23 
It would seem to be clearly due to the arrest of the flow of 
sap, by the dislocation of the ducts through this excessive 
development of woody fibre, that one-half of the tree, after 
languishing for a time, died. At the same time the sap, not 
moving onwards in its accustomed channel, would accumulate 
about the axis, and further tend to increase the development of 
the wood and the enlargement of the callosity. 
Enquiring now into the probable cause of the above monstrosity, 
it does not appear to be referable to that class of hard woody 
excrescences, often found on the stems of certain trees and 
occasionally attaining to a large size, which have been so closely 
investigated by M. Trécul,* and also treated of by Mr. Berkeley 
in the Gardener’s Chronicle,t under the name of “ Knaurs.” Both 
these authors agree in tracing the appearance of these hard lumps 
of wood to adventitious buds, one or more of which may often 
be observed at the extremity of the knaur when in its incipient 
state of growth. These terminal buds are always, in the first 
instance, “ connected by a fibro-vascular system with the woody 
axis upon which they are seated.” At some early period of 
growth the wood itself of the bud increases; changing its 
character, and passing into the form of a hard woody nodule. 
As this nodule enlarges it exercises a pressure upwards upon the 
bark, ending in a rupture of the slender duct connecting the bud 
with the woody axis, the bud itself becoming atrophied. From 
the time of this taking place the nodules keep increasing in size 
until a large knaur is formed. Dr. Maxwell Masters, who 
has briefly spoken of these abnormal woody growths in his 
“Vegetable Teratology,” considers the nodules as originally 
“shortened branches, in which the woody layers become inor- 
dinately developed as if by compensation for the curtailment in 
length.” 
- 
* Ann, des Sci. Nat. 3rd ser. (Botanique) tom, 20. p. 65. 
+ Gard. Chron., 1855, p. 756. 
} Veg. Terat, p. 419. 
