Mary, Mary, quite contrary...

Mary Mary quite contrary,

how does your garden grow?

With silver bells

and cockleshells

and pretty maids all in a row.

This poem/nursery rhyme was written in the 1700s. There are multiple interpretations of what the poem was originally about, but most of them suggest that it is about Mary Tudor or "Bloody Mary," The "pretty maids" are said to refer to the guillotines used at the time. The silver bells and cockle shells were torture devices, and  the questioning of her garden's growth a jab at the fact that she had failed to produce an heir after many miscarriages.

These are, however, still just theories, and the poem has still managed to gain other more pleasant connotations such as it's referencing in the book "The Secret Garden." 
It is also thought by some to have been written about Mary Queen of Scots and the Catholicism of the time.

(see http://socyberty.com/history/the-gory-history-of-mary-mary-quite-contrary/, http://socyberty.com/folklore/the-tudor-origin-of-the-mary-mary-quite-contrary-nursery-rhyme/, http://www.mothergooseclub.com/rhymes_parent.php?id=117)