Review by E.A. Wheeler, IAWA Journal vol. 25 (3)

Author

This new web site is a wonderful resource for anyone interested in the anatomy of central European woods, and, given that the genera included in this site occur elsewhere in the northern hemisphere, it will be useful outside of central Europe. 

The home page of the site states: "This Web-based identification key is a completely revised (text, key) and updated (more and new photographs and new anatomic items) version of the book by Schweingruber F.H., 1990: Microscopic Wood Anatomy; Structural variability of stems and twigs in recent and subfossil woods from Central Europe. 3rd edition 1990. Birmensdorf, Eidgen�ssische Forschungsanstalt WSL."

As you would expect, given the original publication, the images are excellent. The navigation of the site fits the definition of user-friendly. There are pages "Macroscopic characteristics" and "Microscopic characteristics" that provide an introduction to terminology, with an illustrated glossary and comments on the diagnostic value of different characteristics. There are multiple ways to get to species descriptions with 1) multiple images, particularly of transverse sections, to illustrate within species variation, 2) brief descriptions of the features visible in each plane of view, and 3) comments on diagnostic features, including comments such as "The wood of the three Quercus species (Q. robur, Q. petraea, Q. pubescens) cannot be differentiated on the basis of their wood anatomy." 

Thumbnails on the species pages are "live" and provide access to larger images. "Species list" is alphabetical by genus and species list of all species (about 130), "Coniferous wood" and "Dicotyledon wood" list species for those groups. 

The identification key is a synoptic key, with characteristics presented in tabular form. From the key you can access definitions and images for the key characters. It took me a bit time to realize that "Wood types" at the top of the key was a pull-down menu to take you to the major subdivisions within the table: Coniferous wood, Ring-porous wood, Diffuse- and semi-ring-porous wood, Diffuse- and semi-ring-porous wood with aggregate rays.

This site is valuable, as was the 1990 book, for showing both the variability of wood as well as documenting what many find an unpleasant fact, namely that many tree species share similar wood anatomy. For any one who teaches wood anatomy, this is a most useful resource. The site is a model for attractiveness and usability.

Identification key

Coniferous wood		Wood without vessels (pores), with tracheids only
	Pitting in rays	Resin canals	Transversal tracheids	Spiral thickenings in tracheid walls	Species	Key characteristics
	large (pinoid pits)	present	present	absent	Pinus sylvestris	Transversal tracheids with dentated walls, cannot be differentiated from P. mugo and P. nigra.
					Pinus mugo	Transversal tracheids with dentated walls, cannot be differentiated from P. sylvestris and P. nigra.
					Pinus nigra	Transversal tracheids with dentated walls, cannot be differentiated from P. sylvestris and P. mugo, sometimes early-/latewood transition seems more abrupt than in the two other species.
					Pinus cembra	Transversal tracheids with smooth walls, in general small growth rings, latewood zones always narrow.
					Pinus strobus	Transversal tracheids with smooth walls, in general larger growth rings, latewood zones narrow, similar to P. cembra.
	small	present	present	absent	Picea abies	Transition from early- to latewood continuous. Resin canals with thick-walled epithelial cells. Bordered pits in axial tracheids generally uniseriate.
					Larix decidua	Transition from early- to latewood abrupt. Resin canals with thick-walled epithelial cells. Bordered pits in axial tracheids often biseriate.
				present	Pseudotsuga taxifolia	Transition from early- to latewood abrupt. Resin canals with thick-walled epithelial cells. Fine spiral thickenings.
		absent	absent	absent	Abies alba	Transition from early- to latewood abrupt. In radial section the tangential ray cell walls show distinct nodular chains.
					Juniperus communis	Colored deposits in parenchyma cells, smooth walled ray cells.
				present	Taxus baccata	Distinct spiral thickenings.

