Desiccation then
causes the anther to open at its tip (Fig. 1) and pollen is
emitted and may be entrained into the atmosphere by mean
advection and turbulence. It is evident fromFigs. 8–10 that the
morning hour at which the first pollen grains were captured
by the Rotorod samplers, varied (see also Fig. 5). For example,
on 13, 14, 17 and 19 July (Figs. 8 and 10), significant pollen
concentrations at canopy heightwere first measured between
0900 and 1000 EDT whereas on 15 and 16 July (Fig. 9), this
occurred earlier between 0600 and 0700 EDT.