THE GEOMETRY OF PLANT EPIDERMAL CELLS

SUMMARY Six monolayer tissues from various plants were studied for the number of anticlinal walls of non-marginal, unspecialized cells. One class of tissues, including the abaxial epidermis of the scale of Allium cepa, the adaxial epidermis of the leaf of Euonymus fortunei var. vegetus, gametophytic cells of Dryopteris filix-mas, and the surface cells of the bud of Anacharis demo, is characterized by (a) a probability distribution curve with a peak at six walls having a frequency of around 0.40, and (b) tissue growth in two directions. A second class of tissues has the distribution peak of six walls at an approximate frequency of 0.58 and is formed by growth in either one dimension or with regular alternation in two directions, as in the leaf of Anacharis densa and for the colony of Volvox aureus. Models for both classes of tissues were constructed in order to identify those features associated with tissue proliferation that contribute to the variability of cell geometry. Geometric models give a pictorial representation of cell arrangement and are useful in ascertaining cell division patterns whereas algebraic models aid in clarifying spatial relationships between cells. The distinction between packing types and developmental types of models is discussed in the light of the concept of form in plant morphology.