"There is however no reason to doubt that the fossil plants known from the different formations of our earth may all be referred to the great classes of the vegetable kingdom distinguished at the present day, viz.: the thallogens, including such plants as lichens, algae, and fungi; the acrogens, such as ferns and lycopods; the gymnosperms, such as cone-bearing plants and cycads; the endogens, such" . . . .