Let σ be a simple involution of an algebraic semisimple group G and
let H be the subgroup of G of points fixed by σ. If the restricted
root system is of type A, C or BC and G is simply connected or if the
restricted root system is of type B and G is adjoint, then we describe a
standard monomial theory and the equations for the coordinate ring k[G/H]
using the standard monomial theory and the Pl\"ucker relations of an
appropriate (maybe infinite dimensional) Grassmann variety.Comment: 48 page