172 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
wood, both of the stem and branches, as far as I have an 
opportunity of examining it, appeared firm, in good condition, and 
without any indications of decay* The nature of the numerous 
excrescences on this Acacia tree, causing all growth eventually to 
No. 3.—Natural size. 
be stopped, is that of the well known knaur or burrs, commonly so 
called. They are thus referred to in Dr. Masters’ “ Vegetable 
Teratology,” page 419, and my examinations seem entirely to 
confirm what is there stated. 
“ 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 on which the woody layers have become inordinately 
developed as if by compensation for the curtailment in length.” 
Other excrescences on trees sometimes of considerable size 
