56 BOTANY AND PHARMACOGNOSY. 



the gametophyte is rather insignificant in size, while the sporo- 

 phyte constitutes the generation or phase whicli is ordinarily 

 regarded as the plant. In the higher members of the Pterido- 

 phytes the sporophyte is entirely detached from the gametophyte 

 and is able to lead an independent existence. This group also 

 shows a distinct advance in structure. There is a differentiation 

 into root, stem and leaves, and the development of a system of 

 conducting tissue known as the v.\scular system. 



The Pteridophytes include three principal groups, namely, 

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

 (3) Lycopodiales or Clul) 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. 34, C ; 43, F). 



Some of the Pteridophytes, as Selaginella (Fig. 41), are dis- 

 tinguished by the fact that they produce- two kinds of asexual 

 spores, which are known respectively as microspores (Fig. 41, 

 F) and megaspores (Fig. 41, 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. 41) and megasporangia 

 (Fig. 41). 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 gametophytes 

 which give rise to archegonia, and hence called female gameto- 

 phytes. When a plant produces both microspores and mega- 

 spores it is said to be heterosporous, as in SclagincUa (Figs. 41, 

 43, 44) ; while one that produces but one kind of sporangium and 

 one kind of asexual spores is said to be isosporous. In this con- 

 nection attention should be called to the fact that the spores from 

 a single sporangium of an isosporous plant may give rise to male 

 and female gametophytes, which shows that a certain degree of 

 differentiation in the spores has already taken place. The causes 



