Plath took pains to invest her poems with a mythic severity, and in the weeks before she died spoke on the BBC about the need for the modern poet to draw on myth while making "the metaphor-moral ... intrinsic to the poem, working back and forth on itself, not expressed prosaically at the close, like the moral of a fable." (full text of article; link accessed 10 May 2013)
I am hoping that the power of social interneting can help to identify the source of this quote (above, in bold). "We" know Plath prepared a script of poems for the BBC circa 13/14 December 1962. These include poems such as "The Applicant," "Fog Sheep" ("Sheep in Fog"), "Lady Lazarus," "Ariel," "Death & Co.," "Nick and the Candlestick," "Letter in November," "Daddy," "Fever 103˚," "The Bee Meeting," "The Arrival of the Bee Box," and "Wintering." However, the text does not appear in that script. The full-text of these poems and introductions appears in the several different places: the Plath Collection at Smith College, the Alvarez papers in the British Library, and some were printed in Ariel: The Restored Edition (2004).
Plath also reviewed, on 10 January 1963, Donald Hall's anthology Contemporary American Poetry. Smith College holds a typescript of this and the audio was released in the 2010 British Library CD The Spoken Word: Sylvia Plath. The text also does not appear either in this recorded program or in the typescript I have seen (keeping in mind there might be an alternate typescript out there).
So, my question for the faithful, resourceful readers of this blog is: Do you know from where this quote comes?