List of Illustrations. 



v 



TEXT-FIGURES 



Page 



1. (A) Root system of University No. 21 oats 59 days old; (B) Swedish Select 



oats 60 days old 10 



2. (A) University No. 21 oats; (B) Swedish Select oats; at maturity 12 



3. (A) Marquis wheat 20 days old; (B) 70 days old; (C) Durum wheat 60 days old . 14 



4. (A) Durum wheat; (B) Marquis wheat; at maturity 16 



5. (A) Manchuria barley 20 days old; (B) 54 days old 19 



6. Manchuria barley at maturity 20 



7. Root system of Iowa Silver Mine corn 36 days old 21 



8. Root system of corn on July 5 • • 23 



9. Root system of corn on September 2 facing 24 



10. One-half of root system of a potato plant 56 days old 27 



11. One-half of root system of a mature potato plant 28 



12. Water-content in excess of hygroscopic coefficient from March 31 to June 16 34 



13. Water-content in excess of hygroscopic coefficient in the several crop plats 



on May 30 34 



14. Water-content in excess of hygroscopic coefficient in the several crop plats 



on June 23 35 



15. Soil-temperatures at various depths during 1919 37 



16. Average day and night temperatures (solid lines) and average maximum and 



minimum temperatures 37 



17. Oats 31 days old 42 



18. Oats 45 days old 43 



19. Oats 60 days old ■ 44 



20. Average daily air temperature (long broken lines), soil temperature (short 



broken lines), and humidity (solid line), 1920 46 



21. (A) Oats; (B) wheat; at time of blossoming facing 46 



22. Wheat 31 days old 50 



23. (A) Wheat 45 days old; (B) 60 days old 51 



24. (A) Alfalfa 63 days old; (B) sweet clover 63 days old 53 



25. (A) Alfalfa 132 days old; (B) sweet clover 115 days old 55 



26. Average day and average night air temperatures and average daily soil 



temperature (broken line) at Phillipsburg, 1920 59 



27. Wheat roots showing normal differences in branching at Lincoln, L, and 



Burlington, B. 1, at depth of 1.5 feet; 2, root-ends 64 



28. Average day and average night air temperatures and average daily soil 



temperature (broken line), Burlington, 1920 65 



29. Average day humidity (lower lines) and average night humidity (upper lines) 



at Lincoln (solid lines), and Burlington (broken lines), 1920 66 



30. Oats at maturity, Burlington, 1921 67 



31. Alfalfa excavated at Burlington, June 28, 1921, during the second year of 



growth 69 



32. Mean precipitation in inches (black) and precipitation for 1920 at Lincoln 



(left), Phillipsburg, and Burlington 72 



33. Average daily soil temperature at Lincoln (solid line), Phillipsburg (long 



broken lines), and Burlington (short broken lines), 1920 73 



34. Average daily air temperature at Lincoln (solid line), Phillipsburg (long 



broken lines), and Burlington (short broken lines), 1920 73 



35. Hygrothermograph records from Lincoln (upper) and Burlington, June 1921; 



light lines temperature, heavy lines humidity 74 



36. Average daily evaporation at Lincoln (solid line), Phillipsburg (long broken 



lines), and Burlington (short broken lines), 1920 75 



37. Average day air temperatures (heavy lines) and average night temperatures 



(light lines) at Lincoln (solid lines), Phillipsburg (long broken lines), 



and Burlington (short broken lines), 1921 83 



