XYLEM ANATOMICAL TRAITS RELATED TO RESINOUS HEARTWOOD FORMATION IN PINUS-CANARIENSIS SM

Resinous heartwood (lightwood) is an important feature in Pinus canari ensis (Canary Island pine), as this wood has very good mechanical and aesthetic characteristics. In order to determine anatomical traits rel ated to lightwood formation, structure of axial resin canals, xylem ce ll connections and cell contents were studied on wood samples from sit es with different environments. Specimens consisted of radial wood cor es and stem discs at breast height. The unknown presence of a wide par enchymatous sheath in axial resin canals is highlighted, and a general description of this formation is provided. Quantitative anatomical tr aits were examined to explain deviations of heartwood radius from the values predicted by a regression model. Thus, percentage of rays and a xial parenchyma were assayed in ten individuals. Those with a larger h eartwood than predicted by their age and growth tend to display a high er percentage of axial parenchyma in the inner xylem (5th growth ring) . More than 40% of heartwood's dry weight is due to extractives, mainl y resin, fats and phenolic compounds, ranging up to 4% in sapwood. Thi s intense soaking is explained by the high proportion of living cells in the xylem, and their capability to accumulate large quantities of r eserve starch. These traits are closely linked to other important feat ures of the species, such as stem sprouting and resistance to extreme wounding.