DEVELOPMENT OF PLANTS 



307 



specialized group that have branched off from some primitive fern 

 stock in recent geological times and owing to their variations 

 being highly adapted to present conditions upon the earth, they 

 have become very numerous and widely distributed. In tem- 

 perate climates the majority live upon the ground in moist and 

 shady regions and some are aquatic or xerophytic. They attain 



Fig. 219. Christmas fern, Polystichum, with prostrate stem bearing at 

 the tip young coiled leaves covered with chafify scales and further back large 

 leaves of the previous season. The older portions of the stem are covered 

 with the petioles of the dead leaves. — H. O. Hanson. 



their greatest abundance in the mountainous district of tropical 

 countries where they occur in astonishing profusion and variety 

 upon the moist rocks and trunks of trees, as well as upon the 

 earth. The leaves are the most striking feature of the Filicales. 

 They are usually large and divided and are characterized by being 

 coiled when young (Fig. 219). This is due to the stronger 



