THE STRUCTURE OF FERNS. 
17 
branous scales, which are sometimes few and confined to 
the base, and at other times continued along the rachis. 
Sometimes these scales, which are generally brown, are 
large and so numerous that the parts on which they are 
situated acquire a shaggy appearance. The form of the 
scales, as well as their number and position and even 
colour, is found to be 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 are 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 
