Plastic flow in metals occurs by a dislocation mechanism in which strain is accommodated by a dislocation flux. This results in tangled networks of dislocations which self-organize into stable cell structures with two characteristic length scales. These structures have a number of remarkable properties not least of which is that they exhibit scaling. We examine the idea that the evolution of geometrically necessary boundaries is dominated byrandom fluctuations, construct a simple model of cell orientations and show that scaling of misorientation distributions emerges a direct result of Gaussian white noise. We investigate whether hierachical microstructures containing both incidental dislocation boundaries and geometrically necessary boundaries can be studied using the same model. The results are compared with the experimental measurements and show good agreement.