COMPARATIVE HISTOCHEMISTRY AND CELL MORPHOLOGY OF SAPWOOD AND HEARTWOOD OF GLIRICIDIA-SEPIUM (FABACEAE)

Gliricidia sepium (Jacq.) Steud. (Fabaceae) shows a remarkably high ra tio of heartwood to sapwood. Heartwood fibres and vessels have very th ick cell walls and the heartwood vessel elements contain many scleroti c and common tyloses, both with gums and crystals in their cavities. H istochemical analysis of these cells and tyloses showed that the cell walls of fibres, vessels and sclerotic tyloses have great quantities o f lignin and sterified pectins as matrix components, as well as conden sed tannins or phenolic substances in their lumen. Crystals are presen t in common tyloses and axial parenchyma. Most vessel elements in the sapwood contain tyloses that completely fill their lumen. the majority of these structures are of the common type, whereas only a. few of th e sclerotic type are present near the heartwood region. Our observatio ns suggest a fast transformation of sapwood into heartwood. We think t hat the presence of very thick cell walls of fibres, vessels and tylos es, as well as their chemical composition and the inclusion of crystal s, influence the high natural resistance to decay of this wood.