Identification of Timbers using Wood Microstructures.

 

*Ajuziogu, G. C.,Uju, G. C.and Nzekwe, U.

Department of Botany, Faculty of Biological Sciences, University of Nigeria, Nsukka, Enugu, Nigeria

*Corresponding Author E-mail: papagodswill@yahoo.com

ABSTRACT:

The wood microstructure of seventeen timbers of Nigeria were studied and their characteristic features used in the construction of a dichotomous key for their separation and identification. Pairs of contrasting features such as distinct and indistinct growth layers; wide and narrow vessel diameters; wide and narrow ray widths in the transection;   apotracheal and paratracheal axial parenchyma; presence and absence of tyloses, homocellular and heterocellular ray  types were prominent among the features studied. Based on these features observed, a comprehensive indented key was constructed for the separation and identification of the timbers.

 

KEYWORDS: Identification; Wood microstructure.


 

INTRODUCTION:

Quite often after the logging and sawing operations have removed the morphological and floral characters normally used in the taxonomic identification of tree species (Hutchchinson et al., 1958; Keay et al., 1964; Desch and Dinwoodie, 1981 and Haygreen and Bowyer, 1996), the sawn timber can be misidentified by dealers and sold to consumers with serious consequences. Thus Gmelina wood could be sold as teak and erroneously used as such in the construction where teak is recommended. Misidentification of small sized woody materials could also have far reaching implications in pharmaceutical and forensic investigations. In all circumstances really, misidentifications ought to be avoided.

 

Solution to the problem of misidentification of sawn timber and wood material outside the forest in the advanced worlds has relied on microscopic studies of the wood and the use of their contrasting characteristics features to identify the wood from the key provided. Many authours have indicated that the following contrasting anatomical characters are useful in key preparation and wood identification (Jane, 1962; Titmuss, 1971; Metcalte and Chalks, 1983 and Mellerowiez, et al, 2001).

 

These features include the presence of distinct or   indistinct growth layers, the presence or absence of specific wood elements such as vessel members, fibres or treacheids, the porous features of the growth layers in transerves view, (diffuseporous, semi-ringporous or ring-porous patterns of vessel lumen distribution within the growth layers), the presence or absence of tyloses in vessel lumen, presence or absence of organic deposits in vessel lumen. Other important considerations refer to the rays which may be exclusively, predominantly or entirely narrow or wide in T.S; uniseriate, biseriate or multiseriate, storeyed or non-storeyed in T.L.S. and which may also be homocellular or heterocellular in R.L.S. The axial parenchyma abundance and distribution in transverse section are also relevant. Axial parenchyma may be abundant or scanty and its distribution in transverse sections consists of paratracheal and apotracheal forms and their subdivisions.

 

The present study is designed to determine the anatomical differences in seventeen timbers of Nigeria and to apply use these in the construction of a dichotomous key for identification for the timbers.

 

MATERIALS AND METHODS:

Seventeen accurately identified timber samples were procured from the Forestry Department of Enugu, Anambra and Abia states of Nigeria. The names of the timber and their families are given in Table 1.

 

Small blocks of wood samples from the 17 species were fixed in FAA (Formalin -Aceto-Alcohol), to preserve the wood and soften the blocks for easy sectioning with the sledge microtome (Purvis, 1964).

 

Sections of about 25nm thick were cut from the wood of each species in the transverse (TS), the tangential longitudinal (TLS) and in the radial longitudinal plane (RLS). Three petri-dishes were provided for each timber species, and the various sections temporarily stored in distilled water as temporary sections. Microscopic examinations were made on the sections by staining with phloroglucinol and cone. Hydrochloric acid to make the lignified tissues red. Some sections were stained with iodine solution.

 

Table 1: The timber species and their families Species Families

1.

Alstonia booneifte wild

Apocynaceae

2.

Ceiba pentandra (Linn.) Gaerth.

Bombacaceae

3.

Canarium schweinfurthii Engi.

Burseraceae

4.

Terminate superba Engl and Diels

Combretaceae

5.

Diospyros mespiliformis Linn.

Ebenaceae

6.

Afzelia africana sm.

Fabaceae-Caesalpinoidae

7.

Berlinia auriculata (Benth)

Fabaceae-Caesalpinoidae

8.

Brachystepia nigerica Hoyle and A. P. D. Jones

Fabaceae-Caesalpinoidae

9.

Detarium microcarpum Guil. And perr.

Fabaceae-Caesalpinoidae

10.

Gossweilerodendron balsamiferum (verm) Harms

Fabaceae-Caesal pi noidae

11.

