Griffith's general views of the reproduction of all the Vascular Cryptogams was necessarily wrong, since the prime clue of the recognition of the prothallus and plant as distinct had not been found.
We learn from the science of petrifactions much more than we do in the case of Mosses of the importance which the second branch of Prothallus plants--that is, Ferns--have had in the history of the vegetable world.
The group of Prothallus plants, on the other hand, comprises the two branches of Mosses and Ferns, containing a great variety of forms.
In this the Prothallus plants resemble the Flowering plants, and hence the two groups have recently often been classed together as stemmed plants, or Cormophytes.
Spores of only one kind; prothallus bearing antheridia and archegonia.
In germination they develop a minute prothallus which bears archegonia to be fertilized by antherozoids developed from the microspores.
Spores of two kinds, the macrospore producing a prothallus with archegonia, the microspore smaller and developing antheridia.
I have already described how either side of the prothallus of a fern may be made to produce male or female organs, according as it is kept in the light or in the dark.
When the prothallus of a fern has developed normally, it is a flattened leaf-like structure which bears rootlets and male and female genital organs on the lower surface, i.
They are always borne on the lower side next the ground, or next whatever the prothallus may be growing on.
This green cushiony prothallus keeps on growing, its heart-shaped mass becoming divided into an obviously left and right hand side and the rhizoids multiplying in number.
Near the notch of the heart-shaped prothallus are developed a few flask-shaped bodies which contain within them an egg cell or single ovum, the female reproductive body.
These are shed, develop into a protonema which is followed by the prothallus and from this the young moss plant develops.
These spores will produce the prothallusagain when sown.
When these are ripe the body of the prothallus and all its constituent cells fall a prey to natural death.
In the prothallus of many of the higher cryptogams, the formation of a single embryo is followed by natural death; as Goebel[82] points out, the embryo completely absorbs the 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.
The prothallus which arises from the megaspore in the Selaginella closely resembles the endosperm--a special tissue formed to feed the embryo in the case of flowering plants.
It is obviously important that the male and the female prothallus should be together.
However that may be, as soon as the underside of the prothallus has become thoroughly wetted the antheridia open, and certain little bodies called spermatozoids are allowed to escape.
Even then, several more years elapse before the prothallusis sufficiently mature to bear the organs of sex.
In most of the cases where the development of the spore is such a long business the prothallus is produced underground.
The prothallus and the male organ (antheridium) are comparable to the special cell-group in the pollen-grain, whilst the spermatozoids approximate to the generative cells.
That of the male prothallus is usually rather small; on the other hand, the female prothallus is sometimes large, and may have complicated branchings.
As a rule, too, in the prothallus only one of the archegonia shows any further signs of development.
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.
The prothallus is exceedingly small, being little more than a group of cells forming an antheridium.
The prothallus is a small underground body destitute of chlorophyll.
For a while the newly-born Fern relies upon the prothallus for sustenance, but eventually starts an independent existence.
Microspore spherical or oval, with or without a bladder-like extension of the exine, containing a prothallus of two or more cells, one of which produces two non-motile or motile male cells.
A mature pollen-grain contains a prothallus of 3 to 5 cells (Fig.
The genus Ephedra, with its prothallus and archegonia, which are similar to those of other Gymnosperms, may be safely regarded as the most primitive of the Gnetales.
Lotsy has described the occurrence of special cells at the apex of the prothallus of Gnetum Gnemon, which he regards as imperfect archegonia (fig.
Similarly in the Araucarieae and in Widdringtonia the archegonia are numerous and scattered and often sunk in the prothallus tissue.
A young prothallus of a Maiden-hair, moderately enlarged, and an older one with the first fern-leaf developed from near the notch.
Investigation of this prothallus under the microscope resulted in the discovery of a wholly unsuspected kind of fertilization, taking place at this germinating stage of the plant.
On the under side of the prothallus two kinds of organs appear (Fig.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "prothallus" in a variety of sentences. We hope that you will now be able to make sentences using this word.
