DISTRIBUTION OF FOSSIL FERNS. 349 



From the above considerations as to the characters and 

 distribution of living Ferns, M. Ad. Brongniart has applied 

 himself with much ingenuity, to illustrate the varying condi- 

 tion and climate of our Globe, during the successive periods 

 of geological formations. Finding that the fossil remains of 

 Ferns decrease continually in number, as we ascend from 

 the most ancient to the most recent strata, he founds upon 

 this fact an important conjecture, with respect to the succes- 

 sive diminutions of temperature, and changes of climate, 

 which the earth has undergone. Thus, in the great Coal 

 formation there are about 120 known species of Ferns, form- 

 ing almost one half of the entire known Flora of this forma- 

 tion ; these species represent but a small number of the forms 

 which occur among living Ferns, and nearly all belong to 

 the Tribe of Polypodiaceje, in which Tribe we find the 

 greater number of existing arborescent species.* Frag- 

 ments of the stems of arborescent Ferns occur occasionally 

 in the same formation. M. Brongniart considers these cir- 

 cumstances as indicating a vegetation, analogous to that of 

 the Islands in the equinoctial regions of the present Earth : 

 and infers that the same conditions of Heat and Humidity 

 which favour the existing vegetation of these islands, pre- 

 vailed in still greater degree during the formation of the 

 ■Carboniferous strata of the Transition Series. 



hemisphere, and one species is found in New Zealand as far south as lat. 

 46°. See Brown in Appendix to Flinder's Voyage. 



* In Plate 1, figs. 7, and 37, represent two of tlie graceful forms of 

 arborescent Ferns whicli adorn our modern tropics, where they attain the 

 height of forty and fifty feet. 



An arborescent Fern forty-five feet high (Asophila brunoniana,) from 

 Silhet in Bengal, may be seen in the staircase of the British JJuseum. 

 The stems of these Ferns are distinguished from those of all arborescent 

 MonocotyledonoMs plants, by the peculiar form and disposition of the 

 scars, from which the Petioles or leaf stalks have fallen off. In Palms 

 and other arborescent Monocotyledons, the leaves, or Petioles, embrace 

 the stem and leave broad transverse scars, or rings, whose longer diame- 

 ter is horizontal. In the case of Ferns alone, wilh the single exception 



VOL. I. — 30 



