whatTwo fungal colonies grow into a body of scattered nutrients from opposite edges and fill it evenly, the way lungs fill a chest, until they meet along a seam that neither crosses. Click to scatter more nutrients and the nearest colony grows out to them.

whyLungs, veins, river deltas and fungal mats all solve the same problem, reaching every part of a space without wasting a branch, and none of them has a plan. The piece shows how even coverage falls out of a single greedy rule: grow toward what nobody has claimed yet.

howNutrient points are scattered inside a silhouette. Every unclaimed nutrient pulls on the nearest branch tip within reach, each tip grows a short step along the average of its pulls, and any nutrient a tip comes close to is eaten. One more rule, the one real fungi keep: a tip that would grow within reach of the other colony stops. So the nutrients between two colonies lie in reach of both and are eaten by neither, and they remain as a dotted line, the seam. Stroke weight follows how much of the network a branch feeds. The sparkline is the share of nutrients eaten; the readout also measures how evenly the branches are spread and counts the seam.