. The classification of flowering plants. (fig. 5, D). The nucellar tissue between the pollen-chamber and the embryo-sac becomes soft and loose, andultimately disorganised, forming a cavity. 54 FLOWERING PLANTS [CH. In Ceratozamia and Stangeria, according to Treub^ andLang* respectively, the spore-mother-cell divides transversely into three cells (potential mega-spores), the lowest of which be-comes the functional megaspore,enlarging rapidly at the expenseof the others and adjacent Cycas the outer wall of themegaspore becomes cutinized. Fig. 6. Female cone of MacrozamiaPreissii, \ nat
. The classification of flowering plants. (fig. 5, D). The nucellar tissue between the pollen-chamber and the embryo-sac becomes soft and loose, andultimately disorganised, forming a cavity. 54 FLOWERING PLANTS [CH. In Ceratozamia and Stangeria, according to Treub^ andLang* respectively, the spore-mother-cell divides transversely into three cells (potential mega-spores), the lowest of which be-comes the functional megaspore,enlarging rapidly at the expenseof the others and adjacent Cycas the outer wall of themegaspore becomes cutinized. Fig. 6. Female cone of MacrozamiaPreissii, \ nat. size. The cone has beenin part cut lengthwise to shew the attach-ment of the carpels to the axis (a), and theposition of the seeds (unripe). The carpelsare prolonged above in the median lineinto a stiff erect process, a, axis of cone;P, stalk of carpel; «, seeds (unripe), some ofwhich are cut in section. A, single carpelwith pair of seeds under surface of peltatelamina. Drawn from a specimen in theDepartment of Botany, British In germination the nucleus of the megaspore divides and aparietal layer of cells is formed by free-cell-formation liningthe wall of the embryo-sac; cell-walls are formed and a parietaltissue developed which continues to grow and forms a pro-thallium filling the cavity of the sac. In Cycas chxrnalisin absence of fertilisation the prothallium or endosperm hasbeen found to grow out through the micropyle and to developchlorophyll on exposure to the light. Archegonia, generally three to six in number, are developedfrom peripheral cells of the prothallium below the outer neck-cell is cut off by a periclinal wall and becomesdivided by an anticlinal wall to form a two-celled neck. The largecentral ceil grows enormously for some time, for three monthsin Cycas revoluta, and is nourished by the surrounding layerof endosperm cells, the contents of which pass through con-necting perforations into the growing central cell. Immediatelybefore fer
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1904
