[Chap. XLIX FERNS, CLUB MOSSES AND EQUISETUMS 



657 



from the wood of these trees. These species have all become extmct, 

 and only a few of the modern ferns are trees. Most of the modern 

 Pteridophvtes are small and comparatively inconspicuous except when 

 they grow in masses. In the forests of today they are understory plants 

 ( Fig. 305 ) , and are usually most abundant along stream banks, in open 

 glades, in clearings made by man, or where the forests have been de- 

 stroyed by storm and fire. In such areas some of the species reproduce 

 so rapidly and grow in such dense masses that reforestation is greatlv 

 delayed. Some of these species also become troublesome weeds in pas- 

 tures in moist climates. A few species are prized as decorative plants, 

 and others are used in medicine. 



The Ferns 



Ferns grow in a great diversity of habitats. We usually associate them 

 with shade, ample water supply, and warm temperatures. While in gen- 



FiG. 306. A fern (Asplenium) widely distributed on rocks. Photo by C. H. Jones. 



eral this is true, particularly for those of very rapid growth, ferns are 

 not necessarily so restricted. Some species thrive in open fields and on 

 dry hillsides, others on dry exposed rocks (Fig. 306), still others in 

 marshes not especially shaded, and many in the forests of the tropics and 

 semi-tropics as epiphytes (Fig. 307); a few are strictly aquatic. They are 



