REGULAR ARTICLE Mathematical Modeling of Intrusive Growth of Fusiform Initials in Relation to Radial Growth and Expanding Cambial Circumference in Pinus sylvestris L. D. Karczewska Æ J. Karczewski Æ W. Wloch Æ J. Jura-Morawiec Æ P. Kojs Æ M. Iqbal Æ J. Krawczyszyn Received: 30 April 2008 / Accepted: 10 January 2009 / Published online: 29 January 2009 Ó Springer Science+Business Media B.V. 2009 Abstract This study on the cambium of Pinus sylvestris L. examines the intrusive growth of fusiform cambial initials and its possible contribution to the tangential and radial expansions of the cambial cylinder. The location and extent of intrusive growth of the fusiform initials were determined by microscopic observations and by mathematical modeling. In order to meet the required circumferential expansion of the cambial cylinder, the fusiform initials grow in groups by means of a symplastic rather than intrusive growth, leaving no room for the assumption that intrusive growth of the initials takes place between radial walls and has a direct role in the increase of the cambial circumference. Therefore, it is postulated that the fusiform initials grow intrusively between the tangential walls of the neighboring initials and D. Karczewska  J. Karczewski Department of Biophysics and Cell Biology, University of Silesia, ul. Jagiellon ´ska 28, 40-032 Katowice, Poland W. Wloch (&)  P. Kojs Department of Biosystematics, Opole University, Oleska 48, 45-052 Opole, Poland e-mail: wwloch@op.pl W. Wloch  J. Jura-Morawiec  P. Kojs Botanical Garden – Centre for Biological Diversity Conservation of the Polish Academy of Science, Prawdziwka 2, 02-973 Warszawa 76, Poland M. Iqbal Department of Botany, Jamia Hamdard (Hamdard University), Tughlaqabad, New Delhi 110062, India M. Iqbal Department of Plant Production, College of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Kingdom of Saudi Arabia J. Krawczyszyn Australian Dracaena Research Centre, P.O. Box 925, Williamstown, VIC 3016, Australia 123 Acta Biotheor (2009) 57:331–348 DOI 10.1007/s10441-009-9068-y