Part 9 of a series by Eugene Howell
To care for a bonsai tree well, it’s appropriate that we first learn something about how a tree actually works; otherwise we have little ability to understand the true nature of the living thing we’re trying to bend and twist and shape to our desires.
If asked what the major parts of a tree are, what would you answer? As a bonsai artist, if you pause for a moment to think about it, you should come to the conclusion that if you have no understanding of how a tree functions, you won’t know what you need to do to the tree in order to get it to develop into an excellent bonsai. Furthermore, you won’t know how the tree will respond to your actions. This, however, is critical. You must know what to expect from a tree in order to develop it the way you envision the tree as a finished bonsai. The more you know about the basic functioning of a tree, the easier and faster you’ll be able to turn raw material into a beautiful bonsai.
All of this is well and good, but what does it mean? Simply put, you need to know the six organs of a tree, what each one does, and how they work together. With this knowledge you can intuitively figure out how a tree will respond to your training
The organs of a tree are the roots, trunk (which includes the branches), leaves, flowers, fruit, and seeds. From a bonsai standpoint the ones in which we have the most interest are the roots, trunk, and leaves, so let’s first discuss them.
The root system does three jobs. It holds up the plant, takes in water and nutrients, and stores food. In nature, the root system typically extends two or three times further from the trunk than does the tree’s canopy. Water and nutrients are absorbed by the roots through “root hairs”. These very tiny (much thinner than a human hair) one cell structures pass the water and nutrients into the xylem layer. This then transports them to the leaves where they are converted into food through photosynthesis. Interestingly, plants are about the only living things that manufacture their own food. The tree then transports the food to all of its parts for consumption.
The trunk holds up the canopy and gives it sufficient spread to insure that the leaves are exposed to sunlight. It consists of five layers; the bark, phloem, cambium, xylem, and heartwood. The layer of most critical interest to the bonsai enthusiast is the cambium layer, for it is this one that plays the biggest role in the development of a bonsai. By fully understanding what this layer does, you’ll be able to easily understand why a tree does what it does when as you develop it into a bonsai. If you remember only one of these layers, remember the cambium layer
The bark is a water-tight barrier that protects the interior of the trunk from insects and diseases. Because of this, the less damage that is done to the bark, the greater is the probability that the tree will remain healthy.
The layer inside the bark is the phloem. It has the job of transporting food to all parts of the tree. This is important to remember when air-layering a bonsai.
The layer just inside the phloem is the cambium. This is the growth mechanism of the plant. It is this layer, made up of cells called “meristem cells”, that creates all new cells within the tree. If this layer ceases to function properly, the plant dies. When you prune a tree to develop ramification, the cambium layer is what does it. When you watch for new buds to pop on the trunk so you can develop a new branch, you are watching for the cambium layer to do this. When you girdle a branch during air-layering, you are trying to get the cambium layer to start growing roots at that spot. When you defoliate the tree you are counting on the cambium layer to force new, smaller leaves to develop. When you perform root pruning every couple of years, you are counting on the cambium layer to develop finer roots to replace those cut away. When you collect a tree from the wild and chop the trunk to a height of 3 or 4 feet, you are hoping that the cambium layer will develop new buds at the cut so you can grow a new apex.
Understanding how your bonsai will respond when you cut it is essential to being able to create a magnificent bonsai.
Click the link below to the next article in this series and we’ll continue the topic of understanding how your bonsai grows.
Photo Credit: flickr Creative Commons, Leaning Bonsai at the 2011 Philadelphia Flower Show by Dyogi