. Botany for high schools. Botany. GROWTH OF ROOT AND STEM 21 that the elongating part of the root occupies a certain area back of the tip. This elongation is due to the elongation of individual cells which are constantly being formed in the growing point of the tip, and are left behind. These cells elongate slowly at first, then rapidly and then slowly again until they cease to elongate. All of the cells in one cross area of the root grow at about the same rate at the same time. Their united action then is manifest in the slow^ elongation of the root just back of the tip, its more rapid elong
. Botany for high schools. Botany. GROWTH OF ROOT AND STEM 21 that the elongating part of the root occupies a certain area back of the tip. This elongation is due to the elongation of individual cells which are constantly being formed in the growing point of the tip, and are left behind. These cells elongate slowly at first, then rapidly and then slowly again until they cease to elongate. All of the cells in one cross area of the root grow at about the same rate at the same time. Their united action then is manifest in the slow^ elongation of the root just back of the tip, its more rapid elongation further back, followed by the slow elongation again until elongation finally ceases. 33. Region of elongation in stems.—The region of elonga- tion in stems is determined in a similar way. It occurs just back of the growing point, but covers usually a greater area than in the root. 34. The motor zone in roots, or region of curvature.— After a seedling or a plant has been growing in one direction for a time, if its position be changed so that the root and stem are in a horizontal position, or at any angle from the up- right, the root and stem will curve so that the root growls downward and the stem upward The region of curvature of the root under these circumstances corresponds with the re- gion of elongation. This curvature is made possible because the cells in the region of the root are all elongating. Those on the upper side of the root elongate more than those on the underside and bring about the curvature. 35. The perceptive zone in roots.—The perceptive zone in roots is that part of the root which receives the stimulus causing it to turn downward. It is, therefore, a sense organ. The stimulus which causes the root to turn downward is initiated. Fig. 28. Bean seedling placed horizontally and marked to show where the root Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
