Andi Wolfe wrote:

"In the northern hemisphere this is formed in the upper side of the
limb in hardwoods and the lower side in soft woods. The reverse is
true for trees in the southern hemisphere."


Ken - I saw this statement in the book, also, and don't know quite
what to make of it.

Reaction wood is a descriptor for the larger spacing of growth rings
on one side of the pith relative to the other on branches. There is a
difference in how the wood reacts as it's drying, which explains the
name.

I'll have to dig into the literature to see if there is a difference
among plant families in how the branches put on secondary growth. If
the above statement is anecdotal in nature, it may just be referring
to differences among plants that typically occur in one hemisphere vs
the other.

Andi
http://www.AndiWolfe.com

I've heard it called "tension wood" and "compression wood" which is
a better descriptor than "reaction wood". If you think of growth rings
as rubber bands the following makes sense.

For a tree that is leaning off of vertical - the "uphill" side of each
growth ring is in tension, stretched as it tries to bring the tree
vertical, or at least prevent it from falling over farther. The growth
ring on the "downhill" side of the tree isn't be stretched at all - but
rather it's being compressed. Each behaves differently when cut,
as in sawing a cross section into two halves.

Here's an illustrated and annoted explanation that may help

http://web.hypersurf.com/~charlie2/T...insawing3.html