Why does Dr. Rappaccini require his daughter's help in "Rappaccini's Daughter" by Nathaniel Hawthorne?

In
"" by, Dr. Giacomo Rappaccini is a classical evil scientist figure, whose towering
intellect and intellectual curiosity have led him to delve into the science of poisons and
poisonous plants, to the point where is is willing to sacrifice his ethics and family for his
studies. The apparently genial Dr. Pietro...