428 



PTERIDOPHYTES (FERN PLANTS) 



the structures characteristic of the stems of Seed Phmts and are, 

 therefore, not merely stems in appearance as the stem-Hke struc- 

 tures developed by the gametophytes of Mosses and some Liver- 

 worts are. It remained for the sporophyte generation to develop 



Fig. 379. — A Tree Fen 



After Bailey. 



a real stem. At the tip of the Fern sporophyte there is a meriste- 

 matic region which by the rapid growth and division of its cells 

 elongates the stem. Just behind the advancing tip new roots 

 and leaves are developed and stem tissues are formed. A cross 

 section of a stem, as shown in Figure 380, shows an epidermis, 

 cortex, vascular cylinder, and pith — tissues characteristic of 

 the stems of Seed Plants. 



The roots too are true roots and are not simple structures like 

 the rhizoids of gametophytes. They have a root cap, region of 

 growth and elongation, epidermis, root hairs, cortex, and vascu- 

 lar cylinder, thus having the features characteristic of the roots 

 of Seed Plants. 



The leaves, although true leaves, are generally called fronds, a, 

 term formerly applied to them because they were considered a 

 combination of leaf and stem. Fern leaves are usually much 

 branched and are easily identified by the way their veins branch 

 and by the way they develop in the spring. Their veins Ijranch 

 by forking; that is, a vein divides into two veins of equal size 



