86 A TEXT-BOOK OF BOTANY. 



PTERIDOPHYTES. 



The Pteridophytes were formerly known as the VASCULAR 

 CRYPTOGAMS. Like the Bryophytes, these plants show a distinct 

 alternation of generations ; i.e., the gametophyte or sexual genera- 

 tion alternates with the sporophyte or asexual generation. Their 

 relation is, however, somewhat changed. In the Bryophytes the 

 gametophyte is the most conspicuous and is looked upon as con- 

 stituting the plant proper, whereas in the Pteridophytes the 

 gametophyte is rather insignificant in size, while the sporophyte 

 constitutes the generation or phase which is ordinarily regarded 

 as the plant. In the higher members of the Pteridophytes the 

 sporophyte is entirely detached from the gametophyte and is able 

 to lead an independent existence. This group also shows a dis- 

 tinct advance in structure. There is a differentiation into root, 

 stem, and leaves, and the development of a system of conducting 

 tissue known as the VASCULAR SYSTEM. 



The Pteridophytes include three principal groups, namely, ( I ) 

 Filicales or Ferns, (2) Equisetales or Scouring Rushes, and (3) 

 Lycopodiales or Club Mosses, which differ considerably in general 

 appearance and general morphological characters. 



With the exception of the sperms in the Club Mosses, which 

 are biciliate and somewhat resemble those in the Bryophytes, the 

 sperms in the Pteridophytes are spirally coiled and multiciliate, 

 and according to the number of cilia of the sperms some writers 

 divide the Pteridophytes into two classes, namely, biciliate and 

 pluriciliate (Figs. 51, C; 62, F). 



Some of the Pteridophytes, as Selaginella (Fig. 60), are dis- 

 tinguished by the fact that they produce two kinds of asexual 

 spores, which are known respectively as MICROSPORES (Fig. 60, 

 F) and MEGASPORES (Fig. 60, E). The two kinds of spores are 

 formed in separate sporangia, which organs may occur on the 

 same plant or on different plants. The sporangia have the cor- 

 responding names, microsporangia (Fig. 60, B, i) and megaspor- 

 angia (Fig. 60, B,g). This differentiation in sporangia and spores 

 also leads to a differentiation in the resulting gametophytes, the 

 microspores giving rise to gametophytes which produce antheridia, 

 and hence called male gametophytes; and the megaspores to 



