THE PTERIDOPHYTES. The rise and decline of this sub-kingdom of plants comprises One of the most remarkable chapters in the life history of the earth. Pteridophytes probably originated in the Lower Silurian period. although their earli est well-defined remains are from the Devonian. During the Carboniferous period they attained a position which, in respect of actual and relative numbers and high degree of development as a type, has no parallel in the vegetable kingdom; but since that period the sub-kingdom as a whole has steadily declined numerically, and it has also undergone profound biologic degeneration. The ferns are probably the best kmo‘n of the fossil pteridophytes. They were important ele ments in the Devonian flora, and reached a maxi mum of development in the Carboniferous period, at which time they apparently formed about 50 per cent. of the entire flora ; they declined to about 30 per cent. in Mesozoic time, and in Cenozoic time to less than 6 per cent. All the Paleozoic genera (Neuropteris, Pecopteris. Sphenopteris. etc.) are extinct, and so probably are most of those of Mesozoic time, although a number of the latter are considered to be identical with living ones. Tertiary forms are generally re garded as generically and in many cases spe cifically, the same as existing forms.
Rhizocarps. inconspicuous both in size and in numbers at the present time, are but poorly rep resented as fossils, even if all doubtful forms are included. They probably made their first ap pearance during Devonian time. A number of undoubted species of Salvinia are known from Cretaceous and Tertiary deposits of North Amer ica and Europe. The Equisetum type had its
beginning in the Devonian. and perhaps earlier. The remains consist of trunks or stems, leafy branches or fructifications, which are known under the generic name, Calamites. Calamoden drou. Asterophyllites, Calamo,tachys, et.. They attained their maximum of evolution during the Carboniferous period, at which time they formed probably 11) per cent, of the flora. These genera became extinct at the close of Paleozoic time and were succeeded by the Mesozoic genera Schizo neuron, Phyllotheca, etc., and Equisetnin, which latter has continued, through forms which stead ily decreased in numbers and size, down to the present time.
Lycopods were represented very early in geo logic time, probably in the Upper Silurian period or even earlier, but reached their highest develop ment during the Carboniferoms, contributing about 15 per cent. to the flora of that period. Their remains are represented mostly by trunks and limbs. under the generic names of Lephloden dron. Lepidophloios. Knorria. etc.: by the fruit ing spikes. under Lepidostrobus: by foliar organs. under Lepidophyllum. etc. These genera beeaine extinct at the same time with the other pterido phyte genera of Paleozoic time. and were suc ceeded by degenerate descendants which are either identical with or closely related to the living genera 1..yel)podium and Selaginella.