Fundamental concepts of leaf morphology and morphogenesis: A contribution to the interpretation of molecular genetic mutants

As an older and more established discipline, plant morphology is an importa nt but relatively underutilized resource for the interpretation of mutants. Plant morphology has the potential to provide the context for molecular ge netic investigations, especially those concerned with leaf morphogenesis. T his article first reviews the basic organization of vascular plants and the relationship of anatomy to morphology in interpreting gene expression. It demonstrates that these two levels of organization are relatively independe nt of one another and that anatomy cannot be substituted for morphology in analyzing the effects of genes on leaf development. Morphological principle s are then applied to two aspects of leaf development, transectional symmet ry and leaf dissection. According to this perspective, so-called organs in plants are simply regional expansions that carry specific cell and tissue t ypes in a particular orientation in space. Rather than considering specific genes as determining particular organ types, it is more likely that gene e xpression itself is dependent on the morphological, developmental context i n which the genes are expressed.