DEVELOPMENT OF PLANTS 



293 



it to uncoil. The tissues of the leaves are differentiated into an 

 epidermis, stomata, chlorenchyma and vascular bundles as in the 

 higher plants (Fig. 223). The stems are more usually pros- 



FiG. 220. Stem in early spring freed from all of its leaves save the 

 young ones, c, near the tip : r, roots ; v, vascular bundles in base of petiole ; 

 x, region from which the cortex has been removed to show the vascular 

 bundles from the leaves uniting to form a network. 



trate, creeping rhizomes that bear a few large leaves near their 

 growing tips. The stems branch sparingly and so gradually 

 give rise to colonies of ferns. One of the most attractive fea- 



Fig. 221. Cross-section of fern stem: v, concentric vascular bundle, the 

 large cells of the xylem being surrounded by the phloem. Each bundle is 

 surrounded by a compact layer of cells, the endodermis; st, stereome; cr, 

 cortical region. 



tures of certain tropical districts are the tree ferns with erect 

 stems of palm-like appearance which lift their great crowns of 

 leaves 30 to 50 feet in the air. The vascular bundles are of 



