Asexual reproductive cells are not infrequent, but sexual reproduction even in its initial stages is unknown.
Sexual and asexual reproduction prevail.
It will be remembered that, as in most Florideae, the male, female and asexual plants are distinct in this genus.
He divided plants into sexual and asexual, the former being Phanerogamous or flowering, and the latter Cryptogamous or flowerless.
The asexual organs in the case of Cutleria multifida arise on a crustaceous form, Aglaozonia reptans, formerly considered to be a distinct species.
The spore-bearing generation may throughout its phylogenetic history have been independent at one part of its life, and have been derived by modification of individuals homologous with those of the sexual generation, and not by the progressive sterilization of a structure the whole of which was originally devoted to asexual reproduction.
As a rule the asexual cells, and the male and female sexual cells arise upon different plants, so that the species may be said to be trioecious.
Reproduction is both asexual and sexual.
Asexual reproduction universal.
The asexual cells are termed tetraspores on account of the usual occurrence of four in each sporangium.
ferns, horse-tails, club mosses, &c., and Phanerogams or Flowering Plants) the main plant-body, that which we speak of in ordinary language as the plant, is called the sporophyte because it bears the asexual reproductive cells or spores.
Many Euchlorophyceae are endowed with both asexual and sexual reproduction.
Thus in Lemaneaceae asexual spores are unknown; in Batracho-spermum, Bonnemaisonia and Polysiphonia byssoides both kinds of sexual cells appear on the same plant; and in some cases the asexual cells may occur in conjunction with either the male or female sexual cells.
The asexual cells are immotile spores arising in fours in sporangia from superficial cells of the thallus.
Sexual reproduction as above, asexual by sporangia or conidia or both: Mucoraceae.
The Ascomycetes, at least the Carpoascomycetes, exhibit a well-marked alternation of sexual and asexual generations.
Here the asexual cells are borne upon the so-called Aglaozonia reptans and the sexual cells upon the plants known as Cutleria.
Von Linstow has indeed suggested that Gyrodactylus is a larval form capable of reproduction by an asexual method.
Zoospores are of two kinds: (I) Those which come to rest and germinate to form a new plant; these are asexual and are zoospores proper.
From a comparison of those Euchlorophyceae which have been most closely investigated, it appears probable that sexual reproductive cells have in the course of evolution arisen as the result of specialization among asexual reproductive cells, and that in turn oogamous reproduction has arisen as the result of differentiation of the two conjugating cells into the smaller male gamete and the larger male gamete.
When a species resorts to both methods, it is generally found that the asexual method prevails in the early part of the vegetative period and the sexual towards the close of that period.
In one view they are mere asexual conidia, and the term pycnoconidia is accordingly applied since they are borne in structures like the non-sexual pycnidia of other fungi.
Reproduction is mainly asexual, the females producing living young without the agency of a male.
True reproduction of the asexual kind occurs, however, in the formation of sporangia, particularly in the Chamaesiphonaceae.
Such are Coleochaete, Oedogonium, Cylindrocapsa, Ulothrix, Vaucheria, Volvox, &c. In others only the asexual method is yet known.
It will be remembered that in M usci, the asexual spore somewhat similarly gives rise to a protonema, from which the adult plant is produced as a lateral bud.
Fucaceae are marked by an entire absence of the asexual method.
The discovery by Brebner of the specific identity of Haplospora globosa and Scaphospora speciosa marks an important step in the advance of our knowledge of the group. Three kinds of reproductive organs are known: first, sporangia, which each give rise to a single tetra-, or multi-nucleate non-motile, probably asexual spore; second, plurilocular sporangia, which are probably antheridia, generating antherozoids; and third, sporangia, which are probably oogonia, giving rise to single uninucleate non-motile oospheres.
It would thus seem that the explanation of the existence of two kinds of sporangia, unilocular and plurilocular, among Phaeosporeae, lies in the fact that unilocular sporangia are for asexual reproduction, and that plurilocular sporangia are gametangia - potential or actual.
Among the Polychaeta the sexual worm is often more marked from the asexual form, so much so that these latter have been placed in different species or even genera.
While the spore of Bryophyta on germination gives rise to the sexual plant, the carpospore of the alga may give rise on germination to a plant bearing a second sort of asexual cells, viz.
Asexual reproduction only in Naids.
They are characterized especially by the zygospores, but the asexual organs (sporangia) exhibit interesting series of changes, beginning with the typical sporangium of Mucor containing numerous endospores, passing to cases where, as in Thamnidium, these are accompanied with more numerous small sporangia (sporangioles) containing few spores, and thence to Chaetocladium and Piptocephalis, where the sporangioles form but one spore and fall and germinate as a whole; that is to say, the monosporous sporangium has become a conidium, and Brefeld regarded these and similar series of changes as explaining the relation of ascus to conidium in higher fungi.
