The two-dimensional integrated Pedersen conductivity model for F region plasma cloud striation development may be cast in dimensionless form. The result implies that a structure's stability against bifurcation depends upon whether a diffusion parameter R exceeds a critical value. The critical R for striations is determined by high resolution computer simulation for conductivity ratios M from 2 to 30. Our results combined with electron diffusivity of order 1 m2/s agree with observed minimum scale sizes of 15 m. For turbulent diffusivity of order 100 m2/s, our results agree with frequent observations of kilometer scale structures which 'freeze up' and last for times of order 104 s. This lifetime is also predicted by our results.