Fertilization sentence example
Fertilization is effected by the union of two nuclei in all those cases which have been carefully investigated.
Many Gastropoda deposit their eggs, after fertilization, enclosed in capsules; others, as Paludina, are viviparous; others, again, as the Zygobranchia, agree with the Lamellibranch Conchifera (the bivalves) in having simple exits for the ova without glandular walls, and therefore discharge their eggs unenclosed in capsules freely into the sea-water; such unencapsuled eggs are merely enclosed each in its own delicate chorion.
The subject of fertilization was one which early excited attention.
Get your soil tested and follow the recommended fertilization schedule.
Cross fertilization, or the impregnation of any given flower by pollen from another flower of the same species on the same or on another plant, has been proved to be of great - g advantage to the plant by securing a more FIG.Advertisement
Fertilization is effected by insects, especially by bees, which are directed in their search by the colour and fragrance of the flowers; but some pollen must also be transported by the wind to the female flowers, especially in arctic species which, in spite of the poverty of insect life, set abundant fruit.
The female lays two kinds of eggs - " summer-eggs," which develop without fertilization, and " winter-eggs" or resting eggs, which require to be fertilized.
No process of fertilization has as yet been observed.
Fertilization is effected by the passive convection of a spermatium from the antheridium to the trichogyne, to which it adheres, and to which it passes over its nucleus through an open communication set up at the point of contact.
This is a necessary consequence of the fusion of two nuclei in fertilization, unless the chromosomes are to be doubled at each generation.Advertisement
The closed ovary implies a mode of fertilization which is profoundly different, and which was probably correlated with a simultaneous development of insect life.
This c and common cross fertilization is often effected by the gland g.
The object of these movements will be appreciated when it is remembered that, if the pollen-masses retained the original direction they had in the anther in which they were formed, they would, when transported by the insect to another flower, merely come in contact with the anther of that flower, where of course they would be of no use; but, owing to the divergences and flexions above alluded to, the pollen-masses come to be so placed that, when transplanted to another flower of the same species, they come in contact with the stigma and so effect the fertilization of that flower.
These illustrations are comparatively simple; it would have been easy to select others of a more complicated nature, but all evidently connected with the visits of insects and the cross fertilization of the flower.
The whole subject of fertilization and development of the embryo has been more recently investigated with great assiduity and zeal, as regards both cryptogamous and phanerogamous plants, and details must be sought in the various special articles.Advertisement
The study of the fertilization, or as it is now generally called "pollination," of flowers, was continued by Darwin and taken up by other workers, notably Friedrich Hildebrand, Federico Delpino and the brothers Fritz and Hermann Muller.
In these cases we should expect to find some reduced process of fertilization similar to that of Humaria granulata among the ordinary Ascomycetes, where in the absence of the antheridia the female nuclei fuse in pairs.
Of the three cells at the micropylar end of the sac, all naked cells (the so-called egg-apparatus), one is the egg-cell or oosphere, the other two, which may be regarded as representing abortive egg-cells (in rare cases capable Of fertilization), are known as synergidae.
This remarkable double fertilization as it has been called, although only recently discovered, has been proved to take place in widely-separated families, and both in Monocotyledons and Dicotyledons, and there is every probability that, perhaps with variations, it is the normal process in Angiosperms. 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.
It has long been known that after fertilization of the egg has taken place, the formation of endosperm begins from the endosperm nucleus, and this had come to be regarded as the recommencement of the development of a prothallium after a pause following the reinvigorating union of the polar nuclei.Advertisement
This view is still maintained by those who differentiate two acts of fertilization within the embryo-sac, and regard that of the egg by the first male-cell, as the true or generative fertilization, and that of the polar nuclei by the second male gamete as a vegetative fertilization which gives a stimulus to development in correlation with the other.
If, on the other hand, the endosperm is the product of an act of fertilization as definite as that giving rise to the embryo itself, we have to recognize that twin-plants are produced within the embryo-sac - one, the embryo, which becomes the angiospermous plant, the other, the endosperm, a short-lived, undifferentiated nurse to assist in the nutrition of the former, even as the subsidiary embryos in a pluri-embryonic Gymnosperm may facilitate the nutrition of the dominant one.
The full number is restored in the fusion of the male and female nuclei in the process of fertilization, and remains until the formation of the cells from which the spores are derived in the new generation.