Periscopsis elata

Fabaceae papilionoidae

12.

Khaya ivorensisk. Chev.

Meliaceae

13.

Antiaris toxicaria var. africana

Moraceae

14.

Milida excelsa (Welw.) CL Berg

Moraceae

15.

Mansonia altissima A. Chev.

Sterculiaceae

16.

Triplochiton sdervxylon. K schum

Sterculiaceae

17.

Gmelina arborea Roxb.

Verbenaceae

 

 

Permanent slides were made after proper staining protocol using safranine and fast-green. Canada balsam was used as the mountant as outlined by Sass (1958). For each of the 17 timber species, the three planes of sectioning were represented.

 

The vessel diameters of the various wood species were measured with the aid of a calibrated ordinary light microscope. A total of thirty measurements were made for each species and their means calculated.

 

The following anatomical features were observed from the T.S, TLS and RLS of the timber species.

a.     The nature of the growth ring layer - in this regard growth layers were grouped as distinct when there is a sharp contrast between the early wood and latewood elements.

b.     Vessel diameter in the radial direction from the TS - In this regard, timber species whose vessel diameters were 0.2mm and above were considered as wide, while those with less than 0.2mm were considered narrow.

c.     The ray width in the TS - In this regard species whose rays were less than 4 cells wide were separated from those whose ray cells width were 4 cells and above.

d.    Axial parenchyma form in the TS.

e.     Presence/Absence of Tyloses in the vessel pores.

f.     Ray type in the RLS - In this regard species with homocellular cell types were separated from those with heterocellular types.

RESULTS:

The wood anatomical features of the seventeen timber species as observed directly from the microscope are summarized in Table 2.

Eleven out of the seventeen timber species showed distinct growth layer. These include timbers 2, 3, 6, 8, 9, 10, 11, 12, 14, 15 and 16. The remaining six showed indistinct growth layers. These include timber 1, 4, 5, 7, 13 and 17.

 

The vessel diameters of timbers 1, 2, 3, 4, 6, 7, 8, 10, 12, 13 and 14 were found to be wide, while those of timbers 5, 9, 11,15, 16 and 17 were narrow.

 

The number of cells across the ray in the TS of the timbers species showed that timbers 1, 3, 5, 6, 7, 8, 10, 11 and 15 had less than four cells across the ray and were separated from timbers 2, 4, 9,12, 13, 14, 16 and 17 whose number of cells across the ray were four and above.

 

Twelve out of the seventeen timber species showed paratracheal axial parenchyma distribution. These were timbers 1, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 17. The other five namely timbers 2, 3, 5, 15 and 16 showed apotracheal axial parenchyma distribution.

 

Tyloses were present in timbers 1, 3, 5, 7, 9, 10, 11, 12, 14 and 15; but absent in 2, 4, 6, 8, 13, 16 and 17.

 

The ray cell type in the RLS was homocellular for eleven species. These timber species were 1, 2, 4, 6, 7, 8, 11, 13, 15, 16 and 17. On the other hand, the other six timbers showed heterocellular cell types. Table 2 gives the descriptive anatomical

 

Characteristics as observed in the seventeen timber species. From these observations, pairs of contrasting characters were selected used in the of construction of a separation/identification key (Fig.l).

 

Figure 1 gives a key to the microscopic separation/identification of the seventeen timber species on the bases of some anatomical features as observed from the sections. Table 2: Descriptive characteristic of the seventeen timber samples as observed from the

microscope in the three sections of view


 

Table 2: Descriptive characteristic of the seventeen timber samples as observed from the microscope in the three sections of view

 

Vessels

Growth ring

Rays In T.S

Axial parenchyma

Boundary

Rays in TLS

Rays in R.LS

 

 

 

 

 

 

 

 

 

 

 

 

 

Aportrachea

Paratracheal

Timber Species

Round shape

Oval shape

Diffusion poron

Ring porins

Large in radial Dir.

Medium in radial Dir.

Small in Rad. Direction

Solitary

Rad. Mul.

Tang. Clus

Tyiosis Pre.

Tyiosis Abs.

Distinct

Indistinct

Narrow 1-3 cells wide

Wide 4 cell and above

Diffused

Diff. Agree.

