_Pelargonium_, 197. Peltate, 190. _Peltigera_, 75; Fig. 45. _Penicillium_, 71; Fig. 42. Pepper, 183. Perianth. See "Perigone." Periblem, 176. Perigone, 143, 148, 151, 170. Perisperm, 163. _Perisporiaceæ_, 66. Periwinkle, 219. _Peronospora_, 60; Fig. 35. _Peronosporeæ_, 57. Persimmon, 212; Fig. 117. Petal, 148, 174, 179. Petiole, 173. Petunia, 215; Fig. 119. _Peziza_, 73; Fig. 43. _Phacelia_, 214. _Phæophyceæ_. See "Brown algæ." Phænogam. See "Spermaphyte." _Phascum_, _-aceæ_, 99, 101; Fig. 65. _Philadelphus_. See "Syringa." Phloem, 110, 124, 135, 137, 150, 173, 176. _Phlox_, 214; Fig. 118. _Phœnix dactylifera_. See "Date-palm." Phosphorus, 2. _Phragmidium_, 81; Fig. 47. _Physarum_, 14. _Physianthus_, 220. Physiology, 3. _Phytolacca_, _-aceæ_. See "Poke-weed." _Phytophthora_, 60. Pickerel-weed, 156, 228; Fig. 84. Picric acid, 156, 233. Pig-weed. See "Amaranth." Pine, 9, 10, 129, 142. Pineapple, 156. Pine-sap, 210; Fig. 116. _Pinguicula_, 218. Pink, 181, 185; Fig. 97. Pink-root, 218; Fig. 122. Pinnate (leaf), 159. veined, 171. _Pinnularia_, 42; Fig. 24. _Pinus sylvestris_. See "Scotch pine." _Piper_. See "Pepper." _Piperineæ_, 183. Pistil, 143, 145, 174. Pitcher-plant, 194, 195; Fig. 105. Pith, 130, 174, 177. Placenta, 148, 179. Plane, 183. _Plantago_, _-ineæ_. See "Plantain." Plantain, 223, 225; Fig. 121. Plasmodium, 12. _Plataneæ_. See "Plane." _Platanus_. See "Sycamore." Plerome, 176. Plum, 207. _Plumbago_, _-ineæ_, 212. Pod, 156. _Podophyllum_. See "May-apple." _Podosphæra_, 66-70; Fig. 39. general structure, 66. structure of filaments, 68. suckers, 68. conidia, 68. sexual organs, 68. spore fruit, 68, 69. spore sac, 69. _Pogonia_, 166. _Poinsettia_, 199. Poison-dogwood, 198. Poison-hemlock, 202. Poison-ivy, 171, 198. Poke-weed, 185; Fig. 97. _Polemonium_, _-aceæ_, 214; Fig. 118. Pollinium, 165. _Polycarpæ_, 185. _Polygala_, _-aceæ_. See "Milkwort." _Polygonatum_. See "Solomon's Seal." _Polygonum_, _-aceæ_, 184; Fig. 98. _Polysiphonia_, 52; Fig. 29. Pomegranate, 206. Pond-scum, 22, 29, 30. Pond-weed, 159; Fig. 86. _Pontederia_. See "Pickerel-weed." Poplar, 181, 183. Poppy, 191. _Portulaca_, _-aceæ_. See "Purslane." Potash (caustic), 4, 5, 59, 67, 75, 97, 106, 111, 151, 176, 179, 180. Potassium, 2. Potato, 215. Potato-fungus. See "_Phytophthora_." _Potentilla_. See "Cinquefoil." _Potomogeton_. See "Pond-weed." Prickly-ash, 198. Prickly fungus. See "_Hydnum_." Prickly-pear, 204. Prickly-poppy. See "_Argemone_." Primrose, 211. _Primula_, _-aceæ_. See "Primrose." Prince's-pine, 210; Fig. 116. Procarp, 51. _Proteaceæ_, 205. Prothallium, 102, 103, 114, 122, 125, 133, 144, 177. _Protococcus_, _-aceæ_, 22, 74; Fig. 11. Protophyte, 11. Protoplasm, 7. movements of, 7. Pteridophyte, 102, 153. _Puccinia_, 81; Fig. 47. See also "Wheat-rust." Puccoon, 215. Puff-ball. See "_Lycoperdon_." Purslane, 185. Putty-root. See "_Aplectrum_."