On Thu, 3 Oct 1996, John R. Porter wrote:
I have looked at several sources to answer the question about the origin
of burls. As a botanist and woodworker, I have more than a casual
interest in the structures. Relatively few botany texts, whether for
theoretical or practical approaches, even broach the subject, but one
does.
Saigo & Saigo, 1983, Botany, Principles and Applications, Prentice-Hall,
Englewood Cliffs, NJ, p 155.
"Burls
Occasionally growth abnormalities occur, resulting in the formation of
bulbous growths called burls on the main trunk or branches (ref to Fig on
pg 156). Burl formation may be stimulated by injury, disease, or
invasion by such parasitic plants as mistletoes. Within a burl, the
cambium proliferates adventitious buds and abnormally large amounts of
xylem tissue, which become rippled and convoluted because it has no room
to grow longitudinally. Dense, swirled patterns form in the wood, making
burls popular for decorative woodwork, such as bowls, veneer panels,
furniture, and pipes."
Another reference, of a woodworking nature, is Constantine, Albert J.,
Jr. (rev by Harry J. Hobbs), 1975, Know Your Woods, Charles Scribner's
Sons, NY, p 64:
"Burls are responsible for the formation of a number of interesting
natural designs. A burl is an abnormal, wartlike excrescence on the
trunk or branches of a tree. Examined closely, it may appear to consist
of a great mass of 'eyes' or dormant buds. The surface of such a bulge
may be smooth or rough. In either case the alignment of the fibers is
very irregular and the burl is thus gnarled. Because of this many
bizarre figures are derived from veneers cut from burls. Causes of burls
are imperfectly understood and the following reasons have been advanced
to explain this unusual growth: injury from frost, fire or mechanical
contact; and irritation of the cambium by bacteria, fungi and possibly
viruses. A legend states that wounds inflicted by woodpeckers cause
burls. However, this is easily discredited in that trees produce burls
in regions where woodpeckers do not exist. Burls can and do grow on all
species of trees; however, they are found more commonly on certain trees,
as for example, the redwood (_Sequoia sempervirens_)."
--
John R. Porter
porter at shrsys.hslc.org
