It is an interesting fact that in plant science the study of development is not equated with embryology. Although the study of embryos has made significant contributions, it is clear that the framework of developmental study in the higher plants has been provided by postembryonic stages. A very important aspect of embryonic differentiation is the establishment of shoot and root apical meristems at approximately opposite poles of the embryonic body. These meristems, whose origins differ somewhat in the various groups of vascular plants, contribute relatively little to the actual development of the embryo, but they are the centers of postembryonic development, and by their continued activity they give rise to the shoot and root systems. The shoot- and root-building activity of these meristems does not represent a mere unfolding of embryonic rudiments; rather, it is a true epigenetic formation of organs and tissues that were not present in the embryo. Thus, all aspects of development – growth and differentiation, histogenesis and organogenesis – may be investigated in relation to the activity of apical meristems, and the size and accessibility of these formative regions, in comparison to the enclosed embryo, has made them favorable sites for both descriptive and experimental studies of plant development.

In the total development of the primary plant body via its meristems, it is obvious that many processes are taking place simultaneously. There can be little doubt that these processes are interrelated and that the interaction among them holds many important keys to the understanding of the plant body, its organization, and its integrated development.