Histology and Histochemistry of Sapwood and Heartwood in Garuga pinnata Roxb. (Burseraceae) and Ougeinia oojeinensis (Roxb). Hoehr.(Leguminosae)

Abstract

Histology and histochemistry of sapwood and heartwood are studied in two broad-leaved species: Garuga pinnata R oxb . and Ougeinia oojeinensis (R oxb .) H oehr . The amount and distribution of excess starch and lipids stored in the wood elements in different zones of wood vary in the two species of the present study. The starch grains diminish in their size and number towards the heartwood boundary by degradation on the surface leaving no grains in the heartwood. The degradation of starch is rapid in Ougeinia which has a narrow sapwood zone, but it is more gradual in Garuga which has a broad sapwood zone. The total lipid content, however, does not show a common pattern of distribution. The lipid content may either increase or decrease towards the heartwood boundary. In Ougeinia the heartwood region contains lipids. The formation and accumulation of extractives during heartwood formation seems to depend on the availability of the reserve materials. The investigated species do not have a distinct transition zone, and the changes leading to heartwood formation may be abrupt or gradual. The process of heartwood formation begins more or less simultaneously in ray and axial systems in Ougeinia , but it begins first in the ray system in Garuga and the axial system is involved in the process.