CHAPTER XX 
THE PTERIDOPHYTES 
The Pteridophytes or Vascular Cryptogams constitute the 
third great division of the Plant Kingdom. ‘They include the 
plants known as ferns, horsetails or scouring rushes, club mosses 
and quillworts. These are the most highly developed crypto- 
gams, showing not only a distinct alternation of generations in 
their life histories, but a considerable structural advance over 
the Thallophytes and Bryophytes. They differ from the Bryo- 
phytes (1) by the sporophyte becoming an independent plant 
which shows differentiation into true root or roots, stem, and 
leaf or leaves each of which possesses a well organized vascular 
bundle ‘system, (2) by the gametophyte body or prothallus 
nourishing the young ~ sporophyte only until the latter has 
produced its own root and leaf after which the gametophyte 
perishes, and (3) by presenting large, conspicuous sporophytes 
and very small gametophytes. 
Pteridophytes formed the chief vegetation of the earth during 
the Carboniferous period. 
The Pteridophytes are grouped into three classes, viz.: 
Crass I. FiiciInE# or FERNS. 
Cuass II. EguiseTinE2# or Horseralts. 
Crass III. LycopopInE#, THE CLuB MossEs_ AND 
QUILLWORTSs. 
THe FERNS 
The ferns, constituting the class Filicinea, represent the largest 
group of the vascular cryptogams. 
Ferns occur in a variety of situations in tropical and temperate 
countries. Most of them prefer damp, shady places. Some 
grow in forests and fields, others in the crevices of rocks, still 
others in water. In the tropics, some ferns become tree-like in 
form, possessing long erect trunks bearing at their summit a 
crown of compound leaves called fronds. In temperate regions, 
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