84 BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
Legumes, such as clovers, soy beans, and cowpeas, on account of 
their ability to secure nitrogen from the atmosphere, are of particular 
value for growth on soils low in organic matter. They include an- 
nuals and biennials of wide range of resistance to drought and frost, 
so that a selection can be made of those which are best adapted to 
almost any conditions, and every farmer should see to it that he has 
thoroughly mastered the growth of one or more legumes in such a way 
as to maintain the nitrogen and organic matter of his soil at its 
highest state. 
EXERCISES, LESSON XL 
(a) Draw a map of the United States, or secure outline maps having State lines, 
then locate and label the important corn, wheat, potato, sweet potato, cotton, tobacco, 
and flax sections by States. Use the Yearbook of the Department of Agriculture for 
1913 to select the States, as follows: 
Corn. — Select five States having highest acreage, page 372. 
Wheat.— Select five States having highest acreage, page 381. 
Potatoes. — Select eight States having highest acreage, page 411. 
Sweet potatoes. — Select six States having highest acreage, page 414. 
Cotton. — Select six States having highest acreage, page 423. 
Tobacco. — Select five States having highest acreage, page 428. 
Flax. — Select five States having highest acreage, page 434. 
(b) Discuss the relation of climate, soils, and rainfall in these sections to the various 
crops named. Consult this lesson, Ref. No. 7, pp. 574-710, and any good general 
cyclopedia. 
REViEW QUESTIONS, LESSON XI. 
1. Name some of the factors which determine the adaptability of crops to soils. 
2. Discuss the relation of corn growing to the climate conditions of the Mississippi 
Valley. 
3. What influence has texture of the soil on the quality of tobacco? 
4. Mention three conditions of soil or climate essential to success in raising sugar 
beets. 
5. For what reasons are potatoes best grown on sandy loam soils? 
6. Explain the relation between fungus diseases of potatoes and the chemical 
reaction of the soil. 
7. What are the special requirements of cabbage and celery? 
8. What conditions of soil are best adapted to the growing of melons and cucumbers? 
9. Explain why grasses are able to grow better on heavy clay soils than root crops can. 
10. On what principle does the classification of soils into grass soils, grain soils, and 
truck soils rest? 
LESSON XII. CROP ROTATIONS AND SOIL FERTILITY. 
(Ref. No. 4, pp. 273-283; or No. 6, pp. 356-372; or No. 7, pp. 505-507; or No. 10, pp. 
298-300.) 
Although it is easier to learn to grow one crop well than to learn 
to grow several crops well, nevertheless, there are distinct reasons 
why it is best to grow more than one crop on most farms. It permits 
a more economical and efficient use of labor; it involves less chance 
of failure, which may be entire in case of loss of a single crop grown; 
