Origin and development of stomatal microanatomy in two species ofEucalyptus

Summary Development of the stomata ofEucalyptus orbifolia (in which they are relatively superficial) andE. incrassata (in which they are deeply sunken) is described from light microscopy of thin sections of resin-embedded material. The envelope of the guard mother cell is retained intact while in the daughter cells (guard cells) the inner and outer thickenings are formed. The mother cell envelope may even remain discrete and intact during early stages of formation of the separation spaces, precursors of the future stomatal pore, between the thickenings. Remnants of the guard mother cell wall may be retained as parts of at least the inner stomatal ledges. Likewise, remnants of the wall which divides the mother cell persist on the maturing guard cells.Sudan III-positive materials, probably cutin, are removed from the cuticle over the mother cell soon after it is formed. The cuticle above the guard cell is finally perforated by enzymic attack forming, inE. incrassata, a large cavity outside the developing stoma into which the outer stomatal ledges grow as extensions of the upper guard cell walls.The termostiole is suggested for the aperture in the cuticle. The flanges of cuticle seen in section to bound it are termedostiolar ledges. The ostiolar ledges are to be distinguished from the outer stomatal ledges, which develop from the upper thickenings of the guard cell initials. The distinction is clear inE. incrassata (and other species with deeply sunken stomata) but not in mesophytic plants or species with superficial stomata such asE. orbifolia in which the outer stomatal ledges are fused with the cuticle.Growth of the outer stomatal ledges inE. incrassata involves transport of wall materials through an annular space, the equivalent of an ectocythode.The relevance of the observations to stomatal development in other genera is discussed.