Flowering Plants, beginnings and development, iii, 20, 252, 255, 256-7, xiii, 318-19; classification, 60-1, 173-81; classification place, iii, 251; culmination of plant life, xiii, 73-4; description of parts, 15-62; families and relationships, 168-207; in relation to animal life, iii, 257; none in earliest ages, xiii, 303; number of species, 168, 319, 323; origin of present, 323-5; reproductive methods, 117-54, 167 Flowerless Plants, iii, 251, xiii, 13, 14, 43; evolution, iii, 252, 253; ferns, xiii, 63-6; nonvascular, 66-73; numbers, 168; reproduction, 62-4, 154-65 (see also Cryptogams) Flowers, annuals and perennials, (tables), xiii, 289-97; coloring and fragrance, 124-5; colors in various shrubs, (table), 274-88; family groups determined by, 184; fertilization devices, 48-51, 117, 123-48; fertilization the climax of life, 152; highly cultivated, 51; largest, 363-4; love in, 115; matings of, remarks, 116-17; male and female, 46-7; motion pictures of growth of, iv, 348; of monocotyledons and dicotyledons, xiii, 176, 178, 189-90; parts of, 43-6; purpose, 46, 52-3, 61; various forms and colors, 47-53, 181-207 Flu, (influenza), x, 294-5 Fluctuating Variations, xiii, 328 Flue Gases, electric clearing, vii, 216, 343 Fluids, distinguished by pressure and diffusibility, iv, 22-3; elasticity of, 158; osmosis, xiii, 90-1 (see Osmosis); pressure of, iv, 116-19; pressure on moving inclined planes, i, 287-8; principles applicable to, iv, 126 (see Gases, Liquids) Flukes, sea, xii, 44 Fluorescence, iv, 379-80; produced by X-rays, 318, 320 Fluorescent Screen, iv, 320, vii, 254-5, viii, 184 Fluorine, a halogen, viii, 18, 84, 85, 87; atomic weight and symbol, 383; in apatite, 193; in tissues, 354 Fluorite, iii, 329-30 Fluoroscope, iv, 320 Flushing, of skin, ix, 161, 162, 163, 215 Flute, development of, xv, 316, 317 (fig.); Egyptian, 314 (fig.) Fluxing, of ores, viii, 270 Fly-Catcher (plant), xiii, 40-1 Flying Dragons, xii, 206 Flying Fish, order of, xii, 163; wings of, 134 Flying Mice, xii, 278 Flying Reptiles, iii, 293-4, 320 (Pl. 18), xii, 202, 203 (fig.) Foci of Infection, x, 198-9, 218-26 Focus, defined, iv, 335; of cameras, ix, 108-9; of eye, 110-11; of lenses, iv, 338; real and virtual, 335 Foehn Sickness, i, 328 Foehn Wall, i, 105, 372 Foehn Winds, i, 133, 372 Fog, i, 93-7, 372; aviation effects, 300-2; costs and dispersion, 94, 302; dust nuclei, x, 62, viii, 304; dry (see Dry Fog); light diffraction by, i, 183, 185; rime formed from, 121-2; sound transmission by, 190 Fog Bows, i, 176, 372 Fog Drip, i, 351, 353, 372 Fog Hiccups, i, 195 Fog Signals, audibility, i, 189-91; sirens, iv, 205