​Meristems - Plant Anatomy In “Normal People” Talk

If you are working on getting your Arborists’ Certification, chances are you already have a copy of the ISA’s Arborist Certification Study Guide and maybe some other similar arborist textbooks.

These books are super useful and you are going to want to read them, but let’s be honest and say they can be a bit punishing. The information is super dense and the language is very technical.

Right from the start, they may dive very deep very quickly in tree anatomy, with a focus on Meristems.

We figure not every person who wants to be an arborist is super stoked on getting really technical right away, so we broke down some of this info in a more user-friendly way.

Let’s stop wasting your time and get to it!

What Is A Meristem?

When it comes to trees, Meristems are the parts of a tree where the cells that already existed split up to make new cells.

Why is this important?

These cells dividing and creating new cells is what causes a tree to grow.

Meristems are the places (some books use the word “zones”) where this growth happens. Although the book does not mention this, “Meristematic Tissue” is the stuff like bark and wood that actually grows. If you poke around a little online, you will find that most of the information out there is dealing with the tissue rather than the “zones.”

When we talk about differentiation, that is when the cells at Meristems form new organs or distinct parts of the tree.

What Are Roots And Shoots?

Growth happens in the roots of a tree and the shoots of a tree, meaning the branches and limbs that grow out of a tree’s trunk.

What Are The Types Of Meristems?

Very quickly you are going to be learning about the basic definition of a Meristem to finding out about the two different types of Meristems.  If you are going by a study guide, you may not have had a chance to process exactly what a Meristem is, so just remember that the Meristems are places where roots and shoots grow.

What Are Growing Tips?

Growing Tips are what textbooks call “Apical Meristems.” If you need some help remembering the more technical terminology, they are called “Apical,” because they form at an “Apex,” meaning the tip.

Growing Tips:

  • “Apical Meristem” Is The Technical Term For A Growing Tip
  • These Are The First (Primary) Places Of Growth In A Tree
  • Growing Tips Cause Elongation - A Growth In The Length Of A Root Or Shoot

What Is Lateral Growth?

Now we will talk about Meristems in a secondary region. These are called Lateral Meristems. “Lateral” means side to side, which makes some sense because these guys make stems and trunks grow thicker.

Lateral Meristems:

  • Lateral Means “Side To Side”
  • Lateral Meristems Cause “Secondary Growth”
  • Secondary Growth Means Growing Thicker - A Growth Measured In Diameter
  • Both The Trunk And The Stems Can Grow Thicker In This Type Of Process

You may be asking “Why the hell do I need to know this?” This is a fair question, especially given that most information out there that on Meristems deals with them from the viewpoint of a plant biologist. Rest assured, this information is actually useful to an arborist, and we are about to explain why.

How Do You Even Use This Stuff In Real Life As A Tree Worker?

There is a good chance that you will never use the word “Meristems” in your day-to-day life as an arborist. It can definitely be seen as unfortunate that this stuff is talked about on such a technical level, rather than a practical level.

With that being said, the information itself is useful to an arborist in many ways. To make this more clear, we are going to have to go on a minor side tangent. Sorry if this seems like a waste of time, but it will hopefully clear some things up.

Limits To The Infinite Growth Of A Tree

One of the ways that plants and animals are different is that animals stop growing at a certain size or age, which is not the case for plants. In theory, a plant will never stop growing. These cells will continue to split and cause the tree to grow until something outside of the plant gets in the way and slows down or stops the growth.

As an Arborist, you will want trees to survive and continue growing. If a tree stops growing in a typical pattern, you will want to figure out why this is happening.

Factors That May Stunt Or Stop Growth:

  • Disease
  • A Lack Of Sun Exposure
  • Not Enough Access To Water
  • Not Enough Access To Important Nutrients
  • Not Enough Space Away From Other Plants Using The Same Resources

Here’s where understanding Meristems, Meristematic Tissue, and the way that plants naturally grow comes in handy for an arborist. If you understand this process in at least a basic way, you can better determine how to help a tree.

Let’s say that you are able to recognize that a tree’s growth is being affected by a virus. It is actually possible in some cases to remove only the infected Meristems. If you can do this successfully, the uninfected Meristems will regrow, or regenerate, bringing the tree back to growing in a healthy way.

Times In Real Life Where You Use This Info:

  • Understanding Meristems Will Dictate More Healthy Pruning Practices
  • Learning How To Protect Meristems And Meristematic Tissues When Digging Trees & Other Plants

In recent years, there has been a lot of talks between arborists about stopping the practice of Liontailing, or over-pruning. If you understand how important it is to keep around those healthy Meristems so the tree will grow the correct way, you will better understand why this is such an important issue.

We just went to pretty great lengths to explain what Meristems are in a simple, understandable way. However, if you are getting ready to take a test on the subject, you will need to know how to talk about these things in a more technical manner. Let’s go over some of that stuff.

What You May Need To Know For Certification

Unfortunately, we don’t have a copy of any Arborist Certification Exams but based on some of the textbooks, there is some more technical terminology you will want to get to know.

Some Terms You Should Learn:

Cambium: The Secondary (Lateral) Meristems that create a tree’s vascular system (where the water, sap, and nutrients flow)

Cork Cambiums: The Secondary Meristems that create a tree’s bark from its rings

Xylem: A tree’s wood tissue (You will also want to learn about its functions)

Phloem: A tree’s vascular tissue (used to move sap, water, and nutrients)

Differentiation: The process where a tree grows new organs through cell separation

Summing It All Up

This is a lot of information. Typical textbooks cover this information in a very dense manner, heavy on technical language. Reading our take on this information admittedly probably took you a lot more time, but hopefully, we presented it in a way that was easy for you to understand. In any event, we wish you the best of luck in learning this material and in getting your Arborists’ Certification!

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