. A popular treatise on the physiology of plants for the use of gardeners or for students of horticulture and of agriculture. Plant physiology. FKUITS AND SEEDS 231 membrane, as a perforation or disruption of the cell-wall has not been observed. One can only see that the contents of the pollen tube become squeezed towards the embryo sac by a constricting of the micropyle, and that the tube becomes firmly applied to one of the synergidse. Then the nucleus and vacuole of this cell disappear; it and its sister-cell (Fig. 33, s, s) be- come dim and granular, lose their shape, and are ultimately se
. A popular treatise on the physiology of plants for the use of gardeners or for students of horticulture and of agriculture. Plant physiology. FKUITS AND SEEDS 231 membrane, as a perforation or disruption of the cell-wall has not been observed. One can only see that the contents of the pollen tube become squeezed towards the embryo sac by a constricting of the micropyle, and that the tube becomes firmly applied to one of the synergidse. Then the nucleus and vacuole of this cell disappear; it and its sister-cell (Fig. 33, s, s) be- come dim and granular, lose their shape, and are ultimately seen attached to the egg-cell as colourless and irregular viscid masses. This completes the act of fertilisation, the immediate effect of which is that the egg-cell (e), having temporarily two nuclei (which afterwards fuse), surrounds itself with a delicate membrane. This stage of the development is shown in Fig. 32. Umhr represents the fertilised egg-cell, and we notice that during or shortly after fertili- sation several changes have taken place in the embryo sac. Before fertilisation, as is mentioned above, a fusion of one of the nuclei of the micropylar end with a nucleus from the antipodal end has given rise to a single new nucleus near the centre of this embryo sac. Now by repeated divisions of this nucleus, a large number ^'s- 33- of nuclei (Endsp) have been formed, which are chiefly found in the layer of protoplasm lining the inner wall of the embryo sac. Here each nucleus becomes the centre of a new cell, and by further division the embryo sac becomes entirely filled by a new cellular tissue. This tissue, which fills the entire embryo sac when the latter has completed its growth, is called the albumen or endosperm. It is the tissue in which are stored up the reserve substances which have to nourish the young embryo during its further growth, and it forms the greater part of some seeds. In the case of the wheat-grain and other grass- seeds, we see the small embryo attache
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisherlondo, bookyear1895
