This week along with lots of planting of donated plants, we looked for 'plants in flower'. Gill, one of our volunteers is going to do a survey each month - she was very strict with use we 'had to see a stamen - nothing just in bud.
As a bit of a cheat, I had bought six primroses (three pale yellow and three darker) from a market stall to put in the raised beds. Gill was delighted to see they included 'pin and thrum' variations, studied by Darwin, and we sacrificed one of each type to the cake knife to see the variation and learn a bit about the genetics.
Here is more about what it means: http://www.bbc.co.uk/earth/story/20150421-the-true-primrose-displays .
And a bit more science:
22 January: Gill dropped by and said she had looked up the origin of 'thrum', it is Old English for the frayed end of a cut rope (online dictionary), just like the top of the primrose.