What is stomatal periodicity? What are the categories of stomata?

Stomatal periodicity is the rate of opening and closing of stomata during day and night. Stomata usually open during day and close during night. There are three categories of stomata :
(a) Barley or cereal type : They are dumb-bell shaped.
The stomata usually open during the day for a few hours.
(b) Leuceme or alfalfa type: They open during day and close during night under mesophytic conditions. In succulents, the stomata remain closed during the day. They open only during night.
© Potato Type : Under mesophytic conditions, the stomata can remain open through day and night but close down for different periods and at various times under less water availability.