Placenta (botany)

“ Often this diversity is due merely to the changes that take place during growth; thus, the placentation of Caryophylleæ, Cucurbitaceæ, Papaveraceæ, and many other orders, varies according to the age of the carpel, and if any stasis or arrest of development occurs the placentation becomes altered accordingly.
It is not necessary, in this place, to enter into the question whether the placenta is, in all cases whatsoever, a dependence of the axis, as Payer, Schleiden, and others, have maintained, or whether it be foliar in some cases, axial in others. ”

“ Another organ of the wheat berry which has a most important bearing on the work of the miller is the placenta, which is in effect a cord connecting the berry with its stalk or straw. The placenta serves to filter the food which the plant sucks up from the ground; it passes up the crease of the berry, and is enfolded in the middle skin, being protected on the outer side by the first and having the third or inner skin on its other side. A good deal of the matters filtered by the placenta are mineral in their nature, and such portions as are not digested remain in the crease. ”

“ In every pregnancy the placenta serves in this way as an organ of nutrition, arranging for the passage of food from the mother's blood to the fetal circulation. Occasionally, it is interesting to observe, the placenta performs a very different function, namely, the protection of the unborn child from diseases that may attack the mother. It is able to afford such protection, because the coating of the villi is not permeable to all sorts of substances. In order to pass through their walls, material must be in solution ”

“ Its shreds when expelled are of diagnostic importance, and in early abortions its massive thick tissues, changed by disease, often cause greater trouble than the ovum itself, forming, alone or with the membranes proper of the ovum, what is so commonly but erroneously called the placenta in abortion. ”

“ If the union were vascular, the mother's blood would circulate in the foetal body, and the impulses of the maternal heart might prove too strong for the delicate organism of the embryo. Besides, the separation of the placenta from the uterus might prove fatal to both parent and offspring. The placenta is only a temporary organ, and when its functions are no longer required, it is easily and safely removed. ”

“ When the segmenting egg attaches itself to the uterine wall it does not only produce the embryo proper, but it gives also rise to certain cells which attach themselves to the uterine wall of the mother, and are mainly concerned in transferring food from the mother to the embryo, thus forming the embryonal placenta, the outer layer of which is called the chorionic. These chorionic cells, which are therefore of embryonic origin, migrate already under normal conditions deeply into the uterine wall ”

“ For some embryos have a more perfect structure provided for them, such as that fleshy substance mentioned above, which in some is altogether wanting. In some, also, the placenta is observed to be thicker, larger, and more loaded with blood; whilst in others it is more spongy and white, like the thymus or pancreas. But there is not more variety found in the placenta than in the mamma or viscera generally: for instance, the liver in some animals is red and filled with blood, in others, as is the case with fishes and some cachectic persons in the human species, it is of much paler hue. ”

“ Many of our own researches, and those of various observers, have shown that, during the whole period of pregnancy, defensive ferments circulate in the blood, which are able to reduce placenta albumen. ”

“ Further, all kinds of organs should be subjected in turn to the action of a particular serum.
The sero-diagnosis of pregnancy has been recently employed with success by numerous scientists. [1] While many observers agree with our point of view, that the defensive ferments which appear during pregnancy are directed against the albumen of placenta, other authors are of the opinion that no strictly specific action exists. But surely positive facts have more value than negative ones. ”

“ In very few cases has anything representing prothallial development been observed; generally a small cell (the antheridial or generative cell) is cut off, leaving a larger tube-cell. When placed on the stigma, under favourable circumstances, the pollen-grain puts forth a pollen-tube which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the mouth of an ovule. The nucleus of the tube-cell has meanwhile passed into the tube, as does also the generative nucleus which divides to form two male- or sperm-cells. ”

“ The placenta, according to this point of view, together with the fœtus, never settles down completely within the organism of the mother. With the expulsion of the placenta, in which process, again, ferments probably play a preparatory part, the ferments which are directed against its albumen disappear fairly quickly. It is, of course, quite possible that these placentally active ferments are conditioned by many different forces.
The view we have just discussed gives us an opportunity of demonstrating the initiation of the function of a particular organ. ”

“ In Ovum 19 there was nothing in the least analogous. Though the placenta is imperfectly formed; even in its filiform or mossy or primitive texture, it might serve and has served the purpose, of forwarding the nutrition and growth of the fœtus. The disease which destroyed the latter, being of an inflammatory nature, must have been more rapid in its effect. It put an end to life before there could have been time for growth to be much affected. ”

“ In the oak and hazel, an ovary with three and two cells respectively, and two ovules in each, produces a one-celled fruit with one seed. In the coco-nut, a trilocular and triovular ovary produces a one-celled, one-seeded fruit. This abortion may depend on the pressure caused by the development of certain ovules, or it may proceed from non-fertilization of all the ovules and consequent non-enlargement of the carpels. Again, by the growth of the placenta, or the folding inwards of parts of the carpels, divisions occur in the fruit which did not exist in the ovary. ”

“ Moreover, the above investigations are of special importance for this reason, that they definitely indicate the specific action of the defensive ferments. Fauser and Wegener report that female patients suffering from dementia præcox never decomposed testes, but only ovaries. Conversely, males only attack testicular tissue, but never the ovary. Both authors have also experimented with placenta, and, on the one hand, confirmed the sero-diagnosis of pregnancy, and on the other showed that the male serum never decomposes tissues of placenta. ”

