Only by the complicated method of first a spore then the prothallus, from which archegonia and antheridia are produced, followed by the free swimming male cells fertilizing the female, can a fern reproduce itself.
The female branches are found mostly toward the upper end of the plant and bear the archegonia at their extremities.
The megaspore is filled with tissue as in typical Gymnosperms, and from some of the superficial cells 3 to 5 archegonia are developed, characterized by long multicellular necks.
In Libocedrus decurrens (Cupressineae) Lawson describes the archegonia as varying in number from 6 to 24 (Annals of Botany xxi.
A large pollen-chamber occupies the apex of the nucellus; immediately below this, two or more archegonia (fig.
Lotsy has described the occurrence of special cells at the apex of the prothallus of Gnetum Gnemon, which he regards as imperfect archegonia (fig.
The egg-cells of the archegonia may be in lateral contact (e.
The megaspore becomes filled with tissue (prothallus), and from some of the superficial cells archegonia are produced, usually three to five in number, but in rare cases ten to twenty or even sixty may be present.
Similarly in the Araucarieae and in Widdringtonia the archegonia are numerous and scattered and often sunk in the prothallus tissue.
Defn: A minute jointed filament growing among the archegonia and antheridia of mosses, or with the spore cases, etc.
Defn: Having stamens and pistil in the same head, or, in mosses, having antheridia and archegonia on the same receptacle.
A minute jointed filament growing among the archegonia and antheridia of mosses, or with the spore cases, etc.
Having stamens and pistil in the same head, or, in mosses, having antheridia and archegonia on the same receptacle.
The archegonia he describes as ovules without envelopes consisting of a papilla (the neck) which becomes perforated, giving the spermatozoid access to the embryo-sac within.
For some little time after these discoveries the archegonia of the fern were, on the initiative of Mercklin, commonly referred to as the "organs of Suminski," a custom which happily fell into desuetude.
The sexual organs are borne on the upper surface, and both antheridia and archegonia occur on the same branch (fig.
Marchantia) the archegoniophore corresponds to the repeatedly branched continuation of the thallus, and the archegonia arise in relation to the growing points which are displaced to the lower surface of the disk.
The sexual organs are developed in groups at the apices, the antheridial group usually terminating the main axis while the archegonia are borne on a lateral branch.
The archegonia are protected by being sunk in depressions of the disk or by a special two-lipped involucre.
The necks of the archegonia hardly project above the general surface of the thallus.
In addition special involucres around thearchegonia have arisen independently in several series.
The archegonia (ar) are developed in a group behind the apex, and the latter continues to grow for a time after their formation, so that they come to be seated in a depression of the upper surface.
Other adaptations concern the protection of the sexual organs and sporogonia, and the retention of water in the neighbourhood of the archegonia to enable the spermatozoid to reach the ovum.
In the Acrogynous Jungermanniaceae the plant is throughout foliose, and the archegonia occupy the ends of the main shoot or of its branches.
Their general similarity to the mature antheridia and archegonia of liverworts and the main difference in their development have been referred to.
The archegonia are borne at the apex of the main stem or of a lateral branch.
Lastly Haplomitrium, a rare British genus, forms with the exotic Calobryum, an isolated group which is most naturally placed among the anacrogynous forms although the archegonia are in terminal groups.
Plants with cellular tissue only; both antheridia andarchegonia borne upon the plant itself.
In germination they develop a minute prothallus which bears archegonia to be fertilized by antherozoids developed from the microspores.
Monoecious, with 2 antheridia in each leaf of a spike-like branch, and the archegonia mostly solitary.
After the archegonia are fertilized the outer parts of the ovule become hard and brown, and serve to protect the embryo plant, which reaches a considerable size before the sporangium falls off.
In the seed plants the macrosporangia remain attached to the parent plant, in nearly all cases, until the archegonia are fertilized and the embryo plant formed.
In studying the development of the antheridia, it is only necessary to mount the plants in water and examine them directly; but the study of the archegonia requires careful longitudinal sections of the prothallium.
After a time growth ceases, and is not resumed until the development of the female prothallium and archegonia is nearly complete, which does not occur until more than a year from the time the pollen spore first reaches the ovule.
Those containing the young archegonia are very small; but after one has been fertilized, the leaves enclosing it grow much larger, and the bud becomes quite conspicuous, being surrounded by two or three comparatively large leaves.
In the upper part of the prothallium several large archegonia are formed in much the same way as in the pteridophytes.
The archegonia have a shorter neck than those of the ferns, and the neck is straight.
The archegonia arise from cells of the lower surface, just behind the notch in front (Fig.
By dissecting the young buds, archegonia in all stages of growth may be found.
The latter gives rise to a flat disc of cells producing a number of small archegonia of simple structure (Fig.
Previous to their formation the cells at this point divide by walls parallel to the surface of the plant, so as to form several layers of cells, and from the lowest layer of cells the archegonia arise.
From the underside arise more root hairs, and it is here also that the antheridia (male organs) and the archegonia (female organs) are produced.
At the mouth of the archegonia there is a viscid drop which almost certainly contains chemical substances attractive to the spermatozoids.
In the case of a perfectly normal prothallus the male organs or antheridia are to be found amongst the root hairs, whilst the female organs or archegonia arise from a cushion, several cells deep, more towards the centre of the process.
These are very active, and travel through the agency of water to the archegonia on the female prothallus.
Should there be sufficient moisture about, the spermatozoids which are produced by the antheridium swim towards the archegonia in any female prothallus which may be near.
As a rule, too, in the prothallus only one of the archegonia shows any further signs of development.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "archegonia" in a variety of sentences. We hope that you will now be able to make sentences using this word.
