Although for many plants the amount
of pollen grains that arrive on the stigma is far in excess of the
amount required to fertilize allthe ovules, poor seed set or low yield
is often caused by insufficient pollination (Burd, 1994; Larson and
Barrett, 2000; Ashman et al., 2004) both in animal-pollinated and
wind-pollinated plants (reviewed in Friedman and Barrett, 2009).