	Dicotyledon wood		Wood with vessels (pores)
	Ring-porous wood
	Ray width	Perforation plates	Spiral thickenings	Species	Key characteristics
	uniseriate	simple	absent	Castanea	Latewood with dendritic pore arrangement, rarely biseriate rays.
	bi- to triseriate	simple	absent	Fraxinus	Latewood pores solitary or in small radial groups, thickwalled.
			present	Hippophaë	Ring-porous, sometimes semi-ring-porous, rays generally storied.
	3- to 5-seriate	simple	present	Ulmus	Pores, vascular tracheids and parenchyma in latewood in tangential to slightly oblique bands.
				Robinia	Pores, vascular tracheids and parenchyma in latewood in clusters to short bands, conspicuous tyloses.
	>5-seriate	simple	absent	Vitis	In the narrow latewood pores in radial files and small groups. Rays very wide. Vessels with scalariform pits.
			present	Clematis	Latewood generally narrow, growth ring boundaries festoonlike, large rays.
				Berberis	Ring-porous to semi-ring-porous, latewood pores and vascular tracheids in clusters with a tangential to diagonal or dentritic orientation.
				Laburnum	Growth ring boundaries festoonlike, rays often over 5 cells wide, gum deposits in the heartwood vessels.
				Ailanthus	Often slightly oblique to tangential parenchyma bands, often indistinct ring-porous, variable.
	uni- and multiseriate	simple	absent	Quercus	Dendritic pore groups in the latewood, uniseriate and very broad rays.
			present	Rosa	Broad rays often over 10 mm high.

