Rappaccini comes across as a cold, insensitive man. When Giovanni first sees him tending to his flowers, he observes that the doctor “avoids the actual touch of the flowers, or the direct inhaling of their odors,” almost like he is “walking among malignant influences, such as savage beasts, or deadly snakes, or evil spirits,” instead of beautiful flowers. Thus, when Signor Pietro Baglioni, a Professor of Medicine at the University of Padua, tells him that the doctor Rappaccini “cares more for science than mankind,” and that he has little compassion for other human beings, he is not completely surprised by this information. However, he points out to Baglioni, that from his observations, Rappaccini appears to have great affection for his daughter Beatrice. Baglioni says that it is said that Rappaccini has taught Beatrice all there is to know of his science and that Beatrice is widely known for her beauty. What the two do not know at this point is that Beatrice is as poisonous as the flowers she tends to in the garden. Indeed, as Baglioni himself confesses to Giovanni towards the end of the story, “Rapaccinni was not restrained by natural affection from offering up his child as a victim of his insane zeal for science.” Beatrice’s breath is so poisonous that it causes fresh flowers to wither, and insects and lizards to die.

Having isolated his daughter from all humanity because of his passion for science, Rapaccini seeks to find a companion for Beatrice. This companion is none other than Giovanni, who is himself fed with Rapaccini’s poison until his breath becomes as poisonous as Beatrice’s. When Giovanni learns that he has been caught in Rapaccini’s trap, he says this to Beatrice:

Yes, poisonous thing! Thou hast done it! Thou hast blasted me! Thou hast filled my veins with poison! Thou hast made me as hateful, as ugly, as loathsome, and deadly a creature as thyself – a world’s wonder of hideous monstrosity!

Beatrice, on her part, denies being a part of the plan to turn him into a poisonous being. She says,

It is my father’s fatal science? No, no Giovanni; it was not I! Never, never! I dreamed only to love thee and be with thee a little time, and so to let thee pass away, leaving but thine image in mine heart . . . But my father, he has united us in this fearful sympathy.

By finding a companion for Beatrice, Rapaccini demonstrates a twisted kind of love for his daughter. In fact, Rapaccini seems to think that by making his daughter poisonous he has given her the best gift that a loving father would bequeath his daughter. When his daughter complains of the misery his actions have caused her, he says this:

What mean you, foolish girl? Dost thou deem it misery to be endowed with marvelous gifts, against which no power nor strength could avail an enemy? Misery, to be able to quell the mightiest with a breath? Misery to be as terrible as thou art beautiful? Wouldst thou, then, have preferred the condition of a weak woman, exposed to all evil, and capable of none?

In the end, Rapaccini loses Beatrice, after she drinks the anecdote given to her by Giovanni.

Rappaccini, in the short story "Rappaccini's Daughter" by Nathaniel Hawthorne, loves Beatrice, his daughter, in a literally poisonous way that does not constitute true love. As Baglioni explains to Giovanni in the story, "That this lovely woman had been nourished with poisons from her birth upward, until her whole nature was so imbued with them, that she herself had become the deadliest poison in existence" (page numbers vary according to edition). Her father, Dr. Rappaccini, has constantly fed her poisons, until she is poisonous, and, as Baglioni says, "Her love would have been poison!--her embrace death!" Everything that seems beautiful about her is in fact deadly, and she has no ability to love people other than her father, as she will kill them with her very embrace. 

Beatrice herself mourns her lonely fate. She says to Giovanni, with whom she has fallen in love: "There was an awful doom...the effect of my father's fatal love of science--which estranged me from all society of my kind. Until Heaven sent thee, dearest Giovanni, Oh! how lonely was thy poor Beatrice!" Her father has attempted to protect her and keep her safe by administering poisons to her, but they make her so lonely that they show he is not thinking of her, but of himself, in giving her these potions. He wants to keep her by his side, but he does not consider if her loneliness will make her life unbearable. Therefore, her father's love is not a pure love. 

In the end, her father's poisons render any antidote poisonous. When Giovanni gives Beatrice an antidote to attempt to make it possible for them to be together, "so radically had her earthly part been wrought upon by Rappaccini's skill-- as poison had been life, so the powerful antidote was death." In other words, Rappaccini's attempts to love and protect his daughter have killed her when she tries to live any other life than what the father has imagined for her. The father's love is selfish and cruel and, in the end, deadly for his daughter.