The S-shaped, or sigmoid, curve is typical of the growth pattern of individ-
ual organs, or a whole plant, and of populations of plants (Fig. 1.2). It can
be shown to consist of at least five distinct phases: 1) an initial lag period
during which internal changes occur that are preparatory to growth; 2) a
phase of ever-increasing rate of growth. (Because the logarithm of growth
rate, when plotted against time, gives a straight line during this period, this
phase is frequently referred to as the log period of growth or “the grand
period of growth.”); 3) a phase in which growth rate gradually diminishes;
4) a point at which the organism reaches maturity and growth ceases. If the
curve is prolonged further, a time will arrive when 5) senescence and death
of the organism set in, giving rise to another component of the growth
curve (Mitchell, 1970, p. 95)
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