  This note is concerned with an important for modelling question of existence
of solutions of stochastic partial differential equations as proper stochastic
processes, rather than processes in the generalized sense. We consider a first
order stochastic partial differential equations of the form $\pd Ut = DW$, and
$\pd Ut-\pd Ux= DW$, where $D$ is a differential operator and $W(t,x)$ is a
continuous but non-differentiable function (field).
  We give a necessary and sufficient condition for stochastic equations to have
solutions as functions. The result is then applied to the equation for a yield
curve. Proofs are based on probability arguments.