Frequently the influence of fertilization is felt beyond the ovary, and other parts of the flower take part in the formation of the fruit, as the floral receptacle in the apple, strawberry and others.
We should expect the albuminous state of the seed to be an antecedent one to the exalbuminous condition, and the recent discoveries in fertilization tend to confirm this view.Advertisement
Thus among Volvocaceae, a family of Protococcales, while in some of the genera (Chloraster, Sphondylomorum) no sexual union has as yet been observed, in others (Pandorina, Chlorogonium, Stephanosphaera, Sphaerella) conjugation of similar gametes takes place, in others still (Phacotus, Eudorina, Volvox) the union is of the nature of fertilization.
Again, in oogamous reproduction, while in general only one oosphere is differentiated in the oogonium, in Sphaeroplea several oospheres arise in each oogonium; and while the oospheres usually contract away from the oogonial wall, acquiring for themselves a new cell-wall after fertilization, in Coleochaete the oosphere remains throughout in contact with the oogonial wall.
There is usually distinguishable upon the surface of the oosphere an area free from chlorophyll, known as the receptive spot, at which the fusion with the antherozoid takes place; and in many cases, before fertilization, a small mucilaginous mass has been observed to separate itself off from the oosphere at this point and to escape through the pore.
In certain species of Oedogonium minute male plantlets, known as dwarf males, become attached to the female plant in the neighbourhood of the oogonia, thus facilitating fertilization.
In rare cases the oosphere has been known to germinate without fertilization (Oedogonium, Cylindrocapsa).
Remarkable changes of size and outline of the oosphere have recently been described as accompanying fertilization in Halidrys.
Probably the act of fertilization in plants has nowhere been observed in such detail as in Fucaceae.
Fertilization has been observed at Naples; but it apparently depends on climatic conditions, as at Plymouth the oospheres have been observed to germinate parthenogenetically.
The first effect of fertilization is the occlusion of the trichogyne from the fertilized carpogonium.
In the Gigartinales it is already differentiated previous to fertilization; in Rhodymeniales it arises subsequent to fertilization.
After fertilization the equivalent of the oospore divides directly to form a group of carpospores.
Fertilization by means of non-motile spermatia and a trichogyne are known among the Fungi in the families Collemaceae and Laboulbeniaceae.
The doubling process is provided by the act of fertilization, where an antherozoid with the single number of chromosomes fuses with an oosphere also with the single number to provide a fertilized egg with the double number.
Although cultivated with most primitive appliances, and with little or no attempt at irrigation or artificial fertilization, the average yield is eightto twelve-fold annually.
In April the rains come to an end (the " latter rains ") and the winter crops receive their final fertilization.
At the breeding season the walls of the pouches burst and the sexual elements pass into the atrium, whence they are discharged through the atriopore into the water, where fertilization takes place.
Many insects and other invertebrates, mostly noxious, have been accidentally naturalized, and some have been deliberately introduced, like the honey-bee, now feral in Australasia and North America, and the humble-bee, imported into New Zealand to effect the fertilization of red clover.
Hence it is that so-called artificial fertilization is possible; that is to say, fertilization will take place when ripe eggs and milt are artificially pressed from the oysters and allowed to fall into a vessel of sea-water.
The fertilization of the spawn is very easily effected.
The earlier advocates of artificial propagation and fish-hatching seem to have been under the impression that the thousands of fry resulting from a single act of artificial propagation meant a corresponding increase in the numbers of edible fish when once they had been deposited in suitable waters; and also that artificial fertilization ensured a greater proportion of fertilized eggs than the natural process.
Supposing this could be established, the question would still remain whether the same result could not be obtained at far less expense by dispensing with the hatching operations and distributing the eggs directly after fertilization.
While the great majority are simple hermaphrodites, capable of cross and self fertilization, it was discovered by Darwin that, in certain species, minute degraded males exist, attached within the mantle-cavity of the ordinary individuals.
In other species the large individuals have become purely female by atrophy of the male organs, and are entirely dependent on the dwarf males for fertilization.
Ovules naked, rarely without carpellary leaves, usually borne on carpophylls, which assume various forms. The single megaspore enclosed in the nucellus is filled with tissue (prothallus) before fertilization, and contains two or more archegonia, consisting usually of a large egg-cell and a small neck, rarely of an egg-cell only and no neck (Gnetum and Welwitschia).
Before fertilization a neck-canal cell is formed by the division of the ovum-nucleus.
