Petals (handkerchiefs), used as signals, 17, 18, 188, 192, 221, 223, 226. functions of, 188. Pine, cone of, 62. classified, 88, 89. leaves of, 171, 184. flower of, 197. Pins with dust boxes, see “stamens.” Pins without dust boxes, see “pistils.” Pistils (pins without dust boxes), described, 15, 18, 197-202. function of, 188, 198, 199. defined, 190. varieties of, 200. flowers with many, 201, 202. fruit formed from, 202. position of, 227, 228, 248. of strawberry, 233, 234. of berries, 236. Pit or stone, 37. Pitcher plant, 176-178. Pith, defined, 120, 121. Plants, flowering, 22. object of life of, 22, 23. use of, to world, 26, 27. service of, to animals, 26, 27, 156, 157. young, 75-98. nourishment of, 75, 76, 77, 150, 156-160. with two seed leaves (dicotyledons), 85-87. with one seed leaf (monocotyledons), 88. with many seed leaves (polycotyledons), 88, 89. parasitic, 108-111. development of, 112, 113. absorption of water by, 147. perspiration of, 148, 149, 160. as air purifiers, 151-153, 158, 159. breathing of, 158-160. storing of food in, 185, 216, 217. protection of, 214, 215. Plants and animals, difference between, 154, 155. Plum, compared with apple, 36. blossom of, 38. Plum, wild beach, 40. Pods, 35, 54, 55, 58, 65-67, 241, 242. Poison ivy, 107, 115, 116. Pollen (flower dust), described, 14, 196-199. carriers of, 17, 18, 189, 207, 213, 223, 224, 226-230, 233. effect on pistil, 18, 20. fertilizing power of, 18, 20, 196-199. transportation of, 18, 207, 211, 213, 226, 227, 229-231, 233, 250. function of, 188, 198, 199. varieties of, 196, 197. defined, 199, 200. Polycotyledonous plants (plants with many seed leaves), 88, 89. Polygala, 222. Poplar tassels, 211. Poppy seed, dispersal of, 70, 71. Potato, a stem, 104, 131. eyes of, 131, 174. Potato, sweet, 102. Prickles, 174, 175. Primrose, evening, 197, 229, 230. Protoplasm (life substance), 140, 141. Puffballs, 35, 36, 59, 95. Pussy willow, 129. tassels of, 205-207. Q Quince leaf, 135, 136, 137, 165. R Radish root, 102. Raspberry, development of, 237-239. Red baneberry, 49. Red clover, stem of, 117. Red maple, seed of, 92. leaves of, 127. buds of, 127. Rhubarb plant, 164. Robin’s plantain, 251, 252. Root branches, 162-164. Roots, origin of, 81, 113. hairs of, 81, 99-102, 104, 123, 143. function of, 99-103. fibrous, 102, 103. fleshy, 102-104. as food, 103, 104. above-ground, 106-111. varieties of, 106-112. hanging, 107. underground, 111. water, 111, 112. absorbing capacity of, 146. spreading of, 162, 163. position of, 163, 164. Roots and stems, 99-122. Rootstocks, function of, 106, 217. Rose, petals of, 32, 33. stem of, 120.