ADVERTISEMENTS:
In this article we will discuss about the meaning and types of stomata.
Meaning of Stomata:
Stomata are very minute openings found in the epidermal layer of leaves, stem and other aerial parts of the plant. Each stoma remains surrounded by two kidney-shaped or bean-shaped cells called guard cells. Chloroplasts are always present in the guard cells. The inner wall of each guard cell is thicker while its outer wall is thinner. The epidermal cells bordering the guard cells are called subsidiary cells.
In the absence of light, i.e., at nights, the stomata remain closed. On the other hand in the presence of light, i.e., during day time, the stomata remain open. The closing and opening of stomata are due to the movement of guard cells.
ADVERTISEMENTS:
Usually in monocotyledonous leaves, the stomata are arranged in parallel rows whereas in dicotyledonous leaves the stomata remain scattered.
Types of Stomata:
In dicotyledons following four main types of stomata (Fig. 137) are found:
1. Anomocytic or Type – A:
ADVERTISEMENTS:
i. No subsidiary cells are present.
ii. Stoma remains surrounded by several irregularly arranged ordinary epidermal cells.
iii. This type is also called Ranunculaceous type or irregular-celled type.
This type of stomata are found commonly in several dicotyledons, including Tridax, Citrullus, Ranunulus, etc.
ADVERTISEMENTS:
2. Anisocytic or Type – B:
i. Stoma remains surrounded by three subsidiary cells.
ii. Of the three subsidiary cells, one is distinctly- smaller than the other two.
iii. This type of stomata is also called unequal- celled type or Cruciferous type.
ADVERTISEMENTS:
This types of stomata are seen commonly in genera such as Brassica, Sedum etc.
3. Paracytic or Type – C:
i. One or more subsidiary cells are present.
ii. Subsidiary cells flank the stoma parallel with the long axis of the guard cells.
ADVERTISEMENTS:
iii. This type of stomata are also called parallel- ceiled type or Rubiaceous type.
This type is commonly seen in members of Rubiaceae, and genera such as Vigna, etc.
4. Dlacytk or Type – D:
i. Stoma remains surrounded by a pair of subsidiary cells.
ADVERTISEMENTS:
ii. Common walls of subsidiary cells remain at right angles to the long axis of the guard cells.
iii. This type is also called cross-celled type or Caryopbyilaceous type.
This type of stomata are commonly seen in Ocimum, Caryopbyllaceae (e.g., Diantbus), etc.
