DIVISION IV. 



PTERIDOPHYTA. 



CHAPTER XXXI. 



FILICALES. 



The Pteridophyta include the Club-Mosses (Lycopodiales), the 

 Horse-tails (Equisetales), and the Ferns (Filicales), together with 

 certain other less familiar types of Plants, some of which are only 

 known as Fossils. All of these Classes were represented in the 

 Palaeozoic Period : there is thus no doubt of their extreme antiquity, 

 which is shown by their characters as well as by their history. 

 They differ from the Bryophyta in that the leafy " Plant " is the 

 diploid generation or Sporophyte, and it bears spores : whereas 

 in Mosses and Liverworts the " Plant " is the haploid or sexual 

 generation, and it has been seen that it bears antheridia and 

 archegonia. 



A difference in proportion of the leaves of the sporophyte plant Is 

 very marked among the Pteridophyta. In the Lycopodiales and Equi- 

 setales the leaves are small (microphyllous), and the axis rela- 

 tively large (Figs. 404A-406, 413A). But in the Filicales the leaves 

 are relatively large (megaphyllous) , and often highly branched, giving 

 the well-known character of the foliage of Ferns (Figs. 354, 373). In 

 both the shoot is traversed by a conducting system of vascular tissue, 

 often highly elaborated, and accordingly the whole Division has 

 sometimes been styled the Vascular Cryptogams. In all of them the 

 gametophyte is relatively inconspicuous, and is described as the 

 Prothallus. The life-cycle is essentially uniform for them all. and 

 their natural relationship may be accepted, notwithstanding the 

 differences which distinguish the several Classes of them. For the 



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