. Botany for high schools. Botany. Fig. 369. A, section of ovule of zamia, partly diagrammatic, showing germinating pollen tubf entering the nucellar cap. M, micropyle; O, outer portion of ovule (exocarp); /, im stony portion of ovule (endocarp); PC, pollen chamber; A^, nucellar cap; P, endosperm (p thallium); /l,archegonium (pollen grains in pollen chamber are germinating, the pollen tub growing in the tissue of the nucellar cap). B, same a little later, showing basal end of the pollen tubes bending downward as the sperm cells in that end are developing. cell sometimes called) has divided, as
. Botany for high schools. Botany. Fig. 369. A, section of ovule of zamia, partly diagrammatic, showing germinating pollen tubf entering the nucellar cap. M, micropyle; O, outer portion of ovule (exocarp); /, im stony portion of ovule (endocarp); PC, pollen chamber; A^, nucellar cap; P, endosperm (p thallium); /l,archegonium (pollen grains in pollen chamber are germinating, the pollen tub growing in the tissue of the nucellar cap). B, same a little later, showing basal end of the pollen tubes bending downward as the sperm cells in that end are developing. cell sometimes called) has divided, as in pines, into a sterile cell and a generative cell (body cell) which now divides into the two sperm cells,* which are oval in form, and each has a spiral band of numerous cilia around the smaller end (fig. 373). Some of. Fig. 370. Zamia. A, mature pollen grain showing within, the tube cell at the right, the central cell in the middle, the prothallial cell at the left; beginning of germination o*f pollen grain; C, farther stage in the germination of pollen grain, the tube nucleus of cell moving into the tube. (After Webber.) these sperms swim into the egg cases, one unites with an egg nucleus, and the embryo is then formed, thus making a seed. * Two sperm cells are formed in most cycads as in other seed plants, but in Microcycas there are eight generative cells, each of which divides to form two sperms, making sixteen in all for each small spore. 1. 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 Atkinson, George Francis, 1854-1918. New York, H. Holt and Company
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