“ How can we then explain the existence of the defensive ferments during pregnancy? It can only be in very exceptional cases that they are produced by the invasion of morphological elements. In most cases it must be the result of the transfer of particular bodies—the constituents of particular cells, or the products of their decomposition. It may be, of course, that the extraordinarily active metabolic processes, which arise at the junction of the maternal and fœtal organisms, result in an insufficient reduction of many of the products of the cells of the placenta ”

“ He adds the Number, Shape, and Use of these Placentas; and first observes that those that are Kernel-bearing Animals, or chewing the Cud, have many, and those that are Cake-bearing, have for the most part, one Cake for each Fœtus; but a woman commonly but one, though she happen to have many Embryo's.
He annexes a particular description of the Placenta of a Woman, as the most considerable, and teaches, how it may be most conveniently severed from the Vessels, to render them conspicuous, which are a numerous off-spring of Arteries, Veins, and Fibres ”

“ Originating from the same annular disk as the petals are the stamens, seven or eight in number. The ovary is partially adherent, is surmounted by a style, and has two or three loculi with an axile placenta, to which several small curved ovules are attached. The malformed flowers did not present anything peculiar in their outer parts, nor did the ovary, partially immersed within the expanded top of the flower-stalk and the calyx-tube, which is continuous with that organ, show externally any indication of the change within. ”

“ But in the Placentals, where gestation lasts a long time, and the embryo reaches its full development under the protection of its enveloping membranes, there has to be a new mechanism for the direct supply of a large quantity of food, and this is admirably met by the formation of the placenta. ”

“ Now please remember that it is right that the placenta should grow fast to the womb; that is, to its inner surface. It is always grown fast, and should be; but it is possible for it to adhere more firmly in some cases than in others; and in some cases, too, the uterus seems to be so weak that it has not power sufficient to expel it.
In cases when the womb is very active after the birth of the child, the placenta may be expelled very quickly. ”

“ The union is usually most complete at the base; but in Labiatae the styles are united throughout their length, and in Apocynaceae and Asclepiadaceae the stigmas only. When the union is incomplete, the number of the parts of a compound pistil may be determined by the number of styles and stigmas; when complete, the external venation, the grooves on the surface, and the internal divisions of the ovary indicate the number.
The ovules are attached to the placenta, which consists of a mass of cellular tissue, through which the nourishing vessels pass to the ovule. ”

“ On one of the shelves in the Museum in Lincoln’s Inn Fields, I observed one marked 3443, in which a pseudo membrane has formed externally to the placenta, pressing on the cotyledons of the latter. The embryo is stinted. ”

“ In Caryophyllaceae, however, while the placenta is free in the centre, there are often traces found at the base of the ovary of the remains of septa, as if rupture had taken place, and, in rare instances, ovules are found on the margins of the carpels. But in Primulaceae no vestiges of septa or marginal ovules can be perceived at any period of growth; the placenta is always free, and rises in the centre of the ovary. ”

“ We ought to point out here, that we must never rely, in these investigations, upon one particular boiled organ. The great advantage of the whole method of investigation is the fact, that it is possible to make each case absolutely sure by means of control experiments. Placenta, for instance, can always be tested by means of serum from definitely non-pregnant individuals, as well as from males. ”

“ In order to explain the formation of the placenta it is necessary to encroach to some extent on the domain of physiology. Before each menstrual period, during the child-bearing age of a woman, the mucous membrane of the uterus hypertrophies, and, at the period, is cast off and renewed, but if a fertilized ovum reaches the uterus the casting off is postponed until the birth of the child. ”

“ Amongst the existing Mammals provided with a true placenta, the most primitive type is probably retained by those forms in which the placental part of the chorion is confined to a comparatively restricted area on the dorsal side of the embryo; while the false chorion is formed by the [Pg 241] vascular yolk-sack fusing with the remainder of the subzonal membrane. In all the existing forms with this arrangement of fœtal membranes, the placenta is deciduate. ”

“ After the child is breathing properly and the cord is cut, the mother may receive your attention. If the placenta is not expelled spontaneously, place one or both your hands over the uterus, and by friction, squeezing and pressure there, you will probably cause enough contraction of the womb to start the placenta from its attachments. You may then make slight traction on the cord, pulling only gently, and it will probably come down; as it emerges from the vagina gently twist or turn over the afterbirth, and you will secure the removal of the membranes. ”

“ The ovarium is superior, of an obovate figure, one-celled, with a central, free, fungilliform placenta, the lower edge of which has five teeth corresponding to an equal number of peltate ovula; the style is filiform, as long as the tube of the corolla, and continuous with the ovarium; stigma, a minute depressed cup. The capsule is of a cartilaginous texture, surrounded by the persistent calyx; one-celled, with five recurving valves; the seeds are two, peltate, oblong, convex on the outside, concave in the inside, dark brown, covered closely with minute dots or depressions ”

“ We have seen that after the first month of pregnancy the placenta serves the fetus as a combined respiratory and digestive apparatus, not alone in supplying the oxygen and nourishment requisite for life and growth, but also in excreting the broken-down products of fetal life. ”

“ In one capsule, in which the seeds had ceased to swell, apparently from their earliest formation, they adhered together to something like a central placenta: in all the other capsules I found them loose, and suspect the placenta had been absorbed by the liquid remaining in the capsule. A very minute hilum remained always visible, and the three-radiated mark originating there appears to me to be only three stronger ribs of the reticulated cuticle of the seed. ”