All through the spring and summer the wheat kept growing, and finally there appeared at the ends of the stalks clusters of kernels, just like those which the farmer had planted. Some of these kernels had produced families of twenty or thirty. These clusters are called _heads_. [Illustration: FIG. 3.--Harvesting Wheat in Southern California.] As the south wind passed over the field it brought the wheat messages from Minnesota, Iowa, Illinois, Indiana, and other states, telling of relatives who were already turning golden in the summer sunshine. One day some of the kernels thought they heard a voice from California. Do you think they did? The grain in some of the fields was called _winter wheat_. This was because the grain had been sown the autumn before, and had remained in the ground all winter, covered by a blanket of snow. Why was it sown in the fall? The wheat of which I am telling you was called by the farmer _spring wheat_. Soon machines, each drawn by several horses, appeared. They cut the waving grain, and bound it up in bundles called _sheaves_. These were set up in double rows to dry, and afterward put into another machine which separated the kernels from the stalks, which were now called _straw_. This work the farmer calls _threshing_. See if you can find out how this used to be done. After threshing, the wheat was put into sacks and taken to the nearest railroad station. Freight cars then carried it across the level prairies to the beautiful city of Minneapolis, built beside the Falls of Saint Anthony. What river is this city on? Of what use are the falls? There are tall buildings called _elevators_ here in which the wheat was stored for a time. Before being put into the elevators it was examined and _graded_. As there was wheat from many farms it could not be kept separate, so each farmer was told how much he had, and how it graded. [Illustration: FIG. 4.--Threshing Wheat in Southern California.] Some time after this the wheat was taken to one of the great mills to be ground into flour. The largest of these mills manufactures about fifteen thousand barrels of flour every day. This is the largest flour mill in the world. When the kernels reached the mill, they were put into machines called _separators_, to be separated from all companions such as grass seed, mustard seed, and wild buckwheat. They were then placed in an iron box in which brushes were revolving rapidly, and were _scoured_ to free them from fuzz and dirt. Those that were very dirty were washed. [Illustration: FIG. 5.--The Flour Mills in Minneapolis.] [Illustration: FIG. 6.--The Largest Flour Mill in the World.]