Terminology of Relative Growth-Rates

Abstract

FOR many years past, biologists have been interested in the rates of growth of parts of organisms in relation to the whole or to other parts. Such ratios were termed by Huxley¹ constant differential growth-ratios, and the whole process by Pezard² heterogony. The process may obviously be either positive, if the relative size of the part increases with time (that is, grows more rapidly than the whole), or negative, if the relative size diminishes (that is, grows more slowly). If it attains an extreme degree, it might be called, in Champy's phrase³, dysharmonic growth. Some authors, for example, Teissier⁴ (who, with Needham⁵, introduced the application of these concepts to the chemical constitution of the body) at first adopted this usage; but it has not proved acceptable, since, if we liken the organism to a piece of music, the growth of all parts at the same rate would be unison, and their growth at different rates harmony, not disharmony. Later, after the term heterogony had come into very general use, Huxley and Teissier⁶ proposed its replacement by allometry on the ground that heterogony had previously for a long time been employed by sex physiologists to denote a special type of reproductive cycle.