Throughout the novel, plants function as metaphors for people, especially Natalie’s mother. Perennial plants help Natalie metaphorically understand the phenomenon of her mother’s depression before she has a literal word to describe it. Natalie reasons that her mother is similar to a dormant plant, currently sleeping in darkness but not gone forever; she is just waiting for sufficient sunlight to allow her to reemerge. This metaphor gives Natalie hope that a cure is possible, although she learns that healing is not a sudden change, but a slow and involved process. Furthermore, plants are also used to metaphorically describe others. For example, Natalie’s grandmother compares the Korean fire plant to Korean people like herself and Natalie’s father, who remain strong and continue growing despite periods of hardship.

The state of Natalie’s mother’s health is also reflected in her relationship to plants. As a healthy botanist, she studied them in the lab and cared for them in her own greenhouse with Natalie. When she is depressed, she ignores the plants, and they all die.

Natalie uses the scientific method to structure the novel, but science and the scientific method also appear repeatedly as a motif to illustrate the importance of asking questions, gathering legitimate data, analyzing results, and collaborating with others to draw accurate and reasonable conclusions.