. Lectures on the evolution of plants. Botany; Plants. 250 EVOLUTION OF PLANTS While at first sight it would seem that flowers having staraens and pistil together would usually be self-pol- linated, such is rarely the case, at least in showy flowers. An examination of these reveals many effective arrange- ments by which this is prevented and cross-fertilization made necessary. One of the commonest and simplest means is the maturing of the stamens and pistil at dif- ferent times. Usually it is the stamens which are ripe. Fig. 5li (Cross-fSrtilization). — A, flower of Erodium, one of the Geraniu
. Lectures on the evolution of plants. Botany; Plants. 250 EVOLUTION OF PLANTS While at first sight it would seem that flowers having staraens and pistil together would usually be self-pol- linated, such is rarely the case, at least in showy flowers. An examination of these reveals many effective arrange- ments by which this is prevented and cross-fertilization made necessary. One of the commonest and simplest means is the maturing of the stamens and pistil at dif- ferent times. Usually it is the stamens which are ripe. Fig. 5li (Cross-fSrtilization). — A, flower of Erodium, one of the Geranium family; the flower is inconspicuous and capable of self-pollination; B, stamens and carpels of Erodium; the stigmas, st, are mature when the pollen is shed; C, young flower of Pelargonium; the pistil, p, is im- mature ; D, the pistil of an older flower which has shed the anthers; the stigmatic lobes, st, are now ready for pollination; E, young flower of a nasturtium (Tropoeolum); three of the stamens are shedding their pollen and occupy the space in front of the opening of the spur; the other stamens are still closed, and with the immature pistil, st, are bent down; F, stamens and pistil of an old flower; the stamens have all shed their pollen, and the receptive stigma, st, now occupies the position in front of the opening of the sjjur; G, flower of broom (Sarothamnus); the stamens and pistil are included within the keel, i; H, a flower which has had the keel forced down, liberating the stamens and pistil. first (proterandry), but proterogyry, or the earlier maturing of the pistil, may also occur, the common. 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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Keywords: ., bookcentury1900, bookdecade, booksubjectbotany, booksubjectplants
