. Nature and development of plants. Botany. 488 THE CAMPANULALES of this type of flower is more effective than any as yet noticed, and it would appear impossible for any of the numerous insects which frequent these flowers to miss crossing a score of them at a single visit. Crossing between the flowers of a head is effected in some genera by the movements of the flowers. The inner leaves of the involucre fold over the flowers at night and in rainy weather, protecting them like a perianth. This results in crowd-. FiG. 340. Inflorescence of the bur-marigold {Bidens), a common ray form of flower
. Nature and development of plants. Botany. 488 THE CAMPANULALES of this type of flower is more effective than any as yet noticed, and it would appear impossible for any of the numerous insects which frequent these flowers to miss crossing a score of them at a single visit. Crossing between the flowers of a head is effected in some genera by the movements of the flowers. The inner leaves of the involucre fold over the flowers at night and in rainy weather, protecting them like a perianth. This results in crowd-. FiG. 340. Inflorescence of the bur-marigold {Bidens), a common ray form of flower of the Thistle family: in, involucre. ing of the flowers together, and the stigmas are often brought in contact with the spores that have been dusted upon the various parts of adjoining flowers. The outward curving of the stylar lobes may also bring the stigmas in contact with the spore-covered parts of adjoining flowers with a like result. Autogamy is brought about in the dandelion, as in nearly all other members of the order, by the curvature of the lobes of the style which continue to bend back until the stigmatic surface is brought in contact with the spore-covered style (Fig. 341, D). The bloom- ing of the flowers progresses from the margin to the center of the head so that during several days new sets of flowers are exposed for crossing. When the period of bloom is passed the involucre closes over the head and remains in this condition until the fruit is mature (Fig. 338, b). During this period, the stalk. 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 Curtis, Carlton Clarence, 1864-1945. New York, H. Holt
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