All but a relatively few plants are multicellular, and the majority have bodiescomposed of two major systems: the root system and the shoot system. The former is usually underground, and the latter above ground. To succeed and grow simultaneously in two such entirely different environments—air and soil—requires a myriad of adaptations, starting with cellular modifications into specialized kinds oftissues (groups of similar cells that are organized in a structural and functional unit) followed by development of organs (structures composed of several kinds of tissues grouped in a structural and functional unit). The acquisition of form and structure is called morphogenesis and is a highly orchestrated procedure controlled by the DNA of the plant cells but influenced as well by the environment.