from barberry bushes and other plants on which these spores may lodge. These measures and a frequent change of crops will usually prevent the spread of rust.

Have the pupils examine neighboring fields for the appearance of rust. If it is found, ask them to measure a square foot of the field in some part where the disease appears, count the number of plants within the space measured and also the number affected with rust. From these a very fair estimate of the portion of the field affected can be obtained.

29. Smut. Smut attacks wheat, oats, barley, and especially Indian corn. It is developed and propagated by the means of spores, in much the same manner as rusts. However, the spore of the smut fungus works differently from that of the rust fungus. Some spores are capable of attacking the plant only when it is young. The spore penetrates to the interior and grows toward the end of the stalk, dividing wherever the stalk divides and sending a minute filament into each branch until finally it works to the tips of the shoots which bear the fruit. For this reason the presence of smut cannot be detected until the fungus is fully developed. This is best illustrated in corn. With this plant the smut does not appear to cause any damage until the kernels are well formed. Then in the course of a few days those at the end of the ear swell, burst and throw out a large quantity of black powder which consists of the perfected spores. These can be carried long distances by the wind. They lodge in the soil, fall upon manure heaps or find homes in other suitable places, where they develop a second kind of spore which is carried to the corn plant the next season and begins its career on the new crop.

Because of the large number of spores and the way in which the fungus works, smut is very difficult to eradicate. Whenever possible, the ears affected by it should be destroyed and seed from an affected field should not be planted. When smut attacks oats or barley, it may not be discovered until thrashing time; then the escaping spores form clouds of black dust. Spores can be destroyed on the seed by soaking

the seed from ten to fifteen minutes in water raised to a temperature of 132 to 135 degrees Fahrenheit. The heat should not exceed the latter temperature and the seed should be thoroughly stirred so that the water may be brought in contact with the entire surface of every kernel. This treatment does not injure the vitality of the seed and it often saves the farmer a crop. When a field is badly affected with smut it should be planted to some crop upon which this fungus cannot work. One or two seasons of this treatment will eradicate the disease.

30. Potato Blight. There are two forms of potato blight, known as the early and the late blight. The pupils should be asked to look for the appearance of this disease, and if found it should be studied. The early blight is due to the growth in the tissues of the leaves of a fungus which causes the leaves to turn yellow and dry up. This blight does not usually affect the tubers. However, if it begins early in the season, it decreases the yield. The later blight is likely to attack the crop during warm, damp weather. It sends its filaments down the stalk into the tubers and causes them to rot. Farmers not understanding the nature of this disease

WHITE MOLD

think that the rot is due to some condition of the soil. Both of these diseases can be prevented by spraying the vines with Bordeaux mixture (See Section 45). Usually three applications in a season will preserve the plants in good condition. Sometimes the spores from this blight do not develop until the tubers have been stored for the winter, and the farmer is much surprised to find that his potatoes are rapidly decaying.

31. Scab. Another disease which is likely to affect potatoes is scab. Doubtless pupils can bring potatoes that have been attacked in this way. Examine the scabs with the magnifying glass. Each scab is a plant and grows from a

spore. The spores may exist in the soil before the potatoes are planted. This will be true if the ground produced a scabby crop of potatoes the previous season. If affected potatoes are planted, an affected crop may be expected; therefore, only healthy potatoes should be used for seed. The scab can be prevented by dipping the potatoes, before planting, in a solution made by adding a pint of formalin (a liquid that can be obtained of any druggist) to fifteen gallons of water, and allowing them to remain in the solution from one and one-half to two hours. Formalin is not poisonous, but potatoes thus treated should not be eaten nor fed to stock. Study the apple scab in the same manner. Doubtless in the fall numerous apples having black scabs on the surface can be obtained. These are caused by another sort of fungus which works upon the apple in a similar manner.

BLACK MOLD

32. Molds or Mildews. Place a piece of bread in a damp, warm place where it is excluded from the light and allow it to remain for several days. Have the pupils, with a magnifying glass, examine the mold formed. With a glass of good power some very interesting forms will be discovered. There are many species of mold or mildew, and they attack numerous plants, especially the rose, grape, plum and peach, and often cause serious damage. The most common forms are shown in the illustrations printed on pages 96, 97 and 98. They are highly magnified. Mildew on grapes can easily be detected by examining the under side of the leaves, where it appears in the form of pale spots or scales, which are covered with silky, thread-like organs. The mold on fruit usually appears as a whitish bloom or roughish brown coating. The latter is known as brown rot, and it is very destructive to plums and peaches. The fruit so affected

BLUE MOLD

often remains on the tree and dries, forming what are known as mummies. These dried fruits are full of spores, and unless they are destroyed will constitute a source from which the disease will be propagated to the next crop. The brown rot and most other mildews can be prevented by spraying either with a simple solution of copper sulphate in a proportion of one pound of sulphate to eighteen or twenty-five gallons of water, or by a weak solution of Bordeaux mixture. Two or three sprayings during the season will be necessary to preserve the fruit, and the result depends almost entirely upon the thoroughness

MILK MOLD

with which the work is done. Every branch and leaf of the tree should be touched by the spray.

If fruit is grown in the locality in which your school is located, lead the pupils to watch for the appearance of these molds and then secure their interest in spraying trees.

33. Other Diseases. The plans given show what can be done with other plant diseases. If you live in one of the cotton states, you will need to give attention to the numerous diseases which attack the cotton plant. If in a tobacco region, other diseases are important. Send to the experiment station of your state for information on diseases prevalent in that locality, and you will secure much valuable assistance. Send to the Department of Agriculture, Washington, D. C., for Farmers' Bulletin No. 75, on Grain Smuts and How to Prevent Them, also for Bulletin No. 20 of the Bureau of Vegetable Physiology and Pathology. Each of these works will furnish valuable information.

DESTRUCTIVE INSECTS

34. Classes. For the purpose of destroying them, insect pests are considered under two classes, biting insects and

sucking insects.

This distinction is important, because insecticides that are effective with the first class are harmless to the second. Biting insects feed upon foliage, and any preparation which poisons the leaves of the plant destroys the pest. Sucking insects feed upon the juices of plants and extract them by boring through the outer tissue or bark; therefore, poisoning the foliage has no effect upon them. A preparation which poisons the insect by contact must be employed. Spraying mixtures containing Paris green or London purple will usually destroy biting insects, and a preparation of kerosene known as kerosene emulsion, or a solution of tobacco soap, will destroy most sucking insects. Where plants can be enclosed, lice can usually be destroyed by fumigating the plants with tobacco or with carbon disulphide. In all cases spraying or fumigating is most effective if applied early, as soon as the insects are discovered. See Section 45 for spraying preparations.

35. Directions. Lead the pupils to understand the facts here given and to apply them in connection with the study of insect pests. For the life study of these insects, follow the plans given on pages 39-50, Sections 2 to 24, inclusive. In studying insect pests, it is necessary for the pupils to learn:

(1) To recognize the insect in each stage of its growththe egg, the larva, the pupa and the imago.

(2) How long the insect lives in each stage.

(3) Upon what the larvae feed.

(4) The time and place of laying the eggs.

(5) How the insects pass the winter.

(6) How the ravages can be prevented.

To ascertain these facts it will usually be necessary for the class to continue observations through a year.

36. Cabbage Worm. What sort of butterfly is seen around the cabbages about the time the young plants begin to head? Have the pupils catch some of these in the insect net and place them in their cages. Place fresh cabbage leaves in the cage each day. Do the butterflies lay eggs