  A parabolic stochastic PDE is studied analytically and numerically, when a
bifurcation parameter is slowly increased through its critical value. The aim
is to understand the effect of noise on delayed bifurcations in systems with
spatial degrees of freedom. Realisations of the nonautonomous stochastic PDE
remain near the unstable configuration for a long time after the bifurcation
parameter passes through its critical value, then jump to a new configuration.
The effect of the nonlinearity is to freeze in the spatial structure formed
from the noise near the critical value.
