Stomata

At night, or when the plant is short of water, the stomata close and the CAM mechanism is used to store CO 2 produced by respiration for use later in photosynthesis.

CAM-cycling is a less efficient system whereby stomata open in the day, just as in plants using the C 3 mechanism.

Early in their evolutionary history, the ancestors of modern cacti (other than one group of Pereskia species) developed stomata on their stems and began to delay developing bark.

In full CAM, the stomata open only at night, when temperatures and water loss are lowest.

Lack of phosphorus may interfere with the normal opening of the plant leaf stomata, resulting in plant temperatures 10 percent higher than normal.

Root pressure is highest in the morning before the stomata open and allow transpiration to begin.

Stems have stomata and the formation of bark takes place later than in normal trees.

Such stems contain chlorophyll and are able to carry out photosynthesis; they also have stomata (small structures that can open and close to allow passage of gases).

The latter was achieved by tightly controlling the opening of stomata.

This is an important role where water supply is not constant, and indeed stomata appear to have evolved before tracheids, being present in the non-vascular hornworts.