Polly is one of the more usual Scottish (and English) nicknames or pet forms of Mary. Whyte's 'Scottish Forenames' also lists alternative pet forms for Mary as including Molly, Minnie, Mami and (occasionally) Maisie. For those without a specialist forenames book to consult there is also a website for Nicknames at www.tngenweb.org/franklin/frannick.htm which I sometimes find useful. Duncan, Dundee