Galls are growths on plants. They can be simple lumps or have complicated structure. Sometimes they are unsightly and numerous. Galls colors vary in shades some are brightly colored. They form on branches, leaves and twigs. Most cases these galls are not harmful to the tree. Galls on small plants may cause stunting. Some galls form from insects injecting a toxin into the leaves while laying eggs, or while feeding on the leaves. The toxin stimulates rapid and abnormal cell growth. They can also develop due to a fungus, bacteria or virus in the tree.