It is an interesting study--the preparation of homes for the birds. Trees may be pruned to make inviting crotches. A tangled, overgrown corner in the garden will invite some birds to nest. Wrens, bluebirds, chickadees, martins, and some other varieties are all glad to set up housekeeping in man-made houses. The proper size for a bird-room is easily remembered. Give each room six square inches of floor space and make it eight inches high. Old, weathered boards should be used; or, if paint is employed, a dull color to resemble an old tree-trunk will be most inviting. A single opening near the top should be made two inches in diameter for the larger birds; but if the house is to be headquarters for the wren, a one-inch opening is quite large enough, and the small door serves all the better to keep out English sparrows. The barn attic should be turned over to the swallows. Small holes may be cut high up in the gables and left open during the time that the swallows remain with us. They will more than pay for shelter by the good work they do in ridding the barn of flies, gnats, and mosquitoes. SECTION LXVIII. FARMING ON DRY LANDS Almost in the center of the western half of our continent there is a vast area in which very little rain falls. This section includes nearly three hundred million acres of land. It stretches from Canada on the north into Texas on the south, and from the Missouri River (including the Dakotas and western Minnesota) on the east to the Rocky Mountains on the west. In this great area farming has to be done with little water. This sort of farming is therefore called "dry-farming." The soil in this section is as a rule very fertile. Therefore the difference between farming in this dry belt and farming in most of the other sections of our country is a difference mainly due to a lack of moisture.