xiv AGRONOMY 



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CHAPTER VI. THE ELEMENTS NEEDED BY PLANTS ... 95 



Source of the elements. Selective absorption. Use of water to the 

 plant. Root pressure. Carbon dioxide. Nitrogen. Calcium and 

 magnesium. Potassium and phosphorus. Sulphur and iron. Chlorine, 

 silicon, and others. Practical exercises. 



CHAPTER VII. FERTILIZERS 101 



The available mineral in the soil. Toxic substances in the soil. Ele- 

 ments that may be lacking. Sources of the needed elements. Manures. 

 Green manures. Nitrification. Bacteria and nitrification. Nitrogen 

 fixation. Mycorrhizas. Soil inoculation. Denitrifying bacteria. 

 - Harmful organisms in the soil. Limiting factors in plant growth. 

 Practical exercises. 



CHAPTER VIII. THE PLANT IN RELATION TO TEMPERA- 

 TURE, LIGHT, AND MOISTURE 113 



Growth temperature. Hardy and tender plants. Cardinal points. 

 Acclimatization. Frost. Locality and frost. How cold kills plants. 

 Other effects of cold. How plants avoid the effects of cold. Artifi- 

 cial protection from the cold. Treatment of frostbitten plants. 

 Effects of heat. Protection from heat. Need of light. Effects of 

 lack of light. Blanching. Protection from light. Effects of over- 

 watering. Time to water. Effects of lack of water. Water and 

 plant forms. Practical exercises. 



CHAPTER IX. GARDEN MAKING 129 



Location of the garden. Preparing the soil. The garden plan. How 

 to plant. When to plant. Autumn seed bed. Germination. Seed test- 

 ing. Double cropping. Transplanting. Inducing plants to fruit. 

 Thinning. Labels. Saving seed. Seed packets. Practical exercises. 



CHAPTER X. TILLAGE 149 



Need for tillage. Pulverizing the soil. Mulches. Work of earth- 

 worms and ants. Rotation of crops. Practical exercises. 



CHAPTER XI. FORCING AND RETARDING PLANTS .... 157 



Nature of the process. Retarding. Greenhouses and hothouses. Hot- 

 beds. Cold frames. Forcing single hills. Etherization. Forcing 

 plants in the window garden. Practical exercises. 



CHAPTER XII. WEEDS 164 



Definition of a weed. Harmfulness of weeds. Nature of weeds. 

 Eradicating weeds. Purslane. Spreading amaranth. Green ama- 

 ranth. Tumbleweed. Pigweed. Russian thistle. Spotted spurge. 



