. Textbook of botany. Botany. 152 TEXTBOOK OF BOTANY. Fig. 93. — Cross sec- tion through a young bean fruit and a. seed; a, groups of vascular bundles (" strings ") ; b, outer layer of the pod; c, inner layer; d, outer seed coat; e, inner seed coat; /, seed leaf; g, stalk by which the seed is attached to the pod. are the '' strings'' that are familiar to every one who has shelled or cut up green beans. The strings and the inner tough layer of the pod were present in all the earlier varieties of beans; but in more recent years improved varieties have been produced in which the thick-
. Textbook of botany. Botany. 152 TEXTBOOK OF BOTANY. Fig. 93. — Cross sec- tion through a young bean fruit and a. seed; a, groups of vascular bundles (" strings ") ; b, outer layer of the pod; c, inner layer; d, outer seed coat; e, inner seed coat; /, seed leaf; g, stalk by which the seed is attached to the pod. are the '' strings'' that are familiar to every one who has shelled or cut up green beans. The strings and the inner tough layer of the pod were present in all the earlier varieties of beans; but in more recent years improved varieties have been produced in which the thick- walled cells are either lacking altogether from the vascular bundles and the inner layer of the pod, or else are late in developing. 174. Germination of the Seed (Fig. 94). — The conditions under which seeds will germinate have been carefully studied in connection with the bean and some of its relatives. One neces- sary condition is the presence of water, a good deal of which is absorbed by the seed coat and by the embryo. Bean seeds germinate more quickly if they are first placed in cold water and left there overnight. Another necessary condition is a suitable tem- perature. Bean seeds will not germinate, no matter how well they are supplied with water, below 32° F. nor above about 122° F. Another con- dition is the presence of oxy- gen. Seeds will not germinate in an atmosphere from which the oxygen has been removed ; nor will they germinate well in soil which is so thoroughly water-soaked that there is little or no air in its pores. Germination begins by the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Allen, Charles E. (Charles Elmer), b. 1872; Gilbert, Edward Martinius, joint author. Boston, New York [etc. ] D. C. Heath & co
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