When plants are grown in isolation, relationships between stem diameter, height, and plant mass generally show simple allometry (relationships are linear on log-log scale). When plants are competing, however, these relationships are curvilinear or discontinuous. When plants are not competing, the allometric relationships among individuals of different sizes at one point in time and the allometry of individual plants as they grow appear to be similar, but these two classes of allometric relationships are very different for competing plants. A simple model explains both static and dynamic patterns of plant allometry in terms of 1) the allometric responses of individual plants to competition, and 2) the size dependence of growth after the onset of competition. -from Authors