The Determination of Stomata Pattern and Frequency in Anagallis

The stomata of Anagallis arvensis L. are not randomly distributed, and their frequency is about three times greater on the lower than on the upper side of the leaf. Our purpose was (a) to characterize the processes which determine the regularity of the distance between the stomata and (b) to study the role of these processes in determining the differences of stomata frequency on both sides of the leaf. Stomata develop as an orderly complex together with the neighboring epidermal cells, and, on the basis of this "cell lineage," stomata should always be separated by at least one epidermal cell. Measurements of the "stomata-free" area around each stoma, in which additional stomata occur at lower than random frequencies, show that on the lower side of the leaf the stomata-free area corresponds closely to the size of one epidermal cell. On the upper side of the leaf, the minimal distance between stomata is about 20-40 μm greater than on the lower side, even though the size of the epidermal cells is the same. This difference, and the difference in stomata frequency, could be partly the result of a shorter period during which stomatal initiation occurs on the upper side of the leaf. A residual effect might be the expression of an "inhibitory effect" of a stoma on the formation of additional stomata in its immediate neighborhood. Thus, inhibition of stomata development plays a minor role and at most extends to a distance of one epidermal cell at the most.