. Lectures on the evolution of plants. Botany; Plants. 246 EVOLUTION OF PLANTS time, by further modifications of their descendants, other adaptations for cross-pollination would arise. There are many genera, especially among the lower Dicotyledons, which exhibit in a most interesting way all gradations between inconspicuous self-pollinated flowers, and showy ones dependent upon insects. This is shown, for example, A „ ^~,r\ . in the genus Ranun- culus, which includes the various species of buttercup. The in- conspicuous R. abor- tivua is entirely in- dependent of insect aid, while such showy s
. Lectures on the evolution of plants. Botany; Plants. 246 EVOLUTION OF PLANTS time, by further modifications of their descendants, other adaptations for cross-pollination would arise. There are many genera, especially among the lower Dicotyledons, which exhibit in a most interesting way all gradations between inconspicuous self-pollinated flowers, and showy ones dependent upon insects. This is shown, for example, A „ ^~,r\ . in the genus Ranun- culus, which includes the various species of buttercup. The in- conspicuous R. abor- tivua is entirely in- dependent of insect aid, while such showy species as R. acris or R. Galifornicus are visited freely by in- sects, although they are probably not en- tirely dependent upon them to insure fertili- zation. Similar vari- ation is found in the genus Geranium. In the simplest of these " entomophilous " or insect- fertilized flowers, such as the buttercup or anemone (Fig. 55, A), the flower is wide open, with the entirely separate parts arranged radially, and often indefinite in number. We find in such generalized flowers that the variety of insects visiting them is large, and they are seldom incapable of self-pollination in case insect. Fig. 55.—A, flower of Anemone coronaria, the petals absent, but replaced by the showy sepals, s; B, inflorescence of the dogwood (C'oraus ftorida), the incon- spicuous flowers, fl, surrounded by four showy bracts, 6; C, the " calla/-lily" (Richardia), with the central spike of small flowers enclosed by the large white "spathe," « 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 Campbell, Douglas Houghton, 1859-1953. New York, London, The Macmillan company
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