Epidermal Structure and Stomatal Ontogeny in Zornia Gmel

Epidermal structure and development of stomata were studied in the vegetative and fioral organs of Zornia diphylla (L.) Pers. and Z. zeylonensis Pers. Most of the intercostal cells in leaflet, stipule, and bract are large-sized mucilaginous idioblasts. The swollen base of the idioblast compresses the basal part of the adjacent subsidiary or ordinary cell, which hence has a narrow base in contrast to that of the idioblast. Para-mesogenous, aniso-, and tetra-mesoperigenous stomata occur in all organs of the above species. In addition, the outer epidermis of the ovary wall shows aperigenous (anomocytic) stomata. Stomata of the first three types are dolabrate, irrespective of their mesogenous or mesoperigenous development. These types are related, the differences between them depending on the nature of the placement of the second wall of the meristemoid. The present study lends support to an earlier contention that anomocytic (aperigenous) stomata may result from suppression of the divisions of the meristemoid of paracytic type. It is suggested that stomata flanked by two lateral, parallel, meso- genous subsidiaries which do not meet each other at least at one pole (incomplete), should be termed aniso- or tetra-mesoperigenous according to the total number of subsidiary cells of dual origin.