  This paper is a sequel to work of Dynkin on subroot lattices of root lattices
and to work of Carter on presentations of Weyl group elements as products of
reflections. The quotients $L/L_1$ are calculated for all irreducible root
lattices $L$ and all subroot lattices $L_1$. The reduced (i.e. those with
minimal number of reflections) presentations of Weyl group elements as products
of arbitrary reflections are classified. Also nonreduced presentations are
studied. Quasi Coxeter elements and strict quasi Coxeter elements are defined
and classified. An application to extended affine root lattices is given. A
side result is that any set of roots which generates the root lattice contains
a $Z$-basis of the root lattice.
