. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 90 PRACTICAL COURSE IN BOTANY. Fig. 102. — Thorn branches of Holocantha Emoryi, a plant growing in arid regions. is so much used for decoration. The delicate green blades are merely altered stems, shortened and flattened to simulate leaves. 102. Weapons of defense.— Conspicuous examples of these are the bristling thorns of the honey locust. Is their frequent branching any indication of their real nature ? Does it prove any- thing, or must you look for other evidence? What
. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 90 PRACTICAL COURSE IN BOTANY. Fig. 102. — Thorn branches of Holocantha Emoryi, a plant growing in arid regions. is so much used for decoration. The delicate green blades are merely altered stems, shortened and flattened to simulate leaves. 102. Weapons of defense.— Conspicuous examples of these are the bristling thorns of the honey locust. Is their frequent branching any indication of their real nature ? Does it prove any- thing, or must you look for other evidence? What further indi- cations might you expect to find, if they are true branching stems? (100.) On old haw, plum, crab, and pear trees, stems can be found in all stages of transition, from stubby, ill-developed branches, to well- defined thorns. 103. Storage of nourishment. — This is one of the most frequent causes of modifi- cation in both roots and stems. Of stems that grow above ground, the sugar cane probably comes first in economic importance on this account. In hot, arid regions, where the moisture drawn from the earth would, during prolonged drought, be too rapidly dissipated by an expanded surface of leaves, the whole plant, as in the case of the cactus, is sometimes compacted into a greatly thick- ened stem, which fills the triple office of leaf, stalk, and water reservoir. 104. The uses of underground stems. — It is in these that the storage of nourishment Fig. 103.—Melon most frequently takes place, and the modi- ^g'-J^Sl fications that stems undergo for this purpose stem for the storage are in some cases so great that their real ^Ze™*°n °'. 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 Andrews, Eliza Frances, b. 1840; Lloyd, Francis Ernest, 1868-1947. ed. New York, Cincinnati [etc. ] Ame
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