  We characterize completely the capacity for (nondegenerate) multistationarity
of mass action reaction networks with one-dimensional stoichiometric subspace
in terms of reaction structure. Specifically, we show that networks with two or
more source complexes have the capacity for multistationarity if and only if
they have both patterns $(\to, \gets)$ and $(\gets, \to)$ in some 1D
projections. Moreover, we specify the classes of networks for which only
degenerate multiple steady states may occur. In particular, we characterize the
capacity for nondegenerate multistationarity of small networks composed of one
irreversible and one reversible reaction, or two reversible reactions
