The emotional and physical backbone of the family, Ma's primary obligation is to take care of her family, to provide them with nourishment, comfort, healing, and support. Her family will only know fear and pain through her, so she works hard to deny these emotions in herself. Likewise, they look to her for laughter, so she builds joy out of small moments. Above all, however, her calm, unflappable strength binds everyone together. Ma finds this strength in love. She is the embodiment of Casy's idea of love, possessing the same intuitive sense of morality that Tom has. Although her primary focus is to take care of her own family, she is the first to nurture others. As Casy observes, "She don't forget nobody."
During the Joad's trek to California, Ma, in her desperation to maintain family unity, finds her role expanding. As crisis threatens to tear the family apart, she shifts to a position of active leadership. With each assault against the unity of her clan, she gradually takes over Pa's role as head of the family. When Tom suggests splitting up the family, she threatens him with the jack. While camped at the Colorado River, she wields a skillet when confronting an officer who orders the family to leave, although her greatest concern is that he will anger Tom. She forces the family to action in the Weedpatch camp and keeps Pa strong by giving him something to fight against. In the end, it is Ma who demands they leave the boxcars for higher ground.
This is not to say that Ma desires to be the leader. Her function within the family remains rooted in traditional feminine traits of nurturing and protection, and her primary desire is to "keep the fambly whole." She wishes nothing more than to reach a place where they can be a family with clear, logical boundaries. Her attempts to school Rosasharn in the way to be a strong woman, keeper of the family, reinforces Ma's attitude toward her function within the family framework.