. Text-book of botany, morphological and physiological. Botany. 554 PHANEROGAMS. the young pollen-cells become free, separate, and float in the granular fluid which fills up the cavity of the anther; and within this they now attain their definite development and size. The fluid being thus used up, tlje mature pollen-grains finally fill up the cavity of the anther in the form of a powdery mass. [The ripe pollen-grain of Angiosperms has been found in many cases to contain two nuclei1. It appears that when the pollen-grains have become isolated from each other, the nucleus of the grain undergoes
. Text-book of botany, morphological and physiological. Botany. 554 PHANEROGAMS. the young pollen-cells become free, separate, and float in the granular fluid which fills up the cavity of the anther; and within this they now attain their definite development and size. The fluid being thus used up, tlje mature pollen-grains finally fill up the cavity of the anther in the form of a powdery mass. [The ripe pollen-grain of Angiosperms has been found in many cases to contain two nuclei1. It appears that when the pollen-grains have become isolated from each other, the nucleus of the grain undergoes division into two, one larger, the other smaller. The smaller nucleus travels to the wall of the grain and becomes invested by protoplasm, thus constituting a primordial cell, which, in some cases, is cut off from the rest of the grain by a wall of cellulose : the larger nucleus remains as the nucleus of the larger cell of the pollen-grain. The smaller nucleus may divide once or twice, thus giving rise to a group of cells; the large nucleus does not divide: the form of the nuclei varies very much. These processes resemble those which have. FIG. 379.—Mother-cell of the pollen oiCucurbita Pepo; sg the outer common layers of the mother-Cell ill the act of being absorbed ; sp the so-called ' special mother-cells,' consisting of masses of layers of Ijie mother-cell which surround the young pollen-cells ; they also are afterwards absorbed ; ph the wall of the pollen-cell; its spines grow outwards and penetrate the special mother-cell; v hemispherical mass of cellulose on the inside of the pollen cell- wall, from which the pollen-tube is afterwards formed ; p the protoplasm contracted { < 550). (The preparation was obtained by making a section of an anther which had lain for some months in absolute alcohol.) been described as taking place in the pollen-grains of the Gymnosperms: the small cell (or the cells derived from it) evidently corresponds to the * vegetative ' cells in the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
