Stomata in Equisetum

Light and scanning electron microscopic studies and guard cell isolation techniques have confirmed the well-known ridges of the Equisetum stomatal apparatus as belonging to the subsidiary cells. Hitherto unknown features of the subsidiary cells such as the presence of a concentrated H 2 SO 4 -resistant region on the ridges and an interlocking mechanism for the closure of the aperture of the subsidiaries are described. These are presented as further evidence for the differences between the two subgenera of Equisetum. Boiling in dilute NaOH is shown to be a simple but effective means for the isolation of the guard cells in Equisetum as well as in several other plants with sunken stomata. Silicification of the outer layer of the epidermis makes cuticular isolation a difficult process by usual methods (treatments with enzymes or cellulose hydrolyzing reagents). Treatment with concentrated sulfuric acid followed by hydrofluoric acid results in the isolation of the cuticular membranes in Equisetum spp. and in similarly silicified grasses. Involvement of potassium ions in stomatal movements is indicated for two ferns and suggested for two species of Equisetum.