These deductions as to the depth to which plant roots will penetrate
the soil in arid regions are fully corroborated by experiments and
general observation. The workers of the Utah Station have repeatedly
observed plant roots on dry-farms to a depth of ten feet. Lucerne
roots from thirty to fifty feet in length are frequently exposed in
the gullies formed by the mountain torrents. Roots of trees,
similarly, go down to great depths. Hilgard observes that he has
found roots of grapevines at a depth of twenty-two feet below the
surface, and quotes Aughey as having found roots of the native
Shepherdia in Nebraska to a depth of fifty feet. Hilgard further
declares that in California fibrous-rooted plants, such as wheat and
barley, may descend in sandy soils from four to seven feet. Orchard
trees in the arid West, grown properly, are similarly observed to
send their roots down to great depths. In fact, it has become a
custom in many arid regions where the soils are easily penetrable to
say that the root system of a tree corresponds in extent and
branching to the part of the tree above ground.
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