DETERMINATION OF THE NUMBER OF CELL-DIVIS ION DURING DEVELOPMENT OF THE STOMATA ON LEAVES OF PRUNELLA-VULGARIS LINN AND PRUNELLA-WEBBIANA HORT (LAMIACEAE, DICOTYLEDONAE)

Stomata can develop in both species along the trimeristic or tetrameri stic pathway, with reference to the size of their cells. On the whole, all of the elements of the tetrameristic stomata are reliably larger than those of the trimeristic stomata. However, the initial difference s in cell size determine the greater or lesser probability of developm ent along a certain pathway due to the absence of a correlation betwee n the sizes of maternal and daughter cells. The final choice of the de velopmental pathway takes place at the stage of tertiary meristemoids: if the latter does not reach the critical size, it transforms into th e maternal cell of closing cells, and if it surpasses the critical siz e, it continues a series of unequal cell divisions. The critical size of the tertiary meristemoids is about 40 mu m(2) and 30 mu m(2) in Pru nella vulgaris and Prunella webbiana, respectively.