What does Alice Walker want to tell us about teaching history in comparing Columbus with a cucumber? The likeness in sound seems far-fetched.
This comparison is at the beginning of the novel "The Color Purple" in the letter starting with "It took him the whole spring, from March to June" and ends "He say, Her cow."
Although there is a slight likeness in sound between the two words and, historically, Columbus was the first to bring cucumbers to American shores, the text seems to point out that there is more to this comparison than simple sound or historical fact. The letter defines the discovery of America as an enterprise where the oppressive forces of colonialism and masculinity joined forces. According to this view, the cucumber associated with Columbus becomes a phallic image and, tellingly, the original female names of his three ships (Nina, Pinta and Santa Maria) become masculine in the text of the letter. Celie's retelling of Nattie's lesson further links masculinity and oppresion as she mentions how a group of Indians had been forced to go back to Europe with Columbus and wait on the queen. Their mentioning leads the reader to associate the discovery of America with the extermination of the Indians. Thus, the history lesson becomes a lesson on the male brutality and violence that Celia has already experienced at the hands of her stepfather and that will characterize her marriage (announced in the letter in the paragraph before the history lesson).
The fact that Nettie describes Columbus in these terms also serves as an ironic commentary on her future experience in Africa. Although she's well-meaning, she will have to work for an organization which operates within colonialist assumptions and whose decisions are taken by whites.