  This paper studies the number conservation property of 1-dimensional
non-uniform cellular automata (CAs). In a non-uniform cellular automaton (CA),
different cells may follow different rules. The present work considers that the
cells follow Wolfram's CAs rules. A characterization tool, named Reachability
tree is used to discover the number conservation property of non-uniform CAs.
Then a decision algorithm is reported to conclude whether a given non-uniform
CA with $n$ cells is number conserving or not. Finally, a synthesis scheme is
developed to get an $n$-cell number conserving non-uniform CA.
