The application of reaction-diffusion models is limited
by one key assumption originally made by Turing: the medium on which the
reaction-diffusion takes place, be it a surface or a line, does not grow.
One of the first computer models of growing biological
structures was proposed by Eden [Ede1960].
Eden's model is very simple. The simulation takes place in a square grid.
A single initial particle is placed in the center of this grid. The subsequent
particles are attached, one by one, to randomly chosen points on the border
of the structure formed in the previous steps.
A sample structure obtained this way is shown in
Plate 8.
The colors indicate the state of the structure at different points in time.
A structure developing according to Eden's model is roughly circular. | 
