Instead, Xia's algorithm takes a hint from a plausible model of how nature might actually work, and proceeds by an iterative process.

The leaf is grown in steps.

Each step involves two substeps.

In the first substep, certain new cells are added to the leaf at its fringes. Pipes are added to the system, connecting the new cells to nearby cells on the fringes.

This is the growth substep.

But after this substep, the resulting transport system may not be optimal.

So, in the next substep, an optimization is performed by tweaking the fine details of this transport system.

Neither our algorithm nor nature has the opportunity to globally the restructure the transport network once the leaf has grown to a certain stage.