	Diffuse- and semi-ring-porous wood
	(uniform distribution of pores)
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	uniseriate	homo- geneous	simple	absent	Populus	Large and simple ray-vessel pits.
				present	Aesculus	Pores solitary or in radial rows of two to some pores.
					Euonymus	Numerous small pores.
			scalariform	absent	Alnus viridis	Pores in radial multiples, rarely in clusters, scattered.
					Alnus glutinosa Alnus incana Corylus	See aggregate rays.
					Betula nana Betula humilis	Extremely small numerous ray-vessel pits, occasionally bi- to 4-seriate rays.
		hetero- geneous	simple	absent	Salix	Large and simple ray-vessel pits.
				present	Daphne	Pores loosely packed in dendritic patterns.
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	bi- to tri- seriate	homo- geneous	simple	absent	Juglans	Pores large, infrequent, solitary or in radial rows of 2 to 4 cells.
				absent to (sometimes: occasionally) present	Maloideae: Amelanchier, Cotoneaster, Crataegus, Cydonia, Mespilus, Pirus, Sorbus	Numerous to very numerous small pores, often indistinctly semi-ring-porous, occasionally with fine spiral thickenings.
				present	Hippophaë	Generally semi-ring-porous, sometimes ring-porous, rays generally storied.
					Acer	Pores widely spaced, solitary or in radial files of 2 to 3 pores.
					Prunus	See 3- to 5-seriate rays, slightly heterogeneous.
					Tilia	Vessel outlines angular, radially orientated pore files and clusters. Rays flare along growth ring boundaries.
			scalariform	absent	Betula	Extremely small numerous ray-vessel pits, scattered pores in radial files of 2 to 4, or clusters.
		hetero- geneous	simple	present	Frangula	Generally semi-ring-porous, pores rather widely spaced, especially in latewood.
					Lonicera	Multiseriate rays conspicuously heterogeneous with numerous rows of square and upright marginal cells.
					Ligustrum	Rays often with 1-2 (4) rows of square and upright marginal cells.
					Ostrya	Pores infrequently, in radial multiples of 2 to 10 pores.
					Prunus	See 3- to 5-seriate rays, slightly heterogeneous.
					Sambucus	See 3- to 5-seriate rays.
			scalariform	absent	Buxus	Narrow pores, round to oval scalariform perforation plates with mostly <10 bars.
					Viburnum	Rays conspicuously heterogeneous, perforation plates scalariform with >20 bars.
					Cornus	Rays markedly heterogeneous, more likely 3- to 5-seriate, scalariform perforation plates with many bars.
				present	Viburnum	Rays conspicuously heterogeneous, perforation plates scalariform with >20 bars. Fine spiral thickenings in the fibre tracheids: Viburnum lantana.
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	3- to 5- seriate	homo- geneous	simple	absent	Juglans	Pores large, infrequent, solitary or in radial rows of 2-4 cells.
				present	Prunus	Diffuse-porous to semi-ring-porous, pores solitary or in radial rows of two to some cells or in clusters, gum deposits in heartwood vessels. Rays in some species frequent >5-seriate.
					Acer	Pores widely spaced, solitary or in radial files of 2 to 3 pores.
					Tilia	Vessel outlines angular, radially orientated pore files and clusters. Rays flare along growth ring boundaries.
			scalariform	absent	Betula	Extremely small numerous ray-vessel pits, scattered pores in radial files of 2 to 4, or clusters.
		hetero- geneous	simple	absent	Sambucus	Pores in clusters, mostly marginal bands of thin-walled vascular tracheids. Rays with sheath cells.
				present	Prunus	Diffuse-porous to semi-ring-porous (P. armeniaca to ring-porous), pores solitary or in radial rows of two to some cells or in clusters, gum deposits in heartwood vessels. Rays in some species frequent >5-seriate.
			scalariform	absent	Cornus	Rays markedly heterogeneous, 3- to 5-seriate, scalariform perforation plates with many bars.
				present	Ilex	Pores small, in long radial files, rays often up to 4mm high.
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	> 5-seriate often or predomi- nantly	homo- geneous	simple	absent	Fagus	Diffuse- to semi-ring-porous, rays very large, perforation plates both simple and scalariform.
					Platanus	Similar to Fagus, more often large rays, pits in vessel walls in horizontal rows.
					Hedera	Pores in clusters, predominantly tangentially orientated.
				present	Clematis	Very large pores, see ring-porous wood.
					Berberis	See ring-porous wood.
			scalariform	absent	Fagus	Diffuse- to semi-ring-porous, rays very large, perforation plates both simple and scalariform.
					Platanus	Similar to Fagus, more often large rays, vessel pits opposite, in horizontal rows.
		hetero- geneous	simple	absent	Hedera	Pores in clusters, predominantly tangentially orientated.
					Vitis	See ring-porous wood.
			scalariform	present	Ilex	Pores small, in long radial files, rays often up to 4mm high.
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	uniseriate and/to multiseriate	homo- geneous to hetero- geneous	simple	absent	Fagus	Diffuse- to semi-ring-porous, rays very large, perforation plates both simple and scalariform.
					ClematisQuercus  Fraxinus	Ring-porous wood with very narrow rings appears sometimes similar to diffuse-porous wood, see ring-porous wood.
				present	Rosa	Ring-porous wood with very narrow rings appears sometimes similar to diffuse-porous wood, see ring-porous wood.
					Prunus	Diffuse-porous to semi-ring-porous (P. armeniaca to ring-porous), pores solitary or in radial rows of two to some cells or in clusters, gum deposits in heartwood vessels.
			scalariform	absent	Ribes	Rays often with sheath cells.
				present	Fagus	Diffuse- to semi-ring-porous, rays very large, perforation plates both simple and scalariform.

	Diffuse- and semi-ring-porous wood with aggregate rays
	(uniform distribution of pores)
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	uniseriate and irregularly multiseriate	homo- geneous to hetero- geneous	simple	present	Carpinus	Pores in long radial files.
			scalariform	absent	Alnus glutinosa	Pores in radial multiples, perforation plates with generally more than 10 bars.
					Alnus incana	Cannot be differentiated from A. glutinosa.
					Corylus	Pores in radial multiples, often in dendritic arrangement, perforation plates with 5 to 10 bars.
				present	Corylus	Fine spiral thickenings are frequent.
	Diffuse- and semi-ring-porous wood, dendritic groups of pores
	Ray width	Ray type	Perforation plates	Spiral thickenings	Species	Key characteristics
	2- to 3- seriate	homo- geneous to hetero- geneous	simple	present	Rhamnus	Dendritic pore distribution.
					Daphne	Pores loosely packed in a dendritic pattern.
	Diffuse- and semi-ring-porous wood, pores hardly differentiable from axial and ray parenchyma
					Species	Key characteristics
					Viscum album	Vessels, parenchyma and growth ring boundaries indistinct.

