  A topology $\tau$ on a set $X$ is called maximal connected if it is
connected, but no strictly finer topology $\tau^* > \tau$ is connected. We
consider a construction of so-called tree sums of topological spaces, and we
show how this construction preserves maximal connectedness and also related
properties of strong connectedness and essential connectedness.
  We also recall the characterization of finitely generated maximal connected
spaces and reformulate it in the language of specialization preorder and
graphs, from which it is clear that finitely generated maximal connected spaces
are precisely $T_\frac{1}{2}$ tree sums of copies of the Sierpi\'nski space.
