The novel's climactic section, "The White Mulberry Tree" opens on a June afternoon, with Emil Bergson's return from a year-long stay in Mexico City. He accompanies his sister Alexandra to a supper and fair at the local Catholic church. Marie Shabata is there, as well. The two discover that their love has only grown during the year and, during an opportune blackout, they kiss for the first time.
Following the wedding of Signa, Alexandra's maid, and Nelse Jensen, Emil walks Marie back to her farm, and they finally discuss their love openly. Marie recognizes, however, that she cannot run away with him; Emil resolves to leave the Divide soon.
Just over a week later, Emil rides to the farm of his best friend Amedee Chevalier, the prosperous and happy father of a baby boy. Amedee collapses in a field, and it is discovered that he has a ruptured appendix. The operation comes too late, and Amedee dies. Marie Shabata considers the fact that Emil did not come to tell her about Amedee as a sign that he has cut her loose. Overcome by bittersweet emotion in the moonlit beauty of the prairie, Marie determines to embrace a new, ecstatic freedom: "a new life of perfect love."
The following Saturday, the local Catholic bishop is to confirm a hundred children. Emil attends the church ceremony, the joy of which is tempered by the sadness of Amedee's death. Overcome by emotion and the choir music, Emil experiences a rapture that gives him a vivid awareness of life and transcends fears of death. Still in this ecstasy, he goes to say his farewells to Marie. He finds her lying in her orchard, still drifting in her own reverie, and lies down with her. Frank Shabata comes down to the orchard with his gun when he sees Emil's horse in the stable. Shocked to see his jealousy justified, Frank reacts mechanically, shooting blindly through the bushes at the two lovers. Horrified by his actions, Frank mounts Emil's horse and rides wildly away into the countryside.
The next morning, Ivar finds Emil's horse, which has returned to the stable. Fearing something wrong, Ivar goes in search of Emil, and finds both Emil and Marie Shabata dead in her orchard. Aghast, Ivar runs to tell Alexandra.
Some of the most vivid scenes in the novel, such as the fairs at the French Church and the conversations between Alexandra and Marie, do not play particularly important roles in advancing the plot of the novel. But these brief scenes of prairie existence help paint a picture of both the beauty and the difficulty of pioneer life. The novel takes as one of its central themes the role of the prototypical pioneer individual in American society. The fact that the protagonist is female demonstrates Cather's interest in the relationships and communal functions that made prairie life bearable for women; Alexandra's friendships with Marie and Mrs. Lee, and even with her maid, Signa, are integral parts of her life. The great historian Frederick Jackson Turner famously observed that it was in the small, isolated pioneer settlements where raw necessity was the rule that the authentic stuff of American democracy, that sense of coherence among men and women of different ethnicities and classes, was shaped.