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.
Sessiliflora, after fertilization, enlarged.
The subject of fertilization was one which early excited attention.
Recent Work on the Results of Fertilization in Angiosperms, Ann.
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.
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.
Modern experiments in cross-fertilization in Lancashire by the Garton Brothers have evolved the most extraordinary "sports," showing, it is claimed, that the plant has probably passed through stages of which until the present day there had been no conception.
The spermatogenesis and maturation and fertilization of the germ-cells present nothing out of the common and need not be C.
This is a necessary consequence of the fusion of two nuclei in fertilization, unless the chromosomes are to be doubled at each generation.
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.
Only where there is no such struggle for existence does self-fertilization often prove satisfactory for many generations."
In subsequent generations produced by self-fertilization of the hybrids it was found that the positive character was not present in all the individuals, but that a result was obtained showing that in the formation of the reproductive cells (ova and sperms) of the hybrid, half were endowed with the positive character and half with the negative.
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.
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.
4, B, C, D), it appears to take no part in the fertilization phenomena, nor in the subsequent division of the nucleus.
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 irregular construction of the flower is connected with fertilization by insect agency.
The anthers are so situated that the pollen on escaping comes into contact with the stigma; in such flowers self-fertilization is compulsory and very effectual, as seeds in profusion are produced.
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 greatest difference of opinion exists among botanists as to their number and the bounds to be assigned to each; and the cross-fertilization that takes place between the species intensifies the difficulty.
Angulata) have the sexes separate, and fertilization is effected in the open water after the discharge of the ova and the spermatozoa from the females and males respectively.
Only the females suck blood; the act is believed to be necessary for fertilization and reproduction.
See Darwin's Fertilization of Orchids and similar works.
Culture of classical ages was slightly more developed in Greece so far as the husbandman of Greece and Rome was less able to leave to nature the fertilization of the soil.
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.
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.
The proboscis, passing down this groove to the spur, becomes dusted with pollen; as it is drawn back, it presses up the lip-like valve of the stigma so that no pollen can enter the stigmatic chamber; but as it enters the next flower it leaves some pollen on the upper surface of the valve, and thus cross-fertilization is effected.
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.
Do not ripen their fruit owing to imperfect fertilization, - is to be sought in this natural tendency to dioecism.
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.
They differ structurally from the normal form in being capable of self-fertilization only, and in the shape and details of their spermatozoa.
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.
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.
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.
In 1799 an Englishman, Thomas Andrew Knight, after experiments on the cross-fertilization of cultivated plants, formulated the conclusion that no plant fertilizes itself through many generations.
Darwin's works on dimorphic flowers and the fertilization of orchids gave powerful support to this statement.
The female lays two kinds of eggs - " summer-eggs," which develop without fertilization, and " winter-eggs" or resting eggs, which require to be fertilized.
Sexes separate, fertilization by spermatophores.
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.
There was thus very strong circumstantial evidence in favour of fertilization, although the male nucleus was not traced.
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.
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.
The seed is enclosed when ripe in the fruit, a development of the ovary as a result of fertilization of the egg-cell.
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.
With another similar protoplast, which constitutes what we call fertilization, the next stage in complexity already noted may be observed, the protoplasm becoming clothed by a cell-membrane.
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.
The observations of Darwin as to the fertilization of orchids, Primula, Linum and Lythrum, and other plants, and the part which insects take in this function, gave an explanation of the observations of Christian Konrad Sprengel, made at the close of the 18th century, and opened up a new phase in the study of botany, which has been followed by Hermann Miller, Federico Delphic) and others, and more recently by Paul Knuth.
Fertilization.The formation of the zygote or egg-cell takes place usually by the fusion of the contents of two cells, and always includes, as -
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.