CHAPTER XXVII 

 PTERIDOPHYTES 



Tins group is much more highly differentiated than the pre- 

 ceding in that we now find true roots, stems and leaves com- 

 posed of tissues very similar to those found in the higher plants, 

 although the arrangement differs in some degree. They are 

 very similar to the Bryophytes in that they possess alternation 

 of generations, but in this group the Sporophyte is larger than 

 the Gametophyte and becomes entirely independent of it. 



The archegonium is also a characteristic organ and very 

 similar to that found in the Bryophytes. We have already called 

 attention to the fact that the Bryophytes and Pteridophytes are 

 sometimes referred to as the archegoniates. Owing to the fact 

 that the Pteridophytes contain fibro-vascular tissues, they are 

 sometimes referred to as the vascular cryptogams.* This group 

 was no doubt much larger in past ages than at the present time 

 and may have been an important factor in the formation of the 

 great beds of coal. Some of the ancient species were very 

 large, in fact, tree-like in size and appearance. The group 

 includes: (1) Lycopodales or club mosses, (2) the Equise- 

 tales or horsetails or scouring brushes, (3) Filicales or true 

 ferns (Fig. 143) and some smaller divisions. We will omit the 

 first group. 



The Gametophyte generation of a true fern (Fig. 144) is a 

 small thallus structure resembling a liverwort and known as the 

 prothallus. It lies flat on the ground and has numerous rhizoids. 

 In some species the prothallia are monoecious and in others di- 

 oecious. The archegonia are borne on the under surface of the 

 prothallium, the body or center embedded in the thallus and the 



* Cryptogam is an old term meaning " hidden marriage," and is used to 

 include all plants other than the Spermatophytes. 



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