rounded in cross section

compared to the nearly rectangular shape ofsoftwood tracheids.

– Fibers are typically thick walled and have borderedpits with less-developed borders than softwoodtracheids.

Fibers

• Fibers appearas dark masseswhen viewedwith a handlens

Fiber Functions• Softwood tracheids are responsible for conduction

and wood strength.– Thin walled early wood tracheids result in low wood

strength compared with latewood.• In Hardwoods vessel elements are responsible for

conduction, while the thick-walled fibers areresponsible for mechanical support.

• Density and strength of hardwoods is more related tothe portion of wood volume occupied by fibersrelative to that accounted for by vessels than withsoftwoods

Parenchyma

• Parenchyma cells arethin-walled storageunits.

• In hardwoods,parenchyma is long,tapered longitudinalcells, brick shapedepithelium around gumcanals, and ray cells.

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Parenchyma

• Paratracheal Parenchyma – axialparenchyma the cells of which are obviouslyassociated with the vessels (pores in crosssection)

• Apotracheal Parenchyma – axialparenchyma cells which are separated from thepores by rays or fibers.

Apotracheal ParenchymaArrangement

• Diffuse parenchyma – single, isolatedapotracheal parenchyma. Typically cannot beseen without a microscope.

Apotracheal Parenchyma Arrangement• Diffuse-in-Aggregates

Parenchyma – apotrachealparenchyma occurring in shorttangential lines. Seen with amicroscope in basswood andbirch, visible with hand lens inblack walnut and butternut.

Paratracheal Parenchyma Arrangement

• Paratracheal Scanty – single, isolated cells ofparatracheal parenchyma. Cannot be seen withhand lens magnification.

Paratracheal Parenchyma Arrangement• Paratrachael vasicentric

– parenchyma cellsnumerous enough to forma complete or partiallycomplete sheath around apore.

White Ash

Paratracheal Parenchyma Arrangement• Aliform Parenchyma –

Vascentric parenchymathat occurs in a well-developed layer withadditional cellsforming tangentialwing-like extensionson either side.

Ramin

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Paratracheal Parenchyma Arrangement• Paratracheal Confluent

– Parenchyma that forms acontinuous tangential ordiagonal zone connectingtwo or more pores.

Honeylocust

Paratracheal Parenchyma Arrangement• Marginal Parenchyma

– parenchyma occurringat the growth-ringboundary, sometimescalled initial or terminalparenchyma.Conspicuous in yellow-poplar and Americanmahogany.

Yellow-poplar

Paratracheal Parenchyma Arrangement• Banded parenchyma – distinct

tangential lines of cells, usuallyoccurring with fairly regularspacing.

• Reticulate parenchyma – linesof banded parenchyma join withray lines of approximately thesame width to from a mesh ornet-like pattern – hickory andpersimmon.

Hickory

Strand Parenchyma

• Axial Strand Parenchyma – cells of axialparenchyma arranged in a row along the grain;such a row is formed through further(postcambial) division of a single axial(longitudinal) cell cut off from a fusiforminitial in the cambium.

Crystals• Deposits of crystalline or gummy deposits

found in parenchyma cells, useful fordifferentiating black walnut from butternut andEnglish walnut.

Rays

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Ray Width

• In Hardwoods, Raysmay be:– Uniserate – one cell

wide– Biserate – two cells

wide– Multi-serate – many

cells wide.• Ray width varies

between and withinspecies.

Sugar Maple

Hardwood Ray Parenchyma Cells

• Softwoods rays may contain ray tracheids aswell as ray parenchyma, where hardwood raysconsist entirely of ray parenchyma cells.

• There are two types of ray parenchyma cells inhardwoods.

Ray cells• In radial view,

procumbent ray cellsare elongatedhorizontally.

• Upright ray cells areeither squarish orvertically oriented

Yellow-poplar

Heterocellular• Hardwood rays that

contain both upright andprocumbent ray cells arecalled heterocellular orheterogenous, where theupright cells are usuallylocated in one or morerows along the marginsof the rays.

Yellow-poplar

Homocellular

• Homocellular or homogenous rays arecomposed of only one type of cells,typically only porcumbent cells.

Node Rays• Rays that swell at the growth-ring boundary.

Beech

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Ray Width Comparisons• Comparing ray with to pore diameter quickly distinguishes

species, like maple (the largest rays are about the same widthas the largest pores) and birch (the largest rays are narrowerthan the largest pores).

birch maple

Widest ray is narrower than largest pore

Birch

Widest rays are about the same as thelargest pores

Maple – Diffuse porous or ring porous?

Rays

• Ray Fleck – portion ofray as it appears on thequarter surface

Aggregate Rays• Composite structure,

consisting of anumber of small rays,fibers, and sometimesalso vessels, which tothe unaided eye or atlow magnificationappears as a singlebroad ray.

Storied Rays

• Rays arranged intiers or in echelons,as viewed on atengential surfaceor in a tangentialsection, formingripple marks

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Ripple Marks

• Striations acrossthe grain on thetangential surfaceof a wood,occasioned bystoried rays or bythese and otherstoried elements.

In Summary

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