CHAPTER XIV 

 THE PTERIDOPHYTA : FILICALES, THE FERNS 



The phylum Pteridophyta includes those plants which are sometimes called 

 the Vascular Cryptogams. The term Cryptogam is an old name which 

 covers all the non-flowering plants, in which, at one time, the sexual 

 reproduction was unknown. The epithet " vascular " distinguishes the 

 Pteridophyta from the Bryophyta and other lower groups, in which no true 

 xylem is formed. Furthermore this group shows the same morphological 

 division of the body into stem, leaf and root which is characteristic of the 

 higher group, the Flowering Plants. In the Bryophyta, it will be remembered, 

 there may be stems with leaves, but there are no roots. 



The Pteridophyta includes not only a large number of present-day genera, 

 but also a great many fossil types. In fact the modern species are considered 

 to represent only the remains of what was once a far more important group, 

 and it seems probable that in the late Devonian and Carboniferous geological 

 periods they made up a considerable part of the vegetation. Many of the 

 genera which at the present day are quite small plants are descended from 

 ancient groups which, in their day, formed large trees. Lycopodium and 

 Equisetiim, which to-day seldom reach more than a foot or two in height, 

 are the remains of a group which in the Coal Measures produced extensive 

 forests. In more recent times these Coal Measure plants have been succeeded 

 by the Spermatophyta or Flowering Plants, which have relegated the 

 Pteridophyta to a subordinate position in the world's flora. 



The members of the Pteridophyta vary very greatly in form, and we can 

 distinguish two main evolutionary tendencies. One resulted in the pro- 

 duction of large leaves and relatively small stems, which are collectively 

 spoken of as the megaphyllous types, and are represented by the Ferns ; 

 and the second, in which the leaves are small in relation to the stem, which 

 are called the microphyllous types, represented by the Club Mosses and 

 the Horse-tails. 



The anatomy of these plants is to some extent dependent upon the type 

 of leaf which thev bear, but in all of them the stem is divided into an outer 

 cortex, which is composed of parenchyma, together with, generally, a 

 certain amount of sclerenchyma, and a central conducting system or stele. 

 This latter structure contains the xylem and phloem, together with certain 

 other types of cells. A similar, though generally simpler, structure is found 

 in the roots. The leaves in megaphyllous types consist of leaf stalk or 

 petiole and a flat blade or lamina. Branches of the stele, or leaf traces, 

 pass out along the petiole and thence by further ramification into the lamina, 

 forming the " veins." Microphyllous leaves are much simpler, with no 

 petiole and usually only one vein. 



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