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I used to think mistakenly that these growths on the trunks of trees were called
boles but I've now discovered that
bole is the botanical name for the tree trunk (
the main wooden axis of a tree says Wikipedia), and that this knotty lump is a
burl - or in England a
burr. Sometimes you see beautiful turned bowls made from burr wood with the unusual grain providing intricate patterns.
Here is some good information about burls from
T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network
Burls on trees
Burl
(British bur or burr) is a tree growth in which the grain has grown in a
deformed manner. It is commonly found in the form of a rounded
outgrowth on a tree trunk or branch that is filled with small knots from
dormant buds. A burl results from a tree undergoing some form of
stress. It may be environmental or introduced by humans. Most burls grow
beneath the ground, attached to the roots as a type of malignancy that
is generally not discovered until the tree dies or falls over. Such
burls sometimes appear as groups of bulbous protrusions connected by a
system of rope-like roots. Almost all burl wood is covered by bark, even
if it is underground. Insect infestation and certain types of mold
infestation are the most common causes of this condition.
