. Botany for agricultural students . Botany. 466 SPERMATOPHYTES (SEED PLANTS) connection with double fertilization it should be noted that the endosperm nucleus contains the contents of three nuclei, since it is a product of a triple fusion, involving a sperm and the two polar nuclei. Embryo. — The first cells produced by the division of the fer- tilized egg form a filament which pushes down into the embryo sac. This filament is called the proembryo. The terminal cell of the proembryo develops the embryo, while the remainder of the filament remains as a stalk called suspensor. After the termi-

. Botany for agricultural students . Botany. 466 SPERMATOPHYTES (SEED PLANTS) connection with double fertilization it should be noted that the endosperm nucleus contains the contents of three nuclei, since it is a product of a triple fusion, involving a sperm and the two polar nuclei. Embryo. — The first cells produced by the division of the fer- tilized egg form a filament which pushes down into the embryo sac. This filament is called the proembryo. The terminal cell of the proembryo develops the embryo, while the remainder of the filament remains as a stalk called suspensor. After the termi-

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. Botany for agricultural students . Botany. 466 SPERMATOPHYTES (SEED PLANTS) connection with double fertilization it should be noted that the endosperm nucleus contains the contents of three nuclei, since it is a product of a triple fusion, involving a sperm and the two polar nuclei. Embryo. — The first cells produced by the division of the fer- tilized egg form a filament which pushes down into the embryo sac. This filament is called the proembryo. The terminal cell of the proembryo develops the embryo, while the remainder of the filament remains as a stalk called suspensor. After the termi-. FiG. 412. — Development of the embryo and endosperm in the Shepherd's Purse. A, section through ovule with embryo and endosperm in early stage of development, showing the proembryo which consists of the suspensor (b) and the terminal three-celled embryo (a), and also showing the endosperm (c) as a chain of free nuclei around the wall of the embryo sac. B, the same as A, excepting that the proembryo and endosperm are more developed. C, section through a mature seed showing the seed coat (s), and the mature embryo with cotyledons at h, plumule at p, hypocotyl at e, and radicle at d. nal cell divides a number of times, the parts of the embryo begin to be differentiated. In Dicotyledons two lobes appear at the end farthest from the micropyle and these become the two coty- ledons characteristic of dicotyledonous Angiosperms. Between the cotyledons the plumule is formed, while the axis of the embryo below the cotyledons is differentiated into the hypocotyl, which is the main part of the axis, and the radicle at its lower end (Fig. U2). The embryos of monocotyledonous Angiosperms have a radicle, hypocotyl, plumule, but only one cotyledon. They also differ. 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 work.. Marti