ied.]

=Enlargement of axile organs.=--All the species of _Pelargonium_,
_Geranium_, _Mirabilis,_ as well as those of _Caryophylleae_ and other
orders, have tumid nodes as a normal occurrence. In the genus
_Pelargonium_ this swelling is sometimes not confined to the nodes, but
extends to the interspaces between them, _e.g._ _P. spinosum_. This
condition, which happens as a natural feature in the species just named,
may also occur as an exceptional thing in others. The author is indebted
to Dr. Sankey for a branch of _Pelargonium_ which was thus thickened,
the remaining branches not being in any way affected. The leaves on the
swollen branch were smaller than the others, and their stalks more
flattened. There was, in this instance, no trace of fungus or insect to
account for the swelling of a single branch, which might, therefore, be
due to bud-variation, perhaps to reversion to some ancestral form. The
repeated cross fertilisations to which Pelargoniums have been subjected
render this hypothesis not an improbable one.

As an accompaniment to a spiral torsion of the woody fibres, this
distension of the stem is frequently met with, as in _Valeriana_,
_Dipsacus,_ &c. (See Spiral Torsion.)

=Knaurs.=--On certain trees, such as the oak, the hornbeam, some species
of _Crataegus_, &c., hard woody lumps may occasionally be seen
projecting, varying greatly in size, from that of a pea to that of a
cocoa-nut. They are covered with bark, and consist in the interior of
very hard layers of wood disposed irregularly, so as to form objects of
beauty for cabinet-makers' purposes. From the frequent presence of small
atrophied leaf-buds on their surface, it would seem as if the structures
in question were shortened branches, in which the woody layers had
become inordinately developed, as if by compensation for the curtailment
in length.[488] The cause of their formation is not known, but it has
been ascertained that they are not due to insect agency. Knaurs may
occasionally be used for purposes of propagation, as in the case of the
"uovoli of the olive" and the "burrs" that are formed on some varieties
of apple, from which both roots and leaf-shoots are produced in
abundance.

A distinction must be drawn between those instances in which the
swelling is solid throughout from the excessive formation of cellular
tissue, and those wherein it is hollow from the more rapid growth of the
outer as contrasted with the inner portions. These lat