. Botany; principles and problems. Botany. THE SPERMATOPHYTA 357 Reproduction.—The gyinnospenns are all wiud-pollinated, and many of the lower angiospcrms resemble them in this respect and have inconspicuous, cone-like reproductive organs (Fig. 107) often not differing remarkably in general appearance and function from the gymnosperm type, except in the possession of C D Fig. 228.—The process of seed-production in a flowering plant. Longitudinal diagrams of flower and fruit, the calyx and corolla solid black; the ovule, seed- coats and embryo dotted, and the ovary wall, style and sti
. Botany; principles and problems. Botany. THE SPERMATOPHYTA 357 Reproduction.—The gyinnospenns are all wiud-pollinated, and many of the lower angiospcrms resemble them in this respect and have inconspicuous, cone-like reproductive organs (Fig. 107) often not differing remarkably in general appearance and function from the gymnosperm type, except in the possession of C D Fig. 228.—The process of seed-production in a flowering plant. Longitudinal diagrams of flower and fruit, the calyx and corolla solid black; the ovule, seed- coats and embryo dotted, and the ovary wall, style and stigma lined. A, young bud, the stamens and the single ovule beginning to develop. B, bud ready to unfold. The embryo-sac within the ovule is fully developed and the egg (below) and double endosperm nucleus (in center) are ready for fertilization. C, fully opened flower. The anthers have burst and pollination has taken place, pollen grains being transferred to the stigma. Two grains have germinated, and the pollen-tube from one of them has penetrated the style, entered the ovary, passed through the micropyle of the ovule and discharged its contents—the two male gametes—into the embryo-sac. Double fertilization is taking place, one male gamete uniting with the egg and the other with the endosperm nucleus. D, ripe fruit. Sepals, petals and stamens have dropped off; the ovary wall has hardened into the pericarp; the micropyle has closed; the integuments have become seed coats and the ovule has developed into the seed. The embryo, in the center of the seed, has grown from the fertilized egg, and the endosperm surrounding it (shown in white) from the endosperm nucleus. The higher members, however, have come to depend upon insects to transport their pollen, and have evolved the charac- teristic flower (Fig. 227) which we have described in a previous chapter, with its protective calyx, composed of sepals; its attrac-. Please note that these images are extracted from scanned page
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1923
