Why was Pearl crying at the end of chapter seven?

At the end of Chapter 7, Mr. Radley (Boo's brother) figures out about the gifts that Boo has been secretly leaving in the tree for the children to find. It is Boo's way to communicate to the children and try to be their friends. Unfortunatley once Mr. Radley finds this out he quickly cements up the knothole. And when asked about this by Jem, Mr. Radley says that the tree was dying when the tree is clearly healthy. Jem starts crying because he realizes that Mr. Radley knows about their "communication" and tries to hide Boo more from the world. He doesn't understand why Mr. Radley is unfair to Boo in this way. This is another example of how Jem is growing up and experiencing life's cruelty and unfairness.