52. Antheridium and spermatozoids of Pteris serrulata 338 53. Archegonium of Pteris serrulata 338 54. Section of footstalk of fern frond 341 55. Pinnule of Polypodium bearing sori 342 56. Sporangia of Polypodiaceous ferns 343 57. Pinnule of Lastrea Filix-mas with sori 346 58. Sorus and indusium of Polystichum or Aspidium 347 59. Pinna of Polystichum Lonchitis 348 60. Sorus and cup-shaped indusium of Deparia prolifera 350 61. Scolopendrium vulgare 351 62. Athyrium Filix-fœmina 353 63. Asplenium Ruta-muraria 353 64. Ceterach officinarum 355 65. Blechnum Spicant 357 66. Pteris aquilina 357 67. Adiantum Capillus-Veneris 359 68. Trichomanes radicans 361 69. Hymenophyllum tunbridgense 362 70. Equisetum giganteum 368 71. Pilularia minuta 371 72. Orchis mascula, side view of flower 389 73. Orchis mascula, front view of flower 390 74. Orchis mascula, pollinium 391 75. Orchis mascula, pollen grains 391 76. Orchis mascula, pollinia 392 77. Orchis pyramidalis, front view of flower 393 78. Orchis pyramidalis, side view of flower 394 79. Orchis pyramidalis, disc with one pollinium 395 80. Orchis pyramidalis, pollinia, attached to disc 395 81. Orchis pyramidalis, pollinia, with disc contracted 395 82. Orchis pyramidalis, pollinia, withdrawn 395 83. Epipactis palustris, side views of flower 397 84. Epipactis palustris, side view and dissection of 398 flower 85. Listera ovata, side view of flower 399 _Errata._ Page 3, _line_ 5 _from bottom, insert_ the _before_ earth 59, _line_ 19, _dele_ the 59, _line_ 21, _dele_ the 59, _lines_ 20 _and_ 22, _for_ part _read_ parts 100, _In the Table of Atomic Weights, read_ Copper 32; Zinc 32·5; Rubidium 86; Cæsium 133 101, _lines_ 10 _and_ 33, _for_ 32 _read_ 32·5 104, _line_ 12 _from bottom, for_ 29 _read_ 32