. Carnegie Institution of Washington publication. 148 Hydration and Growth. afterward, beginning actual shrinkage by 9 a. m. Growth of the leaf of middle age slows down with the low temperature of daybreak, but accelerates at 9 a. m., at the time the older leaf begins shrinking, at 17° C. The youngest pair of leaves grows with a high rate all night, with a perceptible slowing at daybreak, but it also accelerates at 9 a. m. with the rising temperature, at the time the oldest leaves are shrinking (fig. 37). 12 m. 12 m. 5 15 25 35 45 55 65 1 ! ! v / / V / ; I4°C.\ 22°C. \ \ ^20 V
. Carnegie Institution of Washington publication. 148 Hydration and Growth. afterward, beginning actual shrinkage by 9 a. m. Growth of the leaf of middle age slows down with the low temperature of daybreak, but accelerates at 9 a. m., at the time the older leaf begins shrinking, at 17° C. The youngest pair of leaves grows with a high rate all night, with a perceptible slowing at daybreak, but it also accelerates at 9 a. m. with the rising temperature, at the time the oldest leaves are shrinking (fig. 37). 12 m. 12 m. 5 15 25 35 45 55 65 1 ! ! v / / V / ; I4°C.\ 22°C. \ \ ^20 Vo \ \ \ \ | 5 15 25 35 45 55 X20 15 35 FIG. 36.—A, auxographic record of elongation of pair of leaves 2 cm. long during a 24-hour period; temperatures of 14° to 25° C. Retardation during period of highest temperature is illustrated. X20. B, action of same leaves in shade. The general features of growth under the usual varying conditions of alternating daylight-high temperature and night-low temperature complexes being determined, it became necessary to test the swelling of the leaves, as had been done with the joints of Opuntia to ascertain their unsatisfied hydration capacity. Preparations f or testing the swell- ing of living material of leaves were made by placing these triangular organs on a flat surface alongside a 25 guide of 5 mm. in thickness. A razor slid along this slices away the uppermost angle, leaving a trun- 45 cated section 5 mm. in thickness, in ss which the central fibrovascular tissue could be seen through the translucent parenchymatous tissue. Segments about 1 cm. long were taken, to the exclusion of the basal and apical parts of the leaf. It is to be noted that active enlargement is usually in progress morning and evening in young leaves, while mature leaves are enlarging in the morning but shrinking in the afternoon and night. The results of the hydrations are shown in table 110. In the above tests the amount of swelling was most in distilled w
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