CHAPTER FORTY-FOUR 



THE PTERIDOPHYTES 



The Pteridophytes (Greek: pteris, fern, 

 phyton, plant) include a series of several phyla 

 that have formed a conspicuous part of the 

 earth's vegetation since Paleozoic times. The 

 prevailing modern representatives of these 

 ancient groups are the ferns, the equisetums, 

 and the lycopods. About 8000 species have 

 been described, of which 7000 belong to the 

 ferns. 



Like the Bryophytes, the Pteridophytes re- 

 produce by spores, but in contrast to them the 

 two generations of the life cycle are distinct 

 plants, both living on the soil, and the con- 

 spicuous generation is the sporophyte. Fur- 

 thermore, the sporophyte is differentiated into 

 leaves, stems, and roots. Some of these plants 

 attain large size, with stems 10 to 50 feet in 

 height and leaves 10 to 30 feet in length. 

 This remarkable differentiation is made pos- 

 sible by the presence of vascular bundles 

 and mechanical tissues that are not very dif- 

 ferent from those of the seed plants. 



477 



Fig. 292. The walk- 

 ing fern (Camptosorus 

 rhyzophyllus). New 

 plants are developed 

 from buds at the ends 

 of the leaves. 



