Thursday, 6 February 2014

Thrum-eyed and pin-eyed

I treated myself to a tray of Primulas today from Banbury market and was pleased to note that both thrum-eyed and pin-eyed forms were present. The thrum-eyed form has long anthers (the male pollen-bearing organs) and they form a fringe around the top of the corolla tube.

Thrum-eyed Primula. 6 February, 2014

In the thrum-eyed form the female organs cannot be seen as they are situated half way down the corolla tube.

Pin-eyed Primula. 6 February, 2014

In the pin-eyed form the situation is reversed: the female stigma, looking like a drumstick, clearly protrudes from the mouth of the corolla tube; the male organs cannot be seen.

Ideally a visiting insect will go to a thrum-eyed flower first and receive a dusting of pollen from the male organs. It will go on to a female flower and deposit pollen on the sticky stigma and pollination is achieved.

The object of the exercise is, of course, to try and ensure cross-pollination. Although our wild Primrose, Primula vulgaris, is far less common than a century ago it is still abundant in places, testimony to the success of this arrangement. All our other native primulas - Bird's Eye Primrose (Primula farinosa), Oxlip (Primula elatior)  and Cowslip, (Primula veris) have similar arrangements.

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