Concentric

Scanty

Unilateral

Vasicentric

Alifom

Alifom confluent

Banded

Initial

Terminal

Exclusive uniseriate

Pred. Multi

Storeyed

Nonstoreyed

Homocellular

heterocellular

1

+

++

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-

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2

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4

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1 Alstonia boonei  2 = Ceiba pentandra 3 =Canarium schweinfurthii 4 = Terminal superba 5 = Diospyro mespiliformis 6 = Afzelia africana   7= Berlinia auriculata 8 = Brachystagia nigerica 9 = Detarium microcapum 10= Gossweilerodendron balsamiferum 11 = Periscopsis alata   12 = Khaya ivoremsis 13 = Antiaris toxicaria 14 = Milicia excelsa  15 = Mansonia altissima 16 = Triplochiton scleroxylon  17 = Gmelina arbeorea

 

Characters present are denoted by (+) and characters absent are denoted by (-) In cases where there are presence of two contrasting characters, the predominant of the two is denoted by (++) and less characters denoted by (+). (±) Denotes equal proportion

 

Figure 1:

4.1.20. Key to Microscopic separation/identification of the timbers on the basis of some anatomical features of the transverse sections, the tangential longitudinal sections and the radial longitudinal sections

la Growth layer distinct/present..... .............................................

    2a Vessel radial diameter 0.2mm and above .................................

         3a Rays 4 cells and above wide in TS . .. .................................

              4a Axial parenchyma paratracheal.. ..................................

                    5a Paratracheal axial parenchyma of scanty type .... Khaya ivorensis

                    5b Paratracheal axial parenchyma not of scanty type .... Milicia excelsa

              4b Axial parenchyma Apotracheal.... Ceiba pentandra

         3b Rays less than 4 cells wide in the T.S,.... ..............................

                       6a Tyloses present in vessel pores .... ..........................

7a The axial parenchyma Apotracheal.... Canahum scheinfurthii

7b The axial parenchyma paratracheal.... Gossweinerodendron balsamiferum.

                       6b . Tyloses Absent in the vessel pores .... ......................

8a . Ray-tissue cells in T.L.S Exclusively uniseriate .... Brachystagia nigerica

8b . Ray-tissue cells in T.LS. not Exclusively uniseriate .... Afzelia afracana

   2b Vessel radial diameter below 0.2mm. .... .........................................

9a. The rays 4 cell and above wide in the T.S .. . Triplochiton sderoxylon

 9b. The rays less than 4 cells wide in the T.S.......

 

10a Axial parenchyma Apotracheal.... Mansonia altissima

10b Axial parenchyma paratracheal. ............

11a Paratracheal parenchyma Aliform .... Deter/urn microcapum

11b Paratracheal parenchyma not Aliform ... Periscopsis data

1b Growth layer not distinct/Absent. .. ...................................................................

                                                             12a. Rays 4 cells and above wide in T.S.. .. Gmelina arborea

                                                             12b. Rays less than 4 cells wide in T.S................

                                                                 13a. Tyioses present in same vessel pores .. . . ......

                                                                    14a. The axial parenchyma Apotracheal........

                                                                          15a. Apotracheal axial parenchyma diffused in Aggregate.Diospyros mespiliformis15b. Apotracheal axial parenchyma not diffused in Aggregate . .Alstonia boonei

                                                                    14b. The axial parenchyma paratracheal.... Berlinia auriculata

    13b Tyioses Absent in the vessel pores .... ................

16a. Aliform parenchyma coalesced into a confluent. . Antiaris toxicaria

16b. Aliform parenchyma not coalesced into a confluent.. Terminalia superba

 

Anatomical features used

Growth layer (2) Vessel diameter in the radial direction of the T.S. (3) Width of ray cells in the T.S. (4) Axial parenchyma form in the T.S. (5) Presence/Absence of Tyioses in the vessel pores. (6) Ray - type in the T.S. (7) Ray- cel

 

 


DISCUSSION:

The seventeen timber species studied shared some common features which made the preparation of a separation and identification key more difficult and relying on some minute details. The timbers were all angiosperms as they all possess vessel members, the xylem or xylary fibres and xylem parenchyma (Oladele, 1991; Jourez, et al, 2001 and Plomion, et al, 2001).

 

The taxonomic value of wood anatomy is seen only limited by the small number of well-authenticated wood specimens available for study throughout the world. Their number is minute when compared with the vastly greater number of herbarium specimens to which taxonomists have access. A species can seldom be identified from wood structure alone. This according to Brazier (1968), is because wood is often more conservative in its structure than are other parts of the plant, and it responds only slowly to evolutionary change. This has the advantage that the relationships of genera and families stand out more dearly in the wood than any other parts of the plant.

