Monthly variation in centrum edge type (n=205) and mean
monthly marginal increment ratios (MIR)±1 standard error (n=139) determined
from pooled sexes and size classes. Values within the histogram
represent the number of samples included in monthly centrum edge analyses.
Sample sizes incorporated into MIR analysis are listed in parentheses
below the x-axis. T1, narrow translucent edge; T2, broad translucent edge;
O1, narrow opaque edge; O2, broad opaque edge.