Stomata

Stomata consist of specialised cells that mainly occur on the underside of leaves. They regulate the gas exchange between the plant and it’s environment, the plant is 'breathing' through them, as it were. Stomata are very recognizable by the two bean-shaped guard cells that regulate the size of the opening. The guard cells contain vacuoles that change their shape when water is absorbed due to a process called turgor, causing the stomata to open. The stomata are opened by stimuli like high humidity and bright light. The photo above shows the stomata of Brugmansia (Angel's trumpet).

Stomata are fascinating objects to study, in each plant they look a bit different or are positioned differently. To observe stomata we need to peel off the epidermis from the underside of a leaf. If you tear a leaf apart, often a small piece of the epidermis will come off. Especially with thicker leaves this works quite well. Easy to begin with are the leaves of Hosta, Prunus laurocerasus (Cherry laurel) and Tradescantia.

Stomata in a Hosta leaf.

A plant that has always fascinated me is the Tradescantia. This plant has large cells and stomata. When I started with a toy microscope a very long time ago, I observed Tradescantia a lot. At home we had several plants of what was then called Setcreasea purpurea. It’s present name is Tradescantia pallida, a plant native to Mexico. Tradescantia pallida you will find not that often in an average plant store, usually these stores have Tradescantia zebrina, at least in the Netherlands. The latter plant has shorter leaves and a striped pattern. On a microscopical level I could not see any difference between Tradescantia pallida and Tradescantia zebrina.

Stomata in the epidermis of Tradescantia zebrina.

If you look at an intact leaf of Tradescantia zebrina through the microscope, a special picture emerges. The leaves of this plant are quite thick so it’s only possible to use an objective with a long working distance, like a lower magnification objective. Also, a bright light source is needed to shine through the leaf.

The underside of an intact leaf of Tradescantia zebrina.

A plant worth investigating is Yucca filamentosa (Palm lily). The stomata of the Palm Lily look quite special. This plant has thick leaves and the epidermis is easy to peel off. The material for the image below came from a Palm Lily that was located at a garden in Kessel (Limburg) and the microscope image was also made on location.

Stomata in the epidermis of Yucca filamentosa. Also visible are many oil droplets.

Epidermis from a leaf of Canna. In addition to the three stomata, there are many calcium oxalate crystals visible in the cells.

Stomata in the epidermis from Ivy.

Like the surface of another planet: the epidermis of Acanthus. The patterns are formed by cuticle, a waxy layer that acts as a water repellent.

Stomata of Cherry Laurel.

Objectives used

Zeiss-Winkel 40/0.65, Zeiss Neofluar 25/0.60 and Zeiss apochromat 40/1.0.