The outer or external layer of a pollen grain's wall; the outermost component of pollen's protective coating.
From Latin 'extimus' (outermost) + '-ine' (suffix indicating substance or part). Coined in 19th-century botanists' terminology to contrast with 'intine' (the inner wall layer).
Pollen grains have two walls: the tough, fancy-patterned extine on the outside and the delicate intine inside—and the extine's shape is so unique that scientists can identify plant species just by looking at a pollen grain!
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