The English holly (Ilex aquifolium) is a dioecious species, meaning that it has separate male and female plants. At the beginning of spring, honey bees move pollen from the creamy white flowers produced by male plants to the nearly identical flowers produced by the female plants. The process by which male flowers produce pollen and female flowers yield sex cells ready for pollination is called meiosis.
During meiosis, the number of chromosomes of each male and female holly plant is reduced by half from what are called diploid to haploid cells. Through pollination the haploid cells of each parent are combined to form a sex cell called a gamete. A gamete divides and grows into an adult plant. The union of male and female holly haploids produces a plant that is genetically different from its parents.
Although at a glance, both male and female holly flowers look the same, they are not. Both have four or five egg-shaped sepals with a membranous coating; these green sepals are located beneath the white flower petals. Holly stamens, the male parts of the plant that produce pollen, have oblong anthers that sit atop filaments; the anthers hold the pollen.The female flowers have less prominent male stamens that are usually sterile.
On most female flowers, the stigma that receives the male pollen has a stalk; the stigma of a holly plant does not. Four holly stigma contain a sticky substance to attract and hold pollen; the stigma lie directly on top of the ovary at the bottom of the flower. The ovary contains ovules; fertilized ovules produce plant eggs.
In the male holly flower, microsporangium, tiny organisms that produce spores, undergo meiosis, yielding DNA copies of both its maternal and paternal parents. This is followed by mitosis, the process by which the chromosomes in a cell divide into the centers of two cells, each of which contains an identical set of chromosomes. Meiosis plus mitosis yields pollen that contains DNA from both parents of the male plant.
The ovules inside the holly female ovary have outer layers called the nucellus; these surround the female gametophyte or embryo sac. Through the process of meiosis, the embro sac produces an egg cell ready to be fertilized by pollen. Once a holly egg cell receives pollen from a male flower, it develops into a zygote that becomes a seed containing the genetic characteristics of both its parents.