burls growing into and around
each other, forming a giant mass
of burl growth and grain."
Burl forms offer many
sculptural possibilities. Some
burls are quietly round, whether
shallow or deep, definitely
suggesting a bowl. Others are
twisted and convoluted,
evoking a sense of animation.
No matter how much energy
shows on the outside, though,
it is no clue to the incredible
explosion of energy inside—a
swirling, frozen pot of
marbleized color, texture and
structure, creating patterns
too complex to understand or
predict. It is one of nature's
amazing mysteries—the starry
galaxy within is greater than the
form containing it. "
Scientists are only
beginning to understand burl
growth. They believe that many
burls are caused by injury to the
cambium (the growth layer near
the bark), either by fire or frost, or
by something striking the tree.
Burls have been induced on trees
by mechanical injury, and by fire.
Interestingly, when trees have
been repeatedly burned on one
side, they form burls on the
opposite side. Fungal or bacterial
irritation of the cambium also
causes burl formations,
particularly the more gnarly,
rough-barked ones. Some
scientists suggest that a mutation
or hereditary factor, combined with
environmental conditions, is
responsible for burl growth. This
might explain why several trees of
the same species growing in a
Page 4
particular area (which quite likely are related) may
all grow burls."
Burls are generally divided into two
categories: above-ground burls and root burls,
either of which can occur on any tree. Root burls
(called crown galls by scientists) may be caused
by bacteria from infected soil entering the tree
through plant damage. They tend to be less hard
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