It came from Mammy Judy, Sally's old nurse.

It's part of their regular Hoo-doo.

She bewitched Miss Sally when she was a baby, so that everybody is bound to HER as long as they care for her, and she isn't bound to THEM in any way.

All their luck goes to her as soon as the spell is on them," she added darkly.
"I think I know the rest," returned Courtland with still greater solemnity.

"You gather the buds of the witch-hazel in April when the moon is full.