broadcasting, reaped by sickles, and threshed by flails. The kernels were then taken to a grist mill for grinding into flour. In 1830, it took four people and two oxen, working 10 hours a day, to produce 200 bushels. New technology greatly increased productivity in the 19th century, as sowing with drills replaced broadcasting, cradles took the place of sickles, and the cradles in turn were replaced by reapers and binders. Steam-powered threshing machines superseded flails. By 1895, in Bonanza farms in the Dakotas, it took six people and 36 horses pulling huge harvesters, working 10 hours a day, to produce 20,000 bushels. In the 1930s the gasoline powered "combine" combined reaping and threshing into one operation that took one person to operate. Production grew from 85 million bushels in 1839, 500 million in 1880, 600 million in 1900, and peaked at 1.0 billion bushels in 1915. Prices fluctuated erratically, with a downward trend in the 1890s that caused great distress in the Plains states. The marketing of wheat was modernized as well, as the cost of transportation steadily fell and more and more distant markets opened up. Before 1850, the crop was sacked, shipped by wagon or canal boat, and stored in warehouses. With the rapid growth of the nation's railroad network in the 1850s–1870s, farmers took their harvest by wagon for sale to the nearest country elevators. The wheat moved to terminal elevators, where it was sold through grain exchanges to flour millers and exporters. Since the elevators and railroads generally had a local monopoly, farmers soon had targets besides the weather for their complaints. They sometimes accused the elevator men of undergrading, shortweighting, and excessive dockage. Scandinavian immigrants in the Midwest took control over marketing through the organization of cooperatives. Varieties Following the invention of the steel roller mill in 1878, hard varieties of wheat such as Turkey Red became more popular than soft, which had been previously preferred because they were easier for grist mills to grind. Wheat production witnessed major changes in varieties and cultural practices since 1870. Thanks to these innovations, vast expanses of the wheat belt now support commercial production, and yields have resisted the negative impact of insects, diseases, and weeds. Biological innovations contributed roughly half of labor-productivity growth between 1839 and 1909. In the late 19th century, hardy new wheat varieties from the Russian steppes were introduced on the Great Plains