Question

2) Wood Anatomy You find a 2x4 in a lumberyard whose end looks as shown in the sketch below (asymmetric growth rings and dark streaks). a) Do you detect anything unusual about it? If so, what is it? b) How do the dark streaks look at the cell level (if you had a really strong magnifying lens and could look at the cell wall c) What are the problems you will likely face if you bought this piece?

Answer 1

Wood Anatomy

The figure that you have shared out here shows growth rings that are asymmetrical. You also mentioned that the wood-block has dark streaks.

a)

In this part, you have asked if there was something unusual about the wooden block selected. Well I am not sure, but as what I see in the diagram is that there is something unusual with the pattern n the growth rings.

When you look at the growth ring (whether symmetrical or asymmetrical type), it has a particular pattern. Firstly, growth rings develop as the tree advances in growth. So these rings are observed in the trunk part of the tree.

As the tree trunk is cylindrical, so it is obvious that it grows equally in outer circumference. It is also true that growth rings are having less dark streaks when it is a younger age while at later stages, these dark streaks get denser.

But looking at the figure that you have provided, the dark streak maintains the same consistency from central towards the outer regions. So as per your image provided for wooden block, the tree has been growing at the same rate throughout its life cycle.

In general, during the younger stage, growth rings are much closer to each other, because at this stage the plant shows fast growth (the circumference is also smaller). With age the dark rings (growth rings) move far apart with wider or more regions of Dark streaks. During this time, as the circumference of the tree trunk is much bigger so its growth rate seems slower. The outer portion of the growth rings always have to be more denser as compared to the inner growth rings.

b)

Next, you have asked how dark streaks look at the cell level if looking through a magnifying glass. Even if you are noticing via a simple magnifying lens, still you won't be able to see in much depth at the cellular level. Using a magnifying lens you will be able to notice both light and dark growth rings very clear and distinctive from each other.

On the outer layer of the bark, you will be able to see the lenticels like structure. To see more of Xylem and Phloem it is obvious that you need to observe it under a powerful microscope. But through a magnifying lens, you should be able to see the Cambial marks, which are very often found on the outer bark on account of any external injury to the tree trunk or external bark.

To dig in much in-depth and to notice cell formations, you may need a microscope.

c)

next, you asked the type of problems that will be faced the moment this piece of wooden block is bought?

From the figure this it is not possible to mention the quality of the wooden block. It is just that wooden blocks that have symmetrical rings certainly are considered to be durable as compared to ones that have asymmetrical growth rings.

Looking at one of the sides, it also looks like a scar in the outer bark. A healthy growing tree would show symmetrical growth rings, and the wood obtained from such tree is more durable.