Stomal Density

Stomatal density: refers to the number of stomata per unit area on the surface of a lead

Varies between different plant species, varieties and even within the same plant under different environmental conditions

Measuring stomata density

  1. A sample of epidermis is peeled off of the lead, mounted in water on a microscope slide and examined

  2. Colourless nail varnish is painted on small areas of the epidermis

The varnish forms a cast of the leaf surface

When dry, it is peeled off, mounted on a microscope slide and examined

  1. The surface of the leaf is photographed, and the resulting micrograph used for stomatal counts

Stomatal density = stomata/mm^2

Field of view is the diameter of the area visible through the microscope.

On low power, to determine the diameter of your field of view, place a transparent metric ruler under the low power objective of a microscope

The diameter of the field of view under high power often can not be measured directly and must be calculated using the following equation:

Diameter (HP) = (diameter (LP) x magnification of LP objective) / magnification of HP objective

  • Make at least 5 repeat observations in order to evaluate reliability - ensures that the measurements, observations or data collected are dependable and can be trusted to accurately represent the independent variable

  • Repeated trials allow the evaluation in the reliability of data

  • Standard deviation is a calculation of consistency

Low standard deviation = high reliability

High standard deviation = low reliability

Error bars show the standard deviation

Overlapping error bars indicate that there is no statistically significant difference between the levels of the independent variable

Non-overlapping error bars strongly suggest that you might have a statistically significant difference between the levels of the independent variable

  • Controlled variables must be kept the same in order to make sure the results are fair and accurate

Increased validity that changes to the dependent variable were caused by the changes made to the independent variable