Adventitious roots of whole plants: their forms, functions, and evolution

Abstract

Many plants have two root systems that differ in origin. One is the primary root system whose origin can be traced back to the radicle developed during embryogenesis. The other is an adventitious root system which arises on parts of the plant not originating from the embryonic root — that is, the roots arise on parts of the shoot. Adventitious roots usually initiate endogenously from tissue within the parent plant (see Chapter 4) though a few cases of exogenous origin are known [1]. Roots which arise on the primary root out of the usual acropetal sequence that characterises lateral roots, either as a normal part of development or after experimental treatment, are sometimes also called adventitious. The term adventive can perhaps be applied to such roots to distinguish them from roots of shoot origin.