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.
74. Q. What other families of plants are examples of Acrogens? A. Ferns and Mosses.
75. Q. What are Endogens? A. Plants whose vessels and woody fibers first grow within the stem. The seed has but a single lobe, or cotyledon.
76. Q. What families of plants are found in the type of Endogens? A. Grasses, Rushes, Lilies, and Palms, with similar families.
77. Q. In the growing plant what part grows from the axis upward, and what part from the axis downward? A. The stem grows from the axis upward, and the root downward.
78. Q. What is the root formed by the downward elongation of the axis called? A. It is called the primary root.