. Botany; principles and problems. Botany. 196 BOTANY: PRINCIPLES AND PROBLEMS ment in such families of irregular-flowered plants as the legumes and orchids, and have long excited the curiosity and admiration of naturalists. Fertilization.—Pollination, however, is only a step toward the union of male and female gametes which we know as fertilization. Fig. llO.^The process of seed-production in a flowering plant. Longitudinal diagrams of flower and fruit, the calyx and corolla solid black; the ov-ule, seed- coats and embryo dotted, and the ovary wall, style and stigma lined. A, young bud, the s
. Botany; principles and problems. Botany. 196 BOTANY: PRINCIPLES AND PROBLEMS ment in such families of irregular-flowered plants as the legumes and orchids, and have long excited the curiosity and admiration of naturalists. Fertilization.—Pollination, however, is only a step toward the union of male and female gametes which we know as fertilization. Fig. llO.^The process of seed-production in a flowering plant. Longitudinal diagrams of flower and fruit, the calyx and corolla solid black; the ov-ule, 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 hard- ened 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. (Fig. 110). Although the pollen grain is a single cell, it is not the male gamete. At about the time of pollination, the nucleus of the grain divides into two, one of which, the tube-nucleus, remains free in the cytoplasm. The other nucleus surrounds itself with a. Please note that these images are extracted from scanned page images that may
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1923
