  We consider the exact superpotential of N=1 super Yang-Mills theory with
gauge group SO(N) and arbitrary tree-level polynomial superpotential of one
adjoint Higgs field. A field-theoretic derivation of the glueball
superpotential is given, based on factorization of the N=2 Seiberg-Witten
curve. Following the conjecture of Dijkgraaf and Vafa, the result is matched
with the corresponding SO(N) matrix model prediction. The verification involves
an explicit solution of the first non-trivial loop equation, relating the
spherical free energy to that of the non-orientable surfaces with topology
$RP^2$.
