Parenchyma Cell Rings and Wood Grain

Info about parynchyma cell rings, a structure similar to growth rings that can affect the appearance of sawn lumber. October 1, 2009

To Gene Wengert, Forum Technical Advisor:

In a recent post on the mystery wood there was some mentioning on parenchyma cells, which I now understand to be the tiny rings that run parallel to growth rings in woods like American elm, and sometimes black cherry.

Are these cell rings due to significant rainfalls of that specific yearís seasonal conditions? I have looked into my small inventory of American elm and red elm (I think red elm is classified as winged or slippery elm but have not taken the time to figure out proper exact identification by scientific name and characteristics) and have counted different numbers of parenchyma cell rings between annual rings for different years.

This makes sense to me, for rainfall is going to vary every year, and I can definitely see years on my boards that would signify drought not only because the parenchyma cell rings are low in count, but because the growth rings are very tight. About half of the black cherry I have seen exhibits these cell growth rings very visibly, and the other half does not exhibit these cell rings at all to the naked eye. Can you please explain these odd growth rings?

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Parenchyma cells do run parallel to the annual growth rings. They also are found in the ray cells. In some species, the pattern that the parenchyma cells make helps with identification. For example, in elm they are wavy. In cherry, they are small and often appear as white lines. Sometimes the pattern appears as flame-like and they seem to run perpendicular to the rings (or from ring to ring).

I would guess that the growth rate affects the number of parenchyma cells and therefore the overall pattern appearance. Red elm usually means Ulmus rubra. American elm is Ulmus americana. American elm has a single row of large earlywood cells, while red elm has several rows. Both have those undulating parenchymas cells that create the wonderful overall "busy" look to elm flatsawn lumber or veneer.

From contributor W:
Isn't it the latewood pores that make the beautiful wavy lines in elm rather than parenchyma?

From Gene Wengert, forum technical advisor:
Yes, it is the latewood pores, but the pores are surrounded by many parenchyma cells which is what makes these wavy bands visible.

From the original questioner:
I guess the only way to really figure this one out is study the weather of many years, and record the times of rainfall and figure in time for high ground saturation, and then cut down a tree in that exact area and see if the numbers click into place according to the parenchyma ring count. I have always thought it would be interesting to tell customers that these tiny rings are actual recordings of the rainfall, just like the annual rings are recordings of the total annual weather patterns. Isn't there a name for a scientist who studies tree rings? Maybe I can contact one and find out. Kind of a long distance to go but I am really curious on this whole thing!

From Gene Wengert, forum technical advisor:

From contributor W:
Sometimes magnolia has two bands of marginal parenchyma to yellow poplar's one band. Being in same family, magnolia and yellow poplar both exhibit marginal parenchyma. Itís very distinctive in wood ID.