Primrose way

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https://plantscientist.wordpress.com/2013/04/27/organism-of-the-week-primrose-primula-vulgaris/

Very lovely blog about primroses

“During a field trip in Pembrokeshire as an undergraduate student I spent a couple of days studying primrose flowers. Wild primrose flowers are typically a pale yellow colour like those pictured above but white and pink forms are also seen. There are two forms of flowers, which look almost identical apart from the position of the stigma (female part) and the anthers (male part holding the pollen) in the flower tube in the centre. In “pin” flowers the stigma is positioned at the top of the tube with the anthers positioned halfway down. In “thrum” flowers the stigma is instead positioned halfway down the tube with the anthers at the top.

The two flower types were first described by Charles Darwin in 1862 (1) and he also observed that the pollen produced by the pin flowers was smaller than that of the thrum flowers. He performed a number of crosses (where he took pollen from one flower and placed it on the stigma of another)  between pin-to-pin, thrum-to-thrum, pin-to-thrum, and thrum-to-pin flowers and found that the crosses between the different flower types were more fertile than those between flowers of the same type.”