. Essentials of botany. Botany; Botany. extend their surfaces more nearly in a horizontal direction during the cooler hours. The so-called "sleep" of plants has long been known, but this subject has been most carefully studied rather recently. The wood sorrel, or oxalis, the common bean, clovers, and the locust tree are some of the mo^t fa- miliar of the plants whose leaves assume decidedly different positions at night from those which they occupy during the d^y. Sometimes the leaflets rise at night, and in many instances they droop, as in the red clover (Fig. 76) Fig. 75. Opposite L
. Essentials of botany. Botany; Botany. extend their surfaces more nearly in a horizontal direction during the cooler hours. The so-called "sleep" of plants has long been known, but this subject has been most carefully studied rather recently. The wood sorrel, or oxalis, the common bean, clovers, and the locust tree are some of the mo^t fa- miliar of the plants whose leaves assume decidedly different positions at night from those which they occupy during the d^y. Sometimes the leaflets rise at night, and in many instances they droop, as in the red clover (Fig. 76) Fig. 75. Opposite Leaves of Deutzia, and the acacia (Fig. 77). ^s arranged on a Vertical Branch. One useful purpose, at any rate, that i^ served by the leaf's' taking the nocturnal position is protection from frost. It has been proved experi- V- mentally that when part of the leaves on a plant are prevented from as- suming the folded posi- tion, while others are allowed to do so, and the plant is then exposed during a frosty night, the folded ones may escape while the others are killed. Since many plants in tropical climates fold their leaves at night, it is certain. Fig. 76. A Leaf of Red Clover. At the left, leaf by day; at the right, the same leaf asleep at 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 Bergen, Joseph Y. (Joseph Young), 1851-1917. Boston, Ginn
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