  We recently have shown that a negative streamer in a sufficiently high
homogeneous field can branch spontaneously due to a Laplacian instability,
rather than approach a stationary mode of propagation with fixed radius. In our
previous simulations, the streamer started from a wide initial ionization seed
on the cathode. We here demonstrate in improved simulations that a streamer
emerging from a single electron branches in the same way. In fact, though the
evolving streamer is much more narrow, it branches after an even shorter
propagation distance.
