Fig. 4. (Top) The possible density dependencies of the MT nucleation rate are an increasing function with (1) neither saturation nor threshold behavior (solid curve), (2) without threshold but with saturation (dashed curve), and (3) with both threshold and saturation (dotted curve). (Bottom) The possible density dependencies of the MT minus-end disassembly rate are a decreasing function without threshold behavior (solid curve) and with threshold behavior (dashed curve). The granule density, nucleation rate and disassembly rate are plotted in the non-dimensional units described in the text [g=1 in the untreated fragment, n(1)=1, v(0)=1].