Comparative histochemistry and cell morphology of sapwood and heartwood of Gliricidia sepium (Fabaceae)

Gliricidia sepium (Jacq.) Steud. (Fabaceae) shows a remarkably high ratio of heartwood to sapwood. Heartwood fibres and vessels have very thick cell walls and the heartwood vessel elements contain many sclerotic and common tyloses, both with gums and crystals in their cavities. Histochemical analysis of these cells and tyloses showed that the cell walls of fibres, vessels and sclerotic tyloses have great quantities of lignin and sterified pectins as matrix components, as well as condensed tannins or phenolic substances in their lumen. Crystals are present 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 the sclerotic type are present near the heartwood region. Our observations suggest a fast transformation of sapwood into heartwood. We think that the presence of very thick cell walls of fibres, vessels and tyloses, as well as their chemical composition and the inclusion of crystals, influence the high natural resistance to decay of this wood.