ability for a cell to differentiate into other cell types — wiki
ability to specialise, and then undifferentiate, cycling between muddled/clear water — dao-de-jing
This, precisely, is the proposition the reader is invited to meditate upon: the unhistorical and the historical are necessary in equal measure for the health of an individual, of a people and of a culture.
I mean by plastic power the capacity to develop out of oneself in one's own way, to transform and incorporate into oneself what is past and foreign, to heal wounds, to replace what has been lost, to recreate broken moulds.
(NB here renewal, source of "new" being the past, not the future for Nietzsche)