Addendum

My annoyingly well-educated daughter informed me that when Rochester calls Jane his "little mustard seed" he is referring to Shakespeare's Midsummer Night's Dream.

After a little research, I discovered that Mustardseed is one of four fairies that Tatiana, the Fairy Queen, calls upon to wait on her new-found love--the clown Bottom, now changed by Puck into a man with the head of an ass. Throughout Bronte's book, Rochester attributes elf and fairy-like qualities to Jane, as though her magic alone can redeem him. The morning after she agrees to marry him, he continues the analogy, drunk on happiness and his belief that a life with Jane will bring him salvation.

The exact lines are "Is this my little elf? Is this my little mustard seed?"