Epidermis-2

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Epidermis-2
The Stomatal Apparatus or Stoma consists of two Guard Cells which open to create the Stomatal Pore. Subsidiary Cells may also be present. The Inner Radial Walls of Guard Cells are free at the center. They are thick and usually contain projections called Ledges. The ledges provide microenvironments which have a role in Transpiration. I use the term Stomata to indicate the Stomatal Apparatus, however, Stoma is the more recent term used by others.
	The Subsidiary Cells play an active role in the opening and closing of the Guard Cells. They are evident with Tradescantia leaves. Subsidiary Cells are usually anatomically distinct compared to "typical" Epidermal Cells. They lack Chloroplasts, however.
	Locate the Subsidiary Cells in this Image taken using the "Epidermal Window Method". Note the Chloroplasts in the Guard Cells.
	Surface view of Agave epidermis. Note the shape of the typical Epidermal cells. Locate the Stomata (stoma). The Stomatal Apparatus is composed of Guard Cells with their Stomatal Pore. Agave Guard Cells are "sunken" and the Cuticle forms a low wall that extends above the surface. These are both adaptations for Xeric (dry) environments.
	*Surface Replica of Arabidopsis* Leaf showing a Stoma (Stomatal Apparatus).**
	*Lily (Lilium) epidermis with elongated epidermal cells plus Stoma. There are no Subsidiary Cells.*
	Fuchsia epidermis with highly undulating epidermal cell walls and Guard Cells. Note the Chloroplasts in the Guard Cells. Typical Epidermal cells have poorly differentiated plastids. However, the Guard Cells have chloroplasts which are important for stomatal opening and closing.
	*Higher magnification of Guard Cells from Fuchsia* epidermis. Note the Chloroplasts.**
	Epidermis of Coconut Palm - Note the diversity of cell types! Epidermal wall patterns can be very complex and can be used to identify plants.
	*Stomata from Bryophyllum* - Locate the Guard Cells & the Subsidiary Cells.**
	*Stomata of Peony* Locate the Guard Cells & the Subsidiary Cells, if present.**
	The Cellulose Fibrils of Guard Cells have an asymmetric radial organization that is indicated by the red lines. The outer radial wall of the guard cell can expand but the inner (free) radial wall can not.
		When Guard Cells become turgid, the outer radial walls enlarge. This creates a stress which pulls the inner radial walls apart so that the Stomatal Pore opens.
	The Guard Cells often have projections from the outer tangential walls which border the Stoma. These help to create a compartment which forms a buffer between the atmosphere and the leaf interior when Stomata open. Locate these in this picture! Locate the Plastids without looking at the pictures below!
	Stomata of Hawaiian Silversword: These appear to be above the surface BUT this may be an artifact due to the methods used to create this image. Note similarities to the example on the left.
	Anthocyanins are often found in the Vacuoles of Epidermal cells. What are the potential functions of these? The vacuoles in Guard Cells also play an important role in stomatal functions.