In general structure they approach the Phanerogams with which they form collectively the Vascular Plants as contrasted with the Cellular PlantsThallophyta and Bryophyta.
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.
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.
