Pollination mechanisms are those that enhance the
precise deposition of pollen on bird and stigma. These
include both spatial and temporal relations of the reproductive
organs to the position of pollinating birds. The
long exserted stamens of bird-pollinated species of
Aquilegia (e.g. A. formosa), Fuchsia, and Ribes (e.g.
R. speciosum Pursh) dust birds’ heads or even backs, with
pollen. In the radially symmetrical Ipomopsis aggregata
the ring of five stamens place pollen all around the base of
the birds’ beaks. Zygomorphic flowers, on the other hand,
tend to place pollen on the top of the beak or on the top of
the bird’s head.