. Lectures on the evolution of plants. Botany; Plants. 178 EVOLUTION OF PLANTS rounded by the floral envelopes, corolla and calyx, made up respectively of the petals and sepals. The base of the carpel forms the ovary, while above it is prolonged into the style tipped by the stigma, or portion upon which the pollen falls (Fig. 44, A). In the number of parts in the flower, as well as in their ar- rangement and form, the Angio- sperms show almost infinite variety. The petals are very frequently brightly colored, and this, together with many modi- fications in the other structures, is intimately a
. Lectures on the evolution of plants. Botany; Plants. 178 EVOLUTION OF PLANTS rounded by the floral envelopes, corolla and calyx, made up respectively of the petals and sepals. The base of the carpel forms the ovary, while above it is prolonged into the style tipped by the stigma, or portion upon which the pollen falls (Fig. 44, A). In the number of parts in the flower, as well as in their ar- rangement and form, the Angio- sperms show almost infinite variety. The petals are very frequently brightly colored, and this, together with many modi- fications in the other structures, is intimately associated with pollination through insect aid, which has undoubtedly played an important part in the evolu- tion of the floral structures of the Angiosperms. The gametophyte in the An- giosperms is so much reduced and so inconspicuous that it is usually quite ignored in the ordinary study of these plants; but it must be borne in mind that the gametophyte is always present, although in a very re- duced form. As in the Gymnosperms, the ovule cor- responds to the macrosporangium of the heterosporous Pteridophytes, and within it is formed the single macro-. FiG. 43. — Flowers of a pond- weed (Naias); the male flower, A, and the female, B, are much alike. Each consists of a single sporan- gium invested with an in- tegument, in, the whole enclosed in a tubular leaf with spiny processes at the summit. This sheath-like leaf is usually considered . in the female flower to be a carpel. Fig. C shows a section through the base of the female flower, with the enclosed macrosporangi- um, or ovule, ma, and two integuments, ill, and the contained embryo-sao, or macrospore, 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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