INTERLOCKED GRAIN, CAMBIAL DOMAINS, ENDOGENOUS RHYTHMS, AND TIME RELATIONS, WITH EMPHASIS ON NYSSA SYLVATICA

Interlocked grain in wood of Nyssa sylvatica Marsh. is a lapse-time record of cyclical changes in inclination (rightward or leftward) of fusiform initial cells in the cambium. Typically the inclination cycles have periods of a decade or more. Such cycles can be interpreted as manifestations of long-term endogenous rhythms. Interlocked grain in N. sylvatica is not the result of whole-stem spiral grain that reverses periodically. As wavy grain in other species is a record of wavelike migration of orientational domains along the cambium, interlocked grain in N. sylvatica can be interpreted as being related to a more complex system of domains having long axial dimensions. These domains migrate or change their efficacy and directional sense in place in such a way that some regularity of inclination cycles is maintained at the various stem levels. Inclination cycle lengths have a closer relation to calendar time than they do to the amount of radial growth of the stem. This is affirmed by data from paired stems of similar ages but which grew in diameter at widely different rates. IN IDEAL TREES the long axes of the cambial fusiform initial cells are parallel to the stem axis, and wood derived from their progeny is straight grained. In real trees the wood grain is sometimes straight, but more often there are deviations. Commonly, fusiform initials are slightly inclined to the stem axis and the wood grain has a spiral course. Often the inclination of the initials in the same cambial locality changes with time. The scale and temporal aspects of these cell inclination changes in the cambium determine whether the wood grain is straight, spiral, wavy, or interlocked, or whether it has a more complex pattern (Braun, 1854; Bannan, 1966; Hejnowicz, 1968; Hejnowicz and Krawczyszyn, 1969; Hejnowicz and Romberger, 1973, 1979; Pyszynski, 1977). If grain inclination of the wood produced by the same area of cambium changes cyclically from left (S) to right (Z) repeatedly during the life of a tree, it is possible to determine the cycle length, axially and radially, by study of the wood. When the axial cycles are short, millimeters to a few decimeters, the grain is "wavy"; when axial cycles are long, several decimeters to many meters, we interpret the 1 Received for publication 23 April 1979; revision accepted 19 June 1979. The senior author expresses his appreciation and indebtedness to the Kosciuszko Foundation (New York) for a postdoctoral fellowship at the Forest Physiology Laboratory in Beltsville, Maryland, during the tenure of which some of the work reported here was accomplished. 2 Present address: Department of Botany, Bialystok Division of Warsaw University, Lipowa Street 41, 15424 Bialystok, Poland. grain as "interlocked." Among investigated woods there exists, however, a near-continuous spectrum of cycle lengths; hence it can be shown that both wavy grain and interlocked grain have a similar relation to orientational domains in the cambium (Krawczyszyn, 1972; Hejnowicz, 1973; Hejnowicz and Romberger, 1979). Although interlocked grain has long been recognized as a phenomenon of interest (Martley, 1920; Limaye, 1954; Kadambi, 1956), its spatial and temporal aspects in tree stems have only recently been given serious study. Krawczyszyn (1972, 1977) found that interlocked grain of Platanus can be interpreted as resulting from the upward migration of broad bands of successive S and Z orientational domains in the cambium. These interpretations are compatible with those of Hejnowicz and Romberger (1973) regarding wavy grain. Hejnowicz and Zagorska-Marek (1974) found that similar interpretations of interlocked grain formation apply to storied as well as nonstoried cambia. Recently we (Krawczyszyn and Romberger, 1979) reported that cyclical changes in cell length may accompany the inclination cycles of interlocked grain in woods with storied structure, but we found no such relation in woods with nonstoried structure. Economically both wavy grain and interlocked grain have positive and negative aspects. For decorative uses the figured or striped appearance of wavy or interlockedgrain wood is highly prized, though machining is difficult. These same features may be considered as defects in construction timber (Weddell, 1960; Webb, 1967).