. Carnegie Institution of Washington publication. 100 EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. per minute. Further opening to 25 per cent at 1 p. m. resulted in an increase of water-loss to mg. per minute. At 2 p. m. the stomata closed to 7 per cent and the rate fell to mg. per minute. At 3 p. m. reopening to 17 per cent was accompanied by a rise in the rate to mg. per minute. From this time to the end of the series the stomata closed slowly and the rate of water-loss fell in proportion (fig. 53).. NOON I 2 3 4 5 4 FIG. 53.—Series 33, showing average movement of upper
. Carnegie Institution of Washington publication. 100 EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. per minute. Further opening to 25 per cent at 1 p. m. resulted in an increase of water-loss to mg. per minute. At 2 p. m. the stomata closed to 7 per cent and the rate fell to mg. per minute. At 3 p. m. reopening to 17 per cent was accompanied by a rise in the rate to mg. per minute. From this time to the end of the series the stomata closed slowly and the rate of water-loss fell in proportion (fig. 53).. NOON I 2 3 4 5 4 FIG. 53.—Series 33, showing average movement of upper and lower stomata (A) and transpiration (B) of cow-beets in dry pots. In this series, as well as in the alfalfa, Fouquiera, and Verbena series, direct evidence was found that as the stomatal movement of cut stems and rooted plants differed considerably, so did their rates of water-loss. In this series the leaves in the potometers showed little or no wilting, but their stomata were closed or nearly closed throughout the experiment. At the start the stomata were completely closed and opened to 7 per cent at 7 p. m. At 8 they closed to 1 per cent and at 9 were completely closed. Thus a com- parison shows that the stomatal movement of the cut leaves and the plants in the dry pots was identical at 8 and 9 p. m. and differed not at all in the rates of water-loss at this time. At 1 and 2 a. m. the stomata of the potted plants were practically closed, while those of the cut stems were 2 per cent open; hence at this time the rate of water-loss for the cut leaves was slightly higher than that of the plants. The stomata of the potted plants closed again at 5 and 6 a. m., while the cut leaves showed 4 per cent opening. At this time the transpiration-rate of the potted plants again fell to less than that of the cut leaves. At all other times the transpiration-rate of the cut stems was lower and during the day considerably lower than that of the potted plants. This must be attributed to th
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