embryo once it has hatched. In viviparous animals (animals whose offspring spend at least some time developing within a parent's body), the offspring is typically referred to as an embryo while inside of the parent, and is no longer considered an embryo after birth or exit from the parent. However, the extent of development and growth accomplished while inside of an egg or parent varies significantly from species to species, so much so that the processes that take place after hatching or birth in one species may take place well before those events in another. Therefore, according to one textbook, it is common for scientists interpret the scope of embryology broadly as the study of the development of animals. Plant embryos Flowering plants (angiosperms) create embryos after the fertilization of a haploid ovule by pollen. The DNA from the ovule and pollen combine to form a diploid, single-cell zygote that will develop into an embryo. The zygote, which will divide multiple times as it progresses throughout embryonic development, is one part of a seed. Other seed components include the endosperm, which is tissue rich in nutrients that will help support the growing plant embryo, and the seed coat, which is a protective outer covering. The first cell division of a zygote is asymmetric, resulting in an embryo with one small cell (the apical cell) and one large cell (the basal cell). The small, apical cell will eventually give rise to most of the structures of the mature plant, such as the stem, leaves, and roots. The larger basal cell will give rise to the suspensor, which connects the embryo to the endosperm so that nutrients can pass between them. The plant embryo cells continue to divide and progress through developmental stages named for their general appearance: globular, heart, and torpedo. In the globular stage, three basic tissue types (dermal, ground, and vascular) can be recognized. The dermal tissue will give rise to the epidermis or outer covering of a plant, ground tissue will give rise to inner plant material that functions in photosynthesis, resource storage, and physical support, and vascular tissue will give rise to connective tissue like the xylem and phloem that transport fluid, nutrients, and minerals throughout the plant. In heart stage, one or two cotyledons (embryonic leaves) will form. Meristems (centers of stem cell activity) develop during the torpedo stage, and will eventually produce many of the