In Characeae no fewer than four methods of vegetative reproduction have been described, and the facility with which buds and branches are in these cases detached has been adduced as an evidence of affinity with Bryophyta, which, as a class, are distinguished by their ready resort to vegetative reproduction.
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.
The Mosses and Liverworts include forms with a more or less leaf-like thallus, such as many of the liverworts, and forms in which the plant shows a differentiation into a stem bearing remarkably simple leaves, as in the true mosses.
IFor the histology of the comparatively simple but in many respects aberrant Bog-mosses (Sphagnaceae), see BRYOPHYTA.] The stems of the other mosses resemble one another in their main histological features.
For instance, all the leaves of the Bryophyta are generally homologous inasmuch as they are all developments of the gametophyte.
Thus in the series Bryophyta, Pteridophyta, Phanerogamia, whilst the sporophyte presents progressive development, the gametophyte presents continuous reduction.
In illustration of the indirect response, the evolution of the Bryophyta and of more highly organized plants may be briefly considered.
Full morphological and organographical details are given in the articles on the various groups of plants, such as those on the Algae, Bryophyta, Pteridophyta, Angiosperms, Gymnosperms, &c. The following works may also be consulted:
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 is true that certain Bryophyta (Marchantiaceae, Anthoceroteae) possess a thalloid structure similar to that of Thallophyta, and are at the same time possessed of the colouring matter of the Green Algae.
It much more resembles the antherozoids of Bryophyta and certain Pteridophyta than any known among other algae.
There is here obviously a certain parallelism with the case of Bryophyta, where the sporogonium arising from the oospore is epiphytic and partially parasitic upon the female plant, and always culminates in the production of spores.
Excluding Bangiaceae, however, from consideration, the Euflorideae present in the product of the development of the oospore like Bryophyta a structure partly sterile and partly fertile.
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.
It is possible, however, that the tetraspore formation should be regarded as comparable with the prolific vegetative reproduction of Bryophyta, and in favour of this view there is the fact that the tetraspores originate on the thallus in a different way from carpospores with which the spores of Bryophyta are in the first place to be compared; moreover, in certain Nemalionales the production of tetraspores does not occur, and the difficulty referred to does not arise in such cases.
Upon the evidence it would seem therefore that so far as Nemalion is concerned an alternation occurs comparable with that existing in the lower Bryophyta where the sporophyte is relatively small, being attached to and to some extent parasitic upon the gametophyte.
Considering, however, that it is generally believed that Bryophyta and vascular plants are descended from an algal ancestry, it is natural to suppose that, prior to the luxuriant vegetable growths of the Carboniferous period, there must have existed an age of algae.
The Gymnosperms, with the Angiosperms, constitute the existing groups of seed-bearing plants or Phanerogams: the importance of the seed as a distinguishing feature in the plant kingdom may be emphasized by the use of the designation Spermophyta for these two groups, in contrast to the Pteridophyta and Bryophyta in which true seeds are unknown.
Among the lower classes of plants we have scarcely any knowledge of Palaeozoic Bryophyta; Fungi were probably abundant, but their remains give us little information; while, even among the Algae, which are better represented, well characterized specimens are scanty.
The important class of the Bryophyta, which, on theoretical grounds, is commonly regarded as more primitive than the.
It may be regarded as derived from a wholly dependent sporogonium not unlike that of some of the simpler Bryophyta; the latter are assumed to have arisen from primitive Algal forms, in which, as the first step in the interpolation of the second generation in the life cycle, the fertilized ovum gave rise to a group of swarm spores, each of which developed into a new sexual plant.
Oedogonium, Coleochaete), the Bryophyta, and the simpler Pteridophyta, such as Phylloglossum, have been regarded as illustrating the method of progression, though there is no reason to regard the existing forms as constituting an actual series.
On the one hand from the Bryophyta (in which the sporophyte is throughout its life attached to the gametophyte), and on the other hand from the Gymnosperms and Angiosperms (in which the more or less reduced gametophyte remains enclosed within the tissues of the sporophyte).