Fractal Slime Mould

This is an interesting diagram I found in "Signs Of Life: How Complexity Pervades Biology" by Ricard V Sole.
I had a quick google afterwards and found quite an interesting paper on pattern formation in cellular slime moulds: http://www.math.umn.edu/~othmer/papers/imart.pdf

How has this been done? Are these slices that have been taken from an environment rather than cultivated?