heil has recorded an
instance in _Scabiosa atropurpurea_ in which one of the stem leaves
presented the following peculiarities. It was simple below, but divided
above into two equal lobes, provided each with a median nerve.[71]
Steinheil has also recorded a _Cerastium_ in which one of the leaves was
provided with two midribs; above this leaf was a group of ternate
leaves. I have seen similar instances in the common Elm, _Ulmus
campestris_, and also in the common nettle, _Urtica dioica_, the leaves
of which latter thus resembled those of _Urtica biloba_, which are
habitually bilobed at the summit. M. Clos[72] mentions an instance where
the terminal leaf and first bract of _Orchis sambucina_ were divided
into two segments. The same author also mentions the leaves of
_Anemiopsis californica_, which were divided in their upper halves each
into two lobes--also leaves of a lentil springing from a fasciated stem
and completely divided into two segments, but with only a single bud in
the axil. The axillary branches in like manner showed traces of
cleavage. Fig. 26 represents a case of this kind in _Lamium album_,
conjoined with suppression of the flowers on one side of the stem. I
have also in my herbarium a leaf of _Arum maculatum_, with a stalk
single at the base, but dividing into two separate stalks, each bearing
a hastate lamina, the form of which is so perfect that were it not from
the venation of the sheath it would be considered that there was here a
union of two leaves rather than a bifurcation of one. A garden
Pelargonium presented the same appearance.

[Illustration: FIG. 27.--Bifurcated leaf of _Pelargonium_.]

Fern fronds are particularly liable to this kind of subdivision, and
they exhibit it in almost every degree, from a simple bifurcation of the
frond to the formation of large tufts of small lobes all formed on the
same plan by the repeated forking of the pinnules. These may be
considered as cases of hypertrophy.

Moquin-Tandon, at a meeting of the Botanical Society of France (April
3rd, 1858) exhibited a leaf of _Cerasus Lauro-Cerasus_ divided in such a
manner as to resemble a leaf of _Citrus_ or of _Phyllarthron_. In this
case, therefore, the disunion must have taken place laterally, and not
from apex towards base, as is most common. The leaves of the common
horse-radish, _Cochlearia Armoracia_, are very subject to this pinnated
subdivision of the margin, and numerous other illustrations might be
given.