1.1 Tree Segment
The structure of LIGNUM is modelled with simple basic units called tree compartments. The most important is tree segment. Loosely speaking it correspondence to an annual growth of a tree (e.g., the annual shoot of a Scots pine).
A tree segment consists of heartwood, sapwood and a layer of foliage all modelled as (hollow) cylinders. Heartwood is dead wood material, sapwood is living wood material responsible for nutrient and fluid flow in a tree. Foliage contains chloroplast able to photosynthesize.
1.2 Branching point
Branching point connects two or more tree segments together. Informally it is the place where the branches of the tree fork off from a stem or a branch. Currently no other physiolocal processes are modelled in branching point.
Bud is responsible for creating new tree compartments: buds, branching points and tree segments. Also each living bud has a growth direction and thus they determine the architecture of the tree.