Article: An unexplained feature of the vascular cambial activity in fossil and living gymnosperms

When traced across a growth ring in both fossil and Recent gymnosperm wood, from the earlywood to the latewood, the radial diameters of the tracheids exhibit a variation which is not random. Instead they show a series of gradual increases to a maximum and decreases to a minimum with periodicities of about 6, 9, 11, and 18 cells. Work is described which attempts to explain this effect in terms of differential expansion cells or polyploidy.