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 tube by recognition and hydration of the pollen that allows for germination of the tube and ultimate growth. In the pollen grain, the generative cell gives rise to the sperm, whereas the vegetative cells have a tube cell that grows the pollen tube. There is competition in this step as many pollen grains may compete to reach the egg. The stigma plays a role in guiding the sperm to a receptive ovule, in the case of many ovules. Only compatible pollen grains are allowed to grow as determined by signaling with the stigma. Some plants have mechanisms in place to prevent