Cyclical cell length changes in wood in relation to storied structure and interlocked grain

Abstract

Interlocked grain can result from migration of a succession of left (S) and right (Z) orientational domains along the cambium. This grain pattern occurs both in species having nonstoried and those having storied cambium. In storied cambia, storey height being fixed, geometry requires that cambial fusiform initial cells undergo cyclical length changes in phase with cyclical inclination changes, e.g., a 4% length increase for a 16° inclination. We can expect the length changes to be detectable in wood if vessel member length reflects fusiform initial cell length and if the absolute amount of intrusive growth during differentiation of fibers is nearly invariant. Measurements of cells from maximum S, maximum Z, and axially aligned grain (I) sites along a radius in Entandrophragma cyclindricum and E. utile wood (storied) revealed clearly cyclical length changes in vessel members, parenchyma strands, and xylem fibers. Measurements in Nyssa sylvatica and Platanus acerifolia (nonstoried) revealed no such changes. Hence in species having storied cambium, cyclical changes in length of wood cells can accompany the slow endogenous rhythm manifested by interlocked grain. This is true because intrusive growth in these species, though extensive, does not obi iterate effects of small differences in cambial initial cell length.