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.
This order contains, according to Bentham, but one British species, which, however, is very common, the Milkwort (Polygala vulgaris)) Fig. 59. The structure of the flower is curious, and was first explained by Hildebrand, whose account, however, does not seem to me entirely complete or satisfactory. There are five sepals (Figs. 60, 61 s s), of which three are small, linear, and greenish; the other two much larger, coloured like the petals, and obovate or oblong. The petals form a tube to the inside of which the stamens are attached in two bundles (Fig. 61 a), and which contains a number of white hairs pointing downwards, while near the upper end are two groups of fingerlike lobes. The pistil (Fig. 61 st) occupies the axis of the flower, and ends in a spoon-shaped hollow. The short stamens lie just over this hollow, and shed their pollen into it, after which they withdraw a little to the side. Close behind the hollow is a projection which terminates in a very viscid disk. When the proboscis of an insect is forced down the tube in search of honey, it comes in contact with this viscid disk, and being thus rendered adhesive, when it is withdrawn carries some of the pollen with it, and thus conveys it to the next flower, where it is stripped off the retreating proboscis by the edge of the viscid disk, and is thus accumulated in the stigmatic hollow. Polygala vulgaris is sometimes blue and sometimes pink; why is this? It is, moreover, a variable species in other respects, as for instance in the size and proportions of the different leaves. The use of the curious finger-formed processes has not, I think, been satisfactorily explained.
Fig. 59. -Polygala vulgaris.
Fig. 60. - Flower of Polygala vulgaris.
Fig. 61. - Section of ditto.
There is only one British genus of this order, the well-known Hypericum, which, however, contains eleven British species. The stamens are united into bundles; the styles are generally three in number, alternating with the bundles of stamens. In the large-flowered Hypericum, however (H. calycinum), the styles are five in number, and are raised above the stamens. Hypericum perforatum (the Common Hypericum) is so named from the remarkable peculiarity of having the leaves studded by pellucid dots; and several of the species have the sepals fringed with black or red glands. The flowers belonging to this genus are generally very conspicuous, both from their bright yellow colour and from their association in clusters. They secrete no honey, but are frequently visited by insects, partly for the sake of the pollen, partly perhaps in a vain search for honey. Under these circumstances, cross-fertilisation must frequently occur, though no doubt the flowers often fertilise themselves.
Of this order we have in England only one species, the Common Lime (Tilia Europaa), which, however, is not a native species. The flowers are very sweet, and great favourites with bees. Their abundance and the size of the tree render colour unnecessary. The honey is secreted by the sepals, and is accessible even to short-lipped insects; while, as the flowers hang down, it is completely protected from rain. The stamens are numerous, but, as Hildebrand has pointed out, they have shed their pollen before the stigma is mature, and the flower is therefore incapable of self-fertilisation. The visits of insects are very numerous, and yet in this country the Lime seldom produces ripe seed.