Free access
Issue
Ann. For. Sci.
Volume 64, Number 3, April-May 2007
Page(s) 255 - 265
DOI http://dx.doi.org/10.1051/forest:2007003
Published online 11 April 2007
Ann. For. Sci. 64 (2007) 255-265
DOI: 10.1051/forest:2007003

Measurement of free shrinkage at the tissue level using an optical microscope with an immersion objective: results obtained for Douglas fir (Pseudotsuga menziesii) and spruce (Picea abies)

Patrick Perré and Françoise Huber

LERMaB (Integrated Research Unit of Wood Science), UMR 1093 INRA/ENGREF/University H. Poincaré Nancy I, ENGREF, 14, rue Girardet, 54042 Nancy, France

(Received 17 May 2006; accepted 28 September 2006; published online 11 April 2007)

Abstract - Shrinkage at the tissue level has been evaluated satisfactorily using relatively simple equipment, comprising an optical microscope equipped with reflected light, a standard objective, a water immersion objective of same magnification and a digital camera connected to a computer. Shrinkage is calculated from pairs of images taken at the same magnification, one collected during immersion in water and the other in air-dry state. A novel software program has been developed to determine shrinkage based on a closed chain of reference points chosen from the anatomical markers at the external part of the zone of interest. Measurements were performed on earlywood, latewood and compression wood zones from two softwood species (Douglas fir and spruce), isolated from the rest of the annual ring with the aid of a diamond wire saw. As main results, reference should be made to the low degree of shrinkage and high anisotropy factor of earlywood, the marked and practically isotropic shrinkage in latewood and the low shrinkage (with respect to cell wall thickness) and inverse anisotropy ratio in compression wood.


Résumé - Mesure du retrait libre à l'échelle des tissus à l'aide d'un microscope optique muni d'un objectif à immersion : résultats obtenus chez le Douglas (Pseudotsuga menziesii) et l'épicéa (Picea abies). Le retrait a été évalué de façon satisfaisante à l'échelle tissulaire en utilisant un équipement relativement simple : un microscope optique, un objectif standard, un objectif à immersion de même grossissement et une caméra digitale reliée à un ordinateur personnel. Le retrait est déterminé par comparaison de deux images : l'une obtenue en immersion dans l'eau et l'autre à l'état sec à l'air. Un logiciel nouveau a été développé pour extraire le retrait à partir d'une chaîne fermée de points situés à la périphérie de la zone d'intérêt. Les mesures ont été effectuées sur des zones de bois initial, de bois de compression et de bois final de deux espèces (Douglas et sapin). Ces zones sont isolées du reste de l'accroissement initial à l'aide d'une scie à fil diamanté. Les principaux résultats montrent le faible niveau de retrait et la forte anisotropie du bois initial, le fort retrait, presque isotrope, du bois final et la faible valeur, en rapport à sa densité, avec une anisotropie inversée, du bois de compression.


Key words: image analysis / microscope / shrinkage / softwood / tissue

Mots clés : analyse d'image / microscope / résineux / retrait / tissu

Corresponding author: perre@nancy-engref.inra.fr

© INRA, EDP Sciences 2007

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