During spring, fruit trees grow copious flowers. Contained within the circumference of the petals are the male pollen and female ovules. Pollen is found on the anthers, which top the filaments that surround the ovule containing the pistil. The tip of the pistil is the sticky stigma, and it acts as a receptor for pollen. The process of getting the pollen to the stigma is pollination.
Fruit tree growers rely on beneficial insects, such as honeybees, to pollinate the flowers. Apricot and peach trees can self-pollinate; a bee that brushes against the anthers and then transfers the pollen to the flower's stigma successfully pollinates it. Pears and sweet cherry trees require cross pollination, which requires the bee to transfer pollen from one tree to another.
After pollination occurs, the pollen attached to the stigma germinates and develops a tube that grows through the style into the ovary. Once this process is complete, the sperm contained in the pollen travels through the tube and unites with the ovule. It is at this time that fertilization occurs. Nutrient rich tissue now begins to grow. It becomes the endosperm that will surround the embryo. Only fertilized flowers will become seed bearing fruits on the tree.
Seed-Containing Fruit Production
The fertilized ovule undergoes cell division and growth as it develops to become a seed. The ovary containing the ovule matures, grows and becomes the fruit that surrounds the seed. The fruit functions as protection and also distribution mechanism for the seed.
The amount of fruit a tree produces varies. It depends heavily on external influences. For example, a tree that relies on bees for pollination will suffer when temperatures are so cold---usually below 55 to 60 degrees Fahrenheit---that fewer bees are active. Unseasonably high spring temperatures may result in drying stigma surfaces that make it impossible for pollen to adhere or germinate.
Improper pruning may adversely affect fruit growth. For example, fig trees produce two crops: the first grows on old wood, while the second grows on current wood. Improper pruning of old wood may greatly reduce the first round of fruit production. Nectarines only grow fruit on current-season wood and failure to prune old wood results in reduced new wood growth.