Macroscopic characteristics

	Recent wood can often be identified by macroscopic characteristics, particularly by colour, gloss, odour, weight and structure. As such characteristics are generally modified or destroyed in fossil, historic or carbonized wood, only a few species or species groups of the indigenous flora can be identified with the naked eye or only with the aid of a magnifier (5 to 20x).
	Coniferous wood In coniferous wood it is possible to distinguish the species which have resin canals from those which do not. The transition from earlywood to latewood can be sharp or continuous.		Ring porous dicotyledonous wood The diameter of the pores in the earlywood is much greater than the diameter of the pores in latewood. Arrangement and size of pores in the latewood, fine and large rays can be differentiated.		Semi-ring to diffuse porous dicotyledonous wood In semi-ring porous woods, the pores are more numerous in earlywood, in diffuse porous woods the size of pores and distribution is more regularely. Arrangement and size of pores, fine and large rays differ from species to species.

	An identification key based on macroscopis characters is not given here as it exits e.g. In Bosshard (1974/75) or Gottwald (1958).

Preparation of wood for microscopic examination

Recent, healthy wood | Secondary wood modifications

	Recent, healthy wood
	Preliminary preparation Cut samples to a radial thickness of 1cm. Split samples with a blunt knife along the radial and tangential planes so as to make blocks approximately 8 x 8 mm. Precise anatomical orientation facilitates microtome sectioning. Softening and embedding Dry wood of average hardness can be softened by immersion in boiling water for 1-2 hours (marked with a soft pencil) or in a mixture of 96% alcohol, water, and glycerin in volume proportions 1:1:3. Wood from living trees can be sectioned without softening. Tender and heterogeneous tissues (e.g. bark-cambiumwood) are embedded in carbowax before cutting. Water saturated wood is immersed in a series of Polyethelene 5000 solutions (progressively 30, 60, 100%) and left in each solution for 24 hours. Since PEG is soluble in water, glycerine is used as the lubricant for microtoming. Sectioning Hand microtome: The fine sectionsthus obtained are sufficient for microscopic observation but not for photography. Sliding microtome: With this type of microtome one can produce good sectioned cuts of all the indigenous species. (All the sections presented in this book were cut with a Reichert sliding microtome.) Only wedge-shaped blades which are very sharp produce good sections. A blade is sufficiently sharp when it can cut a hair held in the hand. A perfect blade sharpness is indispensible for the production of thin sections of coni- ferous wood in which the secondary cell wall tends to detach from the primary wall. In our laboratory, the best results have been obtained with American Optical knives sharpened on an American Optical Knife Sharp- ener. Much practice is necessary to make good sections; however, some general guidelines can be indicated. The knife blade and the cutting surface should form an angle of approximately 15° for hardwood and approximately 8 ° for softwood. For wood of heterogeneous density (e.g. larch) approximately only half of the cutting edge of the knife is used to obtain a cut of 0.5 mm in width. The optimal thickness of thin sections: Transversal sections: 15µ in general; 10µ for species with small pores. Radial sections: 15µ for the structure of ray walls; 25µ for the perforation and spiral thickenings. Tangential sections: 15µ. Staining Processes For the study of normal cell structure, the cellular content is destroyed before the section is embedded. Safranin is an easily used stain. Preliminary preparation Immerse in javel water for 15-30 minutes Rinse with water 2-3 times until the odor of the javel water disappears Stain with a solution of 1% safranin for 3-5 minutes Rinse once with water Rinse once with 50% alcohol Rinse with 96% alcohol 2-3 times until the excess stain disappears Rinse once with 100% alcohol Immerse in xylol. If the liquid is murky, rinse again with 100% alcohol Mount in Caedax (synthetic resin) Apply approximately 50 gr. of pressure on the coverslip and harden the resin by drying in a 50-60°C oven for 24 hours. If heartwood is present, the wood is often not stained. In that case, the preparation process begins with the first rinsing with 50% alcohol. Possible difficulties: Frequently the sections roll and it is difficult to flatten them. This can be avoided by pressing on the sample being cut with a paint brush above the microtome blade. The section is placed in glycerine on an object slide, covered with a coverslip, rapidly passed through a flame. To flatten rolled sections, place a point of a pair of conical pincettes in the opening of the stained, rolled sections. Carefully advance the section on the flat back of the pincettes and pour first 100% alcohol over the section and then xylol. The section is then mounted in Caedax on a slide.
