Pteridophyta Sentence Examples
The sporophyte is the plant which is differentiated into stem, leaf and root, which show a wonderful variety 01 form; the internal structure also shows increased complexity and variety as compared with the other group of vascular plants, the Pteridophyta.
The spores, as in the heterosporous Pteridophyta, are of two kindsmicrospores (pollen grains) borne in microsporangia (pollen sacs) on special leaves (sporophylls) known as stamens, and macrospores (embryo-sac) borne in macrosporangia (ovules) on sporophylls known as carpels.
The male gametophyte is represented by one or few cells and, except in a few primitive forms where the male cell still retains the motile character as in the Pteridophyta, is carried passively to the macrospore in a development of the pollen grain, the pollen tube.
The Spermatophyta fall into two classes, Gymncsperms (q.v.) and Angiosperms; the former are the more primitive group, appearing earlier in geological time and showing more resemblance in the course of their life-history to the Pteridophyta.
Companion cells are not found in the Pteridophyta and Gymnosperms. In the latter their place is taken by certain cells of the medullary rays and bast parenchyma.Advertisement
Thus in the series Bryophyta, Pteridophyta, Phanerogamia, whilst the sporophyte presents progressive development, the gametophyte presents continuous reduction.
Moreover, had the evolution of plants proceeded along the line of adaptation, the vegetable kingdom could not be subdivided, as it is, into the morphological groups Thallophyta, Bryophyta, Pteridophyta, Phanerogamia, but only into physiological groups, Xerophyta, Hygrophyta, Tropophyta, &c.
The development of the compound microscope rendered possible the accurate study of their life-histories; and the publication in 1851 of the results of Wilhelm Hofmeister's researches on the comparative embryology of the higher Cryptogamia shed a flood of light on their relationships to each other and to the higher plants, and supplied the basis for the distinction of the great groups Thallophyta, Bryophyta, Pteridophyta and Phanerogamae, the last named including Gymnospermae and Angiospermae.
Fungi Algae Bryophyta Pteridophyta Phanerogamia Gymnosperms Angiosperms Algae in this wide sense may be briefly described as the aggregate of those simpler forms of plant life usually devoid, like the rest of the Thallophyta, of differentiation into root, stem and leaf; but, unlike other Thallophyta, possessed of a colouring matter;.
It much more resembles the antherozoids of Bryophyta and certain Pteridophyta than any known among other algae.Advertisement
Moreover, it is known that the reduction in the number of chromosomes which occurs at the initiation of the gametophyte generation in Pteridophyta occurs of the various constituent groups.
The point common to all Pteridophyta is that from the first the gametophyte is an independent organism, while the sporophyte, though in the first stages of its development it obtains nutriment from the prothallus, becomes physiologically independent when its root develops.
The complete life-history, with its regular alternation of gametophyte and sporophyte, is now known in all except a few rare genera of recent Pteridophyta, and will be described in connexion with the several groups.
The several phyla of Pteridophyta having now been briefly described, their relationship to one another remains for con.
If, as has been suggested by Bower, the strobiloid types are relatively primitive, the large-leaved Pteridophyta must be supposed to have arisenearly from such forms. The question cannot be discussed fully here, but enough has been said above to show that in the light of our present knowledge the main phyla of the Vascular Cryptogams cannot be placed in any serial relationship to one another.Advertisement
It may even be regarded as an open question whether some of them may not have arisen independently and represent parallel lines of evolution from Bryophytic or Algal forms. This leads us to consider the question whether any indications exist as to the manner in which the Pteridophyta arose.
It is with regard to the origin of the spore-bearing generation of the Pteridophyta that differences of opinion exist.
Without entering further into the discussion of these alternative theories, for which the literature of the subject must be consulted, it may be pointed out that on the latter view the strobiloid forms of Pteridophyta would not necessarily be regarded as primitive relatively to the large-leaved forms, and also that the early stages of the origin of the sporophyte in the two cases may have proceeded on different lines.
Another question of great interest, which can only be touched upon here and may fitly close the consideration of this division of the Vegetable Kingdom, concerns the evidence as to the derivation of higher groups from the Pteridophyta.
These forms will, however, be found discussed in the articles treating of extinct plants and the Gymnosperms, but their recognition will serve to emphasize, in conclusion, the important position the Pteridophyta hold with regard to the existing flora.Advertisement
On the other hand, fern-like seed-plants, known as Pteridosperms, and Gymnosperms belonging almost entirely to families now extinct, were abundant, while the Pteridophyta attained a development exceeding anything that they can now show.
Pteridophyta, is as yet scarcely represented among known fossils of Palaeozoic age.
We must bear in mind that throughout the Palaeozoic period, and indeed far beyond it, vascular plants, so far as the existing evidence shows, were represented only by the Pteridophyta, Pteridosperms and Gymnosperms. Although the history of the Angiosperms may probably go much further back than present records show, there is no reason to suppose that they were present, as such, amongst the Palaeozoic vegetation.
If the axis of such a sporogonium were prolonged downwards into the soil to form a fixing and absorptive root, the whole structure would become a physiologically independent plant, exhibiting in many though by no means all respects the leading features of the sporophyte or ordinary vegetative and spore-bearing individual in Ptericlophytes and Phanerogams. These facts, among others, have led to the theory, plausible in some respects, of the origin of this sporophyte by descent from an Anthoceros-like sporogonium (see PTERIDOPHYTA).
The origin of the Pteridophyta (q.v.) is very obscure, but it may be regarded as certain that it is not to be sought among the mosses, which are an extremely specialized and peculiarly differentiated group. Furthermore, both the hydrom and leptom of Pteridophytes have marked peculiarities to which no parallel is to be found among the Bryophytes.Advertisement
The usually fistular pith is surrounded by a ring of collateral vascular bundle, (see Anatomy Of Plants, and Pteridophyta), each of which, with rare exceptions, has an intercellular canal at its inner edge, containing the disorganized spiral tracheae, just as in the recent genus.
The Bryophyta and Pteridophyta have sprung from the higher Thallophyta, and together form the larger group Archegoniatae, so-called from the form of the organ (archegonium) in which the egg-cell is developed.