LIST OF ILLUSTRATIONS 



FIG. Page 



Brigham Young Frontispiece 



1 . Progressive averages of annual rainfall 3 



2. The limited water supply makes it unlikely that more than one- 



tenth of the land will be irrigated 5 



3. The value of water in an arid land 6 



4. Soil is a mixture of particles of very varying size 10 



5. The moisture film surrounding a soil particle 18 



6. Flooding new land 24 



7. Distribution of water in soil immediately after an irrigation. ... 27 



8. Distribution of water in soil under furrow irrigation 31 



9. Penetration of roots of prune tree 36 



10. Evaporation usually exceeds rainfall 44 



11. Relation between temperature and evaporation 48 



12. Evaporation losses from soils protected with mulches of differ- 



ent depths 51 



13. Orchard well cultivated to prevent evaporation 57 



14. Mulching the garden with a hand cultivator 61 



15. Adhesion of hairs due to water 65 



16. Cracked river sediments showing volume changes due to water 68 



17. Midsummer snow in the tops of the mountains 75 



18. Badly corroded ditch due to excessive fall 95 



19. Walled ditch to prevent erosion of easily "washed" soil 97 



20. Daily discharge of Malheur River 99 



21. Daily discarge of Mackenzie River 99 



22. Deposit in field of suspended matter from irrigation water 102 



23. Stomatal apparatus in carnation leaf 132 



24. Determining the transpiration ratio 135 



25. Yield of dry matter of cereals with varying quantities of water. . 149 



26. Yield of dry matter of cereals per inch of irrigation water 149 



27. Crop-producing power of 30 acre-inches (wheat) 152 



28. Crop-producing power of 30 acre-inches (alfalfa) 152 



29. Crop-producing power of 30 acre-inches (sugar beets) 153 



30. Effect of little, medium and much water on wheat 160 



31. Proportion of grain and straw with varying irrigations 168 



32. Plan of a sub-irrigated farm 191 



33. Lee's sub-irrigation system 192 



(xxi) 



