 Subdivision rules were applied by Cannon , Floyd and Parry ( 2000 ) to the study of large @-@ scale growth patterns of biological organisms . Cannon , Floyd and Parry produced a mathematical growth model which demonstrated that some systems determined by simple finite subdivision rules can results in objects ( in their example , a tree trunk ) whose large @-@ scale form oscillates wildly over time even though the local subdivision laws remain the same . Cannon , Floyd and Parry also applied their model to the analysis of the growth patterns of rat tissue . They suggested that the " negatively curved " ( or non @-@ <unk> ) nature of microscopic growth patterns of biological organisms is one of the key reasons why large @-@ scale organisms do not look like crystals or polyhedral shapes but in fact in many cases resemble self @-@ similar fractals . In particular they suggested that such " negatively curved " local structure is manifested in highly folded and highly connected nature of the brain and the lung tissue . 
