The only pathways for the gases which thus pass between the cells of the mesophyll and the outside air are the stomata.
In the leafy shoot this function is mainly localized in the cortical tissue of the leaves, known as mesophyll, Mesophyli.
In fleshy leaves which contain a great bulk of tissue in relation to their chlorophyll content, the central mesophyll contains little or no chlorophyll and acts as waterstorage tissue.
The cells of these sheaths are often distinguished from the rest of the mesophyll by containing little or no chlorophyll.
These bodies, known technically as chioroplaIts, are found embedded in the protoplasm of the cells of the mesophyll of foliage leaves, of certain of the cells of some of the leaves of the flower, and of the cortex of the young twigs and petioles.