THE STRUCTURE OF FERNS. 
13 
The caudex forms an upright or decumbent stock, which 
in our native species seldom elevates itself above the surface 
of the ground, 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, 
when 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 
Hymenophyllums, 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 montana, and 
the Polystichum angulare> have also a tendency, though 
in a less degree, to this mode of growth; but it never 
