In dealing with plants, as with human beings, the great object should be not the cure but the prevention of disease. If disease can be prevented, it is far too costly to wait for it to develop and then to attempt its cure. Men of science are studying the new forms of diseases and new insects as fast as they appear. These men are finding ways of fighting old and new enemies. Young people who expect to farm should early learn to follow their advice. =EXERCISE= How does the squash bug resemble the plant louse? Is this a true bug? Gather some eggs and watch the development of the insects in a breeding-cage. Estimate the damage done to some crops by the flea-beetle. What is the best method of prevention? [Illustration: FIG. 171. AN APPLE TREE SHOWING PROPER CARE] Do you know the large moth that is the mother of the tobacco worm? You may often see her visiting the blossoms of the Jimson weed. Some tobacco-growers cultivate a few of these weeds in a tobacco field. In the blossom they place a little cobalt or "fly-stone" and sirup. When the tobacco-worm moth visits this flower and sips the poisoned nectar, she will of course lay no more troublesome eggs. SECTION XXXIV. THE COTTON-BOLL WEEVIL So far as known, the cotton-boll weevil, an insect which is a native of the tropics, crossed the Rio Grande River into Texas in 1891 and 1892. It settled in the cotton fields around Brownsville. Since then it has widened its destructive area until now it has invaded the whole territory shown by the map on page 177. [Illustration: FIG. 172. ADULT COTTON-BOLL WEEVIL Enlarged] This weevil is a small gray or reddish-brown snout-beetle hardly over a quarter of an inch in length. In proportion to its length it has a long beak. It belongs to a family of beetles which breed in pods, in seeds, and in stalks of plants. It is a greedy eater, but feeds only on the cotton plant. The grown weevils try to outlive the cold of winter by hiding snugly away under grass clumps, cotton-stalks, rubbish, or under the bark of trees. Sometimes they go down into holes in the ground. A comfortable shelter is often found in the forests near the cotton fields, especially in the moss on the trees. The weevils can stand a good deal of cold, but fortunately many are killed by winter weather. Moreover birds destroy many; hence by spring the last year's crop is very greatly diminished.