A frond is said to be pinnate (Latin, _pinna_, a feather), when its primary
divisions extend to the rachis, as in the Christmas fern (Fig. 1). A frond
is bipinnate (Latin, _bis_, twice) when the lobes of the pinnæ extend to
the midvein as in the royal fern (Fig. 2). These divisions of the pinnæ are
called pinnules. When a frond is tripínnate the last complete divisions are
called ultimate pinnules or segments. A frond is pinnátifid when its lobes
extend halfway or more to the rachis or midvein as in the middle lobes
of the pinnátifid spleenwort (Fig. 3). The pinnæ of a frond are often
pinnátifid when the frond itself is pinnate; and a frond may be pinnate
in its lower part and become pinnátifid higher up as in the pinnátifid
spleenwort just mentioned (Fig. 3).
[Illustration: Fig. 1]
[Illustration: Fig. 2]
[Illustration: Fig. 3]
The divisions of a pinnátifid leaf are called segments; of a bipinnátifid
or tripinnátifid leaf, ultimate segments.