FILICALES 



329 



seen in the old leaves of the Male Fern (Fig. 267, B). A general 

 peculiarity of Ferns is the crozier-like curvature of their young leaves 

 the adaxial face growing at first more slowly. But later it catches up 

 the abaxial face, so that the leaf flattens out as it matures. This habit 

 is effective in protecting the curled tip of the leaf, since in Ferns apical 

 growth is long continued, and the tissues are delicate. The stern and 

 leaves, especially while young, are often densely covered either with 



FIG. 268. 



Transverse section of a fossil-Fern, Botryopteris cylindrica, showing a protostele 

 with solid central core of xylem, and peripheral phloem. This is a fossil from 

 the Palaeozoic, and it illustrates how perfect the preservation of structure may 

 sometimes be in fossils of very early periods. 



hairs (Osmunda), or chaffy scales (Nephrodium), which protect the 

 young parts against drought, but are liable to fall away later. 



In their general construction Ferns resemble Flowering Plants. 

 They have a superficial epidermis, and a conducting system of vascular 

 tissue embedded in ground-tissue which is parenchymatous, but often 

 it also encloses strands or islands of hard brown sclerenchyma, while 

 hard stony or horny sheaths frequently form the surface of stem and 

 leaf-stalk. The epidermis and ground tissue call for no detailed 

 description. The chief interest lies in the vascular system. In 

 ancient fossil Ferns, such as Botryopteris, in many primitive living 



