In "Rappaccini's Daughter" by Nathaniel Hawthorne, 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 Baglioni is a rival scientist who may be acting in the story out of benevolence but perhaps out of professional rivalry.
Dr. Rappaccini's garden is filled with plants so poisonous that no ordinary person can touch them safely. The most dangerous of them all is a shrub with purple blossoms growing by a fountain. Dr. Rappaccini himself can only tend his plants while wearing heavy protective garments, including gloves and sometimes a mask. His daughter, brought up among the plants, has developed an immunity to their poisons, and can can tend them barehanded, albeit at the cost of becoming herself toxic to normal people. Thus Dr. Rappaccini needs his daughter because her immunity to the poisons enables her to tend his experiments.