STRUCTURE AND FUNCTIONS OF FERNS. 21 
the stipes is formed is continued into the blade, and 
constitutes there the veins or ribs. The middle 
portion which runs up the whole frond, is called the 
mid-rib. 
The same terms are applied to the shape of the 
frond as to the leaf. When the blade is undivided, as 
in the Hart’s-tongue, it is called entire; when the 
frond is scalloped out, and the indentations do not 
reach the midrib, the frond is said to be pinnatifid; 
when the indentations reach the midrib, and leave a 
series of little leaflets, or pinna , the frond is said to 
be pinnated. Th e pinnce may be again divided down 
to their veins or ribs, and the frond is then said to be 
twice-cut or bi-pinnate. When this occurs a third 
time, it is tri-pinnate; and when oftener, the frond is 
said to be decompoimd. This latter does not, however, 
often occur in British species. The more vigorous 
specimens of the Common Brakes occasionally pre¬ 
sent it. 
When the fronds are first formed in the bud, they 
are rolled up in a peculiar way. The whole frond is 
rolled up from the point to the base, upon itself; and 
when it is divided into pinnae, each pinna is rolled in 
the same way upon itself. This arrangement occurs 
in other plants, and is called circinate. All British 
ferns, with the exception of the Adder’s-tongue and 
Moonwort, have this circinate arrangement of their 
fronds. 
The veins or ribs of the fronds are variously arranged, 
