Avoiding Self Pollination 20 February 2016

Mechanisms to promote cross- pollination Separate male and female plants Separate male and female flowers on one plant Anthers and stigmas developing at different times Structural adaptations to reduce self- pollination (position of anthers and stigma) Incompatibility mechanisms to prevent fertilisation (affects pollen tube formation)

Some flowers offer more than just nectar!

Why go to all this trouble? Cross pollination encourages: cross-fertilisation variation heterozygosity

Primula veris

Thrum Pin

The Cowslip has two arrangements of anther and stigma Pin-eye: The style is the length of the corolla-tube. The anthers are fused to the walls of the corolla-tube, about half-way down. Looking into the flower, the stigma looks like the head of a pin. Thrum-eye: The style is only half the length of the corolla-tube. The anthers are positioned at the mouth of the corolla-tube.

Thrum Pin

Pollen also differs between the flower types In size and in texture

Cross pollination is ensured in a number of ways: Insects will collect pollen easily from the thrum plant Pollen will easily be deposited on the pin plant stigma as the insects collect nectar In the pin eye plant, the stamens are below the stigma Thrum eye plants can self pollinate but the pollen will not germinate and the ovule cannot be fertilised.

More information biol.paisley.ac.uk/bioref/Genetics/Primula_ heterostyly.html