In this paper several
characterizations of arboroids, arcwise connected dendritic spaces, and a related,
wider class of spaces which we call weakly nested are obtained. For example, it is
shown that an arcwise connected Hausdorff space is dendritic if and only if it is
uniquely arcwise connected and each connected subspace is arcwise connected. These
characterizations give considerable insight into the internal structure of such spaces.
Also a number of characterizations of topological intervals and trees are
given, and an interesting embedding theorem for weakly nested spaces is
proved.