Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] LEAVES AND THEIR FUNCTIONS 125 the bud in the axil of the leaf, that is, between the leafstalk and the branch; (2) by the presence of stipules (this is well seen in the rose leaf); (3) by the fact that the arrangement of veins in the leaflet frequently does not follow the same system of branch- ing as would be found in a simple leaf of the same form. Arrangement of Veins. — The shape of the blade of leaves of dicotyledons depends so
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] LEAVES AND THEIR FUNCTIONS 125 the bud in the axil of the leaf, that is, between the leafstalk and the branch; (2) by the presence of stipules (this is well seen in the rose leaf); (3) by the fact that the arrangement of veins in the leaflet frequently does not follow the same system of branch- ing as would be found in a simple leaf of the same form. Arrangement of Veins. — The shape of the blade of leaves of dicotyledons depends somewhat upon the arrangement of the veins. If the blade is long and thin, the veins will be found to go out from the midrib somewhat like the side parts of a feather; hence the leaf is said to be feather veined (or pinnate). If the blade is nearly circular in outline, the veins will leave the petiole to radiate some- what like fingers from the jDalm of the hand. Such venation is said to be pal- mate. The same general arrangement of veins holds true for compound leaves. The pea and locust are examples of pinnately compound leaves, the horse-chestnut of a palmately compound leaf.^ Leaves turn toward the Light. — It is a matter of common knowledge that green leaves turn toward the light. Place growing pea seedlings, oxalis, or any other plants of rapid growth near a win- dow which receives full sunlight. Within a short time the leaves are found to be in positions to receive the most sunlight possible. Home Experiment. — Turn such plants after two or three days so that the leaves are away from the sun. Make observations every hour during some Saturday morning and try to find out just what part of the leaf turns to the Kght. Effect of Light. — We have already found that seedlings grown in total darkness are almost yellow-white in color, that the leaves ' For laboratory work on leaves, see Hunter and Valentine, Manual, pages 39-47. The skeleton of a pinnately veined leaf; M
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