Definitions for "Exine"
n. (L. ex, out of, out) the outer of two layers forming the wall of certain spores (as pollen grains) - called also exosporium.
the outer layer of the wall of a spore or pollen grain (Source: The American Heritage Dictionary of the English Language, 2000)
The outer, very resistant layer of the two major layers forming the wall of spores and pollen, consisting principally of sporopollenin.