Parts of Fer?is. 
5 
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 is 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 
bipinnaie , or 2pinnate , and when the pinnae of these are again 
similarly cut, the frond is tripinnate or g-pinnate, and a further re- 
petition 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 occur either in lines, or bundles, which are known 
as sori, one line or bundle 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, instead 
of the cup, there is only a scale placed under the sorus. In some 
other ferns there is no indusium or involucre whatever. 
The sorus is generally placed on a vein, and the part of the 
