Term:

Spongy mesophyll
Definition:

Referring to loosely group, unorganizedof cells located located between the palisade mesophyll and the abaxial epidermis. Photosynthesis takes place in both palisade and spongy mesophyll.
Notes:

There is considerable variation in the ratio of palisade to spongy mesophyll, e.g., some leaves of some species may appear to have all palisade mesophyll and others all spongy mesophyll. In addition, this ratio may vary in the same tree depending upon whether the leaves are exposed to the sunny conditions of the top of the canopy or the darker conditions of the middle and lower parts of the canopy.