On the origin of intercellular canals in the secondary xylem of selected meliaceae species

The anatomy, frequency, and origin of intercellular canals in the xylem of ten Meliaceae species (Carapa guianensis Aubl., Carapa procera DC., Cedrela odorata L., Cedrela fissilis Vell., Entandrophragma cilindricum Sprague, Entandrophragma utile Sprague, Khaya ivorensis A. Chev., Khaya senegalensis (Desr.) A. Juss., Swietenia macrophylla King, Swietenia mahagoni (L.) Jacq.) were investigated using 327 samples from institutional wood collections, 398 plantation grown trees, and 43 pot cultivated plants. Tangential bands of intercellular canals and single canals were found in the xylem of all ten species. Staining of microtome sections indicated that the chemical composition of the secretion is similar to that of "wound-gums". Studying the origin of the intercellular canals along the stem axis, it became obvious that the formation of the canals can be induced by wounding of the primary meristems (in particular by insect attacks of Hypsipyla spp., wounding of root tips) and by wounding of the cambium (formation of 43-100% of the intercellular canals). In fast growing trees of Carapa spp., Entandrophragma utile, and Khaya ivorensis, planted at an experimental site near Manaus, Brazil, numerous canals were found which were not induced by wounding of the meristems. In these trees an out of phase sequence of xylem cell development and high growth stresses were observed, which are hypothesised to be a further trigger for the traumatic formation of intercellular canals.