Students' handbook to accompany Plants and their uses . many other plants have leavesthat take a special night leaves, as those of the beanand the black locust, have threepositions - - one at night, anotherin ordinary daylight, and a thirdin intense sunlight. The daylightposition is usually almost horizon-tal ; the position for brilliant sunlight is vertical. In the locustthe change from vertical to horizontal occurs quickly enoughto make it worth while to watch it coming on as the sunmoves westward after noon and the leaves are left in the shade. In plants of the Peafamily the d
Students' handbook to accompany Plants and their uses . many other plants have leavesthat take a special night leaves, as those of the beanand the black locust, have threepositions - - one at night, anotherin ordinary daylight, and a thirdin intense sunlight. The daylightposition is usually almost horizon-tal ; the position for brilliant sunlight is vertical. In the locustthe change from vertical to horizontal occurs quickly enoughto make it worth while to watch it coming on as the sunmoves westward after noon and the leaves are left in the shade. In plants of the Peafamily the daily leaf move-ments are brought aboutby means of a sensitive,cushion-like organ, the jnil-vinus, situated at the baseof the leafstalk. It iseasy to see the use of thehorizontal and the verti-cal leaf position, but theimportance of the night position is not so well understood. 76. Self-pruning of leaves and twigs. Many trees and shrubsbegin to shed some of their leaves even in the spring, verysoon after the leaves are well grown. Examples of this are. FIG. 61. A leaf of red clover At the left, leaf by day; at the right, thesame leaf at night. Natural size 78 INTRODUCTION TO 15OTANV the lilacs, the syringa (Philadelphia), the cottonwood, thehorse-chestnut, the box elder, and some lindens. Still morecommon is the loss of leaves during the suminer, which mayamount to oO per cent of the total number of leaves. Thisleaf fall, coming long before the leaves are cast off in theautumn as a preparation for winter, affects chiefly the leavesinside the crown of the tree, which have such scanty lightthat they evidently cannot accomplish much photosynthesis.
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Keywords: ., bookcentury1900, bookcollection, bookdecade191, booksubjectbotany