No asexual generation.
Sexual reproduction by oogonia and antheridia; asexual reproduction by zoospores or conidia.
The cycle of development taken by the Malacocotylea has been generally regarded as an alternation of one or more asexual generations with a sexual one.
Mycelium well developed; sexual reproduction by zygospores; asexual reproduction by sporangia and conidia.
Elsewhere among Siphonales, in those cases where reproductive cells are known, the reproduction is either isogamous or asexual.
Mottier's observation has been confirmed by Lloyd Williams, who has shown, moreover, that the single number occurs in germlings from the tetraspore, and also in the adult stages of all sexual plants, while the double number occurs in germlings from the oospore, and in adult stages of all asexual plants.
For starters, there were only three options, leaving those who identify as pansexual or asexual or something else somewhat adrift.
asexual reproduction, each cell of a colony divides twice to form a daughter colony.
asexual spores 10 to 60 minutes later.
asexual blood stages of malaria parasites.
asexual division but a variety of types of sexual reproduction are also known.
asexual life cycle of Bgh on the host proceeds in a highly ordered fashion.
He also made the first man given a personality in the bible in his image, and he was not asexual.
Understand that in asexual reproduction mitosis produces identical offspring (clones ).
Clonal propagation -- asexual reproduction, including vegetative spread, producing a clone of the parent plant.
Vegetative reproduction - a reproductive process that is asexual and so does not involve a recombination of genetic material.
Clone -- group of plants with the same genetic makeup, derived from asexual reproduction.
sporangiumerent types of asexual ' spores ' called sporangia and chlamydospores are formed.
Fruiting bodies take 4 to 6 hours to develop and they can start releasing asexual spores 10 to 60 minutes later.
wind-borne asexual spores and the dormant phase is as mycelium in dead leaf matter during frosty or dry summer conditions.
Two great divisions are recognized in the Fungi: (i.) the Pycomycetes or Algal Fungi, which retain a definitely sexual method of reproduction as well as asexual (vegetative) methods, and (ii.) the Mycomycetes, characterized by extremely reduced or very doubtful sexual reproduction.
The co-existence of the asexual encysted form and the sexually mature adult in the same host, exceptionally found in 011ulanus and other Nematodes, is the rule in Trichinella; many of the embryos, however, are extruded with the faeces, and complete the life cycle by reaching the alimentary canal of rats and swine which frequently devour human ordure Swine become infested with Trichinella in this way and also by eating the dead bodies of rats, and the parasite is conveyed to the body of man along with the flesh of "trichinized" swine.
Both sexual and asexual reproduction occur, but there is usually no definite succession of the two modes, marking that alternation of sexual generation (gametophyte) and asexual generation (sporophyte) which characterizes the higher groups.
The asexual or indifferent type (fig.
Finally, Simpson has measured the correlation between the pairs of young produced by the simple asexual division, of Paramoecium (Biometrika, vol.
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,.
Two different types of asexual ' spores ' called sporangia and chlamydospores are formed.
It is transmitted by wind-borne asexual spores and the dormant phase is as mycelium in dead leaf matter during frosty or dry summer conditions.
Scientists worried about the survival of the race rush their cloning program, and hurry into asexual reproduction to maintain humanity in the face of the threat.
The scheme of Brefeld, which was based on the view that the Ascomycetes and Basidiomycetes were completely asexual and that these two groups had been derived from one division (Zygomycetes) of the Phycomycetes, has been very widely accepted.
Both asexual and sexual reproduction occur among Euphaeophyceae.
With certain rare exceptions the Saccharomycetes have three methods of asexual reproduction: I.
The root is an axis which never bears either leaves or the proper reproductive organs (whether sexual or asexual) of the plant.
It has been men, tioned that in the Nereids a sexual form occurs which differs structurally from the asexual worms, and was originally placed in a separate genus, Heteronereis; hence the name "Heteronereid" for the sexual worm.
On this view, therefore, at least two asexual generations (embryo and scolex) alternate with a sexual one (proglottides); and in the case of Staphylocystis the cyst contains two asexually produced generations, so that in such forms three stages (embryo, primary scolex-buds, secondary scolices) intervene between the proglottis of a Cestode and that of its offspring.
The green (or blue-green) cells were termed gonidia by Wallroth, who looked upon them as asexual reproductive cells, but when it was later realized that they were not reproductive elements they were considered as mere outgrowths of the hyphae of the thallus which had developed chlorophyll.
They belong to the group of Protozoa, and, as already explained, have a double cycle of existence: (I) a sexual cycle in the body of the mosquito, (2) an asexual cycle in the blood of human beings.
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