Nel's mother Helene assumes an early importance in the novel. Helene is a prostitute's daughter, and she spends her life trying to erase that part of her history. She maintains the utmost propriety and expects the same of everyone around her. She has a lot of influence in town and she uses it to pass judgment on anyone who falls short of her standards of acceptable behavior.
This propriety is challenged on a train trip Helene and Nel take to see Cecile, Helene's grandmother. They are forced to use the bathroom in a field because there are no restrooms for black people on the train. And when a white conductor speaks to Helene in a clearly racist way, she doesn't seem to fight back. She smiles at him, which shocks her daughter, who is used to seeing her mother strong and in control. After Nel returns and befriends Sula, she seems to turn against Helene.
Is it fair to blame Helene for faltering? After all, what might have happened if she had confronted the conductor? This episode shows us cracks in Helene's façade, but also the horrible and demeaning racism that haunts the people of the Bottom.