Things go bump in the night at this time of the year, but in her new book, Wicked Plants: The Weed that Killed Lincoln’s Mother and Other Botanical Atrocities (Algonquin Books $18.95), Amy Stewart takes us on a tour of the more bloodcurdling aspects of botany.             We all know that Abraham Lincoln grew up motherless from the age of nine, but I certainly never knew that it was white snakeroot (Eupatoreum rugosum) that killed his mother in1818.…