 

Another difficulty inherent in the identification and classification of wood from the anatomical structure is caused by the differences between the individual trees and the amount of structural variation related to the position in the tree from which the samples are taker, as well as the differences in structure associated with geographical location of the specimen (Wilcox, et al, 1991 and Herzberg, et al, 2001)

 

Accenting to chalk (1983), one major difficulty in using wood anatomical charters in taxonomy is determining between taxonomic and diagnostic valued. Possession of vessels is regarded as being diagnostic rather than taxonomic in the dense that it is an indication of angiosperms. But it becomes very difficult to use the different vessel characteristics only to classify the carious limber species under the angiosperm. Features that occur sporadically in isolated genera in many widely separated families lack taxonomic significances

 

Other features found in the vessel like thickening pattern, diameter, length and even  number of vessels per square millimeter are functions of certain ecological conditions.

 

The axial parenchyma in many families is predominantly apotracheal or Para tracheal. This according to chalk (1983) is a useful diagnostic character for the woods of families. The nature of the animal parenchyma however, could be influences by the growth condition.

 

The rags and the fibres an no exceptions to the inflect ecological condition on wood anatomy. No single anatomic character in wood could be said to the strictly taxonomic; though most of them are more diagnostic in nature Metcalfe and chalk (1983) suggested that wood anatomical characters should be used are additional criteria in taxonomy

 

In the present work, an attempt has been made to separate and identify seventeen timbers of Nigeria, by mean as of a dichotomous key whose construction was base strictly on inimical characters.

 

As the timbers characteristics used in the construction of the key are conservative, this key can be effectively used in identifying Nigerian timbers.   

 

REFERENCES:

1.       Brazier, J. D. (1968). The contribution of wood anatomy to taxonomy. Proc. Linn. Soc. Lond. 177: 271 – 274.

2.       Desch, H.E. and Dinwoodie, J. M. (1981). Timber, its structure and properties. (6th Ed) . Macmillian Education, London, 410pp.

3.       Haygreen, J. G. and Bowyer, J. L. (1996). Forest product and wood science (3rd. Ed) Iowa State University Press, Iowa, 120pp.

4.       Hertzberg, M., Asperbory, H., Shrader, J., Andersson, A., Erlandsson, R., Blamqvist, K.,  Bhaleroa, R., Uhlem, M., Teeri, T. T., Lunderberg, J., Sundbery, B., Nilsson, P. and Sandbery, G. (2001). A transcriptional roadmap to wood formation. Proc. Natl. Acad. Sci. USA, 98:14732 – 14737.

5.       Hutchinson, J., Dalziel, J. M. and Keay, R. W. J. (1958). Flora of west tropical Africa  Vol. 1 Part I and II. Crown Agents for Oversea Governmnet and Administrations Millbank, London, 828pp.

6.       Jane, F. W. (1962). The structure of wood. Adam and Charles Black Ltd., Soho Square,  London, 427pp.

7.       Jourez, B., Riboux, A and Leclercq, A. (2001). Anatomical characteristics of tension wood and opposite wood in young inclined stems of  (Poulus euramericana CV “Ghoy”). Internalional Association of wood Anatomist Journal, 22: 133 – 157.

8.       Keay, R. W. J., Onochie, C. F. A. and Standfield, D. P. (1964). Nigerian trees Vol II. Federal Department of Forest Research Ibadan, Nigeria, 495pp.

9.       Mellerwoiez, E. J., Baucher, M., Sundberg, B. and Boerjan, W. (2001). Unraveling cell wall formation in woody dicot. Stem. Plant Molecular Biology, 47: 239 – 274.

10.     Metcalfe, C. R. and Chalk, L. (1983). Anatomy of the dicotyledons (2nd Ed) Vol.II. Oxford University Press, London, 297pp.

11.     Oladele, F. A. (1991). Essentials and applications of wood anatomy. J. Olu Oltiregun (Nig.) Company Ltd, 80pp.

12.     Plomion, C., Leprovost, G and Strokes, A. (2001). Wood formation in trees. Plant    Physiology, 127: 1513 – 1523.

13.     Purvis, M. J., Collier, D. C. and Walls, D. (1964). Laboratory techniques in Botany.  Butterworth and Co. (Publishers) Ltd, London, 439pp.

14.     Sass, J. E. (1958). Botanical microtechniques. The Iowa State University Press, Iowa, 288pp.

15.     Titmus, F. H. and Richards, C. H. (1971). Commercial timbers of the world, (4th Ed). C. R. C. Press Claveland, Ohio, 351pp.

16.     Wilcox, W.W., Elmer, E. B. and Hans, K. (1991). Wood as a building material. John Willey and Sons Inc. New York, 215pp.

 

 

 

 

Received on 25.05.2011         Modified on 05.06.2011

Accepted on 26.12.2011         © AJRC All right reserved

Asian J. Research Chem. 5(3):  March 2012; Page 320-324