Bulletin of Mathematical Biology (2006) 68: 753–784 DOI 10.1007/s11538-005-9004-5 ORIGINAL ARTICLE Cellular Modelling of Secondary Radial Growth in Conifer Trees: Application to Pinus radiata (D. Don) Lo¨ ıc Forest a,∗ , Jacques Demongeot a,b a Laboratoire Techniques de l’Imagerie, de la Mod´ elisation et de la Cognition (TIMC UMR CNRS 5525), Institut de l’Ing´ enierie et de l’Information de Sant´ e, Facult´ e de M´ edecine, 38706 La Tronche Cedex, France b Institut Universitaire de France, France Received: 10 November 2004 / Accepted: 13 April 2005 / Published online: 7 April 2006 C  Society for Mathematical Biology 2006 Abstract The radial growth of conifer trees proceeds from the dynamics of a merismatic tissue called vascular cambium or cambium. Cambium is a thin layer of active proliferating cells. The purpose of this paper was to model the main charac- teristics of cambial activity and its consecutive radial growth. Cell growth is under the control of the auxin hormone indole-3-acetic. The model is composed of a dis- crete part, which accounts for cellular proliferation, and a continuous part involv- ing the transport of auxin. Cambium is modeled in a two-dimensional cross-section by a cellular automaton that describes the set of all its constitutive cells. Prolifer- ation is defined as growth and division of cambial cells under neighbouring con- straints, which can eliminate some cells from the cambium. The cell-growth rate is determined from auxin concentration, calculated with the continuous model. We studied the integration of each elementary cambial cell activity into the global co- herent movement of macroscopic morphogenesis. Cases of normal and abnormal growth of Pinus radiata (D. Don) are modelled. Abnormal growth includes de- formed trees where gravity influences auxin transport, producing heterogeneous radial growth. Cross-sectional microscopic views are also provided to validate the model’s hypothesis and results. Keywords Radial growth · Morphogenesis · Cambium · Cell proliferation · Cellular automaton · Auxin transport · Gravitropism 1. Introduction: Natural processes Secondary radial growth in conifer trees was modelled at a cellular scale for the first time in the application case of (Forest et al., 2004). This paper deals with bio- logical context of secondary growth and describes briefly the mathematical basis of ∗ Corresponding author.