The rapid growth of leaf and twig on trees and shrubs in spring is
made from the food stored in the stem the season before.

Sago is a form of starch stored in the stem of the sago palm for the
future use of the plant.

Maple sugar is made from the food material stored in the trunk of the
maple tree for the rapid growth of twig and leaf in the spring.

Cane sugar is the food stored in the sugar cane to produce new plants
the next season.

If we examine the stem of a tree that has been cut down we find that
it is woody, that the wood is arranged in rings or layers and that the
outer part of the stem is covered with bark. We will notice also that
the wood near the centre of the tree is darker than the outer part.
This inner part is called the heart wood of the tree. The lighter
wood is called the sap wood. It is through the outer or sap wood that
the water taken in by the root is passed up to the leaves where the
food which it carries is digested and then sent back to the plant. The
returning digested food is sent back largely through the bark. Between
the bark and the wood is a very thin layer which is called cambium.
This is the active growing tissue of the stem. In the spring it is
very soft and slippery and causes the bark to peel off easily. This
cambium builds a new ring of wood outside of the old wood and a new
ring of bark on the inside of the bark. In this way the tree grows in
diameter.

Now if the bark is injured, or any part of the stem, all parts below
the wound are cut off from the return supply of digested food and