51. Q. What do we find next to the epidermis? A. The cortex, or bark, often composed of cells containing starch or chlorophyll. 52. Q. What is beneath the bark? A. The formative layer or cambium, in which thin-walled cells become transformed into vascular or bast-cells, and thence are changed into permanent cells. 53. Q. What do groups of cells thus formed, united into bundles and penetrating the rest of the tissue, form? A. The fibro-vascular bundles. 54. Q. What are the simpler types of plants that have no fibro-vascular bundles, called? A. Cellular plants. 55. Q. What are the rest termed? A. Vascular plants. 56. Q. Of what does the fundamental tissue generally consist? A. Of thin-walled cells containing starch, although other forms of cells may be present. 57. Q. What is the simplest form of individual plant life? A. A particle of living matter inclosed in a membrane or cell-wall. 58. Q. What are plants of this type of structure called? A. Protophytes. 59. Q. Where are many of these one-celled plants found? A. In the green slime which grows on stones and on boards in damp places. 60. Q. What is one of the simplest forms, often found in rain-water casks, called? A. The protococcus. 61. Q. What are the unicellular plants most interesting to those who study with the microscope? A. Diatoms. 62. Q. In the living state where are diatoms found abundantly? A. In every pond, rivulet, ocean and rock-pool. 63. Q. What do they form in a fossil state? A. Large strata of rock material. 64. Q. What are thallogens? A. Plants composed of a tissue of cells, or bioplasts, but with no clear distinction of stem, root and leaves. 65. Q. What three classes are included under this type? A. Algæ, or sea-weeds; Lichens, or the dry, leafy, or mossy patches on trees, stones, etc.; and Fungi, or mushrooms, molds, and their allies. 66. Q. Into what three orders have Algæ, or sea-weeds, been divided? A. The red, the olive and the green sea-weeds. 67. Q. How are Fungi regarded by some scientists? A. As neither animal nor vegetable, but forming a sort of third kingdom. 68. Q. What seems to be the principal business of the Fungi? A. The removal of the waste material of both animal and vegetable life. 69. Q. What are Acrogens? A. Plants which grow at the summit only, and not in diameter. 70. Q. What plants do we find in fresh-water ponds and rivers, growing in tangled masses of dull green color that illustrate the manner of growth in the type of Acrogens? A. Stone-worts, consisting of two genera, Chara and Nitella. 71. Q. What are the nodes, and what the internodes in the stone-worts? A. The points on the axis, or stem, from which the branchlets spring, are called nodes, and the intervening parts are internodes. 72. Q. How is each internode formed? A. By the growth and elongation of single cells. 73. Q. How are the branchlets produced? A. By the sub-division of single cells.