. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 286 THE STRUCTURE OF FLOWERS.'. carpels; and, secondly, a retrogressive series from carpels to bracts, and thence to leaves ; finally deducing some important conclusions. Progeessive Changes in Bracts.—Bracts are in many cases very obviously modifications of leaves, being sometimes simply complete leaves reduced only in size, as in Epilobium; or a bract consists either of tbe blade alone, as in Buttercups, or else of the petiole only, but now expanded and blade-like in form,as may be well seen in H
. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 286 THE STRUCTURE OF FLOWERS.'. carpels; and, secondly, a retrogressive series from carpels to bracts, and thence to leaves ; finally deducing some important conclusions. Progeessive Changes in Bracts.—Bracts are in many cases very obviously modifications of leaves, being sometimes simply complete leaves reduced only in size, as in Epilobium; or a bract consists either of tbe blade alone, as in Buttercups, or else of the petiole only, but now expanded and blade-like in form,as may be well seen in Hellebores, where transitional states occur between the normal pedate leaf and tnie lan- ceolate bracts (Fig 61, (I, h, c). When bracts are coloured otherwise than green, they then approach nearer to members of the repro- ductive or floral series rather than the vegetative, and in many cases are actually continuous in a spiral series with the sepals and petals, as in Cactus, Calycanthus, etc., and so assist in rendering the flower attractive. Several species of the genus Salvia, S. splendens, S. Bruantii, as well as of Bromeliaceoe, are remarkable for having brilliantly coloured bracts at the base of the flower. In some cases the bracts may be so arranged as to mimic a corblla, and indeed func- tionally replace it, as in species of Oornus (Fig. 62), Danoinia (Fig. 63), and the so-called Everlastings. The presence of bright colours in bracts, as also in sepals, to be described, I take to be due to the same influence as of the normal attractiveness in corollas; viz., the visits of insects: the immediate cause being nourishment; the Fig. 61.—Transitional forms, a, b, from a leaf to a true bract, c, of HdUborUi 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 Henslow, George, 1835-1925. New York
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