The developmental morphology and growth dynamics of the tobacco leaf.

The developmental morphology and growth dynamics of the leaf of Nicotiana tabacum L. cv. Xanthi Nc. are described. Epidermal and internal cell patterns indicate that the leaf axis arises from approx. 100 cells in four layers of the shoot apex, while the lamina arises from several rows of cells in each of three layers of the leaf axis. Cell patterns at the apex and margin of the leaf do not support the classical view that these regions have a specialized meristematic function. Instead the development of the leaf appears to be largely dependent on intercalary growth. The pattern of growth within the lamina is surprisingly complex. In addition to a proximal-distal gradient in the duration of growth and cell division during development, localized transitory changes in the rate of these processes also occur. These observations are discussed in reference to previous discriptions of leaf development in tobacco.