The endosperm detached from a large Ginkgo ovule after fertilization bears a close resemblance to that of a cycad; the apex is occupied by a depression, on the floor of which two small holes mark the position of the archegonia, and the outgrowth from the megaspore apex projects from the centre as a short peg.
After fertilization the ovum-nucleus divides and cell-formation proceeds rapidly, especially in the lower part of the ovum, in which the cotyledon and axis of the embryo are differentiated; the long, tangled suspensor of the cycadean embryo is not found in Ginkgo.
It is often stated that fertilization occurs after the ovules have fallen, but it has been demonstrated by Hirase that this occurs while the ovules are still attached to the tree.
Before fertilization the nucleus of the egg-cell divides and cuts off a ventral canal-cell; this cell may represent a second egg-cell.
In the process of fertilization the two male generative nuclei, accompanied by the pollen-tube nucleus and that of the stalk-cell, pass through an open pit at the apex of the pollen-tube into the protoplasm of the ovum.
After fertilization the nucleus of the egg divides, the first stages of karyokinesis being apparent even before complete fusion of the male and female nuclei has occurred.
After fertilization, some of the uppermost bracts below each flower become red and fleshy; the perianth develops into a woody shell, while the integument remains membranous.
The megaspore of Welwitschia is filled with a prothallus-tissue before fertilization, and some of the prothallus-cells function as egg-cells; these grow upwards as long tubes into the apical region of the nucellus, where they come into contact with the pollen-tubes.
He also carried out important researches on fertilization in animals (1780).
Fertilization is effected by the male transferring spermatophores into the genital orifice of the female by means of his proboscis.
After fertilization the latter surrounds itself with a cell-wall and develops into the sporophyte.
On fertilization the number is doubled and all the cells of the sporebearing generation have the double number.
After fertilization the embryo forms a short suspensor; the apex of the stem, with a leaf on each side of it, is first distinguishable; at the base of this is the foot; while the root arises on the farther side of the latter.
After the prothalli have attained some size and bear sexual organs the pots should be occasionally sunk in water so as to flood the prothalli for a few minutes and facilitate fertilization.
The separation of the glumes, which occurs at the time of fertilization, and which permits the egress of the useless stamens after that operation, occurs only under certain conditions of temperature, when the heat, in fact, is sufficient to cause the lodicules of the flower to become turgid and thus to press apart the glumes.
From what has been said it will be evident that the artificial fertilization of wheat is a very delicate operation.
Among these may be mentioned improved methods of ploughing, tile drainage, use of the press drill, which results in greater immunity against winter killing, crop rotation, and, to a very small extent, fertilization.
In other species which possess receptacula seminis it is probable that fertilization is effected once only in early life before any ova pass into the uterus.
The honey secreted by flowers attracts insects, which, by conveying the pollen to the stigma, effect fertilization.
When this attachment takes place by an articulation, the petals fall off either immediately after expansion (caducous) or after fertilization (deciduous).
Such plants are called dimorphic. Other plants are timorphic, as species of Lythrum, and proper fertilization is only effected by combination of parts of equal length.
In order that fertilization may be effected the pollen must be conveyed to the stigma of the pistil.
They are often horizontal, as in Cathartocarpus Fistula, where they consist of transverse cellular prolongations from the walls of the ovary, only developed after fertilization, and therefore more properly noticed under fruit.
This is particularly abundant when the pistil is ready for fertilization.
The style is deciduous or persists after fertilization.
This cord sometimes becomes much elongated after fertilization.
For an account of the further development of the megaspore, and the formation of the egg-cell, from which after fertilization is formed the embryo, see Gymnosperms and Angiosperms.
When the pistil has reached a certain stage in growth it becomes ready for fertilization.
The male cells in the end of the pollen-tube are then transmitted to the embryo-sac and fertilization is effected.
Nor are the effects of fertilization confined to the ovule; they extend to other parts of the plant.
It is a curious fact that in no case has an embryo been found in any of these seeds; probably fertilization took place after they were shed, and was followed immediately by germination.
Fertilization occurs in the animal pole and this triggers a displacement of the egg cytoplasm.
The phytoplankton increase produced by the iron fertilization was dominated by diatoms.
In vitro fertilization studies will also be conducted using gametes recovered post-mortem to investigate the rate of fertilization by competing sperm.
These conditions allow the inconspicuous gametophyte (about the size of a finger nail) to develop and undergo fertilization.
