Fig.— The flowers of the fig are very minute and crowded on the inner surface of an urnlike receptacle, which becomes the fig fruit. The wild forms of the fig, called capri figs, have three kinds of flowers in their re ceptacles, female flowers that upon fertilization are capable of producing seeds, female flowers (gall flowers) of such a structure that the female insect can easily lay her eggs in them, they serving as food for the young insects, and male flowers. The fig cultivated for its fruit has only the first kind of flowers. A fe male fig wasp (Blastophaga) emerging from a gall flower of a capri-fig finds the male flowers mature and shedding an abundance of pollen so that as she works her way around in the rather limited space in making her exit from the receptacle she becomes covered with pollen. She immediately seeks out an other young receptacle and forces her way in through the narrow opening, leaving her wings behind in the process. She hunts around in the receptacle for the gall flowers and lays an egg in each one she finds. In her search she passes over the stigmas of the other type of female flowers and pollenizes them. Or it may be that she enters the receptacle of a fig in which case she searches in vain for the gall flowers but in her search pollenizes the female flowers. She at length dies of exhaustion, but her work is done so far as the plant is concerned. It is customary for growers of figs to hang branches of capri-figs from which the gall insects are just emerging in the fig trees in order that the latter may set fruit. There are many species
of the genus Ficus and many species of Blas tophaga corresponding. In most species of Ficus there is not so strong a differentiation into gall flowers and fertile flowers as in the capri-fig.
Origin of the Special Much has been written to try to explain the minute correspondence of structures of flowers and the insects that fertilize them. In view of the fact that we are as yet far from any agreement as to the kinetic factors of evolution it may be imagined that these attempted ex planations are mostly in the nature of specula tions in which the writers attempt to find sup port for preconceived theories, rather than to draw up a hypothesis to fit observed facts. It seems almost beyond doubt that natural selec tion has had a large part in the elimination of unfavorable modifications, but we still do not know what causes these variations in the first place or even whether there is an observable relation between the kind of modification and the conditions under which the plants and in sects have developed. Until these questions are in more universal agreement it may be well to leave the subject without further specu lation.
Darwin, 'Forms of Flow ers' (London 1877) ; Knuth, 'Handbook of Flower Pollination> (Eng. trans., Oxford 1906); Kerner von Marilaun, 'Flowers and their Unbidden Guests' (Eng. trans. 1878).