Galls

Among the many and varied interesting phenomena of nature, we find the galls.  Are you familiar with them? Have you ever observed the spherical enlargements on the stem of the goldenrod or the marble-like growth on the oak leaf called “oak apples?”  Often they are also found on the poplar and willow trees.  After observing them, one is confronted with several questions: What causes them?  What do they contain?  How are they constructed? These unusual growths may appear on leaves, stem, fruit,...