Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 138 BOTANY than many other plants. Compare the spines of the honey locust, black locust, and barberry. Look for leaf traces and buds on the stem, and decide from the relative position of the thorns and these structures which of the above-named structures are modified leaves. (Sometimes a spine may be part of a leaf, as the stipule.) Cactus. — In the prickly pear cactus, notice that above the spines are little buds. The position of t
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 138 BOTANY than many other plants. Compare the spines of the honey locust, black locust, and barberry. Look for leaf traces and buds on the stem, and decide from the relative position of the thorns and these structures which of the above-named structures are modified leaves. (Sometimes a spine may be part of a leaf, as the stipule.) Cactus. — In the prickly pear cactus, notice that above the spines are little buds. The position of the bud shows the spine to be a modified leaf. What reason can you give for this modification of the leaf of the cactus ? How is the plant body modified to meet the conditions of life in a desert? Note the thickened stem. If a cactus is cut open, it will be found to contain a very considerable amount of water. The Indians of the New Mexican desert region, when far from a source of water, sometimes cut off the top of a large cactus, mash up the soft interior of the thickened stem, squeeze out the pulp, and thus obtain several quarts of drinkable water. Protection by Hairs. — In the mul- lein, one of our hardiest weeds, the leaf is covered with a coating of finely branched hairs. Might such a covering be of use to the leaf? In what ways? Leaves modified for Use in Climbing. — Sometimes, as in the leaf of the pea, a part of the leaf is modified for the purpose of climbing. In this case a part of the leaf, called the tendril, becomes especially sensitive to the stimulus of touch, and upon touching an object coils around it. Almost any part of the leaf, or indeed the entire leaf, may be modified to become a tendril. What part of the leaf of the pea here forms the tendril? If material can be obtained, work out the morphology of modified parts of the clematis; wild grape; Virginia creeper. Storage of Food or Water in Leaves. — Leaves may be modified for the storage of food or w
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