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 natural order contains only two British genera, Fumaria and Corydalis. The flowers of Fumaria have not yet, I think, been satisfactorily explained. Their form and arrangement are very singular, but they are not very conspicuous, and are said to be little visited by insects, being, according to Muller, self-fertile.
In Corydalis, on the contrary, the flowers are much larger, more conspicuous, and, at least in C. cava, are said to have lost the power of self-fertilisation. Hildebrand has found (Ueber die Bestaiibungs Vorrich-tungen bei den Fumariaceen) that they are absolutely sterile with their own pollen, and only imperfectly fertile with that from other flowers of the same plant, so that they can only be completely fertilised by that from a different plant. The tube of the flower is 12 millimetres long, and as the honey only occupies at most 4 - 5 millimetres, it is inaccessible to the Hive bee, whose proboscis is only 6 mm. long, and almost so to the common humble bee, in which it is 7 - 9, or at most 10 mm. long. The latter can reach the honey, but not lap it conveniently. She however, is in the habit of biting a hole through the tube, by which means she obtains access to the honey, and in some plants the greater number of flowers will be found to have been treated in this manner. Several other bees, for instance, the hive bee, Andrena albicans, K.; A. nitida, Fourc.; Sphecodes gibbus, L.; and Nomada fabricana, L., have been observed by Muller to make use of the entrance thus prepared for them. Moreover, though the hive bees are unable to suck the flowers in their natural condition, the flowers are visited by them for the sake of their pollen.
The upper petal is produced into a long spur. The two middle petals form a sort of sheath, surrounding the stamens and pistil; at about a third of their length from the base is a peculiar fold of the edge, which acts as a sort of hinge, so that the terminal part, which forms a sort of sheath or cap to the anthers and stigma, is somewhat moveable. The stamens are united into an upper and lower group. The upper basal edge of the upper group is produced into a long spur, which lies in the spur of the upper petal, and the tip of which secretes honey. When a bee visits the flower, she depresses the anther cap, and the anthers and pistil thus exposed rub against her breast. When the pressure is removed the cap resumes its place and again protects the anthers and pistil. Our common English Fumaria officinalis is formed on the same plan as Corydahs cava, the spur, however, being quite short. It appears, moreover, to be self-fertile, and in spite of its complex organisation seems to be but rarely visited, at least by day.
Hildebrand never saw an insect on the flowers. H. Muller saw them occasionally visited by the honey bee. In F. officinalis, as in C. cava, the anther cap is elastic, and on the departure of the insect resumes its original place. It is interesting that in other species of each genus (none of which however are English), as for instance C. ochroleuca and F. spicata, the pillar formed by the stamens and pistil is in a state of tension, but is retained in its place by the two petals forming the cap. These are as it were locked together, but when once separated by the pressure of the bee, the pillar formed by the stamens and pistil is set free, and springs up, thus dusting the insect. This process only happens once in each flower. Though these species are not British, I mention this here, because we shall find a very similar process in some of the Leguminosse (p. 86), and it is most interesting to find such a remarkable arrangement thus repeated in very different groups.