Corn, or maize, is a grain plant widely grown in the United States and used as a food crop due to the rich starch content of its seeds, called kernels. Originally only an inch or so long, corn was domesticated by the indigenous peoples of Mesoamerica, and can now grow between 8-40 ft, with several cobs per plant. There are six major types of corn: dent, flint, pod, popcorn, flour and sweet. In temperate areas, corn must be planted in spring, a popular saying among American farmers is 'knee high by the Fourth of July.'