Perfumes of flowers and plants, absorption of radiant heat by the, i. 44 weight of the perfumes, i. 45 chemical combinations forming, i. 97 Peridinium, structure and habitat of, ii. 72 scarlet colour it gives to the sea, ii. 72, 75 mode of propagation of, ii. 75 Perisporacei, structure and habitat of, i. 295 Periwinkle, tongue of, ii. 239 Peronospora infestans, its destruction of the potato, i. 284 structure and mode of working, i. 284, 285 its effects on the branches and wood of trees, i. 285 Perophora Listeri, structure, habitat, and development of, ii. 222, 223 larva of, ii. 224 Petroleum, enormous quantities of, in North America, i. 126 the Babylonian petroleum fountains of Is, i. 126 geological formation in which it occurs, i. 126 dangers of petroleum wells, i. 127 substances yielded by it on destructive distillation, i. 127 Peyssonnelia, habitat of, i. 237 Peziza aurantia, cells of staff-shaped particles of, i. 291 Peziza elegans, beauty and habitat of, i. 291 Peziza vesiculosa, force of its ejection of its sporidia, i. 292 Pezizæ, structure and habitat of the genus, i. 290, 291 fructification of, i. 291 eel-shaped particles or antherozoids of, i. 292 force with which many of them eject their sporidia, i. 292 Phacopsis, organs of reproduction of, i. 307 Phalloidei, structure of, i. 268 Phallus Mokusin, a food of the Chinese, i. 268 Phascei, characters of, i. 329 Phenic acid, i. 123 Phenyle, chemical composition of, i. 128 Philomedusa Vogtii, a parasite of the medusæ, ii. 100 Phonolite stone, on the Rhine, of what it consists, i. 206 Phosphorescence, property of, i. 66 of insects, fish, and plants, i. 67 of inorganic substances, i. 67 essential difference between phosphorescence and fluorescence, i. 67, 68 Phosphorescent light of luminous fungi, i. 264 causes of this, i. 264 Phosphorus, i. 17 whence procured, i. 17 red allotropic, i. 17 takes fire spontaneously in chlorine gas, i. 19 atomic weight of, compared with that of hydrogen, i. 100 Photography, importance of the magnesium light in, i. 154 Phyllodoce, structure of, ii. 157 Phyllopoda, characters of the order, ii. 209 Physalia, or ‘Spanish man-of-war,’ structure, and modes of locomotion and reproduction of, ii. 111-114 Physaliidæ, characters of the order, ii. 111 Physomycetes, characters of the order, i. 296 Physophora hydrostatica, structure and habitat of, ii. 109, 110 Physophoridæ, characters of the family of the, ii. 109-111 Pillwort, structure and habitat of, i. 371, 372 Pilularia globulifera, or pillwort, structure and habitat of, i. 371 Pilularia minuta, structure of, i. 371 Pinna, structure of the shell of, ii. 233 Pitch, manufacture of, i. 120 Planets, spectra of the, i. 157, 158, 161, 162