Resinous heartwood (lightwood) is an important feature in Pinus canariensis (Canary Island pine), as this wood has very good mechanical and aesthetic characteristics. In order to determine anatomical traits related to lightwood formation, structure of axial resin canals, xylem cell connections and cell contents were studied on wood samples from sites with different environments. Specimens consisted of radial wood cores and stem discs at breast height. The unknown presence of a wide parenchymatous sheath in axial resin canals is highlighted, and a general description of this formation is provided. Quantitative anatomical traits were examined to explain deviations of heartwood radius from the values predicted by a regression model. Thus, percentage of rays and axial parenchyma were assayed in ten individuals. Those with a larger heartwood than predicted by their age and growth tend to display a higher percentage of axial parenchyma in the inner xylem (5th growth ring). More than 40% of heartwood′s dry weight is due to extractives, mainly resin, fats and phenolic compounds, ranging up to 4% in sapwood. This intense soaking is explained by the high proportion of living cells in the xylem, and their capability to accumulate large quantities of reserve starch. These traits are closely linked to other important features of the species, such as stem sprouting and resistance to extreme wounding.

Works leading to this paper were officially supported by the Canary Islands Government. All field works were developed with the collaboration of the Canary Island Forest Services. Extractions were held at the Laboratorio de Aceites Esenciales of I.N.I.A. (Madrid), thanks to Concepcion Garcia Vallejo`s precious help and advice

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