Throughout the ages, people have been afraid of those who are different in anyway from themselves. People believed in the purity of white blood and therefore thought that having one drop of black ancestry on you made you impure. This fear manifested in puritan america in the form of the witch hunts. The puritans considered themselves to be the purest worshipers of Christianity. This led to Cotton Mather's "Allegory of Hybridization", which explains, through allegory, how things can become pure and impure.
From beginning, Mather is being extremely literal but slightly symbolic with what he wants to show the audience. He describes a cornfield with three types of corn: red, blue, and yellow corn. he tells the audience that there is only one row of blue/red corn and 7 other rows are described to be completely composed of yellow corn. Then he describes how the "infected" corn makes all the other corn slowly like itself but not completely because the last rows don't turn completely blue and /or red.
Judging from the title, Mather is clearly making an allegory out of this. This is further reinforced by the second word in the title and what it means. Hybridization pretty much means "when two different creatures combine with one from a different species or variety". What Mather seems to be referencing here with the corn is the combination of races and/or beliefs. The yellow corn represents the common majority, while red and blue represent the minority that is asserting itself over the minority. Mather is telling the audience that the minority (witches, blacks, puritans) will slowly corrupt the majority (Christians, whites, Indians) and make them in the image of themselves.
Mather is giving the audience his idea that minorities and the way that they sometimes change the system is bad for the majority. He calls the minority of the corn "infected", to make the audience realize that they should like this change. This makes a lot of sense considering his background of witch hunting. Mather was teaching the puritans to not trust change, and/or anyone different.
