. Elementary agriculture . Courtesy U. S. Dept. of Agriculture Fig. 39. Apples from trees that were sprayed. No farmer can afford to neglect his fruit crop. other materials so as to prevent damage to the plants on which the insects live. Kerosene emulsion is such an insect destroyer. Poisons may be put on the plants before insects appear as a protection, but contact insecticides must be applied to the insects themselves. Moulting of Insects. Insects have no bones or inside skeleton, but the skin becomes very hard and

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Keywords: ., bookcentury1900, bookdecade1910, booksubjectagriculture, bookyear