. A textbook of botany for colleges and universities ... Botany. 846 ECOLOGY. Fig. 1173.—A flowering shoot of the yarrow (Achillea Millefolium), illustrating the massing of flowers into heads {h), and the massing of heads into a compact corymb; r, ray flowers; 2, involucre. be the more specialized, since they contrast more sharply with the foliage, not only in aspect but fundamentally, inasmuch as most yellow petals resemble foliage leaves in hav- ing plastids. In many flowers showiness is increased by the presence of party-colored effects. Sometimes the two halves or lips have different color
. A textbook of botany for colleges and universities ... Botany. 846 ECOLOGY. Fig. 1173.—A flowering shoot of the yarrow (Achillea Millefolium), illustrating the massing of flowers into heads {h), and the massing of heads into a compact corymb; r, ray flowers; 2, involucre. be the more specialized, since they contrast more sharply with the foliage, not only in aspect but fundamentally, inasmuch as most yellow petals resemble foliage leaves in hav- ing plastids. In many flowers showiness is increased by the presence of party-colored effects. Sometimes the two halves or lips have different colors (as in Col- linsia and Viola pedata bicolor), but more commonly the variegation is due to spots or lines on a back- ground of another color. In some plants with vernal flowers (as Hepaiica) a group of individuals may exhibit a number of colors, varying from white through pink to blue, thus greatly increasing the showiness of the plant group as a whole. Often flowers that are inconspicuous individually are so massed into compact inflorescences as to produce a showy effect; such a condition is seen in the umbellifers and even more in the composites, where the inconspicuous central or disk flowers often are surrounded by showy outer or ray flowers, giving the effect of a large simple flower (fig. 1173). The inflorescences of Hydrangea consist similarly of incon- spicuous central and of showy outer flowers, the latter being sterile. In some plants the calyx is the showv organ (as in Abronia and Mirabilis), and in some species of Caslilleja, Euphorbia, and Monarda the bracts, or even the upper leaves, are much showier than are the relatively insignificant flowers. In some dogwoods the involucre is much showier than are the flowers, and in the willows where there is no perianth, the staminate catkins often are showy by reason of the conspicuous stamens. Zygomorphy. — Zygomorphy or irregularity in the corolla often adds to the conspicuousness of flowers. Many flowers are labiate
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
