Young shoots from poplar cuttings (Populus euramericana cv ʻGhoyʼ) were artificially inclined to 30° from vertical to quantify the anatomical modifications induced by this gravitational stimulus. At the end of the growing season, the tension wood tissue (from the upper face of the inclined axis) was compared to the opposite wood tissue (from the lower face), with radial position taken into account. On isolated elements after maceration, fibres and vessels were significantly longer in tension wood tissue. In the cross section, the gelatinous fibres had a smaller radial diameter than normal fibres in opposite wood. Vessel frequency and porosity were significantly lower in tension wood than in opposite wood. Solitary vessels in tension wood were less circular in cross section than in opposite wood, but their surface area did not differ. Rays were more numerous in tension wood than in opposite wood but their height did not differ between the two tissue types. Finally, there was a negative correlation between the proportion of vessel lumina (lowest in tension wood) and the proportion of fibre lumina including the G layer. The very controlled nature of this experiment (greenhouse, young clonal material, detailed anatomical observations within one growth ring) and the image analysis technology (allowing a large number of observations) enabled us to draw conclusions that may not have been seen in less-controlled experiments and /or those with smaller sample sizes.

e t s c h m a n n~ and Andr6 ~e c l e r c q~ From an early status as a "weed tree," poplar has become an important commercial genus in North America during the past 20 years. The many and varied uses of poplar wood now include pulp and paper, lumber, veneer, plywood, composite panels, structural composite lumber, containers, pallets, furniture components, match splints and chopsticks. The high cellulose and relatively low lignin content make poplars well suited for pulp and paper products. The wood can be pulped by all commercial pulping methods, such as mechanical, semi-chemical, sulphate and sulphite processes. Poplar pulps are utilized in fine papers, tissues, paperboard, newsprint and packaging papers. Poplar kraft pulps, when blended with softwood kraft, are particularly well suited for fine paper manufacture because of inherently desirable properties, such as excellent sheet formation, high opacity, good bulk and good printability. While poplar wood continues to be an important raw material in the traditional lumber, veneer and plywood industries, the most remarkable recent achievement in poplar utilization is the phenomenal growth of the oriented strandboard and structural composite lumber industries in North America during the last decade. The future for poplar utilization is bright. On the resource production side, opportunities for genetically modifying important wood properties, such as chemical composition, fibre quality and natural durability of wood, can now be realized. On the resource utilization side, high-value engineered composites and high-yield pulp and paper products will represent the strongest growth sectors for poplar fibre during the coming decades.Key words: poplar wood, utilization, pulp and paper, oriented strandboard, fibre properties A l'origine, une esptce << indksirable D, le peuplier est devenu un genre important en terme commercial en Amkrique du Nord au cours des demitres 20 annkes. Les usages multiples et variks du bois de peuplier comprennent maintenant la p2te et le papier, le bois d'ceuvre, le dtroulage, le contre-plaqut, les panneaux composites, le bois d'ingtnierie pour les charpentes, les conteneurs, les palettes, les composantes de meuble, les allumettes et les baguettes. Le fort contenu en cellulose et la relativement faible portion de lignine font en sorte que les peupliers sont recherchks pour la production de pke et de papier. Le bois peut Stre transformks en p2te selon tous les prockdks commerciaux de mis en p2te qu'il soit mkcanique, semi-chimique, au sulfate ou au sulfite. Les p2tes de peuplier sont utilistes dans les papiers fins, les papiers hygikniques, les cartons, le papier journal et les papiers d'emballage. Les pltes kraft de peuplier, lorsque mklangkes B de la p2te kraft de rksineux, sont particulitrement intkressantes pour la fabrication de papier fin par suite des proprittts inhkrentes recherchkes, comme l'excellente formation de feuille de papier, la grande opacitk, une masse adkquate et une bonne qualitt typographique. MSme si le bois de peuplier con...

In a greenhouse, under controlled conditions, young shoots, taken from poplar cuttings (Populus euramericana (Dole) Guinier cv. Ghoy), were artificially bent to quantify the modifications of physical properties induced by a gravitational stimulus. At the end of the growing season, basic density and longitudinal shrinkage were measured on very small samples taken from pure tension wood tissue observed on the upper face of the inclined axis and compared with opposite wood tissue, free of gelatinous fibers, developed on the opposite lower face. In a second step, shoots bent at two different lean intensities were analyzed. In young poplar wood, gravitational stimulus was found to have a significant effect on physical properties. Relations between basic density and longitudinal shrinkage are different depending on the types of wood considered. Shrinkage appears more sensitive to lean intensity in the range considered here.

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