Using a conformal transformation to set up the iterative nonlinear equation
s, We Study analytically the kinetics of growth of parallel needles. We est
ablish a discrete Fokker-Planck equation for the probability of finding at
time t a given distribution of needle lengths. In the linear regime, it sho
ws a short-wavelength Laplacian instability which we investigate in detail.
From the crossover of the solutions to the nonlinear regime, we deduce ana
lytically the general scale invariance of the two-dimensional models.