	Secondary wood modifications
	Wood attacked by fungi The preliminary preparation and sectioning of the samples is the same as for recent, healthy wood. Staining The thin sections are stained with safranin and picric acid-anilin blue. The sections are dipped for a short time in an aqueous 1% solution of safranin. Excess stain is washed off with water. The section is placed in a drop of picric acid on a slide and heated over a flame to boiling. Next, the section is immersed in a series of progressively increasing concentrations of alcohol and finally in xylol. The section then is mounted in Caedax. (Picric acid-anilin blue: 25 ml of aqueous, saturated anilin blue and 100 ml of aqueous, saturated picric acid.) Subfossil, uncarbonized wood Hand cut sections are made with razor blades which have very hard butting edges. Wood which is slightly compressed may be inflated and cleaned with javel water so that the normal cellular structure can be observed. The identification is done without staining. A phase-contrast microscope is valuable for the observation of fine structures. In order to detect the presence of bacteria, actinomyces and hyphae of fungi, the sections are colored with anilin blue and picric acid. In general, only sections prepared with a microtome can be photographed. The sections are embedded in paraffin and colored with safranin. Charcoal The identification of charcoal requires reflected light. All the characteristics are observed on fractured surfaces. Before examining a sample with a stereoscopic dissection microscope, a fracture is made so as to obtain a transversal surface. If it is necessary to examine longitudinal characteristics, the sample is split with a scalpel under a stereoscopic microscope along radial and tangential planes. The small fragments are to be placed horizontally on a piece of wax on a slide. They are examined under a reflected light microscope with a magnification range between 100-400 X. Reflected light, however, is not convenient for photography and usually the sample must be embedded in plexiglas and cut with a microtome. Procedure Air dried samples are broken along the major orientation planes so as to obtain cubes having 6-8 mm edges. The cubes are soaked twice for 3-4 days in absolute alcohol. (if a sample does not sink in the alcohol, the air can be extracted in a vacuum tube.) The cubes are placed for a duration of two weeks in methy 1-metacry late (pure metacrylic acid-methylic ester with 1% hydroquinone) with activating agent 50% 2.4 dichlor-obenzol-peroxide in a softening agent (product of Flucka, Buchs SG, Switzerland). The solution is replaced after one week. The samples are then placed in gelatine capsules filled with methyl-methacrylate and closed. The capsules are polymerized at 35°C in a vacuum for 2-3 days. The presence of air bubbles in the sample blocks is a consequence of incomplete dehydration, insufficient extraction of air, or excessive heating during polymerization. A block is fixed on the microtome and a preliminary cut is made to prepare the surface for sectioning. A piece of self-adhesive tape is attached to the sectioning surface and when the knife is activated 15 microns below the tape, the sections adhere to the tape. The sections are unglued from the tape with a couple of drops of glycerine and placed on a slide.

Glossary & Links

	Glossary
	English and French glossary of wood (Faculté de foresterie et de géomatique, Université Laval, Québec, Canada) sylva.sbf.ulaval.ca/foret/glossAnat/index.html
	English glossary (School of Biological Sciences, The University of Sydney) BUGS.bio.usyd.edu.au/2003A+Pmodules/glossary.html
	English glossary (Biological Sciences Center,University of Rhode Island) www.uri.edu/cels/bio/plant_anatomy/glossary.html
	Multilingual glossary of dendrochronology (WSL, Switzerland) www.wsl.ch/dbdendro/glossary/index_EN
	Links
	Forest Products Laboratory www2.fpl.fs.fed.us/
	IAWA International Association of Wood Anatomists www.iawa-website.org

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