  We show that a continuous local semiflow of $C^k$-maps on a
finite-dimensional $C^k$-manifold M can be embedded into a local $C^k$-flow on
M under some weak (necessary) assumptions. This result is applied to an open
problem in [fil/tei:01]. We prove that finite-dimensional realizations for
interest rate models are highly regular objects, namely given by submanifolds M
of $D(A^{\infty})$, where A is the generator of a strongly continuous
semigroup.
