Physarum polycephalum

Time in dish0 min

Plasmodium area—

Food left—

Vein network—

Sim rate—

Speed×2

Experiment Show chemical signals

ColoursRecolour every part of the dish and mix your own palette

Palette

What is simulated

Fan-shaped front: the young edge of the plasmodium advances as a lobed sheet in every direction, even with no food nearby.
Adaptive vein network: cytoplasm flows from the food and the inoculum to the fronts and between food sources. Routes that carry more flow thicken and unused ones fade (inspired by Tero et al., 2010).
Arms and mesh: fronts fed by veins grow faster; the rest stall and withdraw. Over time the veins form a looping mesh across the dish.
Masses on food: the plasmodium engulfs each food item with a thick mass while nutrient remains. Well fed, it keeps exploring; with no food left, it migrates and leaves slime behind.
Chemotaxis and feeding: food scent diffuses through the agar and steers growth. Energy is shared across the whole connected plasmodium; isolated fragments starve.

What it avoids

Extracellular slime: withdrawing sheet leaves slime, and the mould will not regrow over it unless it smells food nearby: an external spatial memory (Reid et al., 2012).
Salt and quinine: they dissolve into the agar, slow growth and speed up withdrawal.
Bright light: the plasmodium is photophobic. Paint a lit area and it will not grow into it, parts already inside pull back, and staying there costs it extra energy. In the lab, light is used to steer it.

Scale and limits

A 90 mm dish on a 400 × 400 grid (0.23 mm per cell). Each step is 40 s, calibrated so the front advances at about 1 cm/h. Nutrient and scent values are relative, not measured. It is a 2D territory-and-network model: veins are noisy least-cost routes rather than a full hydraulic calculation, and there is no rhythmic pumping or sporulation.