Spring.wmf (18300 bytes) Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Stomatal Morphology

Background Information:  
    The structure of the stomatal apparatus varies from species to species.  In general, guard cells are either bean-shaped (eudicot type) or barbell-shaped (grass type).  Guard cells may or may not be accompanied by subsidiary cells.

    What is the structure of the stomatal apparatus of plants such as wandering Jew (Tradescantia), Broad bean (Vicia faba), RCBr (Brassica rapa) and maize (Zea mays)?  

Hypotheses:  Since RCBr and Broad bean are eudicots they will have bean-shaped guard cells.  Maize, a monocot, will have barbell-shaped guard cells. 


  1. Obtain a Broad bean leaf and make an epidermal peel from the lower (abaxial) surface.

  2. Mount the strip in a drop of water on a microscope slide and cover with a cover glass.  Examine at 400x. Do not use the oil immersion lens.

  3. Sketch the stomatal apparatus.  Be sure to record the magnification of the object and calculate the plate magnification (= drawing size / actual size; same units).  Be sure to give your diagram a caption and label stomata, guard cells, subsidiary cells and epidermal cells.

  4. Obtain a leaf of a plant from the greenhouse and prepare an epidermal peel.  Use the digital camera to prepare an image from this species.  Record the actual size of the guard cell or stomata.

Data:   Sketch of the stomatal apparatus of broad bean and digital image of a species of your choice.  Label these Fig's 1 & 2). 


  1. What organelles do you observe in the epidermal cells?  Guard cells?

  2. What similarities do you observe between the stomatal apertures of the species?  Differences?

  3. Did they appear as you expected?  Explain.

  4. How good (free of mesophyll) are your epidermal strips?

  5. What organelles do you observe in the guard cells?  other epidermal cells?

  6. Which species was easiest to peel?  Offer an explanation.

  7. Do any of the species you observed have distinct subsidiary cells?  Which ones?  What do they look like?

Further Experiments:

  1. What percent of the epidermal cells are guard cells?

  2. On average, how many epidermal cells are between a stoma and its nearest neighbor?

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Last updated:  01/07/2009     � Copyright  by SG Saupe