During the day in dry habitats the guard cells become flaccid and the stomata close; concurrently carbon dioxide is disallowed to pass to participate in diurnal photosynthesis. Some plants from dry regions solve this problem through the method of nocturnal carbon dioxide fixation. At night, when water loss by transpiration is lower, the stomata open, carbon dioxide enters and it is stored within the parenchymal tissues. During the day the stored gas is mobilized to be used in photosynthesis.   _{Your Comment}