Cindy Bennington. Department of
Biology, Campus Box 8264, Stetson University, DeLand, FL 32720. - in
Floral gender and reproductive success in Passiflora incarnata.
suggest as below that P. incarnata have different flowers with the styles
set in different positions.
''In multiple donor pollinations, pollen load size is expected to
increase pollen competition and affect the paternity of seeds produced. In
Passiflora incarnata, the number of pollen grains received on the
stigmatic surfaces of individual flowers varies widely depending on style
position. In this andromonoecious species, some flowers hold their styles
erect where they are unlikely to come into contact with pollinators.
Others reflex their styles to a position where contact with
pollen-carrying pollinators is likely. Still others partially reflex their
styles, but remain intermediate. In our field study in one Central Florida
population, open-pollinated "male", intermediate, and hermaphroditic
flowers received an average of 8.1 (s.d. = 11.9), 38.8 (s.d. = 38.0), and
385.7 (s.d. = 762.9) pollen grains, respectively. We found that pollen
germination rates tend to be highest on hermaphroditic flowers (56.9%) and
lowest on male flowers (30.9%), although this difference was not
significant (F2,64 = 2.56, p = 0.08). Given that self-pollen
germinates readily (but halts growth quickly), these differences in
germination rates do not appear to be the result of differences among the
amounts of self-pollen that may be received in the three style positions.
Thus, in addition to the mechanical impediment to fruit production caused
by style position, there appears to be a stigma-pollen interaction that
affects the reproductive success of flowers expressing different genders.
We are presently asking whether differences among male, intermediate, and
hermaphroditic flowers may also affect pollen quality and hence the
outcome of pollen competition.''