The number of stomata in clusters of Begonia bracteosa ranges from one to ten with an average of 3.78 and its distribution follows a Poisson process as analyzed by the chi square test with a P value greater than 25%. Each stomatal cluster comes from a single cell with the number of stomata in a cluster directly related to the size of the cell at the time of specialization. The probability distribution frequencies of epidermal cells cam be given as a complex equation that can be simplified into a binomial distribution which, in turn, can be restated as a Poison distribution. This set of mathematical transformations parallels the changes in developmental features from epidermal cells to stomatal clusters.

Key words: begonia, development, stomata