CHAPTER Xn. 



BRANCH VI. PTERIDOPHTTA. 



TBE PEBNWOBTS. 



403. The Fernworts are for the most part leafy-stemmed, 

 root-bearing plants of considerable size, whose leaves bear 

 spores. All are chlorophyll-bearing, and they are mostly 

 terrestrial in habit, comparatively few being aquatic. 



404. Their tissues show a high degree of development. 

 The epidermis is distinct, and contains breathing-pores sim- 

 ilar in form and position to those of the flowering plants. 

 The fibro-vascular bundles are generally of the concentric 

 type, although collateral and radial bundles occur also. 

 The bundles generally possess tracheary and sieve tissues; 

 the former is usually well developed, but the latter not. 

 Fibrous tissue occurs only to a limited extent within the 

 bundles, but it is common in the stems as thick strength- 

 ening masses. These tissues generally develop from a 

 single cell at the apex of the stem, but in the higher orders 

 there are groups of apical cells, as in the flowering plants. 



405. The round of life of a fernwort shows a curious al- 

 ternation of generations. When a spore of a fernwort 

 germinates, it produces a small, flat, green liverwort-like 

 plant upon which sexual organs arise. This is the flrst 

 stage, or sexual generation. After fertilization has taken 

 place in the sexual organs, a leafy-stemmed, long-lived 

 plant is produced directly. This is the second stage, or 



