Within-tree variations in vessel elements, specific gravity and extractive content: their influence on some gluing properties of bok-bok (Xanthophyllum excelsum (Blume) Miq.)

Characteristically, the wood of bok-bok [Xanthophyllum excelsum (Blume) Miq.] is light-colored, straight-grained, moderately coarse-textured, hard, medium heavy, and with low extractive content. Anatomically, vessel elements are empty, very few, and medium-sized to very large; axial parenchyma is apotrachael and paratrachael; wood rays are numerous, uniseriate to biseriate; and fibers are mostly medium-sized and thick-walled. Among height levels and segments were invariably highly significant in all wood features studied. Height level particularly influenced vessel frequency and extractive content. Segment number showed significant differences in each segment means of all wood features. Based on pooled data, systematic patterns of variation in the axial and radial directions were apparent in all wood features. Dry and wet sheer strengths were highly significant among height levels and among segments. Dry wood failure and glue penetration also showed significant variations among segments. Only dry shear strength and dry wood failure were significantly affected by the level of extraction. Strong effects of segment number were particularly noted in glue penetration, wet shear strength and dry shear strength. Systematic patterns of variation along the tree trunk and radius were apparent in some gluing properties. Using the partial correlation and regression analyses, the observed within-tree variations in some wood features contributed mutually to some gluing characteristics of bok-bok. However, specific gravity appeared to be the strongest determinant of shear strength (dry and wet) while variations in vessel diameter contributed largely to variation in glue penetration. The pathway of glue penetration was confirmed by scanning electron microscopy. The migration of adhesive from the glueline to the vessel lumen was through the ray cells and pit pairs.