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 fourteen British genera, including the Clematis, Ranunculus (Buttercup), Anemone, Columbine, Hellebore, Larkspur, Paeony, etc.
In the Buttercup (Ranunculus acris), the anthers commence to discharge their pollen, as soon as the flower opens, beginning from the outside. The stigmas, however, are not as yet mature, nor do the stamens open on the side which is turned towards them, but on the contrary, on their edges; moreover as each stamen ripens, it generally turns outwards. The result of this is that bees and other insects, which visit the flowers in search of honey, are almost sure to dust themselves with pollen; which they carry away with them, and are then very likely to deposit it on another flower. The stigmas are mature before the inner stamens have shed all their pollen, and self-fertilisation must often take place, both by means of the small insects which may almost invariably be found wandering about the flower, and because the inner stamens often touch some of the stigmas. Larger insects, however, which fly from flower to flower, must habitually carry the pollen from the younger flowers, and deposit it on the stigmas of those more advanced.
Clematis recta produces no honey, but is visited for the sake of the pollen. It is proterandrous (see p. 28), but not very decidedly so; for as in other flowers which do not produce honey, if the stamens had shed all their pollen before the pistil came to maturity, insects would cease to visit the flowers before the stigma had attained maturity, and had thus become susceptible of fertilisation.
Like Clematis, Thalictrum produces no honey. The petals are absent and the sepals minute, but the stamens are numerous and brightly coloured.
Caltha palustris has large yellow sepals, but no true petals. In the Hellebore also the petals are minute, but secrete honey. The species of this genus are said by Hildebrand to be proterogynous. (See p. 28.)
In Anemone nemorosa the colouring is given not by the corolla, but by the calyx. The flower does not appear to produce honey, but bees are said to pierce the base of the flower, and lick the sap. Van Tieghem however states that it gives off honey from the whole surface of the receptacle.
Delphinium (the Larkspur) and D. elatiim (Figs. 51 - 54) have been well described by H. Muller. The five sepals are brightly coloured; the upper one is produced into a long spur (x x). The two upper petals are also produced into spurs which lie within the former, and secrete honey. In order to reach this it is necessary for the bee to press its proboscis between the upper and lower petals, through the interval (Figs. 51, 53 m). The lower wall of this orifice is in front closed by the lower petals (Figs. 51, 53 Pe Pe), which are turned upwards and sideways, so as to form the lower wall of the orifice leading to the nectary, and to cover the stamens and pistils. Immediately behind the entrance to the tube, however, these petals contract so as to leave a space (m). The stamens (a) and pistil lie below this space, and as the stamens ripen, they successively raise themselves and their anthers pass through this space, as shown in Fig. 51 a', so that the proboscis of the bee, in passing down to the honey can hardly fail to come in contact with them. After shedding their pollen, they turn down again, and when each anther has thus raised itself and again retired, the pistil in its turn takes possession of the place, as shown in Fig. 53, and 54 .st; and is thus so placed, that a bee which has visited a younger flower and there dusted its proboscis, can hardly fail to deposit some of the pollen on the stigma. Fig 51 represents a young flower seen from the front, and after the removal of the calyx; it shows the entrance leading to the nectary, in which are seen the heads of two mature stamens, a while the others, a a, are situated in a cluster below. Fig. 52 represents a section of the same flower. Fig. 53 represents a somewhat older flower, in the same position as Fig. 51. In this case the stamens have all shed their pollen and retired, while the stigmas st, on the contrary, have risen up, and are seen projecting into the space m. Fig. 54 represents a side view in section of this flower. Anthophorapilipes and Bombus hortorum are the only two North European insects, which have a proboscis long enough to reach to the end of the spur of Delphinium elatum. A.pilipes, however, is a spring insect, and has already disappeared, before the Delphinium comes into flower, which, in the neighbourhood of Lippstatt, appears to depend for its fertilisation entirely on Bombus hortorum, though Boissier assures us that in France and in the Alps it is visited by several other species.
Fig 51. - A young flower of Delphinium elathum, seen from the front, and after removal of the calyx. Fig. 52. - Section of the same flower seen from the side. Fig. 53. - An older flower, seen from the front, after removing the calyx. Fig. 54. - Section of the same flower, seen from the side.
It will be seen that the Ranunculaceae offer very remarkable differences in the manner of their adaptation to insects. Honey is secreted by the sepals in certain Paeonies; by the petals in Ranunculus, Delphinium, Helleborus, etc.; by the stamens in Pulsatilla; by the ovary in Caltha; while it is entirely absent in Clematis, Anemone, and Thalictrum. The conspicuousness of the flower is due to the corolla in Ranunculus; to the calyx in Anemone, Caltha, and Helleborus; to both in Aquilegia and Delphinium; to the stamens in Thalictrum. The honey is in some cases easily accessible, in others it is situated at the end of a long spur. The former species are capable of self-fertilisation, the latter are said by H. Muller to have lost their power.