Growing in fertile soils exposed to abundant sunshine, pear trees (Pyrus spp.) produce flowers in an attempt to reproduce--developing seeds that will yield new pear plants. There are about 45 different species of pears, all native to the temperate climates of the Northern Hemisphere. Pear blossoms are always white in color and often the anthers in them are red-tinted. These ornamental flowers also are saucer- or bowl-shaped when they fully open in springtime.
Pear trees need a pronounced winter dormancy in order to produce flowers the following spring. Typically this dormancy is marked by cool to cold temperatures that last for several weeks or months. This necessary exposure to cold in winter is known as vernalization. Without it, no flower buds will form or greatly reduced numbers of flowers are produced. In some climates, a drought over the winter can lessen the amount of winter cold needed to successfully vernalize.
In early spring before leaves unfurl, flower buds develop on the ends of branches on short woody stubs called spurs. Clusters of flowers appear; each individual blossom comprises five white petals with at least 10 pollen-carrying (male) stamens and a central pistil that houses the (female) ovary. Each pollen grain contains one-half of the pear's genetic materials or DNA, while each ovule in the base of the pistil contains the other half.
The pear blossom is dependent upon insects, mainly species of bees, to visit each blossom in order to transfer male pollen grains onto the tip of the female pistil organ, the stigma. Pollination is the first step in bringing together the two halves of genetic material to create a seed.
Once pollination occurs, enzymes are released from the pollen grains and a burrowing tube forms. This tube facilitates the movement of the pollen grain through the neck tissue of the pistil (the style). Eventually, the pollen grain reaches the ovary, and any one of the many ovules (eggs) at the base of the pistil and fuses with it. This fertilization blends the male genetic material of the pollen grain with that of the female ovule, creating an embryo.
After pollination and fertilization, the ovary of each blossom expands and ripens into a sweet, juicy fleshy body that we recognize as the pear fruit. Inside the fruit, the embryos develop and mature through various influxes of hormones and nutrients. Since each seed contains the full DNA set, it is viable and has the potential to sprout and grow into a new pear plant. The ripening of the fruit coincides with the maturation of the seeds in the fruit's core. If you cut open a ripe pear you will see five chambers, each with one or two seeds. Remember, each of these seeds began as an individual ovule and could not become a seed until fertilized by pollen grains.