EVIDENCE IN DICOTS FOR STOMATAL PATTERNING BY INHIBITION

The arrangement of the simplest type of stomatal complex, the agenous form that has no noticeable subsidiary cells, was examined in three dicots: catalpa (Catalpa speciosa Warder), geranium (Pelargonium zonale L.), and the Chinese scholar tree (Sophora japonica L.). The degree of patterning of stomata in these three species as measured by the method of Clark and Evans is 1.64, 1.62, and 1.65, respectively. The frequencies of stomata (S), cells adjacent to stomata (I), and cells not adjacent to stomata (F) are similar: 0.198, 0.684, and 0.117 for catalpa; 0.189, 0.644, and 0.167 for geranium;. and 0.195, 0.693, and 0.112 for the Chinese scholar tree. Stomatal patterning in clover, Trifolium repens L., and the garden pea, Pisum sativum L. var. arvense cv. Dun, were also examined as nonagenous species for comparison with the other three species. Two models were constructed to depict the purely heterotypic (inhibitory) type of stomatal formation. The geometric model describes this type of stoma determination by a simulation graphics program and determines the frequencies for the three types of cells, i.e., S, I, and F, as 0.163, 0.737, and 0.099. The mathematical model consists of three simultaneous differential equations, one for each type of cell, and their frequencies are solved as 0.172, 0.688, and 0.142. The similarity of the data collected from these two models to those for the three species with agenous stomata indicates that the pattern of stomatal arrangement can be explained by heterotypic induction. Parallel studies made on clover and pea, species previously identified with cell lineage determination of stomata, also can be explained quantitatively by inhibitory models.