THE STRUCTURE OF FERNS. 17 



branous scales, wliicli are sometimes few and confined to 

 the base, and at other times continued alono; the racliis. 

 Sometimes these scales, wluch are generally brown, are 

 large and so numerous that the parts on which tliey are 

 situated acquire a shaggy appearance. The form of the 

 scales, as well as their number and position and even 

 colour, is found to ])e tolerably constant in the different 

 species or varieties, and hence they sometimes afford 

 marks of recognition. Whenever they are produced 

 along the rachis, as well as on the stipes, they are inva- 

 riably largest at the base, and become gradually smaller 

 upwards. 



In some species the leafy portion of the frond is un- 

 divided, that is to say, the margins arc not scalloped or 

 cut away at all : an example of this occurs in the common 

 Hartstongue. Such fronds are called simple. The mar- 

 gin is, however, commonly more or less divided. 



In the simplest mode of division which occurs among 

 the British species, the margin of the frond is deeply 

 divided or scalloped out at short intervals, the divisions 

 extending inwards nearly to the rachis, but not reaching 

 it : this slightly divided form is called pinnatifid. 



The fronds are sometimes divided quite down to the 



c 



