  We determine the maximum distance between any two of the center, centroid,
and subtree core among trees with a given order. Corresponding results are
obtained for trees with given maximum degree and also for trees with given
diameter. The problem of the maximum distance between the centroid and the
subtree core among trees with given order and diameter becomes difficult. It
can be solved in terms of the problem of minimizing the number of
root-containing subtrees in a rooted tree of given order and height. While the
latter problem remains unsolved, we provide a partial characterization of the
extremal structure.
