KNAURS. 4.19 
extends to the interspaces between them, e.g. P. 
spinosum. This condition, which happens as a natural 
feature im the species just named, may also occur 
as an exceptional thing in others. The author is in- 
debted to Dr. Sankey for a branch of Pelargoniuin 
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 horn- 
beam, some species of Crategus, &c., hard woody 
lumps may occasionally be seen projecting, varying 
oreatly 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 irregu- 
larly, so as to form objects of beauty for cabinet- 
makers’ purposes. rom 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 in- 
ordinately developed, as if by compensation for the 
curtailment in length.’ 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 
' On the subject of knaurs, the reader is referred to Trécul, ‘Ann. 
Se. Nat., 3 ser., vol. xx, p. 65; Lindley, ‘Theory of Horticulture;’ Rey. 
M. J. Berkeley, ‘ Gardeners’ Chronicle,’ 1855, p. 756. 
