CONTENTS. xi 



CHAPTER XV. 



COLORS OF SOILS, 283. Black Soils, 283. " Red " Soils, 284. Origin of 

 Red Tints, 285. White Soils, 285. Differences in Arid and Humid 

 Regions, 286. White Alkali Spots, 286. 



CHAPTER XVI. 



CLIMATE, 287. Heat and Moisture Control Climates, 287. Climatic Con- 

 ditions, 287. Ascertainment and Presentation of Temperature Condi- 

 tions, 288. Annual Mean not a Good Criterion, 289. Extremes of 

 Temperature are most Important, 289. Seasonal and Monthly Means, 

 289. Daily Variations, 290. The Rainfall, 290. Annual Rainfall not 

 a Good Criterion, 290. Distribution most Important, 290. Winds, 291. 

 Heat the Cause of Winds, 291. Trade Winds, 291. Cyclones, 292. 

 Influence of the Topography on Winds ; Rains to Windward of 

 Mountains, Arid Climates to Leeward, 293. General Distribution of 

 Rainfall on the Globe. Figure, 294. Ocean Currents, 295. The Gulf 

 Stream, 295. The Japan Stream, 296. Contrast of Climates of N. W. 

 America, 297. Continental, Coast and Insular Climates, 297. Subtropic. 

 Arid Belts, 298. Utilization of the Arid Belts, 299. 



CHAPTER XVII. 



RELATIONS OF SOILS AND PLANT GROWTH TO HEAT, 301. Temperature of 

 Soils, 301. Water Exerts Controlling Influence, 301. Cold and Warm 

 Rains, 302. Solar Radiation, 302. Penetration of the Sun's Heat into 

 the Soil, 302. Change of Temperature with Depth, 303. Surface Con- 

 ditions that Influence Soil Temperature, 303. Heat of High and Low 

 Intensity, 304. Reflection vs. Dispersion of Heat, 304. Influence of 

 Vegetation, and of Mulches, 305. Influence of the Nature of the Soil- 

 Material, 306. Influence of Evaporation, 307. Formation of Dew, 307. 

 Dew rarely adds Moisture, 308. Dew within the Soil, 308. Plant 

 Development under Different Temperature-Conditions, 309. Germin- 

 ation of Seeds ; Optimum Temperature for each Kind, 309. Artificial 

 Heating of Soils ; by Steam Pipes or Water, 310. 



CHAPTER XVIII. 



PHYSICO-CHEMICAL INVESTIGATION OF SOILS IN RELATION TO CROP 

 PRODUCTION, 313. Historical Review of Soil Investigation, 313. 

 Popular Forecasts of Soil Values, 313. Cogency of Conclusions Based 

 upon Native Growth, 314. Ecological Studies, 315. Early Soil Surveys 

 of Kentucky, Arkansas and Mississippi, 316. Investigation of Cultivated 

 Soils, 316. Change of Views, 317. Advantages for Soil Study offered 

 by Virgin Lands, 318. Practical Utility of Soil Analysis ; Permanent 

 Value vs. Immediate Productiveness, 319. Physical and Chemical 

 Conditions of Plant Growth, 319. Condition of Plant-food Ingredients, 

 in the Soil, 319. Water-soluble, Reserve, and Insoluble Part, 320. 

 Hydrous or " Zeolitic " Silicates, 321. Recognition of the Prominent 

 Chemical Character of Soils, 322. Acidity, Neutrality and Alkalinity, 



