6 LIST OF ILLUSTRATIONS. 



Page. 



PLATE XVII. Fig. 1. A few rows of young cottonwood make a fairly dense 

 belt. Fig. 2. When mature, cottonwood must be under- 

 planted 96 



XVIII. Even a very good belt of hard woods forms a poor winter shelter.. 96 

 XIX. Fig. 1. In closely planted groves white pine forms straight 

 clean boles. Fig. 2. Even in belts of a few rows', white 



pine is erect and symmetrical 96 



XX. Fig. 1. Dense and thrifty young white pine grove. Fig. 2. 

 The addition of a few rows of white cedar on the outside 



reenforces the windbreak 96 



DIAGRAMS. 







DIAGRAM 1. Direction, origin, and season of winds injurious to agriculture.. 10 



2. Amount of sunlight cut off by cottonwood groves 24 



3. Amount of sunlight cut off by cottonwood rows 24 



4. Amount of sunlight cut off by ash and maple belts 25 



5. Amount of sunlight cut off by osage orange hedges 25 



6. Amount of sunlight cut off by honey locust rows 26 



7. Yield of crops north of dense groves s . 29 



8. Yield of crops north of shelter belts 29 



9. Yield of crops west and east of cottonwood rows 30 



10. Yield adjacent to osage orange and cottonwood rows 30 



11. Yield of crops east and west of osage orange hedges 31 



12. Yield of alfalfa with various tree species 31 



13. Yield of corn west of various tree species 32 



14. Effects of shading and sapping on the growth of field crops 33 



15. Reduction of mechanical force of wind 40 



16. Protective efficiency of underplanted cottonwood groves 46 



17. Protective efficiency of white pine belt 47 



18. Protective efficiency of cottonwood row 48 



19. Protective efficiency of cottonwood belt 48 



20. Protective efficiency of cottonwood row reinforced with ash 49 



21. Protective efficiency of dense osage orange hedge 50 



22. Protective efficiency of open osage orange hedge 51 



23. Protective efficiency of mulberry hedge 52 



24. Protective efficiency of young honey locust hedge 53 



25. Effect of dense groves on daily range of air temperatures 57 



26. Heating efficiency of various windbreaks during hours of sun- 



dune 58 



27. Heating efficiency of white pine belt during hours of sunshine. . 59 



28. Influence of dense grove on nocturnal cooling of air 60 



29. Influence of cottonwood belt on nocturnal cooling of air 61 



30. Influence of cottonwood row on nocturnal cooling of air 62 



31. Influence of white pine belt on nocturnal cooling of air (53 



32. Effect of dense windbreak on temperature of the soil 04 



33. Effect of windbreaks on velocity and humidity of air currents . . 72 



34. Summation of windbreak influences as shown by yield of crops. . 71 



35. Plan for location of windbreaks on a farm in the Middle West. . 95 



