stratify

Concise Oxford English Dictionary © 2008 Oxford University Press:
stratify /ˈstratɪfʌɪ/

▶verb (stratifies, stratifying, stratified)

• 1 (usu. as adj. stratified) form or arrange into strata.

• 2 arrange or classify.

• 3 place (seeds) close together in layers in moist sand or peat to preserve them or to help them germinate.

– derivatives
stratification noun,
stratiform adjective.