THE STRUCTURE OF FERNS. 13 



The caudcx forms an upright or decumbent stock, which 

 in our native species seldom elevates itself above the surface 

 of the e-round, but in certain exotic ferns reaches from 

 thirty to fifty feet or more in height, and gives a tree-like 

 character to the species. The rhizome extends horizontally 

 either on or beneath the surface of the soil, and forms what 

 is often called a creeping stem. These creeping stems, 

 wlicn not buried in the earth, are generally clothed with 

 hairs or scales, and sometimes to such an extent as to 

 become quite shaggy ; they vary greatly in size, some being- 

 as thick as one's finger, and others, as in our native 

 HymenopJiyllums, as fine as threads. 



The common Polypody has the thickest stem of any of 

 the creeping British species : in this it is nearly as thick 

 as one's little finger ; but the underground stem of the 

 common Bracken, or Pteris, creeps the most extensively. 

 The Osmunda, or Flowering Fern, as it is called, is, of the 

 native upright-growing species, that which most readily 

 gains height, and very old plants of this may sometimes 

 be found with bare stems of a foot or more in length. 

 The common Male Fern, the Lastrea tnontana, and 

 the Pohjstickum annulare, have also a tendency, though 

 in a less degree, to this mode of growth ; but it never 



