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Wednesday, March 27, 2013

Wood Science 101 (9) - More on Wood Identification: The Inside Wood Library

Yesterday's post resulted in a note from Dr. Elisabeth Wheeler at North Carolina State University, advising me of a great wood identification resource called Inside Wood. For those of you that are into wood identification or would like to get into it, and are thinking of putting together a system similar to the Cerre system in yesterday's post, you will be intrigued to know that the Inside Wood Library has over 35,000 images of hardwoods that are searchable by menu, images, taxonomy (family or genus names, alphabetically), or by keyword. In other words, if you're trying to find microscopic detail on a hardwood, you're as likely to find it at Inside Wood as anywhere.

Since I was checking it out, I thought I would dig into an interest of mine. My favorite all-time tree is the mighty American Sycamore, Platanus occidentalis. For some reason, my nose is attuned to the smell of the sycamore, and I can smell one a quarter-mile away, even in a mixed forest. So, for obvious reasons, I've always felt the sycamores were calling out to me, and as my approach confirms their presence, I've always smiled as on the approach of an old friend. I've spent many an hour parked beneath the boughs of big, old sycamores.

But I faced an interesting challenge when I first moved to State College. There are several streets in the area of the university that are lined with sycamores, or so I thought...but I could smell them only weakly, if at all. Then one day, while pontificating over the meaning of life related to the temperature of beer with my friend, colleague, and urban tree scientist Bill Elmendorf, he revealed to me that most of the trees in question were London Plane Trees, Platanus x acerifolia. I was shocked, shocked, to discover that my intimate Platanus friendship had been compromised by these mixed-breed intruders and pretend sycamores.
On the right is a true American sycamore...the one on the left is one of those London interlopers. Charles Dickens mentioned plane-trees fifteen times in "A Tale of Two Cities", so obviously the modern name has something to do with the city. England, you can have them...they don't smell right.

Under the Plane Tree. Frontispiece to A Tale of Two Cities. Image scan and text by Phillip V. Allingham on
Dr. Elmendorf explained to me that the Plane Trees are preferred nowadays over the Sycamore because they are more resistant to a blight called Plane anthracnose, which doesn't kill sycamores but defoliates them pretty badly when they have it. So for the past couple of decades, at least, plane trees have been the urban Platanus of choice. They are distinguished from the sycamore most easily by their seed balls...the sycamore usually only has one ball per stem, while the plane tree usually has two.

For me, the sycamore has that great smell, and the plane tree only does if you use your imagination.

So, I naturally wondered, how does their wood differ? I've never examined them side-by-side, so Inside Wood gives me that opportunity.

First, the American Sycamore, Platanus occidentalis. From Inside Wood I find it to have the following anatomical features...

1Growth ring boundaries distinct
5Wood diffuse-porous
13Simple perforation plates
14Scalariform perforation plates
15Scalariform perforation plates with <= 10 bars
16vScalariform perforation plates with 10 - 20 bars
21Intervessel pits opposite
25Small - 4 - 7 µm
30Vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell
4150 - 100 µm
4940 - 100 vessels per square millimetre
50>= 100 vessels per square millimetre
53350 - 800 µm
56Tyloses common
62Fibres with distinctly bordered pits
66Non-septate fibres present
69Fibres thin- to thick-walled
72900-1600 µm
77Axial parenchyma diffuse-in-aggregates
86Axial parenchyma in narrow bands or lines up to three cells wide
93Eight (5-8) cells per parenchyma strand
98Larger rays commonly 4 - to 10 seriate
99Larger rays commonly > 10-seriate
102Ray height > 1 mm
104All ray cells procumbent
114<= 4 / mm
136Prismatic crystals present
138Prismatic crystals in procumbent ray cells
139Prismatic crystals in radial alignment in procumbent ray cells
154More than one crystal of about the same size per cell or chamber
164Europe and temperate Asia (Brazier and Franklin region 75)
165Europe, excluding Mediterranean
166Mediterranean including Northern Africa and Middle East
167Temperate Asia (China), Japan, Russia
182North America, north of Mexico (Brazier and Franklin region 80)
192Wood of commercial importance
194Basic specific gravity medium, 0.40-0.75
196vHeartwood colour darker than sapwood colour
197Heartwood basically brown or shades of brown
200Heartwood basically white to grey

But this is the same list of features for Platanus x acerifolia, and other related species, Plantanus racemosa, Platanus orientalis, Platanus wrightii, and Platanus mexicana. So, for distinguishing one from the other, I'll have to go to the photos provided.

First, I browsed the twenty-eight images for sycamore on the site. Unfortunately, there are only two images of plane-tree wood. So, I had to compare the two most comparable images of sycamores. Fortunately, the two images of plane tree were provided by a certain Hans Beeckman, and that same person also had taken two comparable images of sycamore. Let's compare.

First, let's take a look at the transverse images of each.

Platanus occidentalis.
Platanus x acerifolia. 
On the left is the sycamore; on the right, plane-tree.

From these two samples, we see an anatomical feature of the genus: large and fairly numerous rays, which are the vertical lines in the photographs. It seems to me that the plane-tree sample shows a more uniform width between and of the rays, but this might easily be a difference in the sample. However, it is interesting to note that in Dr. Hoadley's book, in the transverse photo of sycamore on page 118, the rays also seem to vary in size. I'll have to get many samples of each and make my own study. For his part, Dr. Hoadley states that the woods are "very similar" and implies that they, like the American and European species of beech, are difficult to distinguish from each other.

Next, let's take a look at the tangential images provided. Occasionally, tangential images can provide clues even when transverse images are too similar to call. So, we'll see if that happens in this case.

Add caption
Platanus x acerifolia. 
Once again, the sycamore is on the left, the plane tree on the right.


Well, I've been staring at them for about ten minutes now, and I don't see any difference that seems to be real. (The plane-tree sample is stained a little darker and is a little better focused.) By the way, a tangential view of wood is essentially looking at each ring of tree growth from the side...imagine a log with bark peeled off, and looking at the inner surface, but flattened. That is a tangential view...a microscopic view of the surface of flat-sawn lumber.

So, I'll have to conclude that the wood of sycamore and plane-tree is the same anatomically, and leave it to experts like Drs. Wheeler and Hoadley to weigh in and tell us otherwise. Perhaps some of you Go Wood readers are experts in the area and can comment below.

I forgot to mention...Dr. Elmendorf also said that plane-trees are more greenish-gray, whereas sycamore is more whitish-gray. I always thought that green (not dry) sycamore wood was a little greenish. Wood color differences tend to dissipate in the kiln-drying process, so I would be interested if anyone out there knows if they retain that color difference in dried wood.

Well, that's a little exercise in using the Inside Wood database to investigate something I've been wondering about.  My conclusion: from a wood standpoint, they are the same tree.

But my nose knows better.

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