. Textbook of botany. Botany. 126 TEXTBOOK OF BOTANY micropyle. A sticky liquid is formed in the micropyle and oozes from its mouth. The jarring of the cone by the wind shakes the pollen grains about, and when they come in con- tact with this liquid they are held by it. Then a drying oc- curs within the micropyle and the drop of liquid is sucked back, carrying the pollen grains to the bottom of the micro- pyle. The pollen grains are now in contact with the macro- spore sac, within which is the female plant. The set of proc- esses which thus bring the pollen grain close to the female plant is c
. Textbook of botany. Botany. 126 TEXTBOOK OF BOTANY micropyle. A sticky liquid is formed in the micropyle and oozes from its mouth. The jarring of the cone by the wind shakes the pollen grains about, and when they come in con- tact with this liquid they are held by it. Then a drying oc- curs within the micropyle and the drop of liquid is sucked back, carrying the pollen grains to the bottom of the micro- pyle. The pollen grains are now in contact with the macro- spore sac, within which is the female plant. The set of proc- esses which thus bring the pollen grain close to the female plant is called pollination. It is plain that pollination must take place before fer- tilization can occur. 152. Fertilization. — After the pollen grain has reached the base of the micropyle, its de- velopment into a male plant continues. The vegetative cell of the pollen grain pushes out a long projection — the pollen tube (Fig. 74, t). This tube burrows into the tissues of the macrospore sac, grow- ing very slowly, occasionally branching, and using for food some of the cells of the spore sac. While the tube is growing, the generative cell within the pollen grain divides, forming a stalk cell and a body cell. The body cell next divides into two male gametes, which move, following the vegetative nucleus, toward the growing end of the pollen tube. The gametes are simple cells consisting of nucleus and some cytoplasm, and with no vibrating hairs such as are borne by the male gametes (antherozoids) of mosses and Fig. 74. — A lengthwise section of an ovule older than that shown in Fig. 73, C, showing germinating pollen grains, pollen tubes, t, and the upper part o£ the female plant with three archegones; each arche- gone contains a large egg, e; i, integument; n, an egg 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
Size: 1658px × 1507px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1917
