Excrescences may be divided into those occurring on herbaceous tissues, of which Galls are well-known examples, and those found on the woody stem, branches, &c., and themselves eventually woody, of which Burrs of various kinds afford common illustrations.
Turning now to outgrowths of a woody nature, the well-known burrs or knaurs, so common on elms and other trees are cases in point.
There are many Varieties of burrs, though all woody outgrowths of old trees are not to be confounded with them, e.g.
They were like burrs in his shoes, but he couldn't yet go after them until he'd learned to control his new power.
The knees of Taxodi urn, &c. Many typical burrs might be described as witchesbrooms, with all the twigs arrested to extremely short outgrowths.