slime moulds

the organism

physarum polycephalum is a slime mould. not a fungus — no hyphae, no fruiting body, no relation to the mushrooms next door.

in its plasmodial stage it is one cell. millions of nuclei sharing a single interior with no walls between them, spread across a log at a size you can see without a microscope.

it eats by growing tubes toward food and abandoning the ones that stop paying.

the tubes move by shuttle streaming. calcium-driven contractions squeeze the walls in rhythm and slosh the cytoplasm back and forth at up to a millimetre a second, reversing direction about every two minutes. tubes carrying traffic thicken. tubes that go quiet get resorbed.

that is how it solves mazes. and how it laid out the Tokyo rail network when researchers put oat flakes where the towns are.

what this is

agents. each one samples the trail map at three points ahead, turns toward the strongest, steps, and leaves a deposit behind it. the map blurs and fades. nothing in that loop mentions networks.

it gets the pattern right and the mechanism wrong.

physarum is one cell, so there is no population to split into agents. these particles stand in for cytoplasm.

nothing here oscillates. they crawl forward and never reverse, so the streaming that actually moves material is missing.

and the tubes have no thickness. brightness is trail concentration, not the veins that real reinforcement acts on.

the food is real though. drop some on the plate and it emits, the agents smell it, and the routes between sources get walked often enough to stay lit while everything else fades. nobody computes the route. it is just the paths that keep earning traffic.

and it gets eaten. a flake shrinks as agents graze it, calls more weakly as it empties, and disappears when it is gone. feed it and it thickens. stop, and upkeep outruns what it can find — deposits thin, decay wins, the crawl slows, and the population dies back to a dormant remnant. leave that remnant food and it comes back.

a decent picture of what physarum does. no account of how.