. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. EMBRYOGENY IN ANGIOSPEEMS. 295 agency of wind or insects. The viscid fluid secreted by the stigmatic cells {pi) causes a rupture of the extine, and the intine passes out in the form of a tubular prolongation, -which gradually elongates (tp, tp) as it proceeds down the loose conduct- ing tissue (tc, te) of the style tiU it reaches the ovule. The length attained by the pollen-tube is sometimes very great. In Cereus grandiflorus, Morren estimated that the tubes, when they
. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. EMBRYOGENY IN ANGIOSPEEMS. 295 agency of wind or insects. The viscid fluid secreted by the stigmatic cells {pi) causes a rupture of the extine, and the intine passes out in the form of a tubular prolongation, -which gradually elongates (tp, tp) as it proceeds down the loose conduct- ing tissue (tc, te) of the style tiU it reaches the ovule. The length attained by the pollen-tube is sometimes very great. In Cereus grandiflorus, Morren estimated that the tubes, when they reached the ovary, extended as far as 1150 times the diameter of the pollen- grain ; in Orinum amabile, Hassall says that they reach 1875 times the diameter of the grain; in Oleome speciosa, 2719 times; in Oxyanthus speciosus, 4489, times; and in Oolchicum autumnale, 9000 times. The length of time which the poUen-tabe takes to traverse the conducting tissues of the style in Anglo- sperms varies. On reaching the ovule the pollen- tube enters the foramen, and finally comes into contact with the embryo-sac pj 527 (fig. 528 e). In the interior of this sac one or more nucleated germ-vesicles are produced before impregna- tion in the midst of the endospermal cells and protoplasmic matter (fig. 530 e). In fig. 529 an anatropal ovule is represented with the raphe r, the opening in the primine and secundine ra, en, the nucleus n, the embryo-sac es, and the pollen-tube pt, in contact with the germ-vesicle e. , After the contact of the poUen-tube, one of the embryonal vesicles becomes enlarged, and is then divided by septa into two, the upper division growing out in a filamentous form, constituting the suspensor (fig. 530 s, 531 h), while the lower portion enlarges and divides re- peatedly so as to form a cellular globule—the embryo (fig. 530 s, 531 c). The parts of the embryo being finally differentiated into cotyledonary and radicular portions, as shown in fig. 532, 1-4. Taking a com
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
