This issue's cover: The four panels represent fluorescence micrographs of Pinus sylvestris roots. The top panel shows the roots (left) at 1 and (right) 2 mm behind the root tip after treatment with high molecular size fraction 2. The bottom panel represents the roots (left) at 1 and (right) 2 mm behind the root tip after treatment with low molecular size fraction 2, and it shows a much smaller rate differentiation than does the high molecular size fraction treatment. See Nardi et al., "Chemical and biochemical properties of humic substances isolated from two forest soils affecting plant growth," p. 399-645.