Abstract: Most multicellular organisms can be categorised by two words: hierarchy and composite. The underlying fractal geometry of nature – at least in terms of provision of infrastructure – provides much of the hierarchy, although many materials for which infrastructure is not an integral factor are also strongly hierarchical. Plants can therefore be modelled using recursive computer programs which add structures as the size increases. However, problems with mechanical stability also increase as the structure grows, so the plant changes from deriving stiffness from internal pressure to cross-linking the cell wall components permanently. However, this compromises the ability of the plant to grow and repair itself.