Sensitive growth grammars form an extended variant of L-systems. They were defined by Winfried Kurth and implemented in the software GROGRA. Their definition was guided by the fact that the pure L-systems formalism cannot cope properly with the representation of the great variety of plant architecture and growth behaviour. The new features include:
- Global Sensitivity
- Global sensitivity means a dependence of growth on the overall structure and not only on neighbouring elements. Examples are
- the dependence on orientation: Plant growth is influenced by the directions of gravity (geotropism) and light (phototropism).
- the dependence on density: Plant parts cannot penetrate obstacles such as, e.g., other plant parts or walls; instead, they have to bypass the obstacle by deviating growth movements.
- the dependence on light: Besides the orientation of light, its mere availability is important. This is influenced by overshadowing by other plant parts and obstacles.
- Local Variables
- Local variables can be attached to elements of the growing structure. They may represent local properties like carbon or nutrient pools.
- Tree Calculations
- Tree calculations perform arithmetics on the subtree emerging out of a given element. Such a calculation may determine the total length or mass of a subtree, and these values in turn may have an influence on the further growth of a plant.