In the Grapes of Wrath, Steinbeck uses intercalary chapters to provide background for the various themes of the novel, as well to set the tone of the novel”. The turtle is a metaphor for the working class farmers whose stories and struggles are recounted in The Grapes of Wrath. In Chapter 3, the turtle plods along dutifully, but is consistently confronted with danger and setbacks. Significantly, the dangers posed to the turtle are those of modernity and business.
It is the intrusion of cars and the building of highways that endanger the turtle. The truck that strikes it is a symbol of big business and commerce. “The turtle entered a dust road and jerked itself along, drawing a wavy shallow trench in the dust with its shell” (pg 21) shows that the Joad family that will soon be introduced will experience similar travails as the turtle, as they plod along wishing only to survive, yet are brutally pushed aside by corporate interests.
Chapter 7, another intercalary chapter critiques yet another part of the business system. The owners of the car dealerships mean solely to exploit impoverished buyers. They do not profit from selling cars that will last, but rather from finding the most ill-used vehicle, giving it the appearance of reliability, and pawning it off on desperate farmers wishing to get to California. There is no compassion in the car sales, but rather a perpetual cycle of exploitation.
This indicates what the Joad family must certainly have experienced to get their car to go west, yet places it in a larger context. The chapter makes it clear that they are not the only family to experience this. As the Joad family faces the same trials that the turtle faces, and as the desperate farmers have to deal with car dealerships, the intercalary chapters help to set the tone of, as well as integrate the various themes of The Grapes of Wrath.