PARTS OF FERNS 
5 
the fronds are jointed on to the rhizome, but most frequently 
the tissues of the stem and frond run gradually into one 
another without any joint. 
Frond. — The leaf-like parts of a fern are known as fronds, 
and are connected with the stem by more or less evident 
stalks. When the frond is divided, the continuation of the 
stalk between the leafy parts is known as the rachis , and the 
same term is applied to its further continuation through 
the branches, while the still further continuations of it within 
the substance of the frond are known as veins. If the frond 
be undivided it is said to be simple , and if cut down to the 
rachis it is pinnate , and each division known as a pinna. 
When these pinnae are cut down to the rachis the frond is 
bipinnate , or 2 -pinnate, and when the pinnae of these are again 
similarly cut, the frond is tripinnate or g-pinnate, and a further 
repetition of this makes them 4- pinnate . 
If instead of being cut to the rachis they are only partly 
cut, they are pinnatifid instead of pinnate, and frequently a 
frond, or a pinna, is pinnate below, and only pinnatifid above. 
When the pinnatifid lobes are very unequal as to size, and 
are sometimes reduced to a waved outline, the frond is said 
to be sinuate. 
When the stalk of a frond forks into two pinnae and these 
again into two, it is said to be dichotomous, as in the Gleichenias, 
where the main divisions are dichotomous, and the final 
cutting pinnate. When a frond is 2, 3, or 4-pinnate, the final 
or undivided race of pinnae are known as pinnules. A sinus 
is the bottom of the cut separating two lobes. 
Capsules or sporangia occur either in lines, or groups, 
which are known as sori, one line or group being a sorus. 
In many ferns the sorus is covered, when young, by a thin 
membranous covering known as the indusium , and when the 
sorus is marginal (in a line along the edge of the frond), this 
indusium is generally formed of the turned back margin, 
changed in texture more or less. Instead of this in some 
ferns the sorus is placed inside a little membranous cup 
known as the involucre , and this term is also used where, 
