The history of agriculture is one of progressive simplification in the interests of human convenience and with this simplification has gone an increasing instability. The drive for simplification has gained in momentum in recent years under economic pressure and the widespread desire to substitute mechanical power of human effort. As a result there are ample indications that the instability is becoming an increasingly serious problem. The widespread need for special methods to deal with what appearsto be an increasing variety of diseases and pests and the rapidity with which one treatment has to be replaced by another because of the failure of the first is symptomatic of this instability.
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