FERNS OP GREAT BRITAIN. 



singular and beautiful on the green bank, coiled up and 

 covered with large scales ; and these scales afford too, by 

 their mode of growth, an assistance to the botanist in 

 the determination of species. The true stem of the 

 fern generally lies along the surface of the ground, or 

 below it, and from its resemblance to a root is termed 

 the rhizoma. The stems and fronds of ferns have 

 neither true wood nor bark, but are strengthened by 

 bundles of tubes and fibres, which are embedded in 

 cellular structure. The harder part is external, and the 

 centre . is either hoUow, or more commonly filled with a 

 soft pulpy matter ; so that the stem of a tree fern very 

 much resembles that of a palm in this respect, as well as 

 in the cylindrical form which it often assumes. 



The green expansion of a frond difi'ers in various fa- 

 milies. In some it is delicate and almost transparent — 

 a mere green film; in other cases it is tough and leathery, 

 or thin, crisp, and brittle. Now we find it of bright 

 grass-green, or it is of a dull olive, or of deep dark or 

 brownish, or greyish-green hue. The difference of the 



haet's-tongue. 



