. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. A lily, showing long, narrow leaves. are but slightly developed, and that the stem has developed far more than the leaves. We have also seen (page 99) that a green plant will grow toward the source of light, even against great odds. This effect of light is seen as well in older plants. Any field trip will reveal the fact that in low-lying plants the leaves which are shaded are often yellow and dwarfed. Plants kept in poorly lighted rooms at home show this. Arrangement of Leaves. — A careful
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. A lily, showing long, narrow leaves. are but slightly developed, and that the stem has developed far more than the leaves. We have also seen (page 99) that a green plant will grow toward the source of light, even against great odds. This effect of light is seen as well in older plants. Any field trip will reveal the fact that in low-lying plants the leaves which are shaded are often yellow and dwarfed. Plants kept in poorly lighted rooms at home show this. Arrangement of Leaves. — A careful study of trees in any park, or in the woods, shows that the stems of trees in thick forests are usually tall and straight and that the leaves come out in clusters near the top of the tree. The leaves lower down are often smaller and less numerous than those near the top of the tree. Careful observation of any plant growing outdoors shows us that in almost every case the leaves are so disposed as to get much sunlight. The ivy climbing up the wall, the morning glory, the dandelion, and the burdock all show different arrange- ments of leaves, each pre- senting a large surface to the light. Leaves are usu- ally definitely arranged, fit- ting in between each other so as to present their upper surface to the sun. Such an arrangement is kno^vn as a leaf mosaic. Good examples of such mosaics, or leaf pat- terns, are seen in the alter- nate-leaved trees. Here the leaves turn, by the twisting of the petioles, so that all the leaves present their upper surface to the. ihe dandelion, showing a whorled arrangement of long, narrow 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 Hunter, George William, 1873-1948. New York, American book company
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