How does it all work? We have a combination of the various flower parts working in harmony to produce the fertilised seed.
Flower Opens
Pollen is secreted
During the process of growing the flower inside the bud, the pressure mounts as the parts grow and under that stimulus the anther opens and deposits the pollen onto the style. This happens in the day before the pressure becomes intolerable and the bud opens to let the flower out.
On the species and some of the early hybrids and cultivars much of the pollen is left sticking to the stigma area at the tip of the style, which means they have self-pollinated; However, in most cultivars the anther is set below the stigma and so we have pollen loosely attached to the style and waiting for something to happen. The pollen stays fertile for about 24 hours, and so there is not a lot of time available for the pollination.
Nectar
In the last few days of the flower growing inside the bud it produces nectar in the flower funnel, a sugary substance loved by pollinators as a food.
Pollinators come looking for Nectar
Our Cannas provide a landing stage (the labellum) for bees and other pollinators to sup at their nectar, they are carrying pollen on their bodies from the last flower they drank at, or rub against the waiting pollen, and also rub against the stigma and deposit their attached pollen on its sticky surface.
Stigma germinates the pollen
This is where the process called germination takes place, and begins with a pollen grain alighting on and adhering to the stigma of the flower. If conditions are right, the pollen grain germinates to produce a pollen tube containing two sperm cells. Multiple pollen are normally involved and their tubes race one another for the opportunity to fertilize an egg within an ovule.
Pollen tubes fertilizes the eggs
The pollen tube invades the stigma and grows through the style towards the ovary, where it enters an ovule, penetrates the embryo sac and releases two sperm cells, one of which fertilizes the egg, while the other fuses with an egg cell to form the triploid endosperm.
Why can’t you cross canna with other genus?
Canna has evolved selective mechanisms that stop outcrossing by killing pollen of certain genotypes or by specializing the morphology or timing of reproductive structure development. We have yet to see this mechanism explained fully in Canna.
