  We review the emergence of the ten-dimensional fermionic closed string
theories from subspaces of the Hilbert space of the 26-dimensional bosonic
closed string theory compactified on an $E_8\times SO(16)$ lattice. They arise
from a consistent truncation procedure which generates space-time fermions out
of bosons. This procedure is extended to open string sectors. We prove, from
bosonic considerations alone, that truncation of the unique tadpole-free
$SO(2^{13})$ bosonic string theory compactified on the above lattice determines
the anomaly free Chan-Paton group of the Type I theory. It also yields the
Chan-Paton groups making Type O theories tadpole-free. These results establish
a link between all M-theory strings and the bosonic string within the framework
of conformal field theory. Its significance is discussed.
