ABC model of flower development well as in the determination of the floral meristem. Therefore, the "AG" mutants are devoid of androecium and gynoecium and they have petals and sepals in their place. In addition, the growth in the centre of the flower is undifferentiated, therefore the petals and sepals grow in repetitive verticils. The "PLENA" ("PLE") gene is present in "A. majus", in place of the "AG" gene, although it is not an ortholog. However, the "FARINELLI" ("FAR") gene is an ortholog, which is specific to the development of the anthers and the maturation of pollen. In "Petunia", "Antirrhinum" and in maize the C
Pollen grains often have air bladders, or vesicles, called sacci. The sacci are not actually balloons, but are sponge-like, and increase the buoyancy of the pollen grain and help keep it aloft in the wind, as most gymnosperms are anemophilous. Pollen can be monosaccate, (containing one saccus) or bisaccate (containing two sacci). Modern pine, spruce, and yellowwood trees all produce saccate pollen. The transfer of pollen grains to the female reproductive structure (pistil in angiosperms) is called pollination. This transfer can be mediated by the wind, in which case the plant is described as anemophilous (literally wind-loving). Anemophilous plants typically produce