Differential methylation of DNA sequences associated with imprinted genes is thought to control genomic imprinting, which occurs soon after fertilization.
This membrane confuses me, because I hear that there is no fertilization membrane in Hydrozoa, to which freshwater jellyfish belongs.
Pregnancies and deliveries after in vitro maturation culture followed by in vitro fertilization and embryo transfer without stimulation in women with polycystic ovary syndrome.
For example, the fertilization of an egg by a sperm to produce a progeny with a unique identity.
Since 1986 in the in vitro fertilization program of the clinic nearly 1,500 patients were treated with effected ovulation induction drugs causing superovulation.
If the germcells are differentiated, the offspring arises by syngamy or sexual union of the ordinary type between an ovum and spermatozoon, so-called fertilization of the ovum, or by parthenogenesis, i.e.
It has since been shown by other observers that this double fertilization Occurs in many other Angiosperms, both Dicotyledons and Monocotyledons, so that it is probably of general occurrence throughout the group (see ANGIOSPERMS).
For instance, it has been pointed out in the article on the reproduction of plants that the effect of the fertilization of the female cell in the ovule of a phanerogam is not confined to the female cell, but extends more or less widely outside it, inducing growth and tissue-change.
In the light of Sachss theory the interpretation is this, that the act of fertilization causes the formation in the female cell of substances which are transmitted to adjacent structures and stimulate them to further development.
Hermann Muller's work on The Fertilization of Flowers by Insects and their Reciprocal Adaptations (1873), followed by subsequent works on the same lines, brought together a great number of observations on floral mechanisms and their relation to insect-visits.
In relation to the view that the spermatia are sexual cells, or at least were primitively so, it must be pointed out that although the actual fusion of the spermatial nucleus with a female nucleus has not been observed, yet in a few cases the spermatia have been seen to fuse with a projecting portion (trichogyne) of the ascogonium, as in Collema and Physcia, and there is very strong circumstantial evidence that fertilization takes place (see later in section on development of ascocarp).
As the result of fertilization of an ovum produced by this, the fern plant (sporophyte, asexual generation) originates; from it spores are ultimately set free,.
A classical biology course will cover in vitro fertilization of urchin eggs and their observation.
Identical Twins - The random occurrence of an egg splitting in two after fertilization produces identical twins.
Fertility drugs play a major role in more multiple births as well, as does in vitro fertilization (IVF).
Many mothers of twins find it is a result of in vitro fertilization or other fertility treatments, where multiple births are very common.
The modern term, IVF (in vitro fertilization), has replaced the colloquial "test tube baby" in both scientific and layman vocabularies.
Once the LH levels balanced, the doctors performed laparoscopic surgery under difficult conditions to retrieve a single egg for fertilization.
This successful and groundbreaking research soon allowed doctors to retrieve more than one egg thereby increasing the chances for viable fertilization and transfer.
Due to egg stimulation and fertilization research, the world's first test tube triplets were born in Adelaide, Australia.
This measurement is based on her conception through in-vitro fertilization, however.
While this seemed like a joyous occasion, the press soon reported that Suleman was already a mother to six young children, and that all of her kids were born as a result of In vitro fertilization.
A tie is not always required for fertilization, but if he did ride her and if someone caught them quickly enough she may not have been bred.
It's always good to get a proper tie, but one is not required to ensure fertilization.
The cycle is the result of a hormone fluctuation that signals the ovaries to release eggs for fertilization.
If you decide to breed her again, two good breedings spaced a day apart is usually sufficient to ensure fertilization, and the pups will be more equally developed at delivery time.
The dogs don't actually need to tie to ensure fertilization.
The ideal time to breed is when the bitch's ovaries begin releasing eggs for fertilization, technically referred to as ovulating.
There is a lot of conventional wisdom that says bitches should be bred on days nine through twelve to achieve fertilization.
When progesterone levels rise, so does the pituitary gland's production of lutenizing hormone, and this triggers ovulation during which the eggs are released for fertilization.
This is typically the optimum time to breed, but it should be noted that the eggs take 24 to 48 hours to mature after being released before they are actually ready for fertilization.
This is because fertilization doesn't always take place the same day as the breeding.
The key to proper soil fertilization is soil testing, which tells you how much, if any, nitrogen, phosphorus, potassium, and micronutrients your soils may need.
Many home gardeners choose to create raised beds in which to plant their gardens, as it is easier to control a small area of soil and get the proper acidity and fertilization.
Since you will probably need to plant two or three for fertilization, you should determine the proper spacing between plants.
This will let you know what varieties to plant together to aid fertilization and pollination, along with specific growing conditions.
In the instance of dichorionic-diamniotic twins, division of the fertilized egg occurs within 72 hours past fertilization, before the inner cell mass has developed.
The division of the fertilized egg in this case occurs nine to 13 days past fertilization or near the time of implantation in the uterus.
When this control fails, fertilization of more than one egg is possible.
The chance of multiple gestation with in vitro fertilization (IVF) is about the same as with the use of fertility drugs, because several embryos are inserted into the womb to increase the odds of conception.
While boys and men with CF form normal sperm and have normal levels of sex hormones, sperm are unable to leave the testes, and fertilization is not possible.
Identical, or monozygotic, twins are of the same sex and are genetically identical and physically similar, because they both come from one ovum (egg), which, after fertilization, divides in two and develops into two separate fetuses.
In vitro fertilization increases a woman's chances for having multiple birth.
One factor that may influence the distribution of multiple births is whether the state provides insurance coverage for procedures such as in vitro fertilization (IVF) and other treatments to improve fertility.
Again, as in vitro fertilization is more widely done, the incidence of multiple births will increase.
Contraception (birth control) prevents pregnancy by interfering with the normal process of ovulation, fertilization, and implantation.
There are different kinds of birth control that act at different points in the process, from ovulation through fertilization to implantation.
After an egg is released from the ovary during ovulation, fertilization (the union of sperm and egg) normally occurs in the fallopian tubes.
Preimplantation genetic diagnosis (PGD) is a relatively new technique that involves in-vitro fertilization followed by genetic testing of one cell from each developing embryo.
Most girls with Turner syndrome do not have ovaries with healthy oocytes capable of fertilization and embryo formation.
For fertilization to occur, a sperm must penetrate the tough outer membrane of the egg called the zona pellucida.
Fertilization occurs when the sperm successfully enters the ovum's membrane.
About sixty hours after fertilization, approximately sixteen cells have formed to what is called a morula, still enclosed by the zona pellucida; three days after fertilization, the morula enters the uterus.
An autosomal dominant form of VWD can be inherited from either parent or can occur as a spontaneous gene mutation (change) in the embryo that is formed when the egg and sperm cells come together during fertilization.
The problem occurs sometime shortly after fertilization; during the phase when cells are dividing rapidly.
You can figure out when you ovulate (when your eggs are ready for fertilization).
However, the couple continues to deny rumors that the child was conceived with the help of in vitro fertilization.
Implantation bleeding is light spotting probably caused when the fetus implants into the uterus a few days after fertilization, though no one is exactly sure what causes it.
For example, many experts have speculated she would be a good candidate for in vitro fertilization.
Unless you had in vitro fertilization or some other type of assisted reproduction, your conception date can be traced back to a specific sexual interaction with a man.
The pregnancy begins, of course, with conception, the fertilization of the egg with sperm.
Once fertilization occurs, however, the embryo is at risk.
If they do not achieve a pregnancy after those attempts, they may want to consider in vitro fertilization.
After treatment, couples can then use the banked sperm for in vitro fertilization procedures.
Implantation bleeding can occur six to 12 days after ovulating and fertilization.
An even greater rise following that can indicate fertilization has taken place.
Dosages are carefully timed around ovulation and subsequent avoidance of fertilization following intercourse.
With greater access to assisted reproductive techniques like in vitro fertilization and intrauterine insemination, cancer patients who are infertile have a greater chance of conceiving a child.
The embryonic age is the age of the embryo from the time of fertilization.
The Science of Male Pregnancy outlines a procedure in which a male is impregnated using in vitro fertilization.
Studies indicate that a large percentage of triplet pregnancies occur due to some type of medical intervention such as in vitro fertilization (IVF) or fertility drugs.
During in vitro fertilization, the gender of each embryo can be determined in advance of having them implanted in the uterus.
If you absolutely need to have a boy, going through in vitro fertilization is your best chance at choosing your child's gender.
After the fertilization occurs, physicians can determine the sex of the embryo even before it's implanted.
They may also prevent fertilization from taking place or interfere with implantation after fertilization occurs.
Timing intercourse for the around that time greatly increases your chances of conceiving since there is only a small window of time when fertilization can occur.
This device works to prevent fertilization by contaminating the sperm (copper ions are toxic to the sperm).
This device uses hormones to prevent fertilization.
In vitro fertilization (IVF) is often the last step for many women who have been unable to conceive through timed intercourse or intra uterine insemination (IUI).
This leaves a small window of time for fertilization.
Research continues to look at genetics and the developing chromosomes of the human embryo in hopes of reducing the number of incidences where alterations in chromosomes occur during and after fertilization.
By knowing when you are ovulating, you will know which times of the month are most likely to lead to successful fertilization of an egg.
Whether you become a mom due to good old fashioned sex, Clomid, in vitro fertilization, or adoption, it does not matter.
They'll even tell you what Clomid is and how in vitro fertilization works.
Conception is the moment the sperm penetrates the egg and fertilization occurs.
After couples receive proper testing, they may find that they are good candidates for in vitro fertilization (IVF).
The eggs and sperm are kept in an incubator and the doctor uses a microscope to observe whether fertilization occurs.
Management of infertility in women with endometriosis requires additional treatments beyond pain management, such as in vitro fertilization.
For example, the timing of the egg meeting the sperm has to be almost perfect for fertilization to occur.
These devices cause changes that make it difficult for the fertilization of an egg or implantation of an embryo to occur.
The pregnancy and ovulation calendar takes several components into consideration to predict your ideal fertilization window.
This may include procedures like invetro fertilization or certain transplants.
The two attempted a few bouts of in-vitro fertilization before conceiving child Rene-Charles Angelil in 2001.
All of Suleman's 14 children were conceived through in vitro fertilization.
Margolis has three children, one, named Nicholas, by in-vitro fertilization and twins named Sabrina and Sierra, through a surrogate mother.
The term Cryptogam is archaic, implying a hidden method of reproduction as compared with the obvious method represented by the flower of the Phanerogam; with the aid of a good microscope it is, however, easier to follow the process of fertilization.
This is easy to happen with plants dependent on insects for their fertilization.
Thus Asclepiadeae and Orchideae owe their extraordinary floral complexity to adaptation to insect fertilization.
Doncaster (1906-1907) on the eggs of sawflies, the number of chromosomes is not reduced in parthenogenetic egg-nuclei, while, in eggs capable of fertilization, the usual reduction-divisions occur.
In the first place, the continued study of human population has thrown additional light on some of the questions involved, whilst the progress of microscopical research has given us a clear foundation as to the structural facts connected with the origin of the egg-cell and sperm-cell and the process of fertilization.
Extending from the Gulf northward for one hundred and fifty miles is the outer belt of the Coastal Plain, also called the "Timber Belt," whose soil is sandy and poor, but responds well to fertilization.
Alluvial soils are almost invariably of great fertility; it is due to the alluvial mud annually deposited by the Nile that the dwellers in Egypt have been able to grow their crops for over 4000 years without artificial fertilization.
Now such a gametic (egg or sperm) constitution can only result when two individuals, all or some of whose gametes are pure with regard to the character albinism, meet in fertilization.
When, through the introduction of the male plant from Japan, its fertilization was rendered possible, ripe berries, before unknown, became common ornaments of the shrub.
Whether a spore results from the sexual union of two similar gametes (zygospore) or from the fertilization of an egg-cell by the protoplasm of a male organ (oospore); or is developed asexually as a motile (zoospore) or a quiescent body cut off from a hypha (conidium) or developed along its course (oidium or chlamydospore), or in its protoplasm (endospore), are matters of importance which have their uses in the classification and terminology of spores, though in many respects they are largely of academic interest.
The contents of the antheridium are not set free, but that organ penetrates the oogonium by means of a narrow outgrowth, the fertilizing tube, and a male nucleus then passes over into the single oosphere, which at first multinucleate becomes uninucleate before fertilization.
We thus have a process of "multiple fertilization"; the oosphere really represents a large From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.
De Bary brought forward very strong evidence for the origin of the ascocarp in Sphaerotheca and Erysiphe by a sexual process, but Harper in 1895 was the first to prove conclusively, by the observation of the nuclear fusion, that there was a definite fertilization in Sphaerotheca Humuli by the fusion of a male (antheridial) nucleus with a female, ascogonial (oogonial) nucleus.
Fertilization is external; and in about three days a small ciliated larva, not unlike that of the Echiuroids, but with no trace of segmentation, emerges from the egg-shell.
The flower is a shoot (stem bearing leaves) which has a special form associated with the special function of ensuring the fertilization of the egg and the development of fruit containing seed.
The gametophyte or prothallial generation is thus extremely reduced, consisting of but little more than the male and female sexual cells - the two sperm-cells in the pollen-tube and the egg-cell (with the synergidae) in the embryo-sac. At the period of fertilization the embryo-sac lies in close proximity tube has penetrated, the separating cell-wall becomes absorbed, and the male or sperm-cells are ejected into the embryosac. Guided by the synergidae one male-cell passes into the oosphere with which it fuses, the two nuclei uniting, while the other fuses with the definitive nucleus, or, as it is also called, the endosperm nucleus.
As in Gymnosperms and other groups an interesting qualitative change is associated with the process of fertilization.
The result of fertilization is the development of the ovule into the seed.
The fusion is now known as fertilization, and the product is an oospore.
Reproduction by conjugation is also known as isogamy, by fertilization as oogamy.
The irregular construction of the flower is connected with fertilization by insect agency.
The most probable supposition is that the cup is simply an excrescence or "enation" from the mouth of the flower-tube, and is connected with the fertilization of the flowers by insect agency.
As with other plants, so in fungi the essential process of fertilization consists in the fusion of two nuclei, but owing to the absence of well-marked sexual organs from many fungi, a peculiar interest attaches to certain nuclear fusions in the vegetative cells or in young spores of many forms. Thus in Ustilagineae the chlamydospores, and in Uredineae the teleutospores, each contain two nuclei when young, which fuse as the spores mature.
In this point and in their method of fertilization theLaboulbeniineae suggest a possible relationship of Ascomycetes and the Red Algae.
Only the females suck blood; the act is believed to be necessary for fertilization and reproduction.
Fertilization takes place as the egg is laid, the spermatozoa being ejected from the spermatheca of the female and making their way to the protoplasm of the egg through openings (rnicropyles) in its firm envelope.
Her oldest priestesses, the dew-sisters - Aglauros, Herse, Pandrosos - signify the fertilization of the earth by the dew, and were probably at one time identified with Athena, as surnames of whom both Aglauros and Pandrosos are found.
The most important work in this direction has been done by Fritz Muller (Filr Darwin), by Herman Muller (Fertilization of Plants by Insects), Grade b.
Coincidently, to allow of fertilization and the escape of excess of yolk, and of spermatozoa, other accessory ducts open at this point.
In the endoparasitic trematodes the uterus is the only passage by which fertilization can be effected, and in cases of cross and selfimpregnation this duct is physiologically a vagina.
The mouth of this chamber is protected by a ring of hairs pointing downwards, which allow the entrance but prevent the escape of small flies; after fertilization of the pistils the hairs wither.
Darwin's works on dimorphic flowers and the fertilization of orchids gave powerful support to this statement.
The Garton artificial fertilization experiments have shown endless deviations from the ordinary type, ranging from minute seeds with a closely adhering husk to big berries almost as large as sloes and about as worthless.
It should be noted that butterflies are the chief agents in securing the continued existence of such alpine flowers as depend on insect fertilization, the other insect fertilizers being mostly wanting at great heights.
The seed is enclosed when ripe in the fruit, a development of the ovary as a result of fertilization of the egg-cell.
Botanists were for a long time content to know that the scattering of the pollen from the anther, and its application to the stigma, were necessary for the production of perfect seed, but the stages of the process of fertilization remained unexplored.
There was thus very strong circumstantial evidence in favour of fertilization, although the male nucleus was not traced.
After fertilization the female cell, now called the oospore, divides and part of it develops into the embryo (new sporophyte), which remains dormant for a time still protected by the ovule which has developed to become the seed.
Consequently there were large tracts of untilled " waste " land; but these rapidly responded to fertilization and rotation of crops, often yielding Boo to 1200 lb of cotton per acre, and Georgia in 1899 used more fertilizers than any other state in the Union.
A double fertilization thus takes place.
In regard to the important structures concerned with the fertilization of the egg, Limulus and Scorpio differ entirely from one another.
In Collema and a form like Xanthoria parietina it is probable that actual fertilization takes place, and possibly also in some of the other forms. It is probable, however, that in the majority of cases the ascogonia develop without normal fertilization, as is necessarily the case where the ascogonia have no trichogynes or the spermatia are absent.
It was at one time thought that the centrosomes played an important part in the fertilization of plants, but recent researches seem to indicate that this is not so.