KNAUKS. 410 



extends to the interspaces between tliem, e. g. P. 

 sinnosum. 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 in- 

 debted to Dr. Sankey for a branch of Pelarganium 

 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 foim. 

 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 Yrith, as in Valeriana, Dipsacus, &c. (See Spiral 

 Torsion.) 



Knanrs. On certain trees, such as the oak, the horn- 

 beam, some species of Gratcegiis, &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 irregu- 

 larly, 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 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 knaui-s, the reader is referred to Tr^cul, ' Ann. 

 Sc. Nat.,' 3 ser., vol. xx, p. 65 ; Lindley, 'Tlieoiy of Horticulture;' Rev. 

 M. J. Berkeley, ' Gardenere' Chronicle,' 1855, p. 756. 



