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Fertilization. At the period of fertilization the embryo-sac lies in close proximity to the opening of the micropyle, into which the pollen-tube has penetrated, the separating cell-wall becomes absorbed, and the male or sperm-cells are ejected into the embryo-sac.
Hence there will result an envelope of changed matter, inclosing and protecting the unchanged protoplasm there will result a rudimentary cell-wall. Darwin approved of this expression and occasionally employed it, he did not adopt it for general use; contending, very truly, that the expression Natural Selection is in some cases more convenient. Darwin, these effects are not denied by him.
"It is curious the state I'm in before Aunt Paula sends me away," she said; "I was a nervous child, and though I've outgrown it, I still have attacks of nerve fag or something like it. I can feel them coming on and so can she. You know we've been together so much that it's like like two bees in adjoining cells. The cell-wall has worn thin; we can almost touch. She knows it often before I do.
After impregnation the fertilized oosphere immediately surrounds itself with a cell-wall and becomes the oospore which by a process of growth forms the embryo of the new plant.
An animal may be defined as a living organism, the protoplasm of which does not secrete a cellulose cell-wall, and which requires for its existence proteid material obtained from the living or dead bodies of existing plants or animals. The common use of the word animal as the equivalent of mammal, as opposed to bird or reptile or fish, is erroneous.
The germination of the macrospore consists in the repeated division of its nucleus to form two groups of four, one group at each end of the embryo-sac. One nucleus from each group, the polar nucleus, passes to the centre of the sac, where the two fuse to form the so-called definitive nucleus. The three cells at the opposite end are known as antipodal cells and become invested with a cell-wall.
But if the body of any living creature be divided, it will, at the very least, be seen to consist of a variety of minute distinct particles, called "granules," variously distributed throughout its interior. Cells may, or may not, be enclosed in an investing coat or "cell-wall." Every cell generally contains within it a denser, normally spheroidal, body known as the nucleus.
The ripe human ovum or germ cell is a spheric cell, about 0.2 mm. in diameter, consisting of granular protoplasm, in which lies a nucleus which contains the germinal spot. The proper cell-wall is a structure of great delicacy, outside of which is a secondary envelope. Menstruation. The etiology of menstruation has been variously explained at different epochs.
It is very remarkable after all that according to the experiment of Haberlandt this peculiar relation should become apparent in a process that is so open to our investigation as the filtration of water through the cell-wall of a plant. After what has been said I consider this simple experiment of Haberlandt of great significance; for it is a direct proof of the existence of a vital force.
Describing generally such low forms, some of which are said to have neither nucleus nor vacuole, he remarks that in types somewhat higher "the outer or peripheral border of the protoplasmic mass, while not assuming the character of a distinct cell-wall or so-called cuticle, presents, as compared with the inner substance of that mass, a slightly more solid type of composition."
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