The Place of Roots in Plant Development

Abstract

A plant is a complex system of branched axes, any of which may be in either a vegetative or a reproductive phase of development. Indeed, given the amazing diversity of plant life, repetitive branching of morphologically distinctive axes is probably the only true generality that can be attributed to plants (see Schultz-Schultzenstein 1861). At a more detailed level, in those axes expressing the vegetative phase, it can be seen that their structure is comprised of a set of reiterated morphological units, a structure which, moreover, tends to be recapitulated in each new axis originating from a branching event. But what exactly is the reiterated structure that is so faithfully reproduced by branching? Where do the type of roots termed “adventitious” fit into this branching scheme, and what contribution do they make to the plant’s life cycle? We shall attempt to answer these questions in the following pages but, put briefly, our thesis is that so-called “adventitious roots” comprise a range of shoot-borne roots which are members of a set of reiterated morphological units that, in turn, are integral to plant architecture. Not unexpectedly, these roots are components of a strategem of plant development that is geared to vegetative propagation and nutrient acquisition. These developmental ploys are accomplished in diverse manners, revealing the astonishingly multifarious nature of root growth and development. First, however, it is necessary to clarify what is meant by the two terms alreadyused, “shoot borne-root” and “adventitious root”. In doing so, some explanation is required of the reiterative nature of plant construction which, although more evidently of relevance to the shoot system, does nevertheless emphasise the indissoluble link between root and shoot systems in the life of the plant.