usual.

The increased number of leaves in a whorl may well be designated as
"polyphylly," using the word in the same sense as in ordinary
descriptive botany, while "pleiotaxy" may be applied to those cases in
which the number of whorls is increased.

[Illustration: FIG. 183.--Supernumerary leaflet, _Ulmus campestris_.]

=Pleiophylly.=--As above stated, this term is proposed to designate
those cases in which there is an absolute increase in the number of
leaves starting from one particular point, as well as those in which the
number of leaflets in a compound leaf is preternaturally increased. The
simplest cases are such as are figured in the adjacent cuts, wherein, in
place of a single leaf, two are produced in the elm. In the one case the
new leaflet springs from the apex of the petiole and partially fills
the space consequent on the obliquity of the base of the leaf. In the
other it would seem as if two distinct leaves emerged from the stem in
juxtaposition. This is probably due to a lateral chorisis or subdivision
of the primitive tubercle or growing point, followed by a like
subdivision of the vascular bundle supplying it. There are certain
varieties of elm that very generally present this anomaly on their rank,
coarse, growing shoots. In these cases the new growths have the same
direction as the primary one, but in other cases the supplementary
production is exactly reversed in direction. Thus, in the common hazel
(_Corylus_) a second smaller leaf proceeding from the end of the
leaf-stalk at the base of the primary one may frequently be seen. M.
Germain de Saint Pierre records an instance in a mulberry leaf, from the
base of which proceeded a large leafy expansion divided into two
tubular, horn-like projections, and in the centre a thread-like process
representing the midrib and terminated by a small two-lipped limb.[392]
Dr. Ferdinand Mueller speaks of a leaf of _Pomaderris elliptica_ as
bearing a secondary leaf on its under surface.[393]

[Illustration: FIG. 184.--Supernumerary leaf, _Ulmus montana_.]

[Illustration: FIG. 185.--Supernumerary leaf of hazel.]

The leaves of _Heterocentron macrodon_ have likewise been observed
occasionally to produce leaflets from their upper surface.

To this production of leaves from leaves the late Professor Morren
applied the term "autophyllogeny."[394] The Belgian botanist figures a
small perfect leaf springing from the nerves of the upper surface of the
primary leaf in