Page:Tree Crops; A Permanent Agriculture (1929).pdf/346

 . 123. Top. Top of Appalachian shale hill. Soil too shallow to plow, yet supporting grass and trees, because roots penetrate the cracks.—. 124. Center. Sorrento peninsula, Italy. Background, olives; foreground, walnuts. Every tree grafted. Most of the land utterly unplowable—. 125. Bottom. Central Tunis. Rainfall less than 10 inches. Olives, as far as the eye can see. Tree agriculture is the best of desert agricultures.