THE RESPONSE OF ROOTS AND ROOT SYSTEMS TO THEIR ENVIRONMENT - AN INTERPRETATION DERIVED FROM AN ANALYSIS OF THE HIERARCHICAL ORGANIZATION OF PLANT LIFE

Plant life is viewed as a hierarchy composed of five levels of increasing complexity that extend from the cell to the community. Roots and root systems are included in the organ and organismic levels. Each level has a structuring role by providing elements for the next higher level; each is also a source of information that regulates processes at the lower levels. Interactions between a triplet of levels constitute a homeostat. A common set of sub-systems supports each level. One of these sub-systems is an input transducer which captures information relating to the environment. The environment may be either the immediate environment of the level in question, furnished from the level above, or the ambient environment of soil, atmosphere, etc. The former source of information induces plastic responses at the level which receives it; the latter, if it is of an extreme or life-threatening form, induces regenerative responses. Examples of both of these types of response are discussed, particularly as they apply to roots and root systems of terrestrial plants.