The initial growth of sidebranches in ammonium chloride dendrites.

We report measurements for the initial stages of sidebranching during the dendritic growth of ammonium chloride from supersaturated aqueous solution. The earliest sidebranches are approximately periodic; they are first evident about $36 \rho$ behind the tip, where $\rho$ is the tip radius, and have an average initial spacing of about $5 \rho$, though both values show considerable variation. The initial sidebranch amplitude grows approximately exponentially, but quickly saturates as sidebranches compete and coarsening sets in. This initial sidebranch growth is reasonably consistent with what would be expected for noise-driven sidebranches.