Fig. 2. Cell crowding and division. (A) Cell density saturates with time. The thick black line is the average of three growth experiments. The red and green curves are transformations of the fits performed in panel B. (B) Per capita division rate falls with crowding. The thick black line is a transformation of the experimental data in panel A. A linear fit was performed the two growth regions (spacing<60 µm, red line; and 100 µm<spacing<200 µm, green line). The red and green fits and the boundary line are transformed back into density vs. time space and shown in panel A. (C) Schematic of model cell. Cells are considered to have an incompressible core corresponding to the spacing at which cell division ceases, and compressible zone extending to the distance at which division begins to be sensitive to contact. This allows a calculation of the spacing-dependent division rate on a cell-by-cell basis. (D) Simulation per capita division rates. Several cell culture growth simulations were run with incompressible diameter 47 µm and different compressible zone thicknesses: 9 µm (red), 2 µm (blue), 0 µm (yellow), 50 µm (pink). The experimental data (black) is the same as in panel B.