The Mysterious Wood of Wisteria

Email conversation between Gregory Reighard and Chuck Ray

"My wood anatomy question concerns wisteria. I have been eradicating wisteria from our University forest for the past 3 years and several of the larger vines are at least 60-70 years old based on when the farmsteads were abandoned and obtained by the University. When I cut some of the larger vines, I could not understand what I saw.  The internet did not provide any answers either. What I saw in cross-section (transverse cut) were ~10-12 rows of vessels plus late "wood" (= rings), then a thick solid layer of wood (diffuse?) with no vessels. I saw as many as 6 or 7 of these composite rings (10-12 rows of vessels + late wood each with a solid thick band). If the rings of vessels and late wood were representative of years, what was the solid thick band that appeared every 10-12 "years"? Does the vine at a predetermined time realize it needs to strengthen itself and produces a different type of wood every decade or so?  I have attached pictures of a section that was not polished — just rough cut with a handsaw. "

Thank you for your time:)
Sincerely,
Gregory Reighard

Hey Greg,
Never been asked this one before, and wisteria is not in any wood reference source that I could find.

However, after looking at your pictures, more on the internet, and putting some of our Penn State Xylarium specimens under the scope, I've come to a somewhat educated guess.

I suspected the wide flat rings were bark, but couldn't exactly figure out how they displayed that way. This photo gave me an idea.

Source: Pinterest

I blew up the transverse surface of the picture...

Source: Pinterest

...and noticed how the growth rings sort of seemed to grow together in different directions, meaning of course, that the encompassed bark would have to be in-between the growth rings.

So I put this small juvenile specimen under the scope...

Source: Penn State Xylarium

...which revealed that wisteria is a semi-ring-porous hardwood with uniseriate rays. The first flush of pores are followed by additional pores as the wood grows, and the earlywood and latewood are, practically speaking, indistinguishable. No flat "rings" are visible in this early growth.

I then examined a mature wood specimen.

Source: Penn State Xylarium

Here, we see something similar to what you observed...roughly ten growth rings separated by woody "bands", let's call them. Notice the fiber length on the band at the top mid-right...this strengthened my thought that we were looking at a band of bark.

I measured the growth characteristics...

Source: Penn State Xylarium

and found each growth ring to be about 1 mm, the band of growth rings to be about 9 mm total, and the woody bands on either side to be about 4 mm.

I then turned the specimen so that this same set of bands was seen from a tangential view...

Source: Penn State Xylarium

...which, at the top of the tangential view, exhibited roughly the same dimension of growth rings and bands.

But as I moved down the tangential view...

Source: Penn State Xylarium

...I saw the growth ring bands in the middle shorten and then finally disappear, and the woody bands come together into one wider woody band, roughly the total width of all three bands previously.

And then, a little further down...

Source: Penn State Xylarium

...a new growth ring band begins to appear as the angle of the woody band is transversed.

So, it looks like the "woody bands" every few years are encompassed bark. The bark intersection is eventually encompassed by new growth just as knots are, but are displayed in the transverse (cross-sectional) view of the wood as continuous circular bands created by the intertwining vines and their growth together. That is, the phloem (bark) cells created at the cambium layer expand around each stem as they grow annually (notice the "stripes" in the right-hand band of bark).

A partial proof of this theory would be that the bark bands in the cross-sections should have the same number "stripes" in the outer bark band as growth rings in its adjacent layer of growth rings. It does seem in my lab photos that the right-hand bark stripes roughly equal the number of growth rings in the middle.

It also seems, assuming the cambium layer remains active in each stem, the number of the growth rings and bark stripes should decrease as you move away from the center of the stem. Your cross-sectional photos seem to confirm that in fact, the outer bands of growth rings and "bark bands" have fewer rings than the more inner rings and bands.

Thanks for the great question and photos!

This is a really unique formation of wood that woodworkers rarely see. Another testimony to the wonderful world of wood variation, beauty...and mystery.