Determination of stomatal number and stomatal index

Learn how to determine stomatal number and stomatal index with laboratory procedure. Explore formula, diagram and practical procedure.

Table of Contents

What is Stomata?

Stomata are a type of epidermal cell composed of two kidney-shaped guard cells.
This two-cell aligned with each other in such a way that produces central pore and thus they create a minute epidermal opening.

Number of stomata present in 1 mm sq area of leaf present in midway between the margin and midrib is stomatal number.

Take fresh mature leaves, select the area of leave between the margin and midrib,
Take a superficial cut on the lateral veins in the selected area of the leaf with the help of sharp blade.
Peel out the leave from the cut of the lateral vein with the help of forceps gently.
Arrange Camera lucida and drawing board for making drawings to scale.
Place a stage micrometer on the microscope and using 10% objectives and 5x eyepiece.
Draw a line equivalent to 1 mm as seen through the microscope and draw a square on this line.
Adjust the black paper on board so that you can see the square in the eyepiece, in the center of the field.
Place the slide with the cleared leaf (epidermis on the stage).
Trace all the stomata which seen as superimposed on the 1 sq. mm square.
Count the number of stomata in the square millimeter.
Find the average number of stomata from the four determinations, to get the average values for one sq mm.

Stomatal index define as percentage ratio of stomata surrounded by epidermal cells in the per unit area of leaf.

Take fresh Mature leaves, select the area of leave between the margin and midrib.
Take a superficial cut on the lateral veins in the selected area of the leaf with the help of sharp razor blade.
Pell out the leave from the cut of the lateral vein with the help of forceps gently.
Arrange camera lucida and drawing board for making drawings to scale.
Place stag micrometer on the microscope and using 10x objectives and 5x eyepiece
Now draw a line equivalent to 1 mm as seen through the microscope and draw a square on this line.
Adjust the black paper on board so that you can see the square in the eyepiece, in the center of the field.
Place the slide with the cleared leaf (epidermis on the stage).
Trace all the stomata along with epidermal cells which seen as superimposed on the 1 sq. mm square.
Count the number of stomata and epidermal cells in the square millimeter.
Find the average number of stomata from the four determinations to get the average values for one sq. mm.

Formula

Stomatal index =

Where,
S = Number of stomata per unit area.
E = Number of epidermal cells