Mechanism of changes in grain inclination in wood produced by storeyed cambium

Abstract

The changes in cell orientation in the cambium of <i>Entandrophragma</i> producing wood with interlocked type of grain, and in the cambium of <i>Tilia</i> in a spirally girdled stem are traced through serial tangential sections of wood. In <i>Entandrophragma</i> the changes result from the intrusive growth of a fusiform cell whih repeatedly produces a new pointed tip from one side of the existing tip which disappears. This causes a sort of creeping of cell ends of one storey past those of the adjoining storey. The oppositely directed ends of the cells belonging to one storey creep in opposite directions so that the position of the cell centres remains constant and only the angle between the cells and the stem axis changes. The stratification of short rays in <i>Entandrophragma</i> represents an adaptation to the changes in celi orientation involved in the formation of interlocked grain. The mechanism of changes in grain inclination in <i>Tilia</i> is intermediate between that based on the creeping of cell ends and that based on pseudotransverse division and intrusive elongation which is known in non-storeyed cambia.