HEARTWOOD FORMATION IN QUEBRACHO COLORADO (SCHINOPSIS-BALANSAE ENGL) - TANNIN DISTRIBUTION AND PENETRATION OF EXTRACTIVES INTO THE CELL-WALLS

The distribution of tannins in the cell walls of Quebracho colorado (S chinopsis balansae Engl.) heartwood was investigated by densitometric measurement of the grey levels on TEM micrographs. Lead citrate reagen t (Reynolds 1963) turned out to be an appropriate staining agent as it stains phenolic extractives selectively This method permits the inves tigation of the tannin distribution in cell walls at the high resoluti on level of transmission electron microscopy (TEM). The results obtain ed from observations of wood samples from the transition zone between sapwood and heartwood lead to the conclusion that the penetration of e xtractives into the cell walls begins in the compound middle lamella a nd then continues in the secondary wall layers. The impregnation of th e cell wall with extractives therefore resembles the lignification pro cess.