Stomatal Index Biology • PCM Notes
I = (S / (E + S)) × 100

Stomatal Index is the percentage of stomata relative to total epidermal cells in a given leaf area.

Understanding Stomatal Index

Quick Answer: The stomatal index is a measure of stomatal density relative to total epidermal cells. It is used in plant physiology to compare stomatal development across species or environmental conditions.

Key Formula

Stomatal Index (I) = [S / (E + S)] x 100 where S = number of stomata per unit area, E = number of epidermal cells per unit area. The index is independent of cell size, making it useful for taxonomic studies.

Solved Examples

Example 1
S = 20, E = 80
Total = 100
I = 20/100 x 100 = 20%
Moderate stomatal density
Xerophyte Leaf
S = 8, E = 92
Total = 100
I = 8%
Low stomatal index (adaptation)
Hydrophyte
S = 30, E = 70
I = 30%
High stomatal index

FAQs

Why is stomatal index preferred over stomatal density?

Stomatal index is independent of epidermal cell size, which can vary with leaf expansion. It reflects the developmental pattern rather than just expansion effects.

How does stomatal index help in climate studies?

Fossil leaf stomatal indices are used as proxies for past atmospheric CO2 levels. Lower stomatal index often indicates higher CO2 concentration.

What is a typical stomatal index for dicots?

It varies widely but often ranges between 10% and 25%. Xerophytes have lower indices, while mesophytes and hydrophytes have higher indices.