Influence of environmental factors on cell production and differentiation in the early wood of Picea sitchensis

Three phases are identified in tracheid production by the main stem of a 12th year forest-grown tree of Picea sitchensis: cell production, radial cell expansion and cell wall thickening. For 15 days during formation of early wood daily cell production was positively correlated (P=001) with daily solar radiation. Increases in cell production appear related to time-lagged increases in numbers of cells undergoing expansion and then wall thickening. Radial diameter and wall thickness were measured for each individual cell along the post wall thickened section of radial files of tracheids. The radial diameters of neighbouring cells were positively correlated, groups of 4–5 large cells tending to alternate with groups of small cells. Furthermore, large cells had thicker walls than small cells. It is suggested that this distinctive structure is the result of fluctuations in the environ ment which induce changes in the rates of cell production. An increase in cell production increases the length of the queue of cells waiting to pass successively out of the zones of cell expansion and wall thickening. Consequently cells spend longer in the development stages, they expand to a greater diameter and their walls thicken to a greater thickness than when fewer cells are produced and the queue is shorter. We suggest that to investigate the influence which weather may have on the dynamics of tracheid pro duction it is necessary to sample developing wood with a frequency twice as great as that of the frequency of change of the weather variable under consideration.