GRASSES FOR SPECIAL CONDITIONS 197 



DRY LANDS 



Some of the cultivated grasses are noted for drouth- 

 resistance, and are of great value in regions of com- 

 paratively light rainfall. The most notable of these is 

 brome-grass. In the South, Johnson grass is of some 

 value as a drouth-resister, as is also Bermuda grass. 

 These have. already been discussed. There are many 

 wild grasses that thrive in regions where the rainfall 

 is too slight for farming, and several million acres of 

 such grasses are annually cut for hay in the West. An 

 enumeration of them would be out of place in a treatise 

 on farm grasses. 



ALKAU SOILS 



All soils contain more or less soluble mineral mat- 

 ter. Soil consists mostly of small rock particles com- 

 posed chiefly of quartz, but containing small quantities 

 of numerous substances. As these rock particles disin- 

 tegrate under the aclion of moisture, air. heat, and cold, 

 small portions of soluble substances are set free in the 

 soil. In humid climates these substances are washed 

 out and carried off by streams to the ocean. This is 

 the origin of the saltness of sea-water. This process 

 has been going on ever since rain began to fall on the 

 hot crust of the newly formed earth, and the ocean has 

 thus become the storehouse of vast quantities of solu- 

 ble material formerly constituting part of the rock and 

 soil of the earth's surface. 



In arid climates, where the rainfall is insufficient to 

 saturate the soil down to the water-table below, and 

 where most of the rain that falls is evaporated from the 



