We define a class of two-dimensional Markov random graphs with I, V, T
and Y-shaped nodes (vertices). These are termed polygonal models. The
construction extends our earlier work [1]-[5]. Most of the paper is c
oncerned with consistent polygonal models which are both stationary an
d isotropic and which admit an alternative description in terms of the
trajectories in space and time of a one-dimensional particle system w
ith motion, birth, death and branching. Examples of computer simulatio
ns based on this description are given.