=Importance of American Agriculture.=—Agriculture has always been the most important single industry in the United States. [Sidenote: The crops in earlier days.] It was at one time practically the sole occupation of the people; even today it directly or indirectly engages the attention of more than half the adult male workers of the country. In colonial days the chief task of the people was to raise a food supply sufficient for themselves. Corn was their principal crop, the colonists having learned from the Indians the methods of cultivating it. Corn had the advantage of being well suited to the soil and climate; besides it grows well even in partially cleared land. But in colonial days and even for a time after the Revolution the country did not produce much grain beyond its own needs. The production of large quantities for export came with the opening up of the great agricultural areas of the West. [Sidenote: 1. Mixed farming.] =Types of Agricultural Activity.=—American agriculture has developed, during the past three hundred years, in five or six different directions. The earliest settlers in the northern colonies devoted themselves to general or mixed farming, in other words to the raising of grain, hay, and cattle on the same tract of land. This was because the environment and needs of the northern region alike favored this method. Mixed farming has continued to be the mainstay of agriculture east of the Alleghenies; in some measure it has spread to other parts of the country as well. [Sidenote: 2. Staple or plantation farming.] A second type of agriculture, almost from the very outset, made progress in the South. This involved the raising of certain staple products, such as rice, tobacco, sugar, and cotton on large plantations. The soil, climate, and general environment of the southern colonies all lent themselves to this type of agriculture and it eventually spread itself over the whole region. Cotton in time out-stripped the other staples and became king of the whole South. This was largely because the invention of the cotton gin, an appliance for removing the seeds from the fibre, greatly reduced the cost of preparing cotton for the market. The scarcity of free labor to work these great plantations led to the importation of negro slaves and the institution of slavery had a profound effect upon the subsequent course of American history. Since the emancipation of the negroes, the plantation system has remained although many of the larger tracts have been broken up into small holdings. [Sidenote: 3. Cereal growing.]