America, only one third of the whole surface receives above 20
inches of rainfall annually; one third receives from 10 to 20
inches, and one third receives less than lO inches. That is, about
1,267,000,000 acres in Australia are subject to reclamation by
dry-farming methods. This condition is not far from that which
prevails in the United States, and is representative of every
continent of the world. The following table gives the proportions of
the earth's land surface under various degrees of annual
precipitations:--


Annual Precipitation Proportion of Earth's Land Surface
Under 10 inches 25.0 per cent
From 10 to 20 inches 30.0 per cent
From 20 to 40 inches 20.0 per cent
From 40 to 60 inches 11.0 per cent
From 60 to 80 inches 9.0 per cent
From 100 to 120 inches 4.0 per cent
From 120 to 160 inches 0.5 per cent
Above 160 inches 0.5 per cent
Total 100 per cent


Fifty-five per cent, or more than one half of the total land surface
of the earth, receives an annual precipitation of less than 20
inches, and must be reclaimed, if at all, by dry-farming. At least
10 per cent more receives from 20 to 30 inches under conditions that
make dry-farming methods necessary. A total of about 65 per cent of
the earth's land surface is, therefore, directly interested in
dry-farming. With the future perfected development of irrigation