If pollination is successful and fertilization takes place, a zygote is formed. It will then develop into an embryo that is contained within a seed. A seed is a complex structure. It contains diploid and triploid components. In addition, the outer layers of the seed are derived from maternal ovule tissue. Therefore, in addition to having two different ploidy states, the resulting seed is made up of parental and offspring sporophytic tissue. To examine this more closely, we will explore the development and anatomy of a seed.
The cell that results from the fusion of the egg and one sperm becomes the zygote. It is diploid and begins to form the basic structures of the embryo (i.e., the embryonic root and the cotyledons ). The cotyledons are also called "seed leaves." Plants that belong to Class Monocotyledone contain only one cotyledon and are referred to as monocotyledons or monocots ; some common examples are grass and corn. The other class of angiosperms is Dicotyledone. Plants in this class have two cotyledons and are referred to as dicotyledons or dicots ; some common examples are beans and pumpkins.
The cell that results from the other fertilization event is 3n (triploid). It has a nucleus formed from the fusion of two nuclei from the female gametophyte, and one nucleus from the male gametophyte. The tissue that forms from the triploid cell is known as endosperm , which contains the nutrients needed by the developing embryo. As a dicot embryo matures, most, if not all, of the endosperm is absorbed by the embryo. However, a monocot embryo usually does not absorb all of the endosperm. When we eat corn, the majority of the nutrients we eat are endosperm.
Recall from the nonflowering seed plant tutorial, the seed coat is formed from tissues in the ovule termed integuments. These tissues are diploid and are part of the parent plant. Thus, a seed consists of tissues that are made up entirely of the parental type (maternal sporophytic) and tissues that result from the recent fertilization.
Many seeds have shapes or structures that facilitate dispersal away from their parent plant and other seeds produced by their parent. This is important because once a seed germinates and takes root, it is unable to move, so if it takes root too close to another plant, they will compete for resources. Many seeds are dispersed by the wind. Wind-dispersed seeds often have wings or “parachutes” that help carry them away.
Some flowering plants have seeds that rely on animals for dispersal. In some cases, the animals eat the fruit and the seeds pass through their digestive system and are deposited away from where they were first eating. In other cases, animals will gather seeds (nuts) and hide or store them. While some will be eaten, others will “escape” and go on to germinate. These relationships are a type of mutualism. There are also seeds that will “hitch a ride” on an animal’s fur or a bird’s feathers, and won’t be removed until the animal grooms itself, again depositing them some distance away from where they were first picked up. This relationship is described as a parasitism if the animal's movement is hindered by the attached seeds.