This section is from the book "On British Wild Flowers Considered In Relation To Insects", by John Lubbock. Also available from Amazon: Nature Series On British Wild Flowers Considered In Relation To Insects.
The common Berberry is the only British representative of this order, though Epimedium alpinum has by some been considered to be indigenous; as Mr. Bentham thinks, on insufficient grounds.
In the common Berberry (Berberis vulgaris), the stamens (Figs. 55 f f, 56 a) lie close to the petals and almost at right angles to the pistil, as shown in Fig-- 55- The honey-glands (n n) are twelve in number, situated in pairs at the base of the petals, so that the honey occupies the angle between the bases of the stamens and of the pistil. The papillary edge of the summit of the pistil (e) is the stigma. In open flowers of this kind it is of course obvious that insects will dust themselves with the pollen and then carry it with them to other flowers. In Berberis, however, both advantages, the dusting and the cross-fertilisation, are promoted by a very curious contrivance. The bases of the stamens are highly irritable, and when an insect touches them the stamens spring forward to the position shown in Fig. 56 and strike the insect. The effect of this is not only to shed the pollen over the insect, but also in some cases to startle it and drive it away, so that it carries the pollen, thus acquired, to another flower.
Fig. 55. - Flower seen from above.
Fig. 56. - Pistil with two stamens, after the visit of an insect
This order is represented by two British species. Nymphcea alba, the White Waterlily; and Nuphar lutea, the Yellow Waterlily. According to Delpino, N. alba is fertilised by beetles. Sprengel contrasts the large size of the pistil and the great number of the stamens in N. lutea, where the fertilisation is, as it were, a matter of accident, with the small pistil and four stamens of a Labiate; such, for instance, as the common Dead Nettle, which, as we shall see, are so beautifully arranged with reference to one another, and where consequently so much less pollen is required.
Of this family the Common Poppy is the best known representative, though the Celandine is also common on roadsides, especially near villages. The Poppy has two sepals, which drop off as the flower expands; four petals; numerous stamens, forming a ring round a globular or ovoid pistil, which is crowned by a circular disk, on which the stigmas radiate from the centre. The flowers secrete no honey, but are visited for the sake of the pollen. Owing to the weakness of the petals, insects naturally alight on the stigma, which forms a most convenient stage for them in the centre of the stamens, and they thus naturally carry the pollen from one flower to another.