. Botany; principles and problems. Botany. Fig. 217.—Development of the female gametophyte and .seed in a gyninospcrm (Pine), Longitudinal sections through the base of the cone-scale. A, young ovule, consisting of an integument (1) and a megasporangium or nucellus (2), within which is a row of four megaspores which have developed from a megaspore mother-cell. B, three of the megaspores have aborted, the fourth is enlarging. C, the megaspore has germinated into a young gametophyte or em))ryo-sac (3), which now consists of a layer of free nuclei surrounding a large vacuole. D, the young sac has
. Botany; principles and problems. Botany. Fig. 217.—Development of the female gametophyte and .seed in a gyninospcrm (Pine), Longitudinal sections through the base of the cone-scale. A, young ovule, consisting of an integument (1) and a megasporangium or nucellus (2), within which is a row of four megaspores which have developed from a megaspore mother-cell. B, three of the megaspores have aborted, the fourth is enlarging. C, the megaspore has germinated into a young gametophyte or em))ryo-sac (3), which now consists of a layer of free nuclei surrounding a large vacuole. D, the young sac has developed into the mature female gametopliyte (3), the bulk of which consists of endosperm. At one end are two archegonia (4) within each of which is an egg-cell. Pollen grains have entered the micropyle and alighted on the tip of the nucellus. E, fertilization. Two pollen grains have germinated, sent their tubes down through the nucellus, and discharged their contents into the two archegonia, in each of which one of the male nuclei is fusing with the egg nucleus (5). F, from the fertilized egg have grown two young'embryos (6), one larger than the other, which have been pushed down into the middle of the endo- sperm. G, mature seed. The integument of the ovule has developed into the seed coat, the micropyle has closed, the endosperm has become greatly enlarged, the nucellus has almost disappeared and the embryo has grown to its full size. The smaller embryo in F failed to develop. This seed will now detach from the cone-scale and under favorable conditions will produce a new 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 Sinnott, Edmund Ware, 1888-. New York, McGraw-Hill
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1923
