Miniature trees, 250. Minimum, 288. Minimum temperature, 105. Misconceptions, 12. Mistletoe, 113, 265. Mites, 192, 214, 255. Mixed species, 166. Molecular structure of protoplasm, 273, 274. Mongrel forms, 74. _Monilia_, 217, 231. Monstrosities, 246. Moraine plants, 250. Moths, 110, 145, 206. Moulds, 230, 231, 237, 243. _Mucor_, 230, 231. Mulberry, 244. Mutilations, 252. Mycelial strands, 145. Mycelium, 188. Mycocecidia, 219. Mycorrhiza, 137. Myrtaceae, 258. _Mytilaspis_, 187. Natural checks, 159. Natural demise, 91, 93. Natural Grafts, 269. Natural Selection, 72, 99, 167, 286. Natural Wounds, 204. Nature of soil, 57. Necrosis, 240, 241, 243. _Nectria_, 145, 217, 223, 241, 243, 269. Nematodes, 111, 134, 139, 219, 220. Nettle, 116, 252. _Neurotus_, 219. New formations, 255. Nitrate, 273. Nitrification, 62, 102. Nitrogen, 272. Nodosities, 219. Nodules on roots, 63, 137. Non-living environment, 99. _Notommata_, 140. Nuclear fusion, 267. Nuclear protoplasm, 271, 279, 280, 290. Nuclear substance, 71. Nucleo-plasm, 280. Nuts, 248. Oak, 110, 188, 215, 218, 219, 223, 233. Oak leaf-roller, 254. Oat, 176. Occlusion, 200, 201, 222, 223. Odours, 144. Oedema, 228. Olive, 223. Onion, 231. _Oniscus_, 182. _Oospora_, 216. Optimum temperature, 105, 288. Orange, 173, 187, 235, 247. Orange-coloured spots, 187. Orchard trees, 163. _Orchestes_, 206. Orchids, 113, 266. Organic acids, 50. Organisation, 89. Organised structure, 13. Organisms in soil, 60. _Orobanche_, 112. Osmosis, 26, 29, 46. Osmotic pressures, 18, 41, 52. Over-crowding, 104, 111. Over-feeding, 102. Over-watering, 97. Oxalic acid, 134, 136. Oxidation, 124. Oxygen, 104, 272. Oxygen-respiration, 12, 64. Pallor, 179, 180. Palms, 192. _Pangium_, 134, 165. Parasites, 61, 113, 119, 130, 139, 174, 187, 230, 265, 269, 284. Parasitic algae, 188, 217, 219. Parasitic bacteria, 163. Parasitic diseases, 88, 119, 121. Parasitic epiphyte, 136. Parasitic fungi, 87, 97. Parasitism, 262, 264, 268, 271. _Paris_, 175. "Paris green," 162. Parti-coloured leaves, 191. Parti-coloured spots, 186. Pasture grasses, 69. Pathology, 121, 257. Pathology of cell, 119. Pathological conditions, 168, 170, 246. Pea, 190, 191, 206, 208, 248, 268. Peach, 170, 253. Pear, 179, 187, 189, 191, 216, 218, 231, 240, 248, 249, 253, 257. Pedigree wheats, 69. _Pelargonium_, 198, 253. Peloria, 252. _Penicillium_, 231. _Peridermium Pini_, 223, 234. _Periola_, 238. Permanganate, 162. _Peronospora_, 136, 160, 175, 187, 189, 208. _Petasites_, 188. Petroleum, 162. _Peziza_, 115, 144, 152. Phanerogams, 108, 111. _Phellomyces_, 238. _Phoma_, 217, 243. Phosphorus, 272. Photo-synthesis, 11, 16. _Phragmidium_, 189.