The Genesis of Form in Casuarinaceae

Abstract

The growth and development of the shoot apex of Casuarina distyla, in which the leaves commonly occur in whorls of 6-8 members, is described. The mature apex of C. torulosa, a species with only four leaves per whorl, is also described. Stages in the development of the apex of C. distyla are illustrated with three-dimensional scale drawings.

The fused stem-and-leaf nature of the vegetative axis is recognized and the growth of the blade, tube and buttress portions of the axes is presented in units of length and volume. Stages in the development of axillary buds are illustrated with three-dimensional scale drawings.

Phyllotactic parameters for whorled systems of phyllotaxis in Nerium and Casuarina are presented along with those for decussate systems in Eucalyptus

. The role of physical constraint in the genesis of form and the determination of rates of growth in shoot apices are discussed and it is suggested that rapid maturation of tissues may contribute to the continuous fall in the relative growth rate of the leaves.