thanks for the messages on the weird colonies topic. Brennan (address
unknown) and Ron Sapolsky suggested a very plausible non-biological
Finger-like colonies arise if a cell falls into a ruptured bubble
directly under the agar surface. The colony growing out becomes
physically constrained and finaly "squeezed out like toothpaste"
by the pressure of its own growth. I believe this since the "fingers"
I saw had, indeed, a bubble full of cells at its basis.
So, it is just physics, and no mysterious epigenetic phenomenon...
P.S. I am quite happy with this explanation. Isn't it a worrying
symptom of scientism?