Part 10 of a series by Eugene Howell
To be a good bonsai artist you must first understand how a tree will respond to what you’re doing. This means you must understand the basic parts and functions of a tree. Superficially this may seem to be an overly simple topic. After all, everyone knows a tree has leaves, branches, a trunk and roots. But don’t be fooled, understanding how these parts respond to pruning, wiring and cutting is a bit more complicated and deserves some discussion.
As I stated in the last post the trunk is made up of five layers. The outside layer is the bark, next is the phloem, and the third is the cambium. What the cambium does is extremely important to the bonsai artist.
The remaining layers of the trunk are the xylem and heartwood. The xylem has the task of carrying water and nutrients from the roots to the leaves. The heartwood provides strength for the trunk to withstand winds and hold up the weight of the canopy.
As a tree grows in diameter the cambium continually makes new cells on both its inner and outer surfaces. The cells on the exterior side become phloem and the outside cells of the phloem turn into bark. The cells on the inner surface of the cambium become xylem which then eventually become heartwood and display the distinctive rings inside the tree. As a result of this process, the heartwood continues to increase in diameter and the bark expands its surface area as the tree grows.
The cambium is made up of meristem cells. These cells are able to change their character at will, depending on what the tree needs. For example, when needed, meristem cells can develop into a bud, a leaf or a root. The meristem cells in the cambium layer are what allow branches to grow, leaves to develop, and the tree to get taller.
The leaves of a plant have one primary job; to photosynthesize food for the tree. When a bonsai is defoliated to reduce leaf size, the plant loses the ability to manufacture food until new leaves are produced. However, one of the jobs of the root system is to store food. When all the leaves are removed, the plant extracts this food from the roots while developing new leaves. This process is the same one that keeps a deciduous tree alive during the winter.
In the last two posts of this series I’ve barely scratched the surface of a subject every bonsai artist should know thoroughly. So take some the time to read some more about how trees grow. http://en.wikipedia.org/wiki/Meristem
In the next post we’ll be talking about developing leaf pads on your bonsai.
Photo credit: flickr Creative Commons, Trident Maple (Acer buergerianum) by Cliff1066