Nitrifying germs, 144, 145. Nitrogen, 66. added to the soil by legumes, 68. grown on the farm, 68. in humus, 167. in soils, 67, 148. in plants, 66, 67. in fertilizers, 192. loss of, 67. sources of, 171. Nitrogen-fixing germs, 144. Non-leguminous green manure-crops, 191. Norfolk sand, 28. Oats, soil for, 29. Object of this book, 3. Odorless phosphate, 198. Oil in plants, 64, 66. One-crop system, 221. effect on fertility, 221. Onion, 6. Organic matter, in soils, 32, 62, 220. value of, 61. Osmose, 18. Ovary of flower, 130. Ovules, 130. Oxygen in plants, 66. Paris green to destroy chewing insects, 117. Parsley family, 86. Parsnip root, depth of growth, 13. Parsnips, 4. Pasture, soils for, 30. Pea family, 86. soils, 28. Peach borer, 127. flower, 130. Peanuts, 5. Peat, 30. Peppers, soil for, 28. Percolation of water, 41. Petals, 129. Petunia, 129. Pigweeds, 5, 6. Pistil, 130. function of, 131. Phosphate, odorless, 198. rock, 195. slag, 195, 198. Phosphoric acid, 195. available, 195, 196. in fertilizers, 195. in soil, 148. insoluble, 195, 196. reverted, 196. soluble, 196. sources of, 171. Phosphorus in plants, 66, 67. in soils, 68. Plank harrow, 102, 105. Plant, analysis of, 63. most important part of to plant itself, 7. most important part of to plant grower, 7. Plant diseases, 118. Plant food, 63. and the farmer, 5. Plant food, in soil, 63. in fertilizers, 68, 192, 205. what it is, 63, 69. Planting, corn, 84. grass seed, 84. grain seed, 84. method of, 83. seeds, 81. vegetable seeds, 84. Plants, 5. and the farmer, 5. conditions for growth, 6. composition of food of, 63. for study, 6. living, growing things, 6. parts of, 6. resemble one another, 6. why raised, 6. work of in making soils, 36. Plow beam, 93. coulter, 94. characteristics of, 95. clevis, 93. cutting roots, 15. draft ring, 93. handles, 93. jointer, 95. landside, 94. mouldboard, 94. parts of, 92. shackle, 93. share, 93. standard, 92. truck, 95. Plowing, 90. depth of, 96. effect on soil water, 156. favors root growth, 14. in fall, 99, 157. in spring, 98, 157. importance of deep, 15, 17. objects of, 91, 92. to save water, 92. time for, 98. Plows, 4. Plumule, 78. Pollen, 130. Pollination, 131, 132, 135. cross, 132, 133, 135. of wild goose plum, 134. Potash, 199. in fertilizers, 199. in soils, 149. sources of, 171. Potassium, in plants, 66, 67. in soils, 68. Potato, 6. soils, 28, 29, 161. Potato, sweet, roots of, 13. soils, 28, 160. Properties of a fertile soil, 141. Pruning, 137. Quitch-grass, 121. underground stem of, 121.