Plants, absorption of radiant heat by the perfumes of, i. 44 weight of the perfumes, i. 45 phosphorescence of, i. 67 their synthetic process of rearing their fabrics, i. 96 this process imitated by artificial means, i. 96 chemical nature of the colouring matter of, i. 428, 429 Platinum, properties of, i. 5 how vaporized, i. 30 effect of electricity on, i. 32 crystals of, formed artificially by electricity, i. 74 its resistance to electricity, i. 90 Pleurocarpi, characters and habitat of the group, i. 328 Pleurosigma angulatum, structure of, i. 198, 199 Plumbago, or natural graphite, little or no porosity of, i. 112 Podocyrtis Schomburgi, structure and habitat of, ii. 20, 21 fossil and existing species of, ii. 20 Poisons, vegetable, i. 425, 426 Polarization of light and heat, i. 68, 69 relation of polarization of light and heat to crystallization, i. 70, 71 Pollen of flowering plants, i. 379 Polyatomic theory, the, i. 107 Polycystina, structure and habitat of the, ii. 19, 20 Polygastria, a name for the Infusoria, ii. 71 Polyides rotundus, mode of reproduction of, i. 229 structure and mode of propagation of, i. 237, 238 Polynoë, structure of, ii. 160 Polypary of the Alcyon zoophytes, ii. 123 Polypes. _See_ Hydrozoa Polypodiaceæ, characters of the order, i. 344 sporangia of, i. 343 Polypodineæ, characters of the group, i. 344 habitat of the, i. 345 Polypodium, structure and habitat of the genus, i. 345 vulgare, fronds of, i. 340, 345 sori of, i. 342, 345 structure of, i. 345 Polyporei, structure, habitat, and growth of, i. 264, 265 Polysiphonia, structure of the genus, i. 233 Polysiphonia elongata, structure and mode of propagation of, i. 234 Polystichum, characters of the genus, i. 347 sorus and indusium of, i. 347 Polystichum aculeatum, characters of, i. 348 Polystichum angulare, characters of, i. 348 Polystichum Lonchitis, structure of, i. 347 Polystichum proliferum, organs of reproduction of, i. 348 Polystomella, characters of the genus, ii. 47 Polystomella crispa, form of, ii. 28 structure and habitat of, ii. 47, 48 cristata, form of, ii. 28 striato-punctata, habitat of the, ii. 48 Polytrichei, characters of the tribe, i. 329 Polytrichum commune, organs of fructification of, i. 325 Polytrichum dendroides, structure of, i. 329 Polyzoa, or Bryozoa, characters of, ii. 218 Polyzonia cuneifolia, structure of, i. 242, 243 Porites, or reef-building corals, ii. 140 Porphyra laciniata, structure and habitat of, i. 227 Porphyra vulgaris, structure, habitat, and mode of reproduction of, i. 227 Porpita, characters of the genus, ii. 117 glandifera, structure, habitat, and mode of reproduction of, ii. 117, 118