CHAPTER XXI. 



(B) FILICALES. 



The living Ferns include more than 7000 species, widely spread over 

 the earth's surface from the Equator to the Arctic Regions. Some 

 39 of these are British. Though a few live actually in water, others 

 are distinctly Xerophytic, and able to resist extremes of drought. 

 But the vast majority live in moist and often in shaded positions, 

 and, as will be seen later, external fluid water is necessary for the 

 completion of the normal cycle of their hfe. The Fern Plant is with 

 very few exceptions perennial. It consists of a shoot which may or 

 may not be branched, and is attached to the soil by numerous fibrous 

 roots. The shoot consists of axis and leaves, as in the Flowering 

 Plants, but usually without axillary buds. The leaves are large in 

 proportion to the stem that bears them. Often they are highly 

 Branched, with two rows of lateral pinnae that are branched again 

 repeatedly. This, together with their delicate texture, gives the 

 feathery appearance to the leaves of most Ferns (Fig. 266). It is 

 specially conspicuous in the large Tree-Ferns, where each leaf may 

 be many feet in length. This habit (megaphyllous) contrasts strongly 

 with that of the Lycopods with their small unbranched leaves 

 (microphyllous). 



The Coal Period has been sometimes described as " The Age of Ferns." . It 

 is true that large-leaved Fern-like Plants were frequent then. But many of 

 these have been lately shown to have been Seed-bearing Plants (Pteridosperms^, 

 whereas Ferns have no seeds. The question has then been raised whether 

 Ferns existed at all at that early time. There are at least three types which 

 can only have been Ferns that did live then, and some similar to them survive 

 to the present day. But many of the Ferns we know are relatively modern. 

 It is doubtful whether at any time a more varied Fern-Flora has existed on 

 the earth than at the present day. If that be so, the present is as much the 

 age o± Ferns as any that has gone before. 



The Ferns show a comparatively primitive cycle of life. It consists of 

 two alternating and physiologically independent phases, or generations, 



326 



