figs from thistles
A reference to Matthew 7:15-16: "Beware of false prophets, which
come to you in sheep's clothing, but inwardly they are ravening
wolves. Ye shall know them by their fruits. Do men gather grapes
of thorns, or figs of thistles?"
Wollstonecraft uses the phrase twice: once in Chapter 1, and again in Chapter 13.