ABSTRACT
Introduction This chapter will review structural changes in regenerating plant organs and tissues growing either under ex vitro or in vitro conditions. Such development may result in wound healing (callus formation and histogenesis) (211, 212) or the de novo regeneration of organized structures in the form of roots and buds (213, 214) or bipolar embryos (197, 199). (Note: in this chapter the photographs are arranged in sequence after the text.)
Normal Development of the Intact Plant In seed plants the embryo normally develops from the zygote formed from the fertilization of the egg by a male gamete. However, in Alchemilla (215) and a number of other taxa (Raghavan, 1986; Mauseth, 1988) the ovules produce embryos apomictically, i.e. without fertilization. The embryo is typically a wellorganized, bipolar structure (216) with one pole terminated by the shoot apex (plumule or epicotyl) and the opposite end by the root apex (radicle). In taxa with minute seeds, such as orchids and some parasitic flowering plants, the embryo is not well-differentiated (Mauseth, 1988). In conifers a number of cotyledons are present, but in flowering plants the dicotyledons (71 – A, B, 216) have two cotyledons whilst monocotyledons (71 – C) possess only a single one.
