  As in the first part of this paper (hep-th 9204092), solutions to a string
equation are regarded as fixed points of some additional symmetries of a
hierarchy of integrable equations. In this part matrix hierarchies are studied:
the multi-component KP and KdV hierarchies, and the modified KdV hierarchy as
their reduction. In particular, the action of additional symmetries on the
Grassmannian is found, as well as Virasoro constraints on the $\tau$-functions.
The matrix string equations are known to be involved in some matrix models.
