310 



THE PTERIDOPHYTES 



called filmy ferns, whose stems and fronds are as delicate as 

 mosses. Some peculiar types, as the stag-horn fern (Platy cerium, 

 Figs. 272, 364), grow over the surface of tropical trees and are 

 consequently called epiphytes (meaning upon a plant). These have 

 certain flattened leaves (Fig. 2 7.2) closely pressed against the sur- 

 face to which the plants are attached, where they gather and hold 



moisture and humus. The roots of the filmy 

 ferns and the epiphytes are very poorly devel- 

 oped, or entirely wanting, but the air of a tropi- 

 cal forest is so saturated with water that they 

 obtain all that they need from the dripping mois- 

 ture and wet surfaces upon which they grow. 



All the plants which one would at a glance 

 call ferns are sporophytes,and they consequently 

 produce asexual spores, which are borne upon 

 their fronds. These spores correspond exactly 

 to those developed by the sporophytes of the 



FIG. 273. The walkine fern 



(Camptos ;rus rhizophyllus) 



Showing the manner in which 

 fronds hearing reproductive 

 huds at their tips bend over 

 and establish new plants 



liverworts and mosses, and they give rise to a small sexual 

 generation, the gametophyte. The life history of a pteridophyte 

 can be most easily studied from one of the common ferns famil- 

 iar to us in the woods, greenhouses, and gardens. 1 



1 The moonwort and adder's-tongue (Sec. 315) illustrate more primitive 

 conditions in the pteridophytes than the common ferns, but are not generally 

 available for type studies. 



