LAUSR

The effect of natural and artificial weathering on the anatomy of seven tropical hardwoods: Bangkirai (Shorea obtusa Wall.), Cumaru (Dipteryx odorata (Aubl.) Wild.), Cumaru Rosa (Dipteryx magnifica (Ducke) Ducke), Ipé (Tabebuia serratifolia Nichols.), Jatobá (Hymenaea courbaril L.), Kusia (Nauclea diderrichii Merill) and Massaranduba (Manilkara bidentata A. Chev.), was studied. As a result of weathering some characteristic anatomical changes occurred: the weakening of connections between cell elements related to the degradation of the middle lamella; micro-cracks in cell walls; total degradation of parenchyma cells in xylem rays, or significant thinning of parenchyma cell walls and their extreme shrinkage; micro-cracks in the vicinity of xylem rays; significant transversal disruptions in libriform fibres; ablation of pit membranes in vessels and parenchyma cells; changes in the secondary wall of libriform fibres, for example, their defibrillation and weathering-degradation of the S1 layer; and spherical formations on the S3 layer of cell walls produced from condensing compounds of degraded lignin and hemicelluloses as well as thermo-mechanical wrinkling. The highest incidence of micro-cracks after both modes of weathering was found in the densest species; Cumaru, Ipé, and Massaranduba.