. A textbook of botany for colleges and universities ... Botany. 236 MORPHOLOGY trating the overlying nucellar tissue ; while in Gnetum it enters the embryo sac and encounters the free egg nuclei (fig. 531). Embryo. âThe development of the embryo of Gnetales shows a remarkable modification of the usual gymnosperm method, and varies in accordance with the structure of the gametophyte in each genus. In aU cases the embryo has two cotyledons. Ephedra. ââ In Ephedra there is free nuclear division within the egg until eight free nuclei appear, and then these nuclei enter into the organization of ei
. A textbook of botany for colleges and universities ... Botany. 236 MORPHOLOGY trating the overlying nucellar tissue ; while in Gnetum it enters the embryo sac and encounters the free egg nuclei (fig. 531). Embryo. âThe development of the embryo of Gnetales shows a remarkable modification of the usual gymnosperm method, and varies in accordance with the structure of the gametophyte in each genus. In aU cases the embryo has two cotyledons. Ephedra. ââ In Ephedra there is free nuclear division within the egg until eight free nuclei appear, and then these nuclei enter into the organization of eight free cells (the proembryonal cells, fig. 534). Two or more of these independent proembryonal cells may function as follows : the nucleus divides; the cell develops a prolongation hke a pollen tube (fig. 535), which penetrates the surrounding endo- sperm, and into its tip one of the nuclei passes. Later the tip of this tube, containing the nucleus, is cut off by a wall (fig. 536), and from this cell the embryo is de- veloped (fig. 537). Tumboa. â In Tumboa the Fig. of £Me< three of ^^^.^^ ^^^j^^^ .^ ^^^ the eight free proembryonal cells. â After *â Land. thallial tube) is used in the for- mation of a free and independent cell, which then behaves as do the independent proembryonal cells of Ephedra. It should be noted that in this case the stage of free nuclear di\asion in embryo formation has disappeared, and the first division of the fertihzed egg is accompanied by wall formation, which is an condition. Gnetum. â In Gnetum the fertilized eggs in the micropylar chamber of the embryo sac behave as in the case of Tumboa, and as do the proem- bryonal cells of Ephedra, the tubular prolongation penetrating the endo-. 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 Coult
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
