98 BIOLOGY AND HUMAN LIFE 



4. If there are abandoned farms in your part of the country, find out 

 for what reasons any were abandoned besides the exhaustion of the soil. 



5. If any abandoned farms have been reclaimed, find out what 

 methods were used. 



6. Have fashions changed as to the kinds or varieties of plants raised 

 in your part of the country ? In what ways are the newer plants more 

 advantageous to the gardener or farmer ? 



7. What portion of the area of your state is naturally tillable ? What 

 percentage of the tillable land is being cultivated ? 



8. How much reclaimed swamp or desert land is cultivated in your 

 part of the country ? 



9. Which of our regular commercial crops come largely from re- 

 claimed lands ? 



10. What are the principal sources of soil loss in your part of the 

 country ? How can this waste be prevented ? 



IL How can a knowledge of plant chemistry help to reduce the cost 

 of living ? 



12. How can the cost of living be reduced by preventing the growth 

 of weeds in cultivated areas ? 



13. What is the advantage of increasing the human population of the 

 country ? of the entire earth ? What is the disadvantage ? 



14. How can the earth be made to yield more on each acre cultivated ? 



REFERENCE READINGS 



Bergen and Caldwell. Practical Botany, pp. 434-451. 

 BuRKETT, C. W., and Others. Agriculture for Beginners, chap, i. The Soil. 

 Waters, H. J. Essentials of the New Agriculture, chaps, xxiv-xxxi. 

 United States Department of Agriculture (office of the Secretary). Cir- 

 cular 38, Conservation of Soil (address by President Taft). 

 United States Department of Agriculture. Yearbook for 191 7 : 



Reprint 728, Fertilizers from Industrial Wastes. 



Reprint 729, Sources of our Nitrogen Fertilizers. 



Reprint 730, Phosphate Rock, our Greatest Fertilizer Asset. 



Reprint 733, Conservation of Fertilizer Materials from Minor Sources. 

 United States Department of Agriculture. Yearbook for 1920. Re- 

 print 854, Uses of the Soil Survey. 



