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

The changes in cell orientation in the cambium of Entandrophragma producing wood with interlocked type of grain, and in the cambium of 77/io in a spirally girdled stem arc traced through serial tangential sections of wood. In Entandrophragma 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 ntandrophragma represents an adaptation to the changes in cell orientation involved in the formation of interlocked grain. The mechanism of changes in grain inclination in 77/ia 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