In this paper we study the sidebranching development of solidifying dendrites both experimentally and by numerical integration of
a phase-field model with a noise term. Our results support the idea that sidebranching is originated through the selective amplification of natural noise at the tip. The initial stages turn to be of crucial importance in the selection of the final noisy shape. However, our results suggest that after the stochastic initial disturbance, a deterministic mechanism dominates the growth and
screening-off process of sidebranching.