The stem apical meristem (SAM) has been described as composed of two tunica layers and a corpus based on the classical study of Satina, Blakeslee and Avery in l940. Numerous other plants are found to have from only one to as many as five tunica layers, suggesting this feature varies with the species. A computer model was devised that draws proliferating cells starting with a few that grow and divide into an elongating SAM. To include two formal tunica layers in SAM requires a number of additional constraints or subroutines whereas the model has to be only slighly changed to have cells near and at the surface stretch parallel and divide perpendicular to the surface thereby forming several cell layers

Key words: apex, computer simulation