The John Bartram family is so important in Philadelphia and in horticultural history. I wonder why you did not ever refer to it. Was it to focus on the tension/competition with Kew or to simplify the set of Philadelphia characters? Did you draw from the Bartram family story in creating your characters? As a fervent gardener located near Philadelphia, I loved your book and its wonderful hortictural detail.
GREAT QUESTION! (And good eye, Lin!) The reason that John Bartram and his family don't exist in THE SIGNATURE OF ALL THINGS is that I felt Philadelphia was too small for Henry Whittaker and John Bartram to co-exist. They would have needed to be rivals, and I didn't have space in the story for such a line of narrative. In the end, instead, I just folded the Bartram's history into the Whittaker's history. This is the lucky grace of the novelist!