. Nature and development of plants. Botany. DEVELOPMENT OF PLANTS 491 both, and characterized by free anthers. The more familiar are: The marsh elder {Iva), ragweed {Ambrosia), and clot-bur and cockle-bur {Xanthium). These three alliances are apparently recently evolved of the angiosperms, and owing to theii- numerous variations that have been so successful in meeting the present conditions upon. Fig. 342. A common tubular flower of the Thistle family: A, inflores- cence of the ironweed {Vernonia). B, sectional view of the inflorescence, only the outer flowers in bloom. C, enlarged vi
. Nature and development of plants. Botany. DEVELOPMENT OF PLANTS 491 both, and characterized by free anthers. The more familiar are: The marsh elder {Iva), ragweed {Ambrosia), and clot-bur and cockle-bur {Xanthium). These three alliances are apparently recently evolved of the angiosperms, and owing to theii- numerous variations that have been so successful in meeting the present conditions upon. Fig. 342. A common tubular flower of the Thistle family: A, inflores- cence of the ironweed {Vernonia). B, sectional view of the inflorescence, only the outer flowers in bloom. C, enlarged view of one of the flowers—c, calyx or pappus. D, fruit. the earth, they have become the dominant plants the world over. Their success can be traced to a variety of causes, as the occur- rence in many genera of perennial underground stems, which make them to a degree independent of climate conditions and the depredations of grazing animals. A great many are avoided because of their protective armor of prickles, bitter, acrid juices or oils and resins. Especially to be noted is the seed-like fruit with its numerous devices for distribution. All these features, among others, explain their extensive distribution in open coun- tries. Another advantage appears in the structure of the flower and the inflorescence. The highest type of a flower, as in the case of a machine, is the one that is most efficient. The flower is not so elaborate as the orchid or as those of some other groups, but it is superior because it accomplishes its work with greater' certainty and more economically. Note the significance of these facts—the ovary of the orchid consists of three carpels. 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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