. Heredity and evolution in plants. Heredity; Plants. FUNDAMENTAL PRINCIPLES 35 The fact of a cycle in the hfe history is brought out clearly in the following diagram:. Fig. 29.—Diagram of life-cycle of a fern. 27. Reduction.—Since the sporophyte (descended from the diploid oosperm) has cells of a double nature, resulting from fertilization, and since the spores which give rise to the gametophyte are of a single (or haploid) nature, there must occur, at some stage in the life of the sporo- phyte, a process of reduction, restoring the cells, made diploid by fertilization, to the haploid conditi
. Heredity and evolution in plants. Heredity; Plants. FUNDAMENTAL PRINCIPLES 35 The fact of a cycle in the hfe history is brought out clearly in the following diagram:. Fig. 29.—Diagram of life-cycle of a fern. 27. Reduction.—Since the sporophyte (descended from the diploid oosperm) has cells of a double nature, resulting from fertilization, and since the spores which give rise to the gametophyte are of a single (or haploid) nature, there must occur, at some stage in the life of the sporo- phyte, a process of reduction, restoring the cells, made diploid by fertilization, to the haploid condition. Pains- taking studies of cellular structure and processes has disclosed the fact that this reduction takes place during the two successive divisions (tetrad-divisions) of the spore- mother-cell, resulting in the formation of four spores. The diploid condition persists in all the cells of the sporophyte, and through every cell-division, up to the two divisions preceding spore-formation, just as the single or haploid condition persists in all the cells of the gameto- phyte, up to the very act of 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 Gager, C. Stuart (Charles Stuart), 1872-1943. Philadelphia, P. Blakiston's Son & Co.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectplants, bookyear1920
