PHYSIOLOGICAL PROCESSES IN PLANTS 87 



5. How are the roots of such plants as the dandelion and 

 rhubarb protected from animals ? 



6. What insect damages the roots of the grape in Europe? 



7. What are the advantages of tilling the soil ? 



8. What sort of soil is favorable to evaporation? 



9. What is the relationship of tubercle-bearing plants to 

 man's supply of food ? 



10. What results from the congestion of population in 

 cities ? 



11. Why does such a man as J. J. Hill plead that the people 

 " go back to the soil " ? 



12. Give a method of analyzing soils. 



13. W r hat compound of nitrogen is washed into the soil from 

 the air by rains and snows ? 



14. What is mulching, and why is it done? 



15. Why should the top layer of soil be loose where crops 

 are growing ? 



16. W T hy are the grain crops relatively expensive crops for 

 the farmer to grow ? 



17. What else do plants need from the soil besides nitrogen ? 

 What acid in the soil aids plants in absorbing these substances? 



References (Also see Prob. XIII) 



Hunter, Essentials of Biology. Chap. VII. 



Goff and Mayne, First Principles of Agriculture. 



Wilkinson, Practical Agriculture. 



Bailey, Principles of Agriculture. Chaps. V, VI. 



Osterhout, Experiments with Plants. Chap. III. 



Moore, G. T., " Soil Inoculation." Century Magazine, p. 831, October. 

 1904. 



" Soil Inoculation for Legumes." U. S. Department of Agricul- 

 ture, Bulletin 71, 1905. 



Bailey, "The Rotation of Crops." Cosmopolitan Magazine, Vol. 38, 

 pp. 682-688, April, 1905. 



Hunt, "The Importance of Nitrogen in the Growth of Plants." Cor- 

 nell University Bulletin, Experiment Station, No. 247, June, 1907. 



Laut, "The New Spirit of the Farm." Outing Magazine, May and 

 September, 1908. (Spraying and Bacterial Inoculation. ) 



