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 is a large family and contains fourteen British genera; Dianthus (the wild Pink), Saponaria, Silene, Lychnis (Fig. 50), Sagina, Cherleria, Arenaria, Maenchia, Holosteum, Cerastium, Stellaria (Fig. 62), Sper-gularia, Spergula, and Polycarpon.
In Dianthus, of which we may take D. deltoides, the Maiden Pink, as an illustration, the stamens are united with the petals at the base, and form a yellow, fleshy, swelling which secretes honey. The tube of the flower is so narrow, and so nearly closed by the stamens and pistil, that the proboscis of Lepidoptera alone can reach the honey, though flies and other insects visit it for the pollen. The upper surface of the flower forms a flat disk, pink or spotted with white. The stamens are ten in number. Soon after the flower opens, five of them emerge from the tube, ripen, and the anthers open. When they have shed their pollen, the other five do the same. During this period the pistil is concealed in the tube, but after the anthers have ripened and shed most of their pollen, it also emerges and the two long stigmas expand themselves. These two stages have been already referred to (see Figs. 30 and 31). Under these circumstances the butterflies can hardly fail to carry the pollen from the anthers of young flowers to the stigmas of older ones. Flies also visit this species to feed on the pollen, and though they cannot obtain any nourishment from flowers in the latter condition, still they sometimes come to them, apparently by mistake, and, must therefore occasionally fertilise them. This species appears to have lost the power of self-fertilisation.
I have already referred to Lychnis vespertina and L. duima in the first chapter. L. Githago, like Dianthus, is adapted to butterflies. It agrees with the flowers of that genus in the narrowness of the tube, in the position of the honey, and in being distinctly proterandrous.
Silene nutans is a very interesting species. The life of the flower lasts three days, or rather, three nights. The first evening it opens towards dusk, becomes very fragrant, and expands its petals, while five of the ten anthers burst and expose their pollen. So it remains all night. Towards morning, however, the odour ceases, the petals shrivel and roll up, the stamens drop, and the flower looks dead. The next evening, however, it again opens, again emits a sweet scent, and the second series of five anthers open. Towards morning it again loses its smell, and again closes. The third evening it opens as before, but now the pistil has come to maturity, and the stigmas occupy the position, which the two previous nights had been filled by the anthers.
In Silene inflata (the Bladder Campion) there are, according to Axell ("Om Anord. for de Fan. Vax. Bef." p. 46), three kinds of flowers; some with stamens only, some with a pistil only, some with both.
In Stellaria graminea (Fig. 62) the honey-glands are situated at the base of the five outer stamens. The flowers pass through three stages; firstly,that in which the five outer stamens are mature, and incline towards the middle of the flower. In the second, the five inner stamens are mature. Lastly, the stigmas rise and expand themselves, while the stamens gradually shorten and shrivel up. Before this is accomplished, however, the stigmas have curled over and come into contact with the anthers, so that if the visits of insects are deferred, the flower fertilises itself. Stellaria Holostea is more conspicuous, and the three periods are more distinct, but the flower still retains the power of self-fertilisation.
In S. media (the Chickweed) the flowers are less conspicuous, and the five inner stamens are often rudimentary or entirely absent; nay, two of the five outer ones are sometimes also rudimentary, though their honey-gland is always present. It is also proterandrous.
Fig. 62. - Stellaria graminea.
Cerastium arvense agrees with Stellaria Holostea in the position of the honey-glands, and in the sequence of development of the stamens and pistil. It is much frequented by insects. In other forms of this genus, as, for instance, in C. semidecandrum (which Bentham regards as a variety of C. vulgatuui), the flowers are less conspicuous, and in consequence the visits of insects are fewer, the priority of the stamens is less marked, and self-fertilisation is more frequent*
The inner, honeyless stamens, which in Stellaria minor are often wanting, are in this form always rudimentary, according to Muller, while Bentham says that the whole number is often present. Both observers are so correct, that there is probably a difference in this respect between English and German specimens.
Sagina nodosa is also proterandrous; while Mceli-ringia trinervia is, on the contrary, proterogynous.
The Caryophyllacese constitute therefore a very interesting and varied order. As a general rule the more conspicuous the flower, the more decided the dichogamy; conversely, the smaller the flowers, and therefore the less frequent the visits of insects, the greater are the chances of self-fertilisation. The order also presents us with an interesting series commencing with open-flowered species, the honey of which is accessible even to beetles, and short-tongued flies, through those which are adapted to certain flies (Rhingia) and Bees; to the species of Dianthns, Saponaria, and Lychnis Githago, the honey of which is accessible to Lepidoptera only.