The correct answer is option C) Stomatal index.

Explanation:
Stomata are small openings present on the surface of leaves, stems, and other plant organs. They play a crucial role in the process of photosynthesis and respiration. The stomatal index is a measure of the number of stomata present on the surface of a leaf in relation to the total number of epidermal cells and stomata per unit leaf area.

Stomatal index is used to determine the density and distribution of stomata on a leaf surface. It provides important information about the overall health and functioning of the plant. It can be used to study the adaptation of plants to different environmental conditions and to compare the stomatal characteristics of different plant species.

The stomatal index is calculated using the following formula:

Stomatal Index = (Number of stomata / Number of epidermal cells) x 100

The numerator of the formula represents the number of stomata present on the leaf surface, while the denominator represents the total number of epidermal cells on the same surface. The resulting value is multiplied by 100 to express the stomatal index as a percentage.

The stomatal index can vary depending on various factors such as plant species, leaf age, light intensity, humidity, and other environmental conditions. It is generally higher in plants growing in moist environments compared to those in dry or arid regions.

The stomatal index is an important parameter used by botanists and plant scientists to study plant physiology, ecology, and plant adaptations. It helps in understanding the water relations of plants and their response to environmental factors. By comparing the stomatal index of different plant species, scientists can gain insights into their evolutionary relationships and adaptive strategies.

In conclusion, the stomatal index is a valuable tool in plant science that measures the ratio of stomata to the total number of epidermal cells and stomata per unit leaf area. It provides essential information about the structure and functioning of plant leaves and their adaptation to the environment.

Stomatal index is the percentage which the number of stomata form to the total number of epidermal cells, each stoma being counted as one cell. Stomatal index can be calculated by using the following equation :
Stomatal index=S*100/E+S
where
S=Number of stomata per unit area
E=Number of epidermal